ResearchPad - medical-physics https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Applied Mathematics of Ray Tracing and Perspective Projection in Fiducial-Based Registration of X-Ray Images]]> https://www.researchpad.co/article/elastic_article_16495 Ray tracing (RT) and perspective projection (PP) using fiducial-based registration can be used to determine points of interest in biplanar X-ray imaging. We sought to investigate the implementation of these techniques as they pertain to X-ray imaging geometry. The mathematical solutions are presented and then implemented in a phantom and actual case with numerical tables and imaging. The X-ray imaging is treated like a Cartesian system in millimeters (mm) with a standard frame-based stereotactic system. In this space, the point source is the X-ray emitter (focal spot), the plane is the X-ray detector, and fiducials are in between the source and plane. In a phantom case, RT was able to predict locations of fiducials after moving the point source. Also, a scaled PP matrix could be used to determine imaging geometry, which could then be used in RT. Automated identification of spherical fiducials in 3D was possible using a center of mass computation with average Euclidean error relative to manual measurement of 0.23 mm. For PP, RT projection or a combinatorial approach could be used to facilitate matching 3D to 2D points. Despite being used herein for deep brain stimulation (DBS), utilization of this kind of imaging analysis has wide medical and non-medical applications.

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<![CDATA[The Use of Periareolar Topical Lidocaine Jelly After Needle Localization May Reduce Pain of Subsequent Lymphoscintigraphy]]> https://www.researchpad.co/article/elastic_article_14260 Purpose

Technetium Tc-99m sulfur colloid (99mTc-SC) breast lymphoscintigraphy is commonly performed to identify the sentinel lymph node (SLN) in patients diagnosed with breast carcinoma undergoing lumpectomy. The purpose of this report is to describe how the use of 2% topical lidocaine jelly immediately after the completion of needle localization and prior to scintigraphy may substantially reduce pain associated with the injection of 99mTc-SC.

Materials and methods

This was a quality improvement project. Patients were asked to score the severity of pain associated with the periareolar 99mTc-SC injections for sentinel node lymphoscintigraphy. In order to decrease the discomfort, topical lidocaine was applied to the periareolar skin after the completion of the needle localization, but prior to transferring the patient from the mammography room to the nuclear medicine department for the 99mTc-SC injections. At the time of 99mTc-SC injection, patients were asked to score the pain of injection from 0 (none) to 10 (worst).

Results

The average pain score of the women who did not receive topical lidocaine jelly was 8 (range: 5-9). In the 10 women who received topical lidocaine jelly after needle localization, the average pain score was 2.5 (range: 1-5). Interestingly, the pain score for women who discussed the possible use of lidocaine jelly with the radiologists but still did not receive topical lidocaine jelly was also low at 6.5. For patients who received the lidocaine jelly only five minutes prior to injection, the average pain score was 6.

Conclusion

The application of lidocaine jelly after the conclusion of needle localization, with a 15-40-minute delay prior to periareolar injections with 99mTc-SC for sentinel node lymphoscintigraphy, appears to substantially reduce the pain associated with the injection of 99mTc-SC.

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<![CDATA[Influence of Different Types of Root Canal Irrigation Regimen on Resin-based Sealer Penetration and Pushout Bond Strength]]> https://www.researchpad.co/article/elastic_article_10528 Introduction

The main objective of root canal treatment is to eliminate the micro-organism from the root canal system and three-dimensional obturation. The proper cleaning and shaping can be accomplished only by using appropriate instruments and effective irrigants during the root canal treatment.

Aim

To evaluate the influence of three different final irrigation regimen on depth of penetration of root canal sealers and push-out bond strength of obturation material.

Materials and methods

Thirty-six extracted single-rooted mandibular premolar human teeth with straight canals were decoronated and instrumented according to groups. Group I: Root canals were irrigated with 3% sodium hypochlorite (NaOCl), then irradiated with 980 nm diode laser (n = 12), Group II: Root canals were irrigated with 3% NaOCl, followed by 17% ethylenediaminetetraacetic acid (EDTA) (n = 12), Group III: Root canals were irrigated with 3% NaOCl, followed by 10% citric acid (n = 12). In each sample, single cone obturation was done with gutta-percha using AH plus sealer incorporated with rhodamine B dye. After seven days coronal, middle and apical thin cross sections were made for evaluation of dentinal tubule sealer penetration depth and pushout bond strength using confocal laser scanning microscope (CLSM) and universal testing machine, respectively. Statistical analysis among the three groups was done by using Kruskal-Wallis and post hoc test.

Results

Mean tubular penetration depth between diode laser (136.57 ± 48 µm), EDTA (130.56 ± 53 µm) and citric acid (113.37 ± 34 µm; P < 0.05) showed statistically highly significant results. Pushout bond strength did not differ significantly between diode laser (1.21 ± 0.48 Mpa), EDTA (1.05 ± 0.45 Mpa) and citric acid (0.93 ± 0.44 Mpa; P > 0.05).

Conclusion

Mean tubular penetration depth of AH plus sealer was better in diode laser than in EDTA and citric acid. Average push-out bond strength of obturation material did not differ significantly between diode laser, EDTA and citric acid.

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<![CDATA[Features and Diagnostic Accuracy of Optical Coherence Tomography Angiography in Neovascular Age-related Macular Degeneration]]> https://www.researchpad.co/article/Nac95e44c-0430-4032-b3cf-c486c59f1f3b

Introduction

Age-related macular degeneration (AMD) is one of the important causes of visual impairment in aging population. Fundus fluorescein angiography (FFA) is gold standard for the diagnosis of neovascular AMD (nAMD) while optical coherence tomography (OCT) aids in the diagnosis of nAMD and is very useful for follow-up. OCT angiography (OCTA) is an evolving imaging technology that can be used as a valid diagnostic tool to study morphology of choroidal neovascularization (CNV) that is seen in nAMD. This study was conducted with the objective to determine diagnostic accuracy and OCTA features of occult and classic CNV in patients with nAMD.

Methods

In this prospective observational study, 90 eyes of 58 patients with nAMD were studied with OCT, OCTA and FFA. OCTA scans were analyzed to qualitatively describe the morphological appearance of CNV in terms of location, pattern and configuration. The OCTA sensitivity and specificity for CNV detection were calculated by comparing it with FFA.

Results

FFA detected CNV in 70 of the 90 eyes (77.77%) whereas OCTA identified CNV in 69 eyes (76.7%). Among 69 eyes with CNV, it was well-defined in 51 (73.9%) eyes and poorly defined in 18 (26.1%) eyes. There were four false positive and five false negative cases. The sensitivity, specificity, positive predictive value and negative predictive value of OCTA in detection of nAMD were found to be 92.85%, 80.0%, 94.2 and 76.2, respectively.

Conclusion

OCTA is a useful, noninvasive, reproducible imaging tool for diagnosing, classifying and localizing CNV. The technique has high sensitivity and specificity and can be used reliably in cases where FFA is contraindicated or inconclusive.

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<![CDATA[Outcomes of Multi-disciplinary Management of Metastatic Renal Cell Carcinoma]]> https://www.researchpad.co/article/N2bdbddbe-34d8-499c-bc7a-d4e57d719f47

Metastatic renal cell carcinoma (mRCC) is associated with a poor prognosis. It is traditionally a treatment-resistant disease necessitating multi-modal treatment and close follow-up. We herein report a case of mRCC in a patient who was managed closely by a multi-disciplinary team and still retained a very good performance status and treatment response three years after diagnosis. We highlight the importance of close monitoring, switching systemic therapies at progression, early palliative radiotherapy, and patient education in controlling disease burden and maintaining quality of life in patients with mRCC.

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<![CDATA[Evaluation of an Automated Proton Planning Solution]]> https://www.researchpad.co/article/5c801387d5eed0c484a9c525

Purpose

Intensity-modulated proton therapy (IMPT) treatments are increasing, however, treatment planning remains complex and prone to variability. RapidPlanTMPT (Varian Medical Systems, Palo Alto, California, USA) is a pre-clinical, proton-specific, automated knowledge-based planning solution which could reduce variability and increase efficiency. It uses a library of previous IMPT treatment plans to generate a model which can predict organ-at-risk (OAR) dose for new patients, and guide IMPT optimization. This study details and evaluates RapidPlanTMPT.

Methods

IMPT treatment plans for 50 head-and-neck cancer patients populated the model-library. The model was then used to create knowledge-based plans (KBPs) for 10 evaluation-patients. Model quality and accuracy were evaluated using model-provided OAR regression plots and examining the difference between predicted and achieved KBP mean dose. KBP quality was assessed through comparison with respective manual IMPT plans on the basis of boost/elective planning target volume (PTVB/PTVE) homogeneity and OAR sparing. The time to create KBPs was recorded.

Results

Model quality was good, with an average R2 of 0.85 between dosimetric and geometric features. The model showed high predictive accuracy with differences of <3 Gy between predicted and achieved OAR mean doses for 88/109 OARs. On average, KBPs were comparable to manual IMPT plans with differences of <0.6% in homogeneity. Only 2 of 109 OARs in KBPs had a mean dose >3 Gy more than the manual plan. On average, dose-volume histogram (DVH) predictions required 0.7 minutes while KBP optimization and dose calculation required 4.1 minutes (a ‘continue optimization’ phase, if required, took an additional 2.8 minutes, on average).

Conclusions

RapidPlanTMPT demonstrated efficiency and consistency and IMPT KBPs were comparable to manual plans. Because worse OAR sparing in a KBP was not always associated with geometric-outlier warnings, manual plan checks remain important. Such an automated planning solution could also assist in clinical trial quality assurance and overcome the learning curve associated with IMPT.

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<![CDATA[Prognostic Significance of Tumor Location for Liver Cancer Radiotherapy]]> https://www.researchpad.co/article/5c801490d5eed0c484a9dd9a

Introduction

According to the Surveillance, Epidemiology and End Results (SEER) data, cancerous involvement of the liver is on an increase over the last three decades. It occurs worldwide in all races and carries a poor prognosis. Currently, considerable progress has been made in patient selection, staging, surgery, chemotherapy agents, and stereotactic radiotherapy in both primary and metastatic liver cancers with improved outcomes. While there is evidence of the prognostic factors of liver function, the involvement of the portal vein, inferior vena cava thrombosis, lesion size, radiation dose, number of fractions, and SBRT techniques, there is no study evaluating outcomes with the location of the lesion. Our aim in this retrospective study was to explore the correlation of tumor location from the portal vein bifurcation (vascular wall) and the radiotherapy outcome (survival) in hepatocellular cancer.

Methods

Contrast-enhanced computed tomography (CT) studies in 86 patients with liver cancer were retrospectively reviewed in an institutional review board (IRB)-approved database to determine the distance to the bifurcation point of the portal vein from tumor’s centre of mass (distance tumor bifurcation: DTB) and from the edge point of the planning target volume closest to the bifurcation (distance edge bifurcation: DEB). The mean dose to the sphere of 1 cm diameter around the bifurcation point (mean dose at bifurcation: MDB) was calculated. These parameters were tested as predictors of patient outcomes using univariate and multivariate analysis as two groups of patients.

Results

Only the DEB correlation with survival for hepatocellular carcinoma (HCC) was found to be significant (P = 0.028). A larger MDB is caused by a smaller DTB and a smaller DEB. The hazard ratio for DTB, DEB, and MDB were 0.48, 0.41, and 1.05, respectively. The DEB was found to be a better predictor of outcomes (overall survival) compared to the DTB and MDB parameters. The close proximity of the tumor to the blood supply vessels was a decisive factor. The DTB parameter is also dependent on the size of the tumor and this factor weakens the correlation of this parameter on survival data. The inclusion of the dosimetric and geometric location, as well as distance parameters in predictive models for liver cancer patients, was shown to benefit the pre-selection of treatment options for liver cancer patients treated with radiotherapy.

Conclusion

For hepatocellular cancer patients, the distance between the edge point of the planning treatment volume (PTV) to the portal vein bifurcation (DEB) of more than 2 cm was found to be a predictor of survival.

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<![CDATA[Impact of Multi-leaf Collimator Parameters on Head and Neck Plan Quality and Delivery: A Comparison between Halcyon™ and Truebeam® Treatment Delivery Systems]]> https://www.researchpad.co/article/5c686299d5eed0c484022a26

Purpose

A new dual-layer multi-leaf collimator (MLC) system with several improved characteristics was introduced with the Varian Halcyon™ treatment platform. This study evaluated this new MLC’s impact on head and neck plan quality and delivery efficiency.

Methods

Nine patients were retrospectively studied with Institutional Review Board (IRB) approval. To compare plan quality between the Halcyon dual-layer MLC and Truebeam® MLC, all patients were replanned with the same prescription and target coverage following the institutional clinical protocol for both platforms and using both intensity modulated radiation therapy (IMRT) or volumetrically modulated arc therapy (VMAT) techniques. Organs-at-risk (OAR) dose-volume histogram (DVH) statistics were compared along with total plan monitor units (MU). To evaluate delivery efficiency, actual beam-on time for five patients’ plans were recorded and compared. To evaluate the impact of MLC performance parameters on plan quality, virtual MLC models were generated by matching Truebeam MLC’s parameters to those of the Halcyon dual-layer MLC both individually and combined. OAR doses were then compared between these virtual MLCs, the Truebeam MLC, and the actual Halcyon MLC.

Results

Overall the Halcyon dual-layer MLC provided similar plan quality compared to Truebeam MLC for VMAT plans, and improved sparing for majority of the OARs when using IMRT. Paired comparison showed median dose differences in mean doses to the parotids, cochlea, esophagus, and larynx ranged from -0.83 Gy to 0.37 Gy for VMAT, and from -4.79 Gy to -0.04 Gy for IMRT, with negative values indicating improved performance by Halcyon. Despite a slight increase in plan MU, the Halcyon reduced the total beam-on time by 42.8 ± 8.5%. Virtual MLC simulations demonstrated that matching MLC transmission accounted for nearly half of the total dose difference between Halcyon and Truebeam IMRT plans.

Conclusion

When compared to the Truebeam, the Halcyon’s dual-layer MLC achieved similar plan quality using VMAT, and improved OAR sparing using IMRT, while providing nearly twice as fast treatment delivery. Reduction in MLC transmission is the dominating factor contributing to dosimetric differences in OAR sparing.

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<![CDATA[Ventricular Tachycardia: A Treatment Comparison Study of the CyberKnife with Conventional Linear Accelerators]]> https://www.researchpad.co/article/5c1ec819d5eed0c484b3c376

The work described here compared the available technical solutions for the treatment of ventricular tachycardia with stereotactic body radiation therapy. Due to the complexity of target motion during cardiac and pulmonary motion as well as the several proximate radio-sensitive structures of the tracheobronchial tree and esophagogastrointestinal tract, four potential candidates for this treatment were identified: Accuray CyberKnife (Accuray Incorporated, Sunnyvale, California, United States), Varian TrueBeam (Varian Medical Systems, Palo Alto, California, USA), Elekta Infinity (Elekta, Stockholm, Sweden), and Varian Edge (Varian Medical Systems, Palo Alto, California, USA). All four treatment modalities were evaluated for their ability to deliver a conformal, homogeneous dose to most of the target volume, to spare nearby and distant critical and sensitive anatomical structures as well as for treatment efficiency. It was found that conventional linear accelerator technology was superior in their ability to spare distant critical structures and deliver treatments efficiently while the CyberKnife showed superiority in sparing nearby critical structures more aggressively by creating larger dose gradients at the periphery of the target volume. Both treatment modalities were similar in their ability to cover the entire target with the prescription dose, conform that dose to the target volume, and deliver a homogeneous dose.

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<![CDATA[Four-dimensional Plan Optimization for the Treatment of Lung Tumors Using Pencil-beam Scanning Proton Radiotherapy]]> https://www.researchpad.co/article/5c125785d5eed0c48487f781

Purpose 

This study aimed to evaluate the effectiveness of four-dimensional (4D) robust optimization for proton pencil-beam scanning (PBS) treatment of lung tumors.

Patients and methods 

In seven patients with lung cancer, proton beam therapy was planned using 4D robust optimization over 4D computed tomography (CT) data sets. The gross target volume (GTV) was contoured based on individual breathing phases, and a 5-mm expansion was used to generate the clinical target volume (CTV) for each phase. The 4D optimization was conducted directly on the 4D CT data set. The robust optimization settings included a CT Hounsfield unit (HU) uncertainty of 4% and a setup uncertainty of 5 mm to obtain the CTV. Additional target dose objectives such as those for the internal target volume (ITV) as well as the organ-at-risk (OAR) dose requirements were placed on the average CT. For comparison, three-dimensional (3D) robust optimization was also performed on the average CT. An additional verification 4D CT was performed to verify plan robustness against inter-fractional variations.

Results 

Target coverages were generally higher for 4D optimized plans. The difference was most pronounced for ITV V70Gy when evaluating individual breathing phases. The 4D optimized plans were shown to be able to maintain the ITV coverage at full prescription, while 3D optimized plans could not. More importantly, this difference in ITV V70Gy between the 4D and 3D optimized plans was also consistently observed when evaluating the verification 4D CT, indicating that the 4D optimized plans were more robust against inter-fractional variations. Less difference was seen between the 4D and 3D optimized plans in the lungs criteria: V5Gy and V20Gy.

Conclusion 

The proton PBS treatment plans optimized directly on the 4D CT were shown to be more robust when compared to those optimized on a regular 3D CT. Robust 4D optimization can improve the target coverage for the proton PBS lung treatments.

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<![CDATA[Robust and Fast Whole Brain Mapping of the RF Transmit Field B1 at 7T]]> https://www.researchpad.co/article/5989da6fab0ee8fa60b941ae

In-vivo whole brain mapping of the radio frequency transmit field B1+ is a key aspect of recent method developments in ultra high field MRI. We present an optimized method for fast and robust in-vivo whole-brain B1+ mapping at 7T. The method is based on the acquisition of stimulated and spin echo 3D EPI images and was originally developed at 3T. We further optimized the method for use at 7T. Our optimization significantly improved the robustness of the method against large B1+ deviations and off-resonance effects present at 7T. The mean accuracy and precision of the optimized method across the brain was high with a bias less than 2.6 percent unit (p.u.) and random error less than 0.7 p.u. respectively.

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<![CDATA[Exhaled Air Dispersion during Coughing with and without Wearing a Surgical or N95 Mask]]> https://www.researchpad.co/article/5989da0aab0ee8fa60b7763f

Objectives

We compared the expelled air dispersion distances during coughing from a human patient simulator (HPS) lying at 45° with and without wearing a surgical mask or N95 mask in a negative pressure isolation room.

Methods

Airflow was marked with intrapulmonary smoke. Coughing bouts were generated by short bursts of oxygen flow at 650, 320, and 220L/min to simulate normal, mild and poor coughing efforts, respectively. The coughing jet was revealed by laser light-sheet and images were captured by high definition video. Smoke concentration in the plume was estimated from the light scattered by smoke particles. Significant exposure was arbitrarily defined where there was ≥ 20% of normalized smoke concentration.

Results

During normal cough, expelled air dispersion distances were 68, 30 and 15 cm along the median sagittal plane when the HPS wore no mask, a surgical mask and a N95 mask, respectively. In moderate lung injury, the corresponding air dispersion distances for mild coughing efforts were reduced to 55, 27 and 14 cm, respectively, p < 0.001. The distances were reduced to 30, 24 and 12 cm, respectively during poor coughing effort as in severe lung injury. Lateral dispersion distances during normal cough were 0, 28 and 15 cm when the HPS wore no mask, a surgical mask and a N95 mask, respectively.

Conclusions

Normal cough produced a turbulent jet about 0.7 m towards the end of the bed from the recumbent subject. N95 mask was more effective than surgical mask in preventing expelled air leakage during coughing but there was still significant sideway leakage.

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<![CDATA[Scaling Dynamic Response and Destructive Metabolism in an Immunosurveillant Anti-Tumor System Modulated by Different External Periodic Interventions]]> https://www.researchpad.co/article/5989daefab0ee8fa60bc0787

On the basis of two universal power-law scaling laws, i.e. the scaling dynamic hysteresis in physics and the allometric scaling metabolism in biosystem, we studied the dynamic response and the evolution of an immunosurveillant anti-tumor system subjected to a periodic external intervention, which is equivalent to the scheme of a radiotherapy or chemotherapy, within the framework of the growth dynamics of tumor. Under the modulation of either an abrupt or a gradual change external intervention, the population density of tumors exhibits a dynamic hysteresis to the intervention. The area of dynamic hysteresis loop characterizes a sort of dissipative-therapeutic relationship of the dynamic responding of treated tumors with the dose consumption of accumulated external intervention per cycle of therapy. Scaling the area of dynamic hysteresis loops against the intensity of an external intervention, we deduced a characteristic quantity which was defined as the theoretical therapeutic effectiveness of treated tumor and related with the destructive metabolism of tumor under treatment. The calculated dose-effectiveness profiles, namely the dose cumulant per cycle of intervention versus the therapeutic effectiveness, could be well scaled into a universal quadratic formula regardless of either an abrupt or a gradual change intervention involved. We present a new concept, i.e., the therapy-effect matrix and the dose cumulant matrix, to expound the new finding observed in the growth and regression dynamics of a modulated anti-tumor system.

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<![CDATA[Detailing Radio Frequency Heating Induced by Coronary Stents: A 7.0 Tesla Magnetic Resonance Study]]> https://www.researchpad.co/article/5989da6dab0ee8fa60b935f4

The sensitivity gain of ultrahigh field Magnetic Resonance (UHF-MR) holds the promise to enhance spatial and temporal resolution. Such improvements could be beneficial for cardiovascular MR. However, intracoronary stents used for treatment of coronary artery disease are currently considered to be contra-indications for UHF-MR. The antenna effect induced by a stent together with RF wavelength shortening could increase local radiofrequency (RF) power deposition at 7.0 T and bears the potential to induce local heating, which might cause tissue damage. Realizing these constraints, this work examines RF heating effects of stents using electro-magnetic field (EMF) simulations and phantoms with properties that mimic myocardium. For this purpose, RF power deposition that exceeds the clinical limits was induced by a dedicated birdcage coil. Fiber optic probes and MR thermometry were applied for temperature monitoring using agarose phantoms containing copper tubes or coronary stents. The results demonstrate an agreement between RF heating induced temperature changes derived from EMF simulations versus MR thermometry. The birdcage coil tailored for RF heating was capable of irradiating power exceeding the specific-absorption rate (SAR) limits defined by the IEC guidelines by a factor of three. This setup afforded RF induced temperature changes up to +27 K in a reference phantom. The maximum extra temperature increase, induced by a copper tube or a coronary stent was less than 3 K. The coronary stents examined showed an RF heating behavior similar to a copper tube. Our results suggest that, if IEC guidelines for local/global SAR are followed, the extra RF heating induced in myocardial tissue by stents may not be significant versus the baseline heating induced by the energy deposited by a tailored cardiac transmit RF coil at 7.0 T, and may be smaller if not insignificant than the extra RF heating observed under the circumstances used in this study.

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<![CDATA[Towards the “Baby Connectome”: Mapping the Structural Connectivity of the Newborn Brain]]> https://www.researchpad.co/article/5989da2aab0ee8fa60b823d1

Defining the structural and functional connectivity of the human brain (the human “connectome”) is a basic challenge in neuroscience. Recently, techniques for noninvasively characterizing structural connectivity networks in the adult brain have been developed using diffusion and high-resolution anatomic MRI. The purpose of this study was to establish a framework for assessing structural connectivity in the newborn brain at any stage of development and to show how network properties can be derived in a clinical cohort of six-month old infants sustaining perinatal hypoxic ischemic encephalopathy (HIE). Two different anatomically unconstrained parcellation schemes were proposed and the resulting network metrics were correlated with neurological outcome at 6 months. Elimination and correction of unreliable data, automated parcellation of the cortical surface, and assembling the large-scale baby connectome allowed an unbiased study of the network properties of the newborn brain using graph theoretic analysis. In the application to infants with HIE, a trend to declining brain network integration and segregation was observed with increasing neuromotor deficit scores.

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<![CDATA[Modelling and Detecting Tumour Oxygenation Levels]]> https://www.researchpad.co/article/5989db1fab0ee8fa60bcef5b

Tumours that are low in oxygen (hypoxic) tend to be more aggressive and respond less well to treatment. Knowing the spatial distribution of oxygen within a tumour could therefore play an important role in treatment planning, enabling treatment to be targeted in such a way that higher doses of radiation are given to the more radioresistant tissue. Mapping the spatial distribution of oxygen in vivo is difficult. Radioactive tracers that are sensitive to different levels of oxygen are under development and in the early stages of clinical use. The concentration of these tracer chemicals can be detected via positron emission tomography resulting in a time dependent concentration profile known as a tissue activity curve (TAC). Pharmaco-kinetic models have then been used to deduce oxygen concentration from TACs. Some such models have included the fact that the spatial distribution of oxygen is often highly inhomogeneous and some have not. We show that the oxygen distribution has little impact on the form of a TAC; it is only the mean oxygen concentration that matters. This has significant consequences both in terms of the computational power needed, and in the amount of information that can be deduced from TACs.

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<![CDATA[In Vivo Detection of Activated Platelets Allows Characterizing Rupture of Atherosclerotic Plaques with Molecular Magnetic Resonance Imaging in Mice]]> https://www.researchpad.co/article/5989da97ab0ee8fa60ba2584

Background

Early and non-invasive detection of platelets on micro atherothrombosis provides a means to identify unstable plaque and thereby allowing prophylactic treatment towards prevention of stroke or myocardial infarction. Molecular magnetic resonance imaging (mMRI) of activated platelets as early markers of plaque rupture using targeted contrast agents is a promising strategy. In this study, we aim to specifically image activated platelets in murine atherothrombosis by in vivo mMRI, using a dedicated animal model of plaque rupture.

Methods

An antibody targeting ligand-induced binding sites (LIBS) on the glycoprotein IIb/IIIa-receptor of activated platelets was conjugated to microparticles of iron oxide (MPIO) to form the LIBS-MPIO contrast agent causing a signal-extinction in T2*-weighted MRI. ApoE−/− mice (60 weeks-old) were fed a high fat diet for 5 weeks. Using a small needle, the surface of their carotid plaques was scratched under blood flow to induce atherothrombosis. In vivo 9.4 Tesla MRI was performed before and repetitively after intravenous injection of either LIBS-MPIO versus non-targeted-MPIO.

Results

LIBS-MPIO injected animals showed a significant signal extinction (p<0.05) in MRI, corresponding to the site of plaque rupture and atherothrombosis in histology. The signal attenuation was effective for atherothrombosis occupying ≥2% of the vascular lumen. Histology further confirmed significant binding of LIBS-MPIO compared to control-MPIO on the thrombus developing on the surface of ruptured plaques (p<0.01).

Conclusion

in vivo mMRI detected activated platelets on mechanically ruptured atherosclerotic plaques in ApoE−/− mice with a high sensititvity. This imaging technology represents a unique opportunity for noninvasive detection of atherothrombosis and the identification of unstable atherosclerotic plaques with the ultimate promise to prevent strokes and myocardial infarctions.

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<![CDATA[High-Resolution Micro-CT for Morphologic and Quantitative Assessment of the Sinusoid in Human Cavernous Hemangioma of the Liver]]> https://www.researchpad.co/article/5989db37ab0ee8fa60bd3674

Hepatic sinusoid plays a vital role in human cavernous hemangioma of the liver (CHL), and its morphologic investigation facilitates the understanding of microcirculation mechanism and pathological change of CHL. However, precise anatomical view of the hepatic sinusoid has been limited by the resolution and contrast available from existing imaging techniques. While liver biopsy has traditionally been the reliable method for the assessment of hepatic sinusoids, the invasiveness and sampling error are its inherent limitations. In this study, imaging of CHL samples was performed using in-line phase-contrast imaging (ILPCI) technique with synchrotron radiation. ILPCI allowed clear visualization of soft tissues and revealed structural details that were invisible to conventional radiography. Combining the computed tomography (CT) technique, ILPCI-CT was used to acquire the high-resolution micro-CT images of CHL, and three dimensional (3D) microstructures of hepatic sinusoids were provided for the morphologic depiction and quantitative assessment. Our study demonstrated that ILPCI-CT could substantially improve the radiographic contrast of CHL tissues in vitro with no contrast agent. ILPCI-CT yielded high-resolution micro-CT image of CHL sample at the micron scale, corresponding to information on actual structures revealed at histological section. The 3D visualization provided an excellent view of the hepatic sinusoid. The accurate view of individual hepatic sinusoid was achieved. The valuable morphological parameters of hepatic sinusoids, such as thrombi, diameters, surface areas and volumes, were measured. These parameters were of great importance in the evaluation of CHL, and they provided quantitative descriptors that characterized anatomical properties and pathological features of hepatic sinusoids. The results highlight the high degree of sensitivity of the ILPCI-CT technique and demonstrate the feasibility of accurate visualization of hepatic sinusoids. Moreover, there is a correlation between the CHL and the size or morphology of hepatic sinusoids, which offers a potential use in noninvasive study and analysis of CHL.

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<![CDATA[Reduction of Claustrophobia with Short-Bore versus Open Magnetic Resonance Imaging: A Randomized Controlled Trial]]> https://www.researchpad.co/article/5989da3aab0ee8fa60b877c3

Background

Claustrophobia is a common problem precluding MR imaging. The purpose of the present study was to assess whether a short-bore or an open magnetic resonance (MR) scanner is superior in alleviating claustrophobia.

Methods

Institutional review board approval and patient informed consent were obtained to compare short-bore versus open MR. From June 2008 to August 2009, 174 patients (139 women; mean age = 53.1 [SD 12.8]) with an overall mean score of 2.4 (SD 0.7, range 0 to 4) on the Claustrophobia Questionnaire (CLQ) and a clinical indication for imaging, were randomly assigned to receive evaluation by open or by short-bore MR. The primary outcomes were incomplete MR examinations due to a claustrophobic event. Follow-up was conducted 7 months after MR imaging. The primary analysis was performed according to the intention-to-treat strategy.

Results

With 33 claustrophobic events in the short-bore group (39% [95% confidence interval [CI] 28% to 50%) versus 23 in the open scanner group (26% [95% CI 18% to 37%]; P = 0.08) the difference was not significant. Patients with an event were in the examination room for 3.8 min (SD 4.4) in the short-bore and for 8.5 min (SD 7) in the open group (P = 0.004). This was due to an earlier occurrence of events in the short-bore group. The CLQ suffocation subscale was significantly associated with the occurrence of claustrophobic events (P = 0.003). New findings that explained symptoms were found in 69% of MR examinations and led to changes in medical treatment in 47% and surgery in 10% of patients. After 7 months, perceived claustrophobia increased in 32% of patients with events versus in only 11% of patients without events (P = 0.004).

Conclusions

Even recent MR cannot prevent claustrophobia suggesting that further developments to create a more patient-centered MR scanner environment are needed.

Trial Registration

ClinicalTrials.gov NCT00715806

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<![CDATA[Effectiveness of a Worksite Social & Physical Environment Intervention on Need for Recovery, Physical Activity and Relaxation; Results of a Randomized Controlled Trial]]> https://www.researchpad.co/article/5989dab5ab0ee8fa60bac9fc

Objective

To investigate the effectiveness of a worksite social and physical environment intervention on need for recovery (i.e., early symptoms of work-related mental and physical fatigue), physical activity and relaxation. Also, the effectiveness of the separate interventions was investigated.

Methods

In this 2×2 factorial design study, 412 office employees from a financial service provider participated. Participants were allocated to the combined social and physical intervention, to the social intervention only, to the physical intervention only or to the control group. The primary outcome measure was need for recovery. Secondary outcomes were work-related stress (i.e., exhaustion, detachment and relaxation), small breaks, physical activity (i.e., stair climbing, active commuting, sport activities, light/moderate/vigorous physical activity) and sedentary behavior. Outcomes were measured by questionnaires at baseline, 6 and 12 months follow-up. Multilevel analyses were performed to investigate the effects of the three interventions.

Results

In all intervention groups, a non-significant reduction was found in need for recovery. In the combined intervention (n = 92), exhaustion and vigorous physical activities decreased significantly, and small breaks at work and active commuting increased significantly compared to the control group. The social intervention (n = 118) showed a significant reduction in exhaustion, sedentary behavior at work and a significant increase in small breaks at work and leisure activities. In the physical intervention (n = 96), stair climbing at work and active commuting significantly increased, and sedentary behavior at work decreased significantly compared to the control group.

Conclusion

None of the interventions was effective in improving the need for recovery. It is recommended to implement the social and physical intervention among a population with higher baseline values of need for recovery. Furthermore, the intervention itself could be improved by increasing the intensity of the intervention (for example weekly GMI-sessions), providing physical activity opportunities and exercise schemes, and by more drastic environment interventions (restructuring entire department floor).

Trial Registration

Nederlands Trial Register NTR2553

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