Sound is a vibration which is created when an object pulsates in a medium such as air or water. This vibration travels through the medium as a wave. Sound cannot occur in a vacuum. For example, if a brick falls from a building, it hits the ground. The air pressure around the brick changes when it hits the ground. Due to the collision, it vibrates and produces sound. Sound waves have physical properties, namely, amplitude and frequency. Amplitude is associated with the loudness of sound. Low amplitude refers to a quieter sound and high amplitude refers to a louder sound. The number of repeated sound waves per second is called frequency. Lower and higher frequency sounds are often referred to as low and high pitch, respectively.
Sound has a wide variety of applications in industries such as medicine, dairy and food processing as also in defence and underwater. The objective of this chapter is to provide an overview of all these applications of sound.
• Understand sound therapy and its applications
• Study the use of ultrasound in medicine and medical applications
• Learn how the sound is used in the applications of dairy and food processing industries, underwater, microelectronic manufacturing, emulsion and remote turbulence detection
• Understand how architectural acoustics work in designing theatres, sound studios and so on
• Find how sound is used for navigation and animal echolocation
• Study recent applications of sound for animals like dogs, mosquitoes and as a pest repellent
Sound therapy is a treatment which uses sound to treat mental and physical stress. The technique involves sending sound waves and harmonic vibrations to the body through the use of instruments and the human voice. Sound waves help to facilitate a shift in brainwave conditions by entrainment. Entrainment matches the oscillating brainwaves by providing a stable frequency which they can attune to. It is possible to stimulate the brainwaves by using frequency and rhythm, which makes it possible to downshift normal waking consciousness/state (beta state) to relaxed consciousness/state (alpha state), then to meditative state (theta state) and to sleep state, where internal healing can occur (delta state).1
One of the most common sources of sound therapy is the “Tibetan singing bowl” (Figure 18.1). The bowl produces vibrations in deep tones which allows relaxation of both sides of the brain and helps in muscle regeneration. The vibrations also improve circulation, release tensions or blockages, relieve depression and mood-related concerns, as well as cure anxiety. It treats children with hyperactive disorders too by stimulating the immune system. The bowl is made up of five to seven types of metals which are connected to celestial bodies: mercury (Mercury), copper (Venus), iron (Mars), tin (Jupiter), lead (Saturn), gold (Sun), and silver (Moon).2
The use of sound in clinical assessment has a long history. Stethoscopes are used by doctors to hear the internal sounds of the human body such as of the heart, lungs, blood flow, and so on. Nowadays, scientists are carrying out research and development for advanced applications of sound in clinical applications. Acoustical energy is used, for instance, for imaging and for different ways to cure diseases like cancer, stroke, and Parkinson’s disease.3
Ultrasound technology has proved useful in the pharmaceutical field because of the ease with which the amplitude and frequency of ultrasonic waves can be tuned. It also offers flexibility in controlling the particle size, production of nano and micromaterials, crystallization control, and augmenting the solubility of weak soluble drugs. Ultrasound technology is used in preparing and processing fine biomolecules like nucleic acid and proteins since it verifies the structural integrity of the molecules. Based on the dimension and physical properties of particles, ultrasound is used for separation processes and effluent treatment.4
In 2008, in China, the dairy industry had a big setback as more than 290,000 people, most of them infants, were affected due to the melamine (rich in nitrogen) content in milk.5 Basically, raw milk contains pathogenic organisms like Bacillus cereus, Salmonella spp, and Listeria monocytogenes , which promote growth of microbes and so on. Hence, various techniques are involved in different industries for good post production microbiological control of the milk packages. This is where ultrasound is useful. Both high intensity and low intensity ultrasound are used for this purpose. During the storage or processing of dairy products, monitoring and quality control can be achieved by low intensity ultrasound based on the physicochemical variations. For homogenization, fermentation, extraction, and pasteurization, high intensity ultrasound (HIU) is employed.6 During the production of cheese HIU enhances the gelation and syneresis, and decreases the fermentation time. HIU applications are used in ultrasonication for modifying the colour of dairy products. However, it has been reported that the application of HIU in milk is dangerous because it limits the lightness, chroma, and denaturation of proteins in pasteurized milk.
Food safety is important. Significant research has been done on the development and expansion of fast and reliable food quality control systems. Extraction of intracellular material and cell destruction are the most common applications of sound in the food processing industry. The use of ultrasound in food processing helps develop novel techniques for preservation, activation or deactivation of enzymes; emulsification, stabilization, tenderization of meat, mixing and homogenization; dispersion, oxidation, and ageing; hydrogenation; ripening; dissolution; and crystallization. It also assists in solid–liquid separation, atomization, and degassing of food preparations.7 Ultrasound is used as an alternate method for thermal treatments in food preservation for the removal of microorganisms and enzymes without annihilating the nutrients in foods.
Chemical reactions of proteins can be achieved by ultrasound which modifies the physical and chemical or functional attributes such as emulsification, solubility, foamability, and gelation. Ultrasound irradiation is used for mixing in oil technology. For example, the conversion of soyabean oil to biodiesel can be optimally achieved by using an oil to methanol ratio of 9:1. Ultrasound wave propagation evaluates the type of protein, size, and aggregation state to differentiate between original honey and adulterated honey. On the commercial side, industrialists need to think of minimizing the use of ultrasound in the food industry for achieving maximum results because it causes changes in materials based on the characteristics of the medium.
Sound travels at 1500 m/sec underwater. As the sound wave moves through seawater, the underwater objects vibrate and produce pressure waves that compress and decompress water molecules. Sound waves radiate in all directions from the source. Although identification and classification of underwater acoustic signals is difficult due to low signal-to-noise ratio, it is well known that animals use sound for communication. For example, dolphins use ultrasound for navigation and catching their prey. Dolphins hunt in the dark and have unique signature whistles to identify themselves. Sound propagation in air is complex due to reflection, scattering because of particle size, bubbles, and so on. Similarly, fluctuation in sound propagation in water happens due to a variety of reasons. Water has higher viscosity, heat capacity and conductivity compared to air. So, the speed of sound underwater is more affected by temperature, hydrostatic pressure, dissolved impurities and mass density.8
In 1906, naval architect Lewis Nixon invented sound navigation and ranging, or sonar in short. It was designed and developed to detect icebergs. Later, a large body of research on sonar was carried out during World War I.9 From these and further research, different technologies have been developed in various fields including military and civilian applications. Sound propagation is used by sonar systems for navigation, to find the distance from an object and for obstacle identification, an illustration of which is shown in Figure 18.2. There are two types of sonar system—active and passive. Active sonar systems generate a sound pulse by using an acoustic projector and wait for the pulse to reflect from the target. Passive sonar systems receive the noise radiated by the object, that is, a submarine or a ship. By analyzing the sound waves, one can recognize the object type and find its speed, direction, and distance. In defence applications, sonar is used for tracking, detecting, and localizing enemy targets, such as surface ships or submarines, and acoustic sensors are used for firing of weapons. Radar or optical devices are dedicated for attenuation of electromagnetic waves in seawater compared to that of sound in air.8 The comparison of active and passive sonar systems is shown in Figure 18.2.
Further, as sound waves can propagate underwater, they are used in the application of underwater communication systems. Such a system transmits and receives the vocal sound of humans through audio amplifiers and hydrophones. An acoustic modem is used to convert digital data into sound signals underwater which is also used for communication of higher quality digital data such as pictures and words.8
Underwater acoustics have played an important role in various applications over the last century. Nowadays, underwater acoustics is used widely in defence and also in civilian life, for example, fish finders, a picture of which is shown in Figure 18.3(A). Other sonar devices shown in Figure 18.3(B) and Figure 18.3(C) are used for object detection. Further, a variety of research is carried out for advancement in seismography, tomography, biology, topography, and weather patterns, which allows researchers to acquire deeper knowledge about the planet.8
Architectural acoustics are mainly used in designing theatres, hospitals, schools, colleges, malls, and other big buildings for controlling noise in music acoustics, speech intelligibility, theatre acoustics, or environments designed and developed for pleasant ambient sounds. Architectural acoustics are also used for controlling sound characteristics within designed spaces. In hospitals, sound from beeping equipment and alarms drastically increases because of the reflection of sound by the hard floors and ceilings which leads to increased noise levels. This problem can be avoided by replacing hard tiles with sound-absorbing tiles. In 2004, it was reported that patients in hospitals slept more comfortably after the ceiling tiles were replaced.14 In schools, ambient noise can be controlled by placing acoustic absorbers in classrooms. While designing a theatre, attention is given to two issues: (1) creating sound effects, textures, and subtextual themes, and (2) planning the placement of the microphone and speakers such that the audience has the best feasible sonic experience. Architectural acoustics involves the use of acoustic metamaterials that enable low frequency sound mitigation and manipulation. Most of the materials which absorb sound are nonlinear and they don’t absorb the same fraction of acoustic waves at all frequencies. Acoustic construction materials reflect desired frequencies and absorb undesirable frequencies, that is, noise from machinery in factories and industries which is known to affect workers.15
While designing big buildings, attention is typically paid to the following constraints from the point of view of acoustics.
• Building envelope: A building envelope mainly refers to the outer layer of the structure that envelops or shields the building from outside environments such as heat, wind, water, and noise. It reflects and absorbs sound to reduce noise.
• Interior structure: Structured room, doors, windows, walls, floors, and ducts create a good acoustic environment or reduce noise level. For example, the shape of a theatre allows sound to flow unobstructed from the stage to all the seats and prevents sound from echoing.
• Materials: The selection of building materials is important because sound has properties such as reflection, refraction, absorption, diffraction, diffusion, and transmission. For example, a party wall between two apartments should contain layers of sound insulation to absorb noise.
• Equipment: The selection of equipment like escalators plays an important role in the acoustics of a building. Mechanical equipment that lack beeps and other noisy features are preferred.
• Sound masking- This is achieved by ambient sound that includes noise such as water fountains or electronic noise control that generates noise-cancelling waveforms in real time in response to undesirable noise. Sound masking is also done by using highly dense material which causes less sound to travel through it although it increases the weight of the floor and wall. Decoupling is yet another way of controlling sound.16
Emulsion is a mixture of two liquids which typically do not blend well (e.g., oil and water). Ultrasonication is a low-cost method for emulsion development with an important effect on the emulsion structure and size of droplets. It is known that ultrasonication produces emulsions with higher kinetic stability (i.e., stable for a longer duration of time) than other means of developing emulsions, for example, mechanical agitation. By applying low intensity, resonant ultrasonic fields to the emulsion, separation and recovery of the oil phase from oil-in-water emulsion can be done. Ultrasonication is used in various fields such as cosmetics, paints, food, pharmaceuticals, and agrochemical industries.17 The drops shift towards the pressure antinodes of the standing wave under the influence of the acoustic force. The relative motion of drops is very sensitive to their initial configuration and physical properties, relative size of interacting drops and parameters of acoustic field. Around 80 per cent efficiency of oil retention can be observed in laboratory scale devices.18
Acoustic imaging or microscopy is used for characterization of the quality and detection of problems in manufacturing objects on a microscopic scale. Acoustic microimaging or scanning acoustic microscopy is a nondestructive method that finds problems in biological, elastic samples and electronic circuits. This technique works efficiently to detect physical defects such as voids, delamination, and cracks with high sensitivity by observing the internal features of a sample in 3-D integration.19 There are other techniques such as ultrasound impedance microscopy, which is a two-dimensional acoustic impedance imaging technique for characterization of biological tissue with microscale resolution.20 Similarly, ultrasound scanning acoustic gigahertz microscopy and speed microscopy are used to examine the quality of wafer-bonded interfaces in three-dimensional integration.21
Loss of forest areas due to wildfires, floods or even illegal deforestation is a threat to the planet. Acoustic monitoring is the best solution for such a problem that involves observing and surveying of wildlife and environments remotely. A forest monitoring system consists of sound recorders which collect the data (sound) that is processed to extract useful data such as species occupancy detection, population density, abundance, community composition, monitoring temporal and spatial trends in animals behavior, and calculating acoustic proxies for metrics of biodiversity.22 There has been research and development of devices for monitoring possible hazards, in particular loss of wood due to deforestation. Such a device continuously records the noise level in the forest area. Based on an algorithm in the system, the device has the capability to isolate the audio signal corresponding to the cutting of wood, for example, with a saw. Finally, it produces an alarm at timed intervals when the target event is identified.23
Similar to dolphins using sounds in underwater communication, animals and birds use echoes produced by the sounds they emit to find their path through leaf litter or in caves/tunnels under snow.24 For example, bats use high-pitched sound for echolocation. Birds such as swiftlets and shrews use echolocation for navigation in the dark and for locating insects and other prey, respectively.
Atmospheric turbulence is known to pose danger to aircraft and can cause injuries to crew and passengers. For the safety and efficiency of aircraft transportation, in-flight detection, mitigation, identification, and avoidance of turbulent gusts are very important. Avoidance or mitigation of flying through turbulent air pockets decreases fuel consumption and increases ride comfort.25 Acoustic waves are used to measure the propagation of turbulence which are diffracted by temperature and humidity fluctuations in the index of refraction.26 Technology has helped develop 2D imaging acoustic sensors for detection of Close-In Air Turbulence. These sensors produce high resolution “images” of the air in front of Unmanned Aerial Vehicles.27
Sound, mainly ultrasound, has been used to develop android applications that repel animals like dogs, mosquitoes and other pests. Dogs stop barking when they are afraid of something and get disturbed when they hear loud sounds. Ultrasonic dog repellent sounds provide a number of sounds with different frequencies to stop the animal from barking. In such an application, users need to set a frequency and duration. Mosquitoes are disturbed by high-pitched ultrasound. A few such applications are listed in Table 18.1.
|Application name||Usage||Date of Publishing|
|Ultrasound barrier app||This app is used to get rid of rats, dogs, mosquitoes and other insects.||14-07-2021|
|Ultrasonic Sounds Prank||Used for pranks against annoying people and also for mosquitoes, rodents, rats and other unwanted pests.||20-09-2018|
|UltraSound Detector||It detects ultrasound (ultrasonic) acoustic signals above the user-defined frequency (above 18 kHz by default). It is used in finding the leakage in air-conditioning and refrigeration systems||06-05-2018|
The graph in Figure 18.4 summarizes different industrial applications of sound, that is,, architectural acoustics, food processing industries, underwater acoustics, acoustic microimaging, and so on which cover a wide range of frequencies over 10Hz–-1GHz (including both audible and inaudible sounds). Architectural acoustics use a sound in the frequency range of 16Hz–4kHz for absorbing unwanted sound, blocking outside noise, and improving the sound quality in a location. It creates spaces that enhance the audibility or clarity of speech or music and the qualities of performances in concert halls. Sonar devices utilize a frequency range of 10Hz–1GHz for locating objects, measuring their distance, direction, and speed, and producing images of target objects. They use higher frequencies to provide more accurate location data. However, propagation losses increase with frequency. Lower frequencies are therefore used for long range detection (up to 10 miles) at the cost of location accuracy. As emulsion is often thermodynamically unstable, ultrasound with frequency from 25–45kHz is used to deliver high energy to separate water from oil emulsion, to extract phosvitin from egg yolk, and to separate butter from cream. Underwater acoustics use sound for communication in the ocean. Sound with frequency below 10Hz is not useful as it fails to propagate without penetrating deep into the seabed. On the other hand, sounds with frequency above 1MHz are rarely used for underwater communication as they are absorbed very quickly. Underwater acoustics applications include water exploration (finding the depth) and drilling (oil well). Food processing has a wide range of applications of sound in the dairy and meat industries, which include homogenization, mixing, extraction, filtration, and fermentation. It typically uses a frequency range of 20kHz–10MHz to deactivate the enzymes. Acoustic microimaging is a powerful, nondestructive technique that can detect hidden defects in elastic and biological samples as well as in nontransparent hard materials and monitor physical defects such as cracks and voids. It uses a frequency range of 400MHz–1GHz which allows for a penetration depth of up to several millimeters. Nowadays, android ultrasound applications have also been developed as repellents for animals like dogs, mosquitoes and other pests which use a frequency range of 15kHz–20kHz, where users can set the frequency as required. Ultrasonic sounds create stress and jams the nervous system. This immobilizes the insects and they escape from the source of the ultrasound.
It is clear from the graph that the use of sounds in various applications is gradually increasing year by year. With more research and development, we expect to see more useful applications of sound by exploiting the characteristics of sound in different frequency ranges.
Sound has a large number of applications in various domains. Different frequency ranges of sound are exploited for different purposes. This chapter covers a large number of these applications.
While some of these applications are matured and available for commercial use in clinical and defence scenarios, many of the applications are in the development stage. On the other hand, research is on to develop many new applications of sound. Hence, in the years to come, we expect to see more applications of sound being available for the benefit of human beings.
Sound is a type of energy and propagates through vibrations in a medium. Thus, it requires a medium for propagation. Air is a good transmission medium for sound. Other mediums through which sound travels are solids, liquids and gases but not vacuum (space). Among various mediums, sound travels the slowest through gases, relatively faster through liquids and the fastest through solids.
Sound is classified into three types according to its frequency. Humans can detect the sounds in a frequency range of 20 Hz to 20 kHz, called audible sound. Sound below 20Hz is called infrasound. Sound ranging from 2 MHz to 18MHz is called ultrasound. Audible sound in a nursing home or hospital can bring positive vibes or feelings not only in patients but also among nurses and doctors. As sound can bring changes in the brain waves, several activities that are controlled by the autonomic nervous system can be altered by music. These include breathing, heart rate and activation of the relaxation response. Ultrasound, on the other hand, is used in various fields, especially in the medical field, because of some of its special properties. It is widely used in imaging techniques, therapies, surgeries and so on. This chapter presents the applications of sound in healthcare including different applications of ultrasound in detail.
• Understand different types of sound present in nature, that is, infrasound, audible sound and ultrasound
• Learn about the application of sound in healthcare, that is, in diagnosis, therapy and wearable devices
• Learn about ultrasound, its generation, detection, and its parts and modes
• Examine the purpose of a few ultrasound machines with illustrations
There are different types of sound in the world around us. They have a wide variety of applications as well. However, only some sounds are used in medical applications. They are discussed below.
Sound is classified into three types according to its frequency range as follows.
2. Audible sound
1. Infrasound: These sounds have low a frequency and are inaudible to humans. Typically sounds lower than 20Hz are categorized as infrasound. Infrasound is generated by weather patterns, seasonal winds, volcanoes, storms and some types of earthquakes. Infrasound is also used by animals such as elephants, whales, hippopotamuses, rhinoceroses, giraffes and okapis to communicate over long distances and repel foes.1 The extremely low frequency infrasonic hydrophone is used to locate undersea oil deposits.2 Infrasound is also used in non-contact healing for joints, muscles and so on.3
2. Audible sound: The human ear can detect sound in the frequency range of 20Hz to 20,000Hz, called audible sound. The sounds that humans can hear include speech, music, instruments and crackers.4
3. Ultrasound: Sounds with frequency above 20,000Hz are categorized as ultrasound. The medical field uses ultrasound up to a maximum of 18MHz. Ultrasound is used for a wide variety of industrial applications including packing and separation, and extraction of fats in dairy products. In the medical field, ultrasound is used for medical imaging, therapies, cleaning of surgical equipment and so on.
All three types of sound, infrasound, audible sound and ultrasound, are used in different medical applications. A summary of the broad categories of applications is shown in Figure 19.1 and discussed below.
Diagnosis is the examination of a person for identification of illness or symptoms of illness and other problems. It is undertaken using medical equipment with the help of healthcare providers. On the other hand, assessment is an evaluation made by a doctor to make an informed decision on whether or not to provide treatment, and if yes, what approach to take. Such assessment devices include stethoscopes and audiometers.
Ultrasound has a large number of applications in healthcare mainly in diagnosis. Diagnostic ultrasound, sonography or ultrasonography is a non-invasive method to view the internal organs of the body. It includes imaging of internal organs like the heart, blood vessels, liver and thyroid to diagnose, evaluate and identify their condition; clots; source of pain, swelling and infections; and so on.
Some ultrasound procedures are invasive. For example, a transvaginal ultrasound, used to scan the female reproductive organs, consists of a transducer called a probe, which is inserted into the vagina to scan and produce a detailed image of the organs in the pelvic region.
a. History of Ultrasound
The use of ultrasound in the medical field began during World War II in different parts of the world. In 1942, in Austria, Dr. Karl Theodore Dussik published the first work on medical ultrasonics in imaging which investigated the transmission of ultrasound in the brain.
The development of commercially available systems from the mid-1960s onwards allowed an extensive dissemination of the ultrasound-based techniques. Further rapid growth in technological advances in piezoelectric materials and electronics provided enhancement from bistable to grayscale images and from still images to real-time moving images. The technological advancements led to a quick growth in ultrasound applications. In parallel with the development of imaging technologies, there had been progress in the development of the Doppler ultrasound. The fusion of the two technologies resulted in Duplex scanning. Colour Doppler imaging developed subsequently. These provided more scope for the investigation of blood circulation in and blood supply to organs. In the 1970s, the development of the microchip and increase in processing power allowed faster and more powerful systems including enhancement of signals, digital beamforming, interpreting and displaying data, that is, 3D imaging and power Doppler.5
b. General Working Principle of Ultrasound
Two basic principles need to be understood to know about the working of ultrasound.
1. How ultrasound is generated
2. How the image is formed
1. Ultrasound generation: Ultrasound is generated by a piezoelectric transducer consisting of ceramic crystals, which converts electric current to pulses of sound waves. An electric current is passed through a cable to the crystals, resulting in their deformation and vibration. This vibration produces the ultrasound beam. The frequency of the ultrasound waves created is predetermined by the crystals in the transducer.
2. Image formation: Ultrasound uses the pulse-echo principle to generate an image. Ultrasound waves are produced in the form of pulses but not continuously because the same crystals are used to generate and receive sound waves, and they cannot do both at the same time. In the time between the pulses, the ultrasound beam enters the patient and is reflected back to the transducer. The reflected acoustic waves cause the crystals in the transducer to deform again and generate an electric signal, which is converted into an image and displayed on the monitor. A transducer generally emits ultrasound only 1% of the time; the rest of the time is taken up in receiving the returning echoes.
Depending on the type of the scan, different dimensional images – two-dimensional (2D), three-dimensional (3D), four-dimensional (4D) and five-dimensional (5D) or even higher dimensional (HD) – can be obtained. A black and white picture is obtained in 2D ultrasound images. This flat image helps in showing the skeletal structure and making the internal organs visible. A 3D image of an organ can be created in 3D ultrasound. For example, it allows a pregnant woman to see her baby’s face, rather than just the outline of the face. In 4D ultrasound, a live video is created where a sequence of 3D images are obtained. In such a moving video, the smile or yawn of the baby in the womb can be seen. HD ultrasound images are even clearer and sharper with better resolution as a result of the advancement in ultrasound technology.45
Diagnostic ultrasound is mainly used to view the internal organs like liver, kidneys, uterus and ovaries during pregnancy and monitor the developing baby’s health, diagnose gall bladder disease, examine a breast lump, check thyroid gland, detect genital and prostate problems, evaluate blood flow and metabolic bone disease, and so on. An ultrasound device consists of probes, keyboard, CPU, display, printer and disk storage. Figure 19.2 shows the various parts of a typical ultrasound machine. The parts are briefly described below.
Central Processing Unit (CPU): The CPU is the brain of the ultrasound machine. It is part of a computer and consists of amplifiers, microprocessor, probes and power supply as peripheral parts. The CPU transmits electrical current to the transducer to emit acoustic waves and receives pulses from the transducer which were obtained from the returning echoes. It processes the received pulse data and forms the image to be shown on the monitor. Later it stores the processed data or images on the disk.
Transducer Pulse Controls: This unit is typically meant for an operator of the ultrasound machine, known as the ultrasonographer. With the help of this unit, the ultrasonographer can set the frequency and time period of the ultrasound pulses and also the scan mode of the machine. The commands are received from the operator and translated into changing electric currents, which are applied to the crystals in the probes.
Display: The computer monitor is a display that shows an image or processed data from the CPU. Depending upon the model of the ultrasound machine, the image may be coloured or black and white.
Keyboard and Cursor: Every ultrasound machine has a keyboard and a cursor with an in-built trackball. It allows the operators to add notes and take measurements from the data.
Disk Storage: The disk stores the processed image or data. The disk can be a floppy disk, hard disk, compact discs (CDs) or digital video discs (DVDs). Generally, the scanned image or data are stored on CDs along with the patient’s medical records.
Printers: These are used to take hard copies of an image. Typically, ultrasound has thermal printers which print copies of images from the monitor display.6
An ultrasound that scans internal images or other structures, for example, abdominal ultrasound, transvaginal ultrasound, is usually referred to as anatomical ultrasound. The same anatomical ultrasound which combines the applications of Doppler and colour Doppler effect for measuring and visualizing the blood flow in vessels within the body or in the heart is called a functional ultrasound. It can also measure the speed and direction of the blood flow. Examples include elastography, Doppler ultrasound, ultrafast Doppler (neuro-functional ultrasound), breast ultrasound.7
Every ultrasound consists of probes. The first step before using ultrasound for examination is selecting an appropriate probe, which depends on the patient’s problem, scan depth, exam type and anatomical or functional structure. Probes are nothing but transducers developed on the basis of different criteria such as clinical applications, patient characteristics, examination type etc. Probes are categorized into two types based on the arrangement of crystals. (1) Conventional probes are the main probes used for most applications. Linear, phased and convex probes are conventional probes. (2) Speciality probes are dedicated to specific clinical applications. Endocavitary probes and transesophageal probes are speciality probes.
1. Linear Probe: This probe has crystals arranged in a linear fashion and measures the linear displacement along a single axis in any direction; hence, the name linear probe. An image and functionalities of a linear probe are shown in Table 19.1. A linear probe uses a frequency range of 7.5MHz–11MHz for 3D image formation while a lower frequency range is used for 2D image formation,. It creates high-resolution images near the surface of the body. The 9L-D and the 12L-RS are the bestselling linear probes from General Electric.
2. Curvilinear/Convex Probe: This probe has a curved array which allows it to view a wider field/area shown in the picture in Table 19.1. It uses a frequency range of 2.5MHz–7.5MHz for 3D image formation and a lower frequency range for 2D images. Typically, abdominal scans use this probe due to their wider field of view and deeper penetration. The V6-2 and the C5-1 are the bestselling curvilinear probes from Philips.
3. Phased Array Probe: This probe has a smaller handle with a square-shaped array. It uses a frequency range of 2MHz–7.5MHz as a central frequency. Generally, it scans the image of the heart. Phased array probes have greater depth in order to reach the heart and produce an image.
4. Endocavitary Probe: This probe has a U-shaped array with a much longer handle. It uses a frequency range of 3.5MHz–11.5MHz as a central frequency. These probes are used to scan inside the rectum or the vagina. Endocavitary probes do not have a great range of depth because of the shape but they allow a wider field scan than convex probes. The Mindray SD8-1E and the GE RIC5-9A-RS are the bestselling endocavitary probes.
5. Transesophageal (TEE) Probe: This probe, also known as a pencil probe, is generally used for invasive scanning. It is inserted into the esophagus or the patient’s stomach to provide images to show obstructions in the heart. Its controls are located in the handle and the probe can move in all four directions. It uses a frequency range of 3MHz–10MHz as a central frequency.9
|Probe Type||Examinations or functions||Frequencies|
|Linear Probe||2D imaging – thyroid, tendon, vascular examination, blood vessel, breast visualization
3D imaging – breast, thyroid, arteria carotis of vascular application
|Convex Probe||2D imaging – musculoskeletal, abdominal, vascular, nerves Diagnosis of organs, neonatal and paediatric applications
3D imaging – abdominal examinations
|Phased Array/Cardiac Probe||Cardiac, abdominal, brain and transesophageal
|Endocavitary Probe||These probes provide internal examinations of the patient – examination of the rectal or vaginal area which includes females’ ovaries, uterus, cervix and pelvic area||3.5MHz–11.5MHz|
|Transesophageal (TEE) Probe/Pencil Probe||Usually this is used for invasive techniques of viewing internal organs of the cardiac regions||3MHz–10MHz|
Each probe exhibits different modes which perform a particular function to operate. Ultrasound has four modes, namely, A-mode, B-mode, M-mode and Doppler mode, explained in detail below. Each mode has a specific function whereby the doctor can choose the probe based on the patient’s condition, scan depth, type of images and so on.
• A-mode: It is a simple mode of an ultrasound. Generally it scans a line through the body with the echoes plotted on the screen as a function of depth. It represents one-dimensional images. A-mode focuses on a particular point of the destructive wave energy.
• B-mode: In this mode, a linear array of transducers parallely scans a plane through the body that can be viewed as a 2D image on the display.
• M-mode: M stands for motion. In M-mode a high-speed pattern of B-mode scans, whose images follow each other in sequence on screen, enables doctors to view and measure a range of motion as the organ boundaries that produce reflections move relative to the transducer.
• Doppler mode: This mode uses the Doppler effect to measure and visualize the blood flow in various organs. Doppler sonography plays a vital role in medicine.10
Different probes are used for various examinations. A quick overview of the different ultrasound transducer/probe types and their applications is provided in Table 19.2.
Ultrasound diagnosis includes both invasive and non-invasive techniques. Invasive diagnosis includes the transvaginal ultrasound, which is used to examine and scan the internal organs of the female reproductive system. Transvaginal ultrasound scanning involves insertion of a small ultrasound probe called a transducer into the pelvic area or vagina to obtain detailed scans of the organs in the pelvic region. It evaluates the uterus, ovaries, vagina, fallopian tubes, cervix, gall bladder and so on.11 Some of the invasive ultrasound examinations are presented in Table 19.3. Non-invasive diagnosis includes cardiac regions like the heart and blood vessels, abdominal aorta and its major branches, liver, spleen, gall bladder, pancreas, kidneys, bladder, uterus, ovaries and unborn child (fetus) in pregnant patients, scrotum (testicles), thyroid and parathyroid glands and so on. Some of the non-invasive ultrasound examinations are shown in Table 19.4.
|Ultrasound Devices (Year of invention)||Purpose|
|A. Transvaginal ultrasound (late 1985)||It is used to examine the female reproductive organs such as ovaries, uterus, fallopian tubes, vagina and cervix. The examination is conducted by inserting the probe inside the body. It is also called endovaginal ultrasound.12|
|B. Endoscopic ultrasound (EUS) (1980)||It is used to assess digestive (gastrointestinal) and lung diseases. It helps gastroenterologists examine the stomach and other organs like the bile duct, pancreas, gall bladder and liver. This ultrasound can help identify tumours and surrounding lymph nodes in stomach cancer patients.13|
|C. Ultrasound-guided needle biopsy (1972)||The needle biopsy is used as a safe and effective procedure for collecting tissue specimens from different intrathoracic lesions. Percutaneous biopsy facilitates the differentiation of primary lung cancer from metastases or inflammatory lesions by obtaining tissue samples for diagnosis and staging.14|
|D. Cavitron ultrasonic surgical aspirator (CUSA) (1979)||Hepatobiliary surgery, neurosurgery, urology, gynaecology and gastrointestinal surgery are various multiple surgical subspecialties which use the cavitron ultrasonic surgical aspirator. CUSA is good for ultrasonic surgical aspirator where fragmentation, suction and irrigation occur together.15|
|Ultrasound Devices (Year of invention)||Purpose|
|A. Ultrasonography (1928)||Medical ultrasonography was developed during World War II. In medical ultrasound imaging, ultrasound energy is created which propagates through the tissues of the body in the form of travelling pressure waves.. A frequency of 3MHz to 10MHz is required for imaging. Piezoelectric materials help in ultrasound beam production and detection. These materials vibrate and produce ultrasound when placed in a varying electric field. The signal in the ultrasound scanner is detected by the electric field produced when there is ultrasound reflection.16|
|B. Urodynamic Measurement device (1987)||The urodynamic device measures the amount of urine left in the bladder after urination. Urodynamic evaluations are carried out on patients with hypersensitivity symptoms to assess features such as volume at first sensation of bladder filling, maximum cystometric capacity, increased bladder sensation, the absence or presence of detrusor overactivity and reproduction of bladder pain.17|
|C. Elastography (1991)||Elastography is a non-invasive technology to assess the mechanical properties of tissues. It measures the elasticity or stiffness of a tissue and determines fat in the liver. It is inexpensive, portable and provides good diagnostic accuracy.18|
|D. Ultrasound - foetal heart rate monitor ultrasound machines (Cardiotocography) (1968)||Monitoring the foetal heart rate (fHR) is a common assessment of foetal well- being. Doppler ultrasound is the de facto standard technology for fHR monitoring. For continuous monitoring of fHR during and before labour, the ultrasound transducer is fixed on the maternal abdomen.19|
|E. Musculoskeletal ultrasound (1958)||Ultrasound imaging uses sound waves to produce pictures of muscles, tendons, ligaments, nerves and joints throughout the body. It is used to help diagnose sprains, strains, tears, trapped nerves, arthritis and other musculoskeletal conditions.20|
|F. Abdominal ultrasound (1948)||It is used to examine abdominal regions including the liver, pancreas and gall bladder.21|
|G. Obstetric ultrasound (1958)||It is used to examine pregnant women to view the baby’s growth in the embryo and foetus stage as well as the uterus and ovaries of women.22|
|H. Ultrasound Echography (1953)||Extracorporeal shock waves therapy (ECWT) and high-intensity focused ultrasound (HIFU) are two therapeutic ultrasound modalities for treating ischemic heart disease and cardiac arrhythmias.23|
|I. Three-dimensional ultrasonography (3D USG) (1970)||It is used for diagnosing congenital uterine anomalies and determining lung volume. Real-time 3D ultrasound has gained more attention in medical field because of the following reasons:
1. It gives interactive feedback for a physician to acquire good quality images.
2. It provides timely spatial information of the scanned area.
Therefore an intraoperative ultrasound examination is important.24
|J. Ultrasound biomicroscopy (UBM) (1990)||It is a non-invasive in vivo imaging and high-resolution ultrasound technique. It gives detailed evaluation of anterior segment structures and anterior ocular segment at near light microscopic resolution.25|
|K. Cerebrovascular ultrasonography (1982)||Cerebrovascular ultrasonography is used to detect cerebrovascular disorders, with extremely high temporal resolution and excellent spatial display of brain structures, cerebral vessels and extracranial arteries.26|
|L. Dermoscopy (1992)||It is a device used for evaluation, treatment and diagnosis of dermatological disorders including melanoma and nonmelanoma skin cancer, benign tumours, inflammatory diseases and lipoablation.27|
Assessment refers to an evaluation of a patient’s condition physically using devices like a stethoscope, audiometer and so on. Following the assessment, a doctor gives suggestions for the next examination or treatment. Some of the assessment devices are listed below.
A. Stethoscope: The stethoscope (Figure 19.3) is a low-cost medical device for listening to the internal sounds of the human body. It is a sound-based (acoustic) device having a small circular resonator connected to two tubes with earpieces. The resonator is held to the chest of the subject and the earpieces are inserted in the ears of the clinical staff. This enables the clinical staff to listen to subjects’ heart or breathing action. Although a stethoscope is a basic device used by all clinicians, the environment background should be quiet to listen to the sound. It also takes effort and time to interpret the sound captured by a stethoscope. Due to these limitations, diagnosis is done based on not only a stethoscope but also other medical devices. Currently digital stethoscopes driven by artificial intelligence (AI) are available in the market. These devices are based on digital sensing technology having AI combined with active noise cancellation.28
B. Audiometer: An audiometer is typically used by audiologists and trained professionals who give advice to patients on the right selection of hearing aids. The audiometer is a medical device, as shown in Figure 19.4, using which a subject is tested on his/her hearing loss in a soundproof room. In this test, the subject wears earphones to hear sounds and words. The same tone is repeated at faint levels to find the quietest sound a person can hear. This helps generate an audiogram. One of the solutions derived from an audiogram is to suggest a hearing aid for the subject. The amplification of soft sounds is needed for subjects facing trouble in hearing.29
Therapy is a treatment intended to relieve or heal a pain/disorder. This is sometimes done through ultrasound, audible sound and infrasound.
A. Ultrasound Therapy: It is a type of therapy which uses ultrasound to relieve pain. It is performed by a therapist using an ultrasound therapeutic device. The therapist chooses a small surface area where a gel is applied either to the patient’s skin or to the head of the transducer, which helps the sound waves to uniformly penetrate the skin. This is carried out for 5 to 10 minutes. While ultrasound therapy is not effective for all chronic pains, it may help reduce the pain of any of the following: carpal tunnel syndrome, osteoarthritis, phantom limb pain, myofascial pain syndrome, bursitis, pain caused by scar tissue, sprains and strains. Table 19.5 summarizes various ultrasound therapies.
There are two types of ultrasound therapies based on the rate at which the sound waves penetrate the tissues: (1) Thermal ultrasound therapy and (2) Mechanical ultrasound therapy.
1. Thermal Ultrasound Therapy: This therapy transmits a continuous ultrasound wave. The deep tissue molecules undergo microscopic vibrations caused by the sound waves resulting in heat and friction. Increase in the metabolism action and heating or warming effect at the cellular level encourages the healing in soft tissues.
2. Mechanical Ultrasound Therapy: This therapy uses the pulses of ultrasound waves to penetrate into the tissues. While this has a minor warming effect, it also causes expansion and contraction in tiny gas bubbles in soft tissues. This decreases the inflammatory response, which reduces swelling and decreases pain.30
• Uterine fibroid ablation
• Phacoemulsification (cataract removal)
|• Surgical cutting of tissue and homeostasis
• Transdermal drug delivery
• Promotion of bone fracture healing
• Targeted gene therapy
|• Bacterial control
• Dental hygiene
• Detection of pelvic abnormalities
• Lithotripsy, fragmentation of calculi
B. Infrasound Therapy: It is a type of therapy which uses infrasound to relieve pain, increase bone health by stimulating the healing of fractures, and decrease symptoms of dysponea (an obstructive pulmonary disease) and other lung diseases.32 Infrasound was found to promote proliferation and inhibit apoptosis in bone marrow mesenchymal stem cells (BMSCs). The results indicated that 60 minutes was the most suitable period for applying infrasound treatment to BMSCs.33
C. Sound Therapy (Audible Sound): Sound therapy, in which auditory and vibratory inputs are used to influence a person’s physiological and/or psychological state, includes sound healing, vibroacoustic sound therapy, music and music therapy. Practitioners of sound healing may use chimes, chanting or drumming to create particular sound frequencies at specific intervals in an effort to promote health and healing of the mind and body. Vibroacoustic sound therapy is a sound technology that uses audible sound vibrations to decrease stress, promote relaxation and improve health.
In contrast to sound therapy, research has been conducted to investigate the possible effects of music and music therapy. Several researchers have found that listening to specific types of music can lower blood pressure and heart rate, reduce pain, decrease anxiety and improve sleep.34
Ultrasound surgery is used for destroying uterine fibroids, kidney stones, tumours and so on. High-frequency, high-energy ultrasound waves are used to target and destroy uterine fibroids. For example, in uterine surgery the procedure is carried out while the patient is inside an MRI scanner. The machine allows the doctor to visualize the patient’s uterus, locate any fibroids and destroy the fibroid tissue without making any incisions. For example, Magnetic Resonance-guided Focused Ultrasound (MRgFUS) is a non-invasive ablation method and uses ultrasonic pulses to heat up and destroy fibroid tumours – abnormal benign growths in a woman’s uterus. Focused ultrasound surgery uses MR guidance to accurately target the fibroids and spare the healthy tissue.35
Apart from the diagnosis/assessment and therapy/surgery, ultrasound is used in the medical field in hospitals for monitoring systems, cleaning of surgical instruments and surgical clothes, and so on, and wearable devices such as hearing aids.
Such a system in hospitals uses audible sound making it beneficial for patient care service provided by nurses. The monitoring/calling system is installed in wards and rooms, monitored and actioned by nursing staff at nursing stations. The nurse call button is placed near every patient’s bed so that he or she can easily reach the nurse in case of any urgent need. The audible and visual alert reaches the nurse both on the control station located at the nursing station as well as near the door of the patient’s room. The nurse identifies the right patient based on the location address displayed and acknowledges the call by pressing the acknowledgment button and attends to the patient’s needs. Similar nurse call buttons are installed in patient restrooms, common public restrooms in outpatient areas so that patient care is not compromised in terms of response to a distress call.36
Another advantage of the nurse call system is activation of Code Blue, that is, patients needing pulmonary resuscitation wherein a nurse needs the support of a rapid response team. There are many additional features of nurse call systems such as wireless remote to patient, monitoring of turnaround time of nurse, intercom/cell phone alerts and so on. The nurse call system technology is being integrated with hospitals’ digital blankets and it is a way forward to improve the overall care of patients. A similar audiovisual application of the token system is used in outpatient pharmacy and other diagnostic areas like radiology to improve patient flow. The outpatient queuing management system is yet another audiovisual application to identify and provide patient direction to the desired doctor for consultation.
The discovery of ultrasonic cleaning and use of cleaners as shown in Figure 19.5 has a significant effect on the healthcare industry. Ultrasound is used to clean and sterilize materials and instruments such as surgical instruments, implants, dental instruments and other delicate medical tools and devices. It is also useful for removing bloodstains from clothes, delicate instruments and surgical tools like scissors, forceps and so on. Ultrasound finds use in hospitals, dental care units and clinics. As surgical instruments have to be completely cleaned and sterilized for use, this cleaning method has been perfect for the healthcare industry. The ultrasonic process of cleaning medical equipment is fast and efficient. It makes sure that devices/instruments are cleaned properly and are safe to use.37
Wearable devices play a very prominent role in healthcare because of usage comfort, size, reliability and so on. They serve as a real monitoring system and evidence for future assessment and treatment. Some wearable devices are listed below.
A. Hearing Aids: These aids (Figure 19.6) increase the audible sound entering the ears of hearing-impaired people to help them listen to clearly and loudly. The small earpiece hearing aid has a microphone to receive sound signals. These sound signals are converted to a digital form to get amplified within the amplifier inside the ear piece. The speaker of the amplifier provides the final input to the subject’s ears for smooth hearing. There are various types of hearing aids available in the market such as completely-in-the-canal hearing aid, in-the-ear, behind-the-ear, receiver- in-canal or in-the-ear or visible-open-fit. Battery life, microscope quality and noise reduction technique are a few points to be considered besides the weight while procuring a hearing aid.38
B. Wearable Ultrasound Patch Monitors Blood Pressure Deep Inside Body: This is a non-invasive wearable device which uses ultrasound to monitor blood pressure in arteries deep beneath the skin that helps people in determining their cardiovascular condition with greater precision. It is also used for clinical applications for testing blood pressure. It is used in real-time applications such as continuous monitoring of blood pressure changes in patients with lung and heart disease and also for patients who are critically ill or undergoing surgery. Since it uses ultrasound, it has the potential of tracking other physiological signals and vital signs from places deep inside the body.39
C. Wearable Ultrasound Sensors for Lung Monitoring: This is a wearable device consisting of a sensor that uses ultrasound to monitor the patient’s lungs. These examinations can also be done at patients’ homes, which avoids hospital visits. The sensor consists of a thin film and uses ultrasound technology. The device has the potential to monitor patients’ lung conditions remotely. It shares the results with hospitals and clinics and avoids face-to-face contact, reducing the use of more expensive hospital-based imaging facilities.40 This helps during pandemics such as COVID-19.
Sound, particularly ultrasound, has a wide variety of applications in the medical field. One of the optimistic applications in imaging techniques is ultrasound imaging, which consists of flexible devices such as probes (also known as ultrasound transducers). In most of the cases, ultrasound is typically painless, non-invasive and does not require needles or injections; in a few cases, however, ultrasound can become painful and invasive when it requires the insertion of probes inside the body. Patients aren’t exposed to ionizing radiation, making the procedure safer than diagnostic techniques such as X-rays and CT scans. In fact, it captures images of soft tissues that do not show up well on X-rays. There are not many side effects or harmful effects of ultrasound. It is very accessible, affordable and low cost when compared to X-rays, and CT and PET scans. Studies have shown that ultrasound is generally safe because it does not use radiation.41 Ultrasound has a few drawbacks. It has low penetration through bones or air. For example, it has limited penetration in obese patients. The quality of ultrasonography depends on the equipment and the skills of the operator. On the other hand, MRI, CT and PET scanning have relatively higher cost, they take more time to give a scanned image and require experienced operators or radiologists. Image resolution is less in ultrasound when compared to CT scans and MRIs.42
Sound plays a vital role in healthcare, especially in ultrasound applications like imaging, therapies, surgery, wearable devices and so on. From World War II, imaging has been continuously evolving. Miniaturized and flexible devices, inspired by the advances in technologies, electronics materials, fabrication, digital and wireless communication, have emerged as the next-generation smart devices in health and medicine. Technologies are developing day by day in diagnosis, therapy and wearable devices to make life more comfortable and easy. Researchers have developed a wearable ultrasound scanner which is cost effective, portable and can be powered by a smartphone. Transducer crystals are being replaced by piezoelectric crystals with vibrating drums which are made of polymer resin; such a transducer is called a polymer capacitive micromachined ultrasound transducer. These are low cost and cheaper to manufacture.43 Wearable ultrasound therapy devices have even been developed to treat joint pain.44 All types of sounds, that is, infrasound, audible sound and ultrasound, are used for therapy for different health conditions. With more technological developments in the years to come, more applications of sound in medical applications will be seen.
Music is a collection of well-organized, coordinated sounds, vibrations, and silent moments. It is an auditory stimulus that includes organized elements such as melody, form, style, rhythm, harmony, and timbre (1). Music has been produced and enjoyed across all cultures and throughout history and has been observed as behavior in humans from time immemorial. Music, which is a biological phenomenon, is generally considered a cultural creation (2). It is one of the human cultural universal activities with the power to evoke a broad range of emotions from exhilaration to relaxation, happiness to sadness, and fear to comfort in the listeners or performers (3). It is a universal language that influences human existence by being a medium for communication, which is said to have pleasant and healing experiences. The healing powers of music are now studied by modern science and medicine to understand how and why different approaches and methods work in specific clinical conditions. Music and its healing powers have been acknowledged in all cultures and for time immemorial. Various methods and techniques have been followed for using music in healing. They are being used to target symptoms of several diseases/disorders in a range of clinical conditions such as physical medicine, oncology, paediatrics, neurology, psychiatry, and rehabilitation (4).
• Understanding music as a socio-cultural and biological phenomenon
• Brief history of music therapy and Indian music therapy
• Music and the brain
• Shift in music therapy from a socio-cultural to a neuroscientific perspective
• Need for systematic research in the area of music therapy.
Music can have a positive influence on health and well-being in different ways and in a varied scope of contexts. Musical activities have the potential to be therapeutic and educational and have an enriching experience (5). Musical behaviour is universal in nature and observed in humans across their life spans. It is powerful in modulating emotional experience, and over the last three decades, there is a significant body of literature proving the psychological and physiological benefits of engaging with music both actively and passively. Music has been acknowledged to have a deeper role to play in humans’ life, and it is surely beyond mere entertainment. Music therapy and music-based interventions are therefore gaining a strong scientific base to explain how and why music therapy works and how it impacts the human brain and how specific methods of music interventions are useful in chosen clinical conditions.
The concept of music therapy goes back thousands of years. According to Rolando Benenzon, during 1500 BCE, the use of music to influence the human body was first mentioned in writing in Egyptian medical papyri. Greco-Roman, Arabian, Indian, and Chinese traditional medicines include various concepts of music used in a therapeutic way. Mythological and biblical sources also give proof of this through stories and quotes. The history of modern music therapy starts in the eighteenth century. Music therapy continues to grow and develop internationally.
In 1942, in the United States, a Music Advisory Council of the Joint Army and the Navy was formed by the Secretaries of War and the Navy that involved famous personalities in the world of music. In 1943, music became an integral part of the reconditioning program of the army, in accordance with the advice of Surgeon General Norman T. Kirk. It was then considered as a recreation for the soldiers rather than music therapy. As the military officials observed that music aided the soldiers to keep their morale high, the Army Service Forces (ASF) developed a program called “Music in Reconditioning in ASF Convalescent and General Hospitals’’. With the help of this program, injured soldiers were entertained by women’s military bands. These women further contributed to the medical world by continuing to practice music therapy.
In India, evidence of Gandharva tattva, the science of music, can be traced back to the fourth century B.C. The therapeutic effects of musical melodies are explained in “Raga Chikitsa.” Music was used in treating illness by a sixteenth-century classical musician, Swami Haridas, and a few others. During the seventeenth century, Nayaka King Raghunatha Nayak and his minister Govinda Dikshitar presented the effects of music on emotion in their work “Sangita Sudha.” Remedial use of music in psychological ailments has been recorded in palm leaf manuscripts that are being preserved in the Thanjavur Saraswati Mahal Library. Nada Yoga and Raga Chikitsa are the main pillars of the ancient system of Indian music therapy and stem from a deeper understanding of the healing properties of sound, various pitches, and music. The system of Nada Yoga claims that the universe has evolved from a sound projection. Sound is inherently linked to consciousness according to Indian philosophical practices. The term “Nada” can refer to “flow of consciousness.” Developing an unconstrained relation between sound and consciousness was the concern of this system. Raga chikitsa dealt with the therapeutic effects of ragas. Raga is a sequential set of chosen notes (swaras ). There is no equivalent feature of music in the Western Classical music tradition. The emotional effects of a given raga can be diverse. Raga can impact a wide range of emotions such as happiness or sorrow, peace or anger, calmness, and so forth, depending on their nature, and it is this quality of music that makes it therapeutic. This shows that emotional healing in conditions such as anxiety and stress can be made possible with Indian ragas. In fact, the feature of the raga and phase of raga elaboration is known to have a strong impact on the emotional experience of the listener. Emotional experience is known to vary within the different phases of raga elaboration (like alap to jor jhala) (6). Only a handful of systematic studies have been carried out examining the role of Indian traditional/classical music as a method of treatment (7, 8). A study on one-time listening to Indian classical music excerpts in chronic schizophrenia patients has shown promising results in improving attention as measured by brain electrical activities (electroencephalography – EEG and event-related potential – ERP) (9).
Various schools of thought similar to the ones observed in the field of psychology such as the humanistic school of thought, psychodynamic approach, behavioural approach, and neuroscientific approach provide explanations as to how and why music therapy works. The behavioural approach in music therapy centres around adaptive learning experiences and behaviours. It includes behavioural adaptation, active involvement, and so forth and is generally a problem-oriented approach. It calls for a sound knowledge of the principles of behaviour and capacity to represent the sessions accordingly. The humanistic approach in music therapy is schooled by the theoretical principles of humanistic psychology. This approach is controlled by a holistic and person-centred approach. It focuses on features such as natural creativity, privilege of self-expression and so forth of the client. The recent one that is also considered as a newer frontier in the field of music therapy is the neuroscience-based music therapy approach. With the accumulation of evidence contributing to a deeper understanding of the effect of music on the brain and how various techniques employed in music therapy impact various functioning of the human brain, the neuroscience-based approach is enabling music therapy in general to gain a stronger scientific basis and acceptance as an evidence-based therapy.
Music therapy, music-based intervention, music medicine, and so forth are used interchangeably in scientific literature. However, they carry different meanings. Music therapy is considered as an established integrated health profession that makes use of music to facilitate therapeutic activities. Music therapy may be carried out in one-on-one sessions or as group sessions. Depending on the needs of the client, the session can take around 30 to 50 minutes. Music therapy is delivered via two main intervention methods, namely, active and passive/receptive techniques. Active techniques involve a person making music, by composing, singing, playing instruments, improvising music, moving, or discussing their musical experience. Passive or receptive techniques comprise listening to and responding to music. Both techniques are usually combined during treatment and are used as an initiation for the discussion of feelings, goals, and so forth (10).
Clinicians who have undergone specific and systematic training in a given form or method of music therapy are called certified music therapists. They work in a different setting as part of the healthcare team. Music therapists will decide the effective intervention to be used depending on the needs of the client. There are four methods used by a therapist (11). First is being receptive, where the client is supposed to respond verbally, silently, or using another modality after they listen to music which may be live or a recording. Some may include music-assisted relaxation and the use of music and visuals. This approach is suitable when the client is nonverbal or prefers a passive approach through listening. The second type is re-creation, a music-centred method where the client is motivated to play or sing along a pre-composed music piece. This type of intervention will be applicable for a diverse set of populations, from children with delay in development to those with brain injury, or elderly population suffering from dementia. The third type of approach involves improvization which consists of impetuous music making using one’s voice, simple instruments, and body percussion. In this type of intervention, the therapist is required to hear and interpret, and eventually respond to the client’s performance. A population who are non-verbal or are uncomfortable to express directly make the appropriate set for this type of intervention approach. The fourth type of music intervention approach is composition or song writing, where the client is encouraged by the therapist to create their own music or lyrics, which then can be recorded or performed subsequently (12).
Five factors contribute to the effects of music in a therapeutic scenario. They are power of music in modulation of attention, modulation of emotion, modulation of cognition, modulation of behaviour, and modulation of communication (13). The first factor is the modulation of attention. Music grabs our attention and distracts us from other negative experiences (worry, anxiety etc.). This also explains the effects of listening to music during medical procedures for anxiety and pain reduction. The second aspect is the modulation of emotion. Activity of brain regions that are involved in the initiation, generation, maintenance, termination, and modulation of emotions can be regulated using music. Music also modulates cognition; the third factor that contributes to the effect of music therapy is modulation of cognition. Music is related to memory processes (including the encoding, storage, and decoding of musical information and events related to musical experiences). It is also involved in the analysis of musical syntax and musical meaning. The fourth factor that contributes to the effect of music therapy is modulation of behaviour. Behaviours such as the movement patterns involved in walking, speaking, and grasping can be evoked and conditioned with the help of music. The fifth factor is modulation of communication. Music is a means of communication and can also affect communication. Hence, music can play a major role in promotion of social bonding, improving language functions, and improving social relationships (13).
Music therapy makes use of the dynamic capabilities of music to the betterment of one’s well-being. A person’s relatedness and responses to music to uplift positive changes in mood and overall mental health is used by music therapists. The therapy incorporates creating music with different types of instruments or listening to music. Therapies like cognitive behavioural therapy (CBT) and counselling involve talking, and thus it makes them not suitable for people who face problems with verbal communication. This is where music therapy can be advantageous. As the therapy does not depend on verbal communication, it can be helpful for those who have difficulty in conveying verbally. So, it can be considered as an alternative to therapies such as (CBT), counselling therapy, and so forth.
The experimental process or protocols which use music in its different forms and study its therapeutic effects are referred to as music-based interventions (14). Music interventions can be considered as musical exercises or methods which are primarily composed of music listening, music-making, or singing (15). Listening to music based on the music medicine approach, relational music therapy, general music-based approaches, rehabilitative music therapy, individualized music listening are some of the types of intervention with music in clinical settings. Music therapy should not be confused with music medicine which is a music-based intervention which is done by healthcare professionals.
It is important to know how our body responds to music during different music-based activities. Measuring the electrodermal activity and heart rate gives an idea about the effects of music perception on the activity of the autonomic nervous system. The number and intensity of outlines, shivers, and chills are also investigated which supports this understanding. Music listening has an evident effect on motor functions of a person. Movement initiation by music perception in the way of dancing, tapping, swaying, singing, hopping, head-nodding, and so forth along with music is a very common experience (16).
Different features of music such as melody, pitch, tempo, and so forth are processed by different areas of the brain. Rhythm is processed by the cerebellum, a small portion of the right temporal lobe aids understanding of pitch, and the emotional signals generated by the music are decoded by the frontal lobes. When one hears powerful music, the nucleus accumbens, the reward centre of the brain, can even induce physical signs of pleasure, such as goosebumps. These profound physical responses of the body to music can be used by music therapy to support people with mental health conditions.
Music therapy offers extra benefits to listening or creating music than what other forms of therapies offer. For example, learning and practicing a music excerpt can improve reading, comprehension ability, memory, coordination, and so forth. Participants enjoy a sense of accomplishment by creating a music excerpt, which in turn boosts their self-esteem and mood. Music therapy taps into the creative side of an individual, which turns out to be a better way of introspecting difficult emotions or even suppressed emotions. Both evaluation and enhancement of cognitive, social, emotional, and motor functioning is often possible using music therapy.
Other documented benefits of music therapy include attentiveness, concentration, communication skills, confidence, increased motivation, self-awareness and mindfulness of others, improved self-esteem, emotional release, increased verbalization, beneficial effects on the psychological and physiological health, improved quality of sleep; alleviation of stress, anxiety, substance dependency, autism, personality issues; improved overall quality of life and so forth.
The International Association for Music and Medicine established in 2009 at the University of Limerick, Ireland, aims to explore music therapy, music and medicine, and music-based interventions in healthcare contexts. The American Musical Therapy Association has about 2500 and more members working for hospitals, schools, clinics, rehabilitation centres and private practice settings (1).
Some of the extensive and diverse networks of the brain are said to be activated by music. It activates the auditory cortex, memory regions, and regions of the brain related to motor movements. Emotional music, in addition to activation of the region of emotion, also synchronizes it. As music can activate almost all brain networks, it can keep a number of brain pathways strong. These pathways involve the cognitive function, learning, happiness, well-being, and so forth. Along with psychological effects, music is said to have influence on physiological well-being too. Music boosts one’s immunity, helps to reduce the levels of stress and anxiety, and can also ease depression. Studies show that for patients undergoing surgery results of music listening were far more effective than the prescribed drugs. Listening and playing music is said to have a connection to lower levels of cortisol, the stress hormone.
The pituitary gland, secretions of which affect the nervous system and the flow of blood, is stimulated during music listening. Music listening creates a vibration in the cells of the listener. These vibrations are necessary to change the consciousness of the patients, which in turn can help promote their health. One of the major uses of music listening is that it helps one relax and feel refreshed. Listening to some light music during work can improve one’s efficiency. Negative emotions such as worry, bias, anger, and so forth can be controlled by listening to music. It also helps in improving neurocognitive functions such as attention and memory. In addition, it can also help in addressing stress, pain, blood pressure; help patients recover post-surgery; help growth in premature babies, and so forth.
With time, music which was considered as a socio-cultural activity is now seen in the light of neuro-based practice. Here we can see a paradigm shift, that is, a transition of music-based interventions from a socio-cultural to neuroscientific perspective. Evidence for one such paradigm shift is the emergence of neurologic music therapy (NMT). It is defined as “the therapeutic application of music to cognitive, sensory, and motor dysfunctions due to neurologic disease of the human nervous system” (17). NMT differs from general music therapy in the mode of delivery. General music therapy involves treating different scopes of patients’ needs such as physical, mental, and so forth by adopting the ways such as music listening, playing, or music writing. NMT is an evidence-based practice which focuses mainly on neuroscience of music (18). It is a methodical treatment approach to improve sensorimotor, language, and cognitive functioning through music (17).
It also takes into account the elements of music that cause changes in the brain and its connection, also known as neuropathways. These are done using NMT interventions which is a specific neuroscience research-based technique. This intervention is applied in a manner according to the therapeutic needs of the client.
Music must be viewed as something that can stimulate our brain. It is a non-invasive technique, which has attracted much interest. The therapeutic value of music can be in part explained by its cultural role in facilitating social learning and emotional well-being. However, a number of studies have shown that rhythmic entrainment of motor function can actively facilitate the recovery of movement in patients with stroke, Parkinson’s disease, cerebral palsy, and traumatic brain injury (19). Studies of people with memory disorders, such as Alzheimer’s disease, suggest that neuronal memory traces built through music are deeply ingrained and more resilient to neurodegenerative influences. Findings from individual randomized trials suggest that music therapy is accepted by people with depression and is associated with improvements in mood disorders (20).
Various studies have been conducted to learn the effects of music on the human brain at a neural level. Neuroimaging studies are the major ones that have contributed to understanding the neural underpinning of music-based activities. These studies have recognized different brain regions that are activated by music listening or recall (21). Comprehending how our brain analyses, stores, and retrieves music is one of the most demanding issues in the field of neuroscience. Direct neural recordings acquired from the human brain indicate distributed and overlapping brain regions correlated with music listening and recall (21).
Over the last 30 years, various studies have been conducted to explore the neural underpinnings of music listening. Using imaging techniques such as functional MRI (f MRI) and PET, studies demonstrate the association of music listening with hemodynamic feedbacks in a distributed network which involve the auditory cortex, brain areas associated with motor control, and different other cognitive functions such as memory (e.g., hippocampus, temporal cortex), working memory (e.g., frontal cortex), control of attention and emotion. Various electroencephalography (EEG) researches also have augmented these findings (22).
Neuromusicology looks into the fundamentals of human musical information processing such as neural encoding, localization of functions, and dynamic principles. There is a divergence between sensory and cognitive neuromusicology. Understanding the operation of musical signal processing with respect to functional, physiological, and biochemical undertaking of the auditory system involves sensory neuromusicology. Cognitive neuromusicology focuses on studying the association of different brain regions in cognition in view of music. Both the sensory and the cognitive approaches can be considered as a part of a single research strategy with an objective to explore the neural mechanisms underlying sensory, perceptual, and cognitive information processing (23).
Evidence shows that a group of brain structures involved in various functions like cognitive, sensorimotor, and emotional processing are activated on listening to music or making music. Investigations on the favourable effects of music on psychological and physiological health can be achieved using the existing knowledge on neural correlates of music-evoked emotions and their health-related autonomic, endocrinological, and immunological effects (24). Emotions evoked by music can bring about autonomic and endocrine responses and also facial expression which is a motoric expression of emotion. Studies demonstrate that music enhances individuals’ health and well-being through involvement of neurochemical systems. These are with regard to different aspects such as (i) reward, motivation, and pleasure; (ii) immunity; (iii) social connection; (iv) stress and arousal and so forth (3). These observations provide a basis for using music as a therapeutic technique (24).
Music therapy can assist the brain in re-organizing and creating new neural pathways. This ability of the brain to change and grow following different experiences is considered as neural plasticity (25). Studies in neural plasticity show that music not only has an effect on brain development but can also shape the adult brain. Researches have proved that the plasticity induced by music training is not restricted to developing the brain; it can also improve the functional and structural aspects of different brain regions (25). This functional and structural plasticity can be induced in the anterior and middle part of the hippocampus by music practice, and these changes are followed by increased expertise in musical tasks, working or short-time memory, and fluid intelligence (26). Musical training aids in improving cognitive and perceptual motor function eliciting changes in structure and functions of the brain. In older adults, learning a new skill engages neural plasticity more strongly (26).
Developments in neuroimaging techniques such as f MRI, PET, and EEG make the research on effects of music on neural plasticity more efficient. The studies conducted show that cognitive fall-off and dementia can be put off by recent and past musical activities. Neuroplasticity of the human brain is used to associate musical ideas with motor skills. Music therapy is manifested in rebuilding the motor skills in the elderly whose motor function declined following a stroke (26).
The brain has a neurotransmitter called dopamine that is involved in motivation and reward-seeking behaviour (27), working memory (28), and reinforcement learning (29). According to studies, response of dopamine neurons is translated to stimuli during learning (30). Stegemollar identified three main principles of neural plasticity that demonstrate the effectiveness of music therapy in uplifting behavioural changes (25). The first principle is that music triggers the release of neurotransmitters such as dopamine and serotonin which are associated with the reward system in the brain and are responsible for feelings of happiness. Dopamine plays a major role in neural plasticity as the stimulation of dopaminergic neurons is said to cause cortical remapping. The second principle is the Hebbian theory which states that “neurons which fire together wire together,” meaning that neurons which fire together within tens of milliseconds tend to form a new connection together or strengthen the existing one. This theory is used by therapists to pair music with movement, breathing, vocalization, and so forth to induce simultaneous firing of neurons that control the behaviours described. According to the third principle, plasticity of the brain will be negatively affected by listening to noise, and this results in increased stress which in turn affects the cognition and memory (25).
It is known that music is efficient in inducing strong positive emotions and also in uplifting the mood of a being (31). These qualities of music can certainly be used in clinical arrangements where negative emotions such as pain and anxiety affect one’s well-being, and this will create a need for employment of anaesthetic and analgesic drugs. According to studies, music is considered to lessen the stress during pre- and post-medical procedures including surgery, angiography, colonoscopy, and so forth.
A study was conducted to establish these findings where patients were grouped randomly either to a music group who listened to instrumental music or to a control group which was made to listen to a non-musical placebo stimulus. Both groups were asked to listen to the auditory stimulus about two hours before and in the intra-operative duration. Results demonstrated that, during surgery, compared to the control group, patients of the music group had a lower propofol consumption and lower cortisol levels. This provides evidence to the argument that listening to music reduces sedative requirements to reach light sedation. It also shows that during surgery music can exert a stress-reducing effect under local anaesthesia. These findings stipulate that music can be used as an effective treatment to bring down stress in clinical context (31).
Studies on animal models show that prolonged exposure to music can improve one’s learning due to changes done in the hippocampus (25). This can be due to the fact that acoustic signals of music are more consonant than that of speech (30). Music therapists work with subjects with different kinds of neurologic and physiologic conditions and use the elements of music to make necessary changes in the brain. A Cochrane database systematic review published in 2017 carried reports that in people with depression, music therapy is said to have short-term beneficial effects. When compared to effects of treatments alone, music therapy along with the usual treatments help in reduction of depressive symptoms. The anxiety levels of depressed individuals were found to be reduced and they were found to have improved global functioning.
Music therapy has come a long way since the early twentieth century. Music plays an important role in individual and social development. Music therapy has a broad and extensive history. It has an active relationship with the brain, and it has distinctive advantages when compared to medications. Music is used in the form of therapy and intervention because of its positive effects on both physical and psychological ailments. These interventions have seen a transition from a socio-cultural to neuroscientific perspective. The science of music therapy is still being investigated through advanced methods and techniques. However, we still need to explore to gain full awareness of its potential. There is a significant need to carry out further randomized controlled trials.