Search

The MR-induced gradient artifact affects EMG recordings during simultaneous muscle BOLD/EMG acquisitions. However, no dedicated hardware can remove the gradient artifact easily, and alternative methods are expensive and time-consuming. This study aimed to develop three denoising methods requiring different processing levels and MR-compatible hardware. At two time points, surface EMG was recorded from the lower leg of 6 participants (50:50 sex ratio, age = 26.24.6 yrs., height = 173.59.2 cm, weight = 71.511.4 kg) using a plantar flexion-based block design consisting of 30s of rest followed by 30s of flexion for 5 min, under three conditions: inside the MRI bore, with and without a BOLD sequence (3 T, BOLD sequence, GRE EPI, 10 slices, 64×64 matrix, 2 mm thickness, and TE/TR/flip = 35/3000 ms/70), and outside the MRI environment. Simultaneous BOLD/EMG recordings were denoised using average artifact subtraction with three methods of artifact template creation, each having varying timing and hardware requirements. Method M1 builds the artifact template by recording the scanner triggers coming from the MRI; M2 creates the artifact template with a constant artifact period computed as TR/[number of slices]; M3 estimates the artifact template by looking at the periodicity of the gradient artifact located in the EMG recordings. Following postprocessing, SNR analysis was performed, comparing rest-to-flexion periods, to assess the efficacy of denoising methods and to compare differences between conditions. Linear mixed-effects models showed no significant differences in the mean SNR between denoising methods (p = 0.656). Furthermore, EMG SNR measurements were significantly affected by the magnetic environment (p < 0.05) but not by muscle fatigue over time (p = 0.975). EMG recordings contaminated with gradient artifacts during simultaneous BOLD/EMG can be efficiently denoised using all proposed methods, with two methods requiring no extra hardware. With minimal post-processing, EMG can easily be performed during muscle BOLD MRI studies., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Although hyperpolarized (HP) 129 Xe ventilation MRI can be carried out within a breath hold, it is still challenging for many sick patients. Compressed sensing (CS) is a viable alternative to accelerate this approach. However, undersampled images with identical sampling ratios differ from one another. Twenty subjects (n = 10 healthy and n = 10 patients with asthma) were scanned using a GE MR750 3 T scanner, acquiring fully sampled 2D multi-slice HP 129 Xe lung ventilation images (10 s breath hold, 128 × 80 (FE × PE-frequency encoding × phase encoding) and 16 slices). Using fully sampled data, 500 variable-density Cartesian random undersampling patterns were generated, each at eight different sampling ratios from 10% to 80%. The parallel imaging and compressed sensing (PICS) command from BART was employed to reconstruct undersampled data. The signal to noise ratio (SNR), structural similarity index measurement (SSIM) and sidelobe to peak ratio of each were subsequently compared. There was a high degree of variation in both SNR and SSIM results from each of the 500 masks of each sampling rate. As the undersampling increases, there is more variation in the quantifying metrics, for both healthy and asthmatic individuals. Our study shows that random undersampling poses a significant challenge when applied at sampling ratios less than 60%, despite fulfilling CS's incoherency criteria. Such low sampling ratios will result in a large variety of undersampling patterns. Therefore, skipped segments of k-space cannot be allowed to happen randomly at low sampling rates. By optimizing the sampling pattern, CS will reach its full potential and be able to be applied to a highly undersampled 129 Xe lung dataset., (© 2024 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.)

Our objective was to explore the association between resting-state functional connectivity and accelerometer-measured physical activity in pediatric concussion. Fourteen children with concussion (aged 14.54 ± 2.39 years, 8 female) were included in this secondary data analysis of a larger study. Participants had neuroimaging at 15.3 ± 6.7 days postinjury and subsequently a mean of 11.1 ± 5.0 days of accelerometer data. Intra-network connectivity of the default mode network (DMN), sensorimotor network (SMN), salience network (SN), and frontoparietal network (FPN) was computed using resting-state MRI. We found that, per general linear models (GLMs), only intra-network connectivity of the DMN was associated with physical activity levels. More specifically, increased intra-network connectivity of the DMN was significantly associated with higher levels of subsequent accelerometer-measured light physical activity (LPA; F (2, 11)  = 7.053, p  = 0.011, R a 2  = 0.562; β = 0.469), moderate physical activity (MPA; F (2, 11) = 6.159, p = 0.016, Ra2 = 0.528; β = 0.725), and vigorous physical activity (VPA; F (2, 11)  = 10.855, p  = 0.002, R a 2  = 0.664; β = 0.792). Intra-network connectivity of the DMN did not significantly predict sedentary time. Therefore, these preliminary findings suggest that there is a positive association between the intra-network connectivity of the DMN and device-measured physical activity in children with concussion.

Magnetic Resonance Imaging (MRI) is well-suited for imaging peripheral blood flow due to its non-invasive nature and excellent spatial resolution. Although MRI is routinely used in adults to assess physiological changes in chronic diseases, there are currently no MRI-based data quantifying arterial flow in pediatric or adolescent populations during exercise. Therefore the current research sought to document femoral arterial blood flow at rest and following exercise in a pediatric-adolescent population using phase contrast MRI, and to present test-retest reliability data for this method. Ten healthy children and adolescents (4 male; mean age 14.8 ± 2.4 years) completed bloodwork and resting and exercise MRI. Baseline images consisted of PC-MRI of the femoral artery at rest and following a 5 × 30 s of in-magnet exercise. To evaluate test-retest reliability, five participants returned for repeat testing. All participants successfully completed exercise testing in the MRI. Baseline flow demonstrated excellent reliability (ICC = 0.93, p = 0.006), and peak exercise and delta rest-peak flow demonstrated good reliability (peak exercise ICC = 0.89, p = 0.002, delta rest-peak ICC = 0.87, p = 0.003) between-visits. All three flow measurements demonstrated excellent reliability when assessed with coefficients of variance (CV's) (rest: CV = 6.2%; peak exercise: CV = 7.3%; delta rest-peak: CV = 7.1%). The mean bias was small for femoral arterial flow. There was no significant mean bias between femoral artery flow visits 1 and 2 at peak exercise. There were no correlations between age or height and any of the flow measurements. There were no significant differences between male and female participants for any of the flow measurements. The current study determined that peripheral arterial blood flow in children and adolescents can be evaluated using non-invasive phase contrast MRI. The MRI-based techniques that were used in the current study for measuring arterial flow in pediatric and adolescent patients demonstrated acceptable test-retest reliability both at rest and immediately post-exercise., (© 2022 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

Despite the technical challenges that require lengthy acquisitions to overcome poor signal-to-noise ratio (SNR), sodium ( 23 Na) magnetic resonance imaging (MRI) is an intriguing area of research due to its essential role in human metabolism. Low SNR images can impact the measurement of the point-spread function (PSF) by adding uncertainty into the resulting quantities. Here, we present methods to calculate the PSF by using the modulation transfer function (MTF), and a 3D-printed line-pair phantom in the context of 23 Na MRI. A simulation study investigated the effect of noise on the resulting MTF curves, which were derived by direct modulation (DM) and a method utilizing Fourier harmonics (FHs). Experimental data utilized a line-pair phantom with nine spatial frequencies, filled with different concentrations (15, 30, and 60 mM) of sodium in 3% agar. MTF curves were calculated using both methods from data acquired from density-adapted 3D radial projections (DA-3DRP) and Fermat looped orthogonally encoded trajectories (FLORET). Simulations indicated that the DM method increased variability in the MTF curves at all tested noise levels over the FH method. For the experimental data, the FH method resulted in PSFs with a narrower full width half maximum with reduced variability, although the improvement in variability was not as pronounced as predicted by simulations. The DA-3DRP data indicated an improvement in the PSF over FLORET. It was concluded that a 3D-printed line-pair phantom represents a convenient method to measure the PSF experimentally. The MTFs from the noisy images in 23 Na MRI have reduced variability from a FH method over DM., (© 2021 John Wiley & Sons, Ltd.)

Numerous studies have stressed the importance of exercise in promoting physical and mental health and for aiding in cognition. Encouragingly, physical exercise has been shown to reduce the risk of developing Alzheimer's disease and to mitigate hemiparesis experienced by stroke patients. Additionally, today where over 1.9 billion are overweight, physical exercise is imperative to save lives and to mitigate the burden on the healthcare system. Although the benefits of physical exercise have been explored, the underlying mechanisms to enact these benefits have not been well-characterized. Here we review exercise-induced changes in regional brain activation and modulation. Paradigms differing in intensity, duration, and type of motor movement have been used to assess exercise effects on memory, cognition, and disease mitigation in youth and elderly populations. To evaluate exercise-induced changes in neural activity, the noninvasive imaging technique, functional magnetic resonance imaging (fMRI), is employed. fMRI is recorded either during or after exercise intervention. Post-exercise fMRI is often paired with in-bore tests of cognition to provide insight into the associated brain regions. Whereas, during intervention, fMRI is used to detail muscle-associated neural activation profiles. Characterization of the region and magnitude of brain activation has been used to perform comparative studies and identify specific characteristics from individuals with varying motor and cognitive abilities. Further fMRI and exercise research, with the use of these metrics, could facilitate the development of tools for disease diagnosis or to assess level of dysfunction or progression.

Background and Purpose- Little is known about the association between covert vascular brain injury and cognitive impairment in middle-aged populations. We investigated if scores on a cognitive screen were lower in individuals with higher cardiovascular risk, and those with covert vascular brain injury. Methods- Seven thousand five hundred forty-seven adults, aged 35 to 69 years, free of cardiovascular disease underwent a cognitive assessment using the Digital Symbol Substitution test and Montreal Cognitive Assessment, and magnetic resonance imaging (MRI) to detect covert vascular brain injury (high white matter hyperintensities, lacunar, and nonlacunar brain infarctions). Cardiovascular risk factors were quantified using the INTERHEART (A Global Study of Risk Factors for Acute Myocardial Infarction) risk score. Multivariable mixed models tested for independent determinants of reduced cognitive scores. The population attributable risk of risk factors and MRI vascular brain injury on low cognitive scores was calculated. Results- The mean age of participants was 58 (SD, 9) years; 55% were women. Montreal Cognitive Assessment and Digital Symbol Substitution test scores decreased significantly with increasing age ( P <0.0001), INTERHEART risk score ( P <0.0001), and among individuals with high white matter hyperintensities, nonlacunar brain infarction, and individuals with 3+ silent brain infarctions. Adjusted for age, sex, education, ethnicity covariates, Digital Symbol Substitution test was significantly lowered by 1.0 (95% CI, -1.3 to -0.7) point per 5-point cardiovascular risk score increase, 1.9 (95% CI, -3.2 to -0.6) per high white matter hyperintensities, 3.5 (95% CI, -6.4 to -0.7) per nonlacunar stroke, and 6.8 (95% CI, -11.5 to -2.2) when 3+ silent brain infarctions were present. No postsecondary education accounted for 15% (95% CI, 12-17), moderate and high levels of cardiovascular risk factors accounted for 19% (95% CI, 8-30), and MRI vascular brain injury accounted for 10% (95% CI, -3 to 22) of low test scores. Conclusions- Among a middle-aged community-dwelling population, scores on a cognitive screen were lower in individuals with higher cardiovascular risk factors or MRI vascular brain injury. Much of the population attributable risk of low cognitive scores can be attributed to lower educational attainment, higher cardiovascular risk factors, and MRI vascular brain injury.

Phosphorus MR spectroscopy and spectroscopic imaging ( 31 P-MRS/MRSI) provide information about energy metabolism, membrane degradation and pH in vivo. In spite of their proven utility, 31 P-MRS/MRSI are not often used primarily because of the challenges imposed by the low sensitivity and low concentration of metabolites leading to low signal to noise ratio (SNR), coarse spatial resolution and prolonged acquisition time. More recently there has been considerable interest in compressed sensing as an acceleration method for MR signal acquisition. This approach takes advantage of the intrinsic sparsity of the spectral data. In this work, we present a 31 P-MRSI sequence that combines a flyback EPSI trajectory and compressed sensing, and we compared two different reconstruction methods, L1 norm minimization and low rank Hankel matrix completion. Our phantom results showed good preservation of spectral quality for both ×2.0 and ×3.0 acceleration factors, using both CS reconstruction methods. However, in vivo 31 P-MRS brain data showed the low rank reconstruction approach was most suitable. Overall, this study shows the feasibility of combining a flyback EPSI trajectory and compressed sensing in the acquisition of 31 P-MRSI as well as the better suitability of a low rank reconstruction approach., (Copyright © 2019 Elsevier Inc. All rights reserved.)

With the emergence of research investigating the role of gamma-aminobutyric acid (GABA) in neurological and neuropsychiatric diseases, it is important to understand the variability in GABA as measured through magnetic resonance spectroscopy (MRS) and how this variability may affect the interpretation of results. This review addresses methodological sources of variation documented in the current literature on the measurement of GABA. GABA differences related to hardware, acquisition, post-processing and quantification are discussed, and methods to account for or remove this variability are highlighted. Additionally, factors such as time, age, biological sex, hormones, and brain region, which may affect GABA MRS, are reviewed to aid in study design. This review is meant to assist in measuring GABA comparably between studies and improve GABA methodology to allow the use of GABA MRS in a clinical setting in the future.

Magnetic resonance imaging (MRI) has superior soft tissue contrast and lower interobserver variability compared to computed tomography and advances in equipment and pseudo-CT estimation have allowed for MR-only radiation therapy planning. Dedicated MR sequences have been used to localize paramagnetic structures with positive contrast, and most implanted seeds are gold fiducial markers (GFMs). We used a fast, dual-plane co-RASOR sequence to localize implanted GFMs with positive contrast in phantom and tissue to assess their resolution and registration accuracy of registration to CT. Off-resonant reconstructions of co-RASOR images were able to resolve GFMs down to 5 mm apart at 12 cm FOV. No systematic biases were observed by comparing registration of co-RASOR and bSSFP to CT images in an MR-compatible Lego phantom with a set of highly visible known points. The standard deviations of the MR to CT distance errors were  <0.5 mm in all directions. We separated the component due to registration by comparing the two MR sequences, which had a maximum standard deviation of 0.36 mm in the SI-direction. Registration using the positive contrast points in a porcine sample phantom showed increased errors, but co-RASOR still performs acceptably with a target registration error of  <0.75 mm. The dual-plane co-RASOR sequence could then be used for both registration and image tracking when performing MR-only radiation therapy planning.

The goal of this work was to use an undersampled, dual-plane centre-out radial sampling acquisition pulse sequence, with off-resonance reception, to localize fiducial markers with reduced acquisition time. Two iterative reconstruction techniques, conjugate gradient CG-SENSE and the variational penalty Total Generalized Variation (TGV), were investigated to minimize the undersampling artifacts in off-resonant radial imaging. Simulations of a field perturber were performed at sub-millimeter resolution and reconstructed to display signal pileups that can be radially compressed towards the geometric centre of the perturber for high contrast visualization, but contrast is non-recoverable as the echo time increases. A cylindrical platinum fiducial marker, placed in a phantom parallel and perpendicular to the B 0 -field was imaged with a short-TE half-echo readout. Contrast-to-Noise (CNR) between the signal of the fiducial its adjacent surrounding shell and half-maximum area were used to compare reconstruction methods and undersampling factors. For single slice acquisitions centred about the fiducial, each slice can be performed in as little as 2.8s. The total acquisition time to localize the fiducial marker in a phantom was reduced to 73s by undersampling (R=8) 37 axial and 15 coronal slices, effectively encoding 1.4s/slice. The noise present in undersampled images, for both scan planes and fiducial orientations, decreased significantly using TGV and CG-SENSE reconstructions, with TGV displaying better spatial resolution from reduced half-maximum area., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Purpose To perform a preliminary evaluation of a noninvasive measurement system to assess gadolinium deposition in bone and to investigate the relationship between the administration of gadolinium-based contrast agents (GBCAs) and gadolinium retention in bone. Materials and Methods In vivo measurement of gadolinium retention in tibia bones was performed in 11 exposed subjects who previously received GBCAs (six exposed subjects were from a study performed 5 years previously involving injection of GBCAs in healthy volunteers; five exposed subjects had self-reported GBCA exposure), and 11 sex- and age-matched control subjects without a history of GBCA exposure. Each subject underwent one measurement of gadolinium retention in the tibia with x-ray fluorescence in a laboratory at McMaster University. A one-tailed t test was performed to compare gadolinium concentration in the exposed group with that in the control group. The relationship between the dose of GBCA administered and the gadolinium concentration measured in bone was analyzed with linear regression. Results Gadolinium concentration in bone was significantly higher in exposed subjects (mean, 1.19 μg Gd/g bone mineral ± 0.73 [standard deviation]) than in control subjects (mean, -1.06 μg Gd/g bone mineral ± 0.71) (P = .01). There was also a positive correlation between the dose of GBCA administered and the gadolinium concentration measured in bone (R 2 = 0.41); gadolinium concentration in bone increased by 0.39 μg Gd/g bone mineral ± 0.14 per 1 mL of GBCA administered. Gadolinium was detected in bone up to 5 years after one GBCA administration. Conclusion This x-ray fluorescence system is capable of measuring gadolinium deposition in bone noninvasively in vivo. Gadolinium can be retained in bone after one dose of GBCA in healthy subjects. © RSNA, 2017 Online supplemental material is available for this article.

Background: Brain connectivity in autism spectrum disorders (ASD) has proven difficult to characterize due to the heterogeneous nature of the spectrum. Connectivity in the brain occurs in a complex, multilevel and multi-temporal manner, driving the fluctuations observed in local oxygen demand. These fluctuations can be characterized as fractals, as they auto-correlate at different time scales. In this study, we propose a model-free complexity analysis based on the fractal dimension of the rs-BOLD signal, acquired with magnetic resonance imaging. The fractal dimension can be interpreted as measure of signal complexity and connectivity. Previous studies have suggested that reduction in signal complexity can be associated with disease. Therefore, we hypothesized that a detectable difference in rs-BOLD signal complexity could be observed between ASD patients and Controls., Methods and Findings: Anatomical and functional data from fifty-five subjects with ASD (12.7 ± 2.4 y/o) and 55 age-matched (14.1 ± 3.1 y/o) healthy controls were accessed through the NITRC database and the ABIDE project. Subjects were scanned using a 3T GE Signa MRI and a 32-channel RF-coil. Axial FSPGR-3D images were used to prescribe rs-BOLD (TE/TR = 30/2000ms) where 300 time points were acquired. Motion correction was performed on the functional data and anatomical and functional images were aligned and spatially warped to the N27 standard brain atlas. Fractal analysis, performed on a grey matter mask, was done by estimating the Hurst exponent in the frequency domain using a power spectral density approach and refining the estimation in the time domain with de-trended fluctuation analysis and signal summation conversion methods. Voxel-wise fractal dimension (FD) was calculated for every subject in the control group and in the ASD group to create ROI-based Z-scores for the ASD patients. Voxel-wise validation of FD normality across controls was confirmed, and non-Gaussian voxels were eliminated from subsequent analysis. To maintain a 95% confidence level, only regions where Z-score values were at least 2 standard deviations away from the mean (i.e. where |Z| > 2.0) were included in the analysis. We found that the main regions, where signal complexity significantly decreased among ASD patients, were the amygdala (p = 0.001), the vermis (p = 0.02), the basal ganglia (p = 0.01) and the hippocampus (p = 0.02). No regions reported significant increase in signal complexity in this study. Our findings were correlated with ADIR and ADOS assessment tools, reporting the highest correlation with the ADOS metrics., Conclusions: Brain connectivity is best modeled as a complex system. Therefore, a measure of complexity as the fractal dimension of fluctuations in brain oxygen demand and utilization could provide important information about connectivity issues in ASD. Moreover, this technique can be used in the characterization of a single subject, with respect to controls, without the need for group analysis. Our novel approach provides an ideal avenue for personalized diagnostics, thus providing unique patient specific assessment that could help in individualizing treatments.

Purpose: The aim of this study was to evaluate the effect of the pseudohepatic anisotropy artifact on liver intravoxel incoherent motion (IVIM) metrics and whether the use of multiple gradient directions in the IVIM acquisition minimizes the artifact., Materials and Methods: Multiple breath-holding and forced shallow free-breathing IVIM scans were performed on 8 healthy volunteers using 1 and 6 gradient directions. Cluster analysis was carried out to separate motion-contaminated parenchyma from liver parenchyma and vessels. Nonlinear motion analysis was also performed to look for a possible link between IVIM metrics and nonlinear liver motion., Results: On the basis of the resulted clusters, motion-contaminated parenchyma is often noted in the left liver lobe, where the prominent pseudohepatic artifact has previously been identified. A significant reduction in outliers was obtained with the acquisition of 6 noncoplanar gradient directions and when using forced shallow free-breathing., Conclusion: The pseudohepatic anisotropy artifact can be minimized when using multiple diffusion-encoding gradient directions and forced free-breathing during IVIM acquisition.

Objectives: Numerous neuroimaging techniques have been recently used to investigate central mechanisms involved in pain perception and to examine morphological and functional brain alterations associated with chronic pain. Compared to self-reporting approaches, objective imaging techniques are expected to potentially lead to better pain assessment and guide management. This comprehensive scoping review aims to identify recent magnetic resonance imaging (MRI) approaches that have been used to characterize the brain of chronic pain subjects, using structural, chemical and functional MRI techniques., Methods: A systematic search and review of the literature was conducted and the resultant studies were critically examined for relevance., Results: MRI neuroimaging of various chronic pain conditions were summarized. We classified the collected studies into: structural brain alterations, VBM (voxel based morphology) examination of structural changes, DTI, changes in brain chemistry, functional and blood flow brain alterations., Discussion: From our clinical experience, we have noted that most clinicians are not aware of the capabilities of advanced MRI methods in assessing cortical manifestations of chronic pain. In addition, many clinicians are not aware of the cortical alterations present in individuals with chronic pain. This comprehensive scoping review thus sets out to first summarize MRI neuroimaging techniques that are available in the current literature to examine chronic pain. We then identify cortical MR approaches that have been able to reliably predict transition from acute to chronic pain. Finally, we summarize MRI neuroimaging techniques that have been used to track treatment response of individuals with chronic pain.

fMRI and EEG during mental imagery provide alternative methods of detecting awareness in patients with disorders of consciousness (DOC) without reliance on behaviour. Because using fMRI in patients with DOC is difficult, studies increasingly employ EEG. However, there has been no verification that these modalities provide converging information at the individual subject level. The present study examined simultaneous EEG and fMRI in healthy volunteers during six mental imagery tasks to determine whether one mental imagery task generates more robust activation across subjects; whether activation can be predicted from familiarity with the imagined activity; and whether EEG and fMRI converge upon the same conclusions about individual imagery performance. Mental arithmetic generated the most robust activation in the majority of subjects for both EEG and fMRI, and level of activation could not be predicted from familiarity, with either modality. We conclude that overall, EEG and fMRI agree regarding individual mental imagery performance., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Purpose: To develop an inexpensive magnetic resonance imaging (MRI)-compatible electrical muscle stimulation (EMS) unit and test it for safety and efficacy., Materials and Methods: A simple MRI-compatible EMS device was developed using radiofrequency (RF) translucent electrodes at 3T. RF heating concerns were assessed using optical temperature measurements at electrode sites, during scanning of a phantom. EMS efficacy and consistency was investigated through in vivo (n = 5) measures of 31 P-MRS phosphocreatine (PCr) reduction, and altered blood oxygen level-dependent (BOLD) signal and the results were compared to effects from equivalent voluntary effort on the same subjects., Results: The presence of an EMS pulse did not interfere with the T 2 * signal in a phantom. However, signal-to-noise ratio (SNR) was reduced by 70% at electrode sites, but only by 10% 4 cm distally. Under RF intense conditions, the temperature at the electrode site increased by only 4.7°C over a 16-minute time span. In vivo muscle stimulation resulted in 13.5 ± 1.8% reduction in PCr, which was not significantly (P < 0.195) different from voluntary contraction. Reproducible muscle BOLD signal changes following EMS were noted, with a maximal increase of 10.0 ± 2.6% seen in the central soleus. For soleus and gastrocnemius compartments, EMS produced significantly higher BOLD signal change compared to voluntary contraction (P < 0.05)., Conclusion: A safe and inexpensive MRI-compatible EMS unit can be easily built for evaluating muscle function and metabolism within a 3T MRI scanner. Clinical applications might include evaluating skeletal muscle function in patients with limited or absent voluntary skeletal motor function or inadequate exercise capacity. J. Magn. Reson. Imaging 2016;44:1530-1538., (© 2016 International Society for Magnetic Resonance in Medicine.)

Multimodality imaging is driven by the rising demand for highly integrated diagnostic information from in vivo imaging. We provide a comprehensive review of multimodality imaging techniques available in nuclear medicine, including magnetic resonance imaging (MRI) combined with ultrasound and MRI combined with stereotactic methods for image-guided breast biopsies and MR-guided stereotactic neurosurgery. Commercially available and investigative hardware- and software-based platforms for multimodality imaging are evaluated critically and their advantages and limitations are outlined.

Object: There have been no studies to investigate the effects of cycling exercise protocols, as well as repeated bouts of exercise, on the blood oxygen level-dependent (BOLD) response in the quadriceps muscles. This study characterized BOLD signal recovery following non-ischemic bouts of exercise in the quadriceps muscles of healthy adults in order to provide a basis for application of a protocol for clinical populations., Materials and Methods: Healthy male subjects (23.7 ± 2.0 years of age, n = 10) completed three cycles of one-minute exercise (65 % of maximum workload), with two minutes of rest between each bout, on an MRI-compatible ergometer. The BOLD responses during recovery were fitted to a sigmoid model, and response kinetics (post-exercise intensity [S0]), response time (α), change in baseline BOLD signal (κ), and inflection point (β)] were measured., Results: The sigmoid function fit well to the post-exercise BOLD data (r (2) = 0.95 ± 0.04). The mean response time was 10.5 ± 3.8 seconds, change in baseline BOLD intensity was 0.15 ± 0.068, and time to half-peak was 20.2 ± 8.6 seconds., Conclusion: The proposed sigmoid model is a robust method for quantifying quadriceps BOLD response post-exercise without induced ischemia. Extension of this model to evaluate microvascular responses in patients with chronic disease could improve our understanding of exercise intolerance.

Object: The object was to assess whether cross-sectional area (CSA) and water diffusion properties of leg muscles in young and older women change with increased time spent in supine rest., Materials and Methods: Healthy young (n = 9, aged 20-30 years) and older (n = 9, aged 65-75 years) women underwent MRI scanning of the right leg at baseline, 30 and 60 min of supine rest. Muscle CSA was derived from proton density images. Water diffusion properties [apparent diffusion coefficient (ADC) and fractional anisotropy (FA)] of the tibialis anterior and posterior, soleus, and medial and lateral heads of the gastrocnemius were derived from diffusion tensor imaging (DTI). Repeated measures ANOVAs and Bonferroni post hoc tests determined the effects of time and group on each muscle outcome., Results: In both groups, muscle CSA and FA did not significantly change over time, whereas ADC significantly decreased. A greater decline at 30 min for young women was only observed for ADC in the medial gastrocnemius., Conclusion: Regardless of age, ADC values decreased with fluid shift associated with time spent supine, whereas CSA and FA were not affected. For leg muscle assessment in young and older women, DTI scanning protocols should consider the amount of time spent in a recumbent position.

Electroencephalography data recorded during functional magnetic resonance imaging acquisition are subject to large cardiac-related artifacts that must be corrected during postprocessing. This study compared two widely used ballistocardiogram (BCG) correction algorithms as implemented in two software programs. Reduction of BCG amplitude, correlation of corrected data with electrocardiogram traces, correlation of independent components with electrocardiogram traces, and event-related potential signal-to-noise ratio from each algorithm were compared. Both algorithms effectively reduced the BCG artifact, with a slight advantage of average artifact subtraction over the optimal basis set method (0.1-2.2%) when the quality of the correction was examined at the individual subject level. This study provides users of these software tools with an important, practical, and previously unavailable comparison of the performance of these two methods.

Magnetic resonance imaging (MRI) sialolithography is a useful technique for evaluating acute and chronic sialadenitis. However, its major weakness is that stones are not imaged directly. We have developed an MRI technique that allows specific identification and localization of calculi within the submandibular salivary gland or duct. This test is noninvasive and does not require ionizing radiation or a sialogogue. By using 3-dimensional susceptibility-weighted imaging, one can probe MRI signal phase changes. Corrected positive filtered phase and magnitude images, acquired using susceptibility-weighted imaging, allowed identification and anatomical localization of calcified calculi in the submandibular gland with efficacy comparable to computed tomography.

Objective: To investigate blood oxygen level-dependent (BOLD) response of human liver to hyperoxic exposure under fasting and postprandial conditions., Methods: Twelve healthy volunteers and 1 patient with chronic liver disease underwent liver BOLD magnetic resonance imaging at 3.0T. The BOLD images of a single slice were collected (1 image per second) during 3 breathing cycles of hyperoxia (3 minutes, 100% oxygen) with 5 minutes medical air (20.8% oxygen) in both preprandial and postprandial states. The BOLD signal time courses were correlated with a predefined stimulus paradigm., Results: Eight healthy subjects showed increased BOLD signal within 44.6% +/- 21.1% liver area in the fasting state with gas cycling. Two showed slightly reduced BOLD signal within 23.4% +/- 14.9% liver area in the fasting state with gas cycling. In the postprandial state, the degree of change in BOLD signal with gas cycling was reduced for both the subjects having increased and those having decreased signal with gas cycling (13.4% +/- 12.6% positive, 10.9% +/- 10.1% negative; P < 0.05). Chronic liver disease also demonstrated increased BOLD signal with gas cycling, but the correlation decreased postprandially., Conclusions: The proposed physiological challenges induce certain BOLD signal response patterns in healthy and diseased livers, which may be useful for assessing liver function.

Diagnostic imaging procedures for muscle evaluation have typically provided basic information concerning gross anatomical change resulting from pathology. Up until recently the musculoskeletal radiologist has been fairly limited to using simple proton-density weighted fat-saturated and short tau inversion recovery magnetic resonance imaging scans for assessment of skeletal muscle. Recent advances, however, have resulted in development of newer scans and postprocessing methods that provide much more than gross muscle structure. Scans providing fine structure, muscle function, and metabolism can easily be done using clinical scanners. Here we describe how diffusion tensor imaging (DTI) and blood oxygenation level-dependent (BOLD) imaging together can provide detailed information on muscle structural and functional changes. DTI is useful for visualizing muscle tears, and BOLD can be used for vascular insufficiency (e.g., compartment syndrome). In clinical sites that are gaining experience using these techniques, imaging of muscle pathology is becoming increasingly thorough. In the future, these methods will reduce the need for invasive approaches to study muscle pathology.

Objective: To assess the effects of alterations in PaCO(2) and PaO(2) on blood oxygenation level-dependent (BOLD) signal intensity determined by use of susceptibility-weighted magnetic resonance imaging in brains of isoflurane-anesthetized dogs., Animals: 6 healthy dogs., Procedures: In each dog, anesthesia was induced with propofol (6 to 8 mg/kg, IV) and maintained with isoflurane (1.7%) and atracurium (0.2 mg/kg, IV, q 30 min). During 1 magnetic resonance imaging session in each dog, targeted values of PaCO(2) (20, 40, or 80 mm Hg) and PaO(2) (100 or 500 mm Hg) were combined to establish 6 experimental conditions, including a control condition (PaCO(2), 40 mm Hg; PaO(2), 100 mm Hg). Dogs were randomly assigned to different sequences of conditions. Each condition was established for a period of >or= 5 minutes before susceptibility-weighted imaging was performed. Signal intensity was measured in 6 regions of interest in the brain, and data were analyzed by use of an ANCOVA and post hoc Tukey-Kramer adjustments., Results: Compared with control condition findings, BOLD signal intensity did not differ significantly in any region of interest. However, signal intensities in the thalamus and diencephalic gray matter decreased significantly during both hypocapnic conditions, compared with all other conditions except for the control condition., Conclusions and Clinical Relevance: In isoflurane-anesthetized dogs, certain regions of gray matter appeared to have greater cerebrovascular responses to changes in PaCO(2) and PaO(2) than did others. Both PaO(2) and PaCO(2) should be controlled during magnetic resonance imaging procedures that involve BOLD signaling and taken into account when interpreting findings.

Modeling tracer kinetics from dynamic magnetic resonance imaging (dMRI) to understand microvascular characteristics typically requires acquisitions longer than 1 breath-hold. This has limited the application of dMRI in assessment of the upper abdomen. Here we present a template-based motion correction strategy for dMRI of liver metastases based on the correlation coefficient (CC), originally developed for tracking coronary arteries. This postprocessing method allows patient free breathing during sagittal dMRI acquisition and allows a more precise parametric mapping using tracer kinetic models. In a study of 6 subjects, a 64 x 64 template was accurately tracked retrospectively with mean CC = 0.72 +/- 0.07. Mean superior-inferior displacement tracked was 1.82 +/- 1.20 pixels, whereas mean anterior-posterior displacement was 7.72 +/- 4.58 pixels. Application of the CC method significantly improved the global fit (chi2) of a tracer kinetic model throughout tumor regions. Therefore, use of the CC postprocessing method for dMRI scans can improve the precision of dMRI tracer kinetic models.

Purpose: To evaluate whether the BOLD signal from skeletal muscle can be modulated by exercise and ingestion of vasoactive substances., Materials and Methods: The right calf muscles of healthy adult volunteers were imaged using a GE 1.5-Tesla scanner and a gradient-echo sequence with spiral readout. Time-varying changes in the BOLD signal were induced through cyclic phases of normoxia (90 seconds of 20.8% O2) and hyperoxia (45 seconds of 100% O2 at 22 L/minute). Superimposed on this paradigm were pre- and post-exercise regimes, with and without ingestion of caffeine (100 mg) or antihistamine (4 mg chlorpheniramine). The numbers of voxels within slow-twitch (soleus) and fast-twitch (gastrocnemius) muscles that significantly responded to the paradigms were scored and compared using the AFNI software (NIMH)., Results: Cycling-inspired O2 produced a corresponding BOLD modulation that increased in magnitude with exercise. Chlorpheniramine significantly (P<0.01) prevented the overall increase in exercise-induced soleus muscle BOLD signal, while caffeine accentuated the increase (P<0.05) in the gastrocnemius relative to control (no vasomodulator) conditions., Conclusion: BOLD signal changes with exercise can be modulated by standard doses of chlorpheniramine (antihistamine) and caffeine. We suggest that chlorpheniramine may act detrimentally on slow-twitch muscle contractility, while caffeine appears to improve fast-twitch muscle function., (Copyright (c) 2006 Wiley-Liss, Inc.)

Blood-oxygen-level-dependent (BOLD) imaging was a concept introduced in 1990 for evaluating brain activation. The method relies on magnetic resonance imaging (MRI) contrast resulting from changes in the microvascular ratio of oxyhaemoglobin (oxyHb) to deoxyhaemoglobin (deoxyHb). OxyHb is diamagnetic, whereas deoxyHb is paramagnetic, which produces a local bulk magnetic susceptibility effect and subsequent MRI signal change. The changes are typically observed in T(2)*-weighted functional MRI scans. However, there has recently been interest in BOLD as a way to evaluate microcirculation of any normal or diseased tissue. This review focuses on the application of BOLD imaging in the understanding of normal and diseased skeletal muscle. In addition we present new findings showing the possible application of BOLD imaging with hyperoxia for evaluating skeletal muscle physiology.

A great deal of heterogeneity exists in fMRI data. Even within the same subject, results on successive days or scan sessions often differ in the number of significantly activated pixels and/or the intensity of activation. We sought to assess whether controllable physiologic modulators, such as dietary factors, could influence the outcome of fMRI data. A high fat diet, for example, prior to a fMRI scan could change microvascular blood rheologic factors and potentially alter brain blood oxygen-level dependent (BOLD) signal patterns. In healthy adult volunteers, we measured brain BOLD signal during bilateral finger tapping (2 Hz) in the fasted state, and at 40 and 100 minutes post-ingestion of a 235 mL can of Ensure Plus (Ross Labs), alone or supplemented with either 25 cc or 50 cc of canola oil. Both the 25 cc and 50 cc Canola oil treatments produced a significant bilateral decrease in BOLD signal 40 and 100 minutes postprandial. No significant effect was observed with Ensure in the absence of oil. Therefore, to decrease fMRI within and between subject heterogeneity, and thereby increase fMRI statistical power, it is suggested that scanning within 2 hours post high fat ingestion should be avoided. As a corollary, a thorough understanding of a subject's physiological state, prior to an fMRI exam, may reduce the impact of other confounding variables., (Copyright 2003 Wiley-Liss, Inc.)

Introduction: The ideal contrast agents for ventilation SPECT and MRI are Technegas and 129Xe gas, respectively. Despite increasing interest in the clinical utility of ventilation imaging, these modalities have not been directly compared. Therefore, our objective was to compare the ventilation defect percent (VDP) assessed by Technegas SPECT and hyperpolarized 129Xe MRI in patients scheduled to undergo lung cancer resection with and without pre-existing obstructive lung disease. Methods: Forty-one adults scheduled to undergo lung cancer resection performed same-day Technegas SPECT, hyperpolarized 129Xe MRI, spirometry, and diffusing capacity of the lung for carbon monoxide (DLCO). Ventilation abnormalities were quantified as the VDP using two different methods: adaptive thresholding (VDPT) and k-means clustering (VDPK). Correlation and agreement between VDP quantified by Technegas SPECT and 129Xe MRI were determined by Spearman correlation and Bland-Altman analysis, respectively. Results: VDP measured by Technegas SPECT and 129Xe MRI were correlated (VDPT: r = 0.48, p = 0.001; VDPK: r = 0.63, p < 0.0001). A 2.0% and 1.6% bias towards higher Technegas SPECT VDP was measured using the adaptive threshold method (VDPT: 23.0% ± 14.0% vs. 21.0% ± 5.2%, p = 0.81) and k-means method (VDPK: 9.4% ± 9.4% vs. 7.8% ± 10.0%, p = 0.02), respectively. For both modalities, higher VDP was correlated with lower FEV1/FVC (SPECT VDPT: r = -0.38, p = 0.01; MRI VDPK: r=-0.46, p = 0.002) and DLCO (SPECT VDPT: r=-0.61, p < 0.0001; MRI VDPK: r = -0.68, p < 0.0001). Subgroup analysis revealed that VDP measured by both modalities was significantly higher for participants with COPD (n = 13) than those with asthma (n = 6; SPECT VDPT: p = 0.007, MRI VDPK: p = 0.006) and those with no history of obstructive lung disease (n = 21; SPECT VDPT: p = 0.0003, MRI VDPK: p = 0.0003). Discussion: The burden of ventilation defects quantified by Technegas SPECT and 129Xe MRI VDP was correlated and greater in participants with COPD when compared to those without. Our observations indicate that, despite substantial differences between the imaging modalities, quantitative assessment of ventilation defects by Technegas SPECT and 129Xe MRI is comparable. [ABSTRACT FROM AUTHOR]

Objective: This proof-of-principle study integrates joint reaction forces (JRFs) and bone shape to assess acute cartilage changes from walking and cycling. Methods: Sixteen women with symptomatic knee osteoarthritis were recruited. Biomechanical assessment estimated JRFs during walking and cycling. Subsamples had magnetic resonance imaging (MRI) performed before and after a 25-min walking (n = 7) and/or cycling (n = 9) activity. MRI scans were obtained to assess cartilage shape and composition (T2 relaxation time). Bone shape was quantified using a statistical shape model built from 13 local participants and 100 MRI scans from the Osteoarthritis Initiative. Statistical parametric mapping quantified cartilage change and correlations between cartilage change with JRFs and statistical shape model features. Results: Cartilage thickness (interior lateral, Δ − 0.10 mm) and T2 (medial, Δ − 4 ms) decreased on the tibial plateau. On the femur, T2 change depended on the activity. Greater tibiofemoral JRF was associated with more cartilage deformation on the lateral femoral trochlea after walking (r − 0.56). Knees more consistent with osteoarthritis showed smaller decreases in tibial cartilage thickness. Discussion: Walking and cycling caused distinct patterns of cartilage deformation, which depended on knee JRFs and bone morphology. For the first time, these results show that cartilage deformation is dependent on bone shapes and JRFs in vivo. [ABSTRACT FROM AUTHOR]

Childhood obesity is a growing worldwide problem. In adults, lower cold-induced brown adipose tissue (BAT) activity is linked to obesity and metabolic dysfunction; this relationship remains uncertain in children. In this cross-sectional study, we compared cold-induced supraclavicular (SCV) BAT activity (percent change in proton density fat fraction [PDFF]) within the SCV region after 1 h of whole-body cold exposure (18°C), using MRI in 26 boys aged 8-10 years: 13 with normal BMI and 13 with overweight/obesity. Anthropometry, body composition, hepatic fat, visceral adipose tissue (VAT), and pre- and postcold PDFF of the subcutaneous adipose tissue (SAT) in the posterior neck region and the abdomen were measured. Boys with overweight/obesity had lower cold-induced percent decline in SCV PDFF compared with those with normal BMI (1.6 ± 0.8 vs. 4.7 ± 1.2%, P = 0.044). SCV PDFF declined significantly in boys with normal BMI (2.7 ± 0.7%, P = 0.003) but not in boys with overweight/obesity (1.1 ± 0.5%, P = 0.053). No cold-induced changes in the PDFF of either neck SAT (-0.89 ± 0.7%, P = 0.250, vs. 0.37 ± 0.3%, P = 0.230) or abdominal SAT (-0.39 ± 0.5%, P = 0.409, and 0.25 ± 0.2%, P = 0.139, for normal BMI and overweight/obesity groups, respectively) were seen. The cold-induced percent decline in SCV PDFF was inversely related to BMI (r = -0.39, P = 0.047), waist circumference (r = -0.48, P = 0.014), and VAT (r = -0.47, P = 0.014). Thus, in young boys, as in adults, BAT activity is lower in those with overweight/obesity, suggesting that restoring activity may be important for improving metabolic health. [ABSTRACT FROM AUTHOR]

Despite the technical challenges that require lengthy acquisitions to overcome poor signal‐to‐noise ratio (SNR), sodium (23Na) magnetic resonance imaging (MRI) is an intriguing area of research due to its essential role in human metabolism. Low SNR images can impact the measurement of the point‐spread function (PSF) by adding uncertainty into the resulting quantities. Here, we present methods to calculate the PSF by using the modulation transfer function (MTF), and a 3D‐printed line‐pair phantom in the context of 23Na MRI. A simulation study investigated the effect of noise on the resulting MTF curves, which were derived by direct modulation (DM) and a method utilizing Fourier harmonics (FHs). Experimental data utilized a line‐pair phantom with nine spatial frequencies, filled with different concentrations (15, 30, and 60 mM) of sodium in 3% agar. MTF curves were calculated using both methods from data acquired from density‐adapted 3D radial projections (DA‐3DRP) and Fermat looped orthogonally encoded trajectories (FLORET). Simulations indicated that the DM method increased variability in the MTF curves at all tested noise levels over the FH method. For the experimental data, the FH method resulted in PSFs with a narrower full width half maximum with reduced variability, although the improvement in variability was not as pronounced as predicted by simulations. The DA‐3DRP data indicated an improvement in the PSF over FLORET. It was concluded that a 3D‐printed line‐pair phantom represents a convenient method to measure the PSF experimentally. The MTFs from the noisy images in 23Na MRI have reduced variability from a FH method over DM. [ABSTRACT FROM AUTHOR]

The most common cause of chronic musculoskeletal pain is chronic myofascial pain syndrome (MPS). MPS often presents with increased muscle stiffness, and the myofascial trigger point (MTrP). Imaging modalities have been used to identify the MTrP, but their role in the detection and diagnosis of MPS remains unclear. The purpose of this review was to identify evidence in literature for the use of imaging in the role of classifying and explaining the physiology of MTrPs. Since few imaging techniques have been performed on MTrPs, we explored the imaging techniques that can effectively image complex skeletal muscle microstructure, and how they could be used. As part of a scoping review, we conducted a systematic search from three medical databases (CINAHL, EMBASE and MEDLINE) from year to year to analyze past MTrP imaging, as well as analyzing imaging techniques performed on the microstructure of muscle. Previously, ultrasound has been used to differentiate active, latent MTrPs, but these studies do not adequately address their underlying anatomical structure. MRI remains the standard method of imaging skeletal muscle. The existing MRI literature suggests that the DTI technique can quantify muscle injury, strain, and structure. However, theoretically, HARDI and DKI techniques seem to provide more information for complex structural areas, although these modalities have a disadvantage of longer scan times and have not been widely used on skeletal muscle. Our review suggests that DTI is the most effective imaging modality that has been used to define the microstructure of muscle and hence, could be optimal to image the MTrP. HARDI and DKI are techniques with theoretical potential for analysis of muscle, which may provide more detailed information representative of finer muscle structural features. Future research utilizing MRI techniques to image muscle are necessary to provide a more robust means of imaging skeletal muscle and the MTrP. [ABSTRACT FROM AUTHOR]

Context In rodents, cold exposure induces the activation of brown adipose tissue (BAT) and the induction of intracellular triacylglycerol (TAG) lipolysis. However, in humans, the kinetics of supraclavicular (SCV) BAT activation and the potential importance of TAG stores remain poorly defined. Objective To determine the time course of BAT activation and changes in intracellular TAG using MRI assessment of the SCV (i.e., BAT depot) and fat in the posterior neck region (i.e., non-BAT). Design Cross-sectional. Setting Clinical research center. Patients or Other Participants Twelve healthy male volunteers aged 18 to 29 years [body mass index = 24.7 ± 2.8 kg/m2 and body fat percentage = 25.0% ± 7.4% (both, mean ± SD)]. Intervention(s) Standardized whole-body cold exposure (180 minutes at 18°C) and immediate rewarming (30 minutes at 32°C). Main Outcome Measure(s) Proton density fat fraction (PDFF) and T2* of the SCV and posterior neck fat pads. Acquisitions occurred at 5- to 15-minute intervals during cooling and subsequent warming. Results SCV PDFF declined significantly after only 10 minutes of cold exposure [−1.6% (SE: 0.44%; P = 0.007)] and continued to decline until 35 minutes, after which time it remained stable until 180 minutes. A similar time course was also observed for SCV T2*. In the posterior neck fat (non-BAT), there were no cold-induced changes in PDFF or T2*. Rewarming did not result in a change in SCV PDFF or T2*. Conclusions The rapid cold-induced decline in SCV PDFF suggests that in humans BAT is activated quickly in response to cold and that TAG is a primary substrate. [ABSTRACT FROM AUTHOR]

The activation of brown adipose tissue (BAT) is associated with reductions in circulating lipids and glucose in rodents and contributes to energy expenditure in humans indicating the potential therapeutic importance of targetting this tissue for the treatment of a variety of metabolic disorders. In order to evaluate the therapeutic potential of human BAT, a variety of methodologies for assessing the volume and metabolic activity of BAT are utilized. Cold exposure is often utilized to increase BAT activity but inconsistencies in the characteristics of the exposure protocols make it challenging to compare findings. The metabolic activity of BAT in response to cold exposure has most commonly been measured by static positron emission tomography of 18F-fluorodeoxyglucose in combination with computed tomography (18F-FDG PET-CT) imaging, but recent studies suggest that under some conditions this may not always reflect BAT thermogenic activity. Therefore, recent studies have used alternative positron emission tomography and computed tomography (PET-CT) imaging strategies and radiotracers that may offer important insights. In addition to PET-CT, there are numerous emerging techniques that may have utility for assessing BATmetabolic activity including magnetic resonance imaging (MRI), skin temperaturemeasurements, near-infrared spectroscopy (NIRS) and contrast ultrasound (CU). In this review, we discuss and critically evaluate the various methodologies used to measure BAT metabolic activity in humans and provide a contemporary assessment of protocols which may be useful in interpreting research findings and guiding the development of future studies. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Medical Imaging & Radiation Sciences is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Purpose To compare the acute effect of running and bicycling of an equivalent cumulative load on knee cartilage composition and morphometry in healthy young men. A secondary analysis investigated the relationship between activity history and the change in cartilage composition after activity. Methods In fifteen men (25.8±4.2 years), the vertical ground reaction force was measured to determine the cumulative load exposure of a 15-min run. The vertical pedal reaction force was recorded during bicycling to define the bicycling duration of an equivalent cumulative load. On separate visits that were spaced on average 17 days apart, participants completed these running and bicycling bouts. Mean cartilage transverse relaxation times ( T 2 ) were determined for cartilage on the tibia and weight-bearing femur before and after each exercise. T 2 was measured using a multi-echo spin-echo sequence and 3T MRI. Cartilage of the weight bearing femur and tibia was segmented using a highly-automated segmentation algorithm. Activity history was captured using the International Physical Activity Questionnaire. Results The response of T 2 to bicycling and running was different ( p =0.019; mean T 2 : pre-running=34.27 ms, pre-bicycling=32.93 ms, post-running=31.82 ms, post-bicycling=32.36 ms). While bicycling produced no change (−1.7%, p =0.300), running shortened T 2 (−7.1%, p <0.001). Greater activity history predicted smaller changes in tibial, but not femoral, T 2 . Conclusions Changes in knee cartilage vary based on activity type, independent of total load exposure, in healthy young men. Smaller changes in T 2 were observed after bicycling relative to running. Activity history was inversely related to tibial T 2 , suggesting cartilage conditioning. [ABSTRACT FROM AUTHOR]

Background: Conventional imaging techniques are unable to detect abnormalities in the brain following mild traumatic brain injury (mTBI). Yet patients with mTBI typically show delayed response on neuropsychological evaluation. Because fractal geometry represents complexity, we explored its utility in measuring temporal fluctuations of brain resting state blood oxygen level dependent (rs-BOLD) signal. We hypothesized that there could be a detectable difference in rs-BOLD signal complexity between healthy subjects and mTBI patients based on previous studies that associated reduction in signal complexity with disease. Methods: Fifteen subjects (13.4 ± 2.3 y/o) and 56 age-matched (13.5 ± 2.34 y/o) healthy controls were scanned using a GE Discovery MR750 3T MRI and 32-channel RF-coil. Axial FSPGR-3D images were used to prescribe rs-BOLD (TE/TR = 35/2000ms), acquired over 6 minutes. Motion correction was performed and anatomical and functional images were aligned and spatially warped to the N27 standard atlas. Fractal analysis, performed on grey matter, was done by estimating the Hurst exponent using de-trended fluctuation analysis and signal summation conversion methods. Results and Conclusions: Voxel-wise fractal dimension (FD) was calculated for every subject in the control group to generate mean and standard deviation maps for regional Z-score analysis. Voxel-wise validation of FD normality across controls was confirmed, and non-Gaussian voxels (3.05% over the brain) were eliminated from subsequent analysis. For each mTBI patient, regions where Z-score values were at least 2 standard deviations away from the mean (i.e. where |Z| > 2.0) were identified. In individual patients the frequently affected regions were amygdala (p = 0.02), vermis(p = 0.03), caudate head (p = 0.04), hippocampus(p = 0.03), and hypothalamus(p = 0.04), all previously reported as dysfunctional after mTBI, but based on group analysis. It is well known that the brain is best modeled as a complex system. Therefore a measure of complexity using rs-BOLD signal FD could provide an additional method to grade and monitor mTBI. Furthermore, this approach can be personalized thus providing unique patient specific assessment. [ABSTRACT FROM AUTHOR]

A cadmium zinc telluride (CZT) based detector system has been developed with the goal of combining molecular breast imaging (MBI) and magnetic resonance imaging (MRI) to address shortcomings of each modality. The CZT detector system is comprised of four CZT modules tiled in a $2\times 2$ array. Each module consists of 256 pixels ( $16\times 16$ , 2.4 mm pixels) and features a built-in ASIC and FPGA. A custom digital readout circuit board was designed to interface the four modules with a microcontroller to a data acquisition PC. The system was placed within the bore of a 3 T GE Discovery MR750 and imaging performance of each modality evaluated using both sequential and simultaneous imaging protocols. The mean energy resolution of the gamma camera both inside and outside the MRI is 7.3% at 140 keV. The maximum increase in the integral uniformity was 3% when using a gradient echo MRI sequence while the mean differential uniformity when inside the MRI increased by 1%. Spatial resolution varied in a predictable manner from 2.4 mm FWHM at the collimator face to 6.9 mm at 10 cm from the collimator. Performance of the 3 T GE Discovery MR750 using a 16-channel breast RF coil array was measured with and without the gamma camera present using a gradient echo and spoiled gradient echo imaging sequence. A realistic 99mTc-filled breast-like phantom containing two lesions (30:1 lesion to background ratio) was used to assess the feasibility of both serial and simultaneous hybrid imaging. Sequential imaging resulted in a reduction in MRI SNR of 70-80% and a further decrease of 93-98% was observed when performing simultaneous MR/scintigraphy imaging, likely a result of RF interference originating from the CZT detector modules and associated analog electronics. Co-registered scintigraphic and MRI images display negligible geometric distortion when imaged with both simultaneous and serial imaging modes, thus indicating the feasibility of combining MBI with breast MRI. [ABSTRACT FROM AUTHOR]

This paper examines two artifacts facing researchers who use gradient echo (GRE) echo planar imaging (EPI) for time series studies of skeletal muscles in limbs. The first is through-plane blood flow during the acquisition, causing a vessel motion artifact that inhibits proper motion correction of the data. The second is distortion of EPI images caused by B 0 field inhomogeneities. Though software tools are available for correcting these artifacts in brain EPI images, the tools do not perform well on muscle images. The severity of the two artifacts was described using image similarity measures, and the data was processed with both a conventional motion correction program and custom written tools. The conventional program did not perform well on the limb images, in fact significantly degrading image quality in some trials. Data is presented which proves that arterial pulsatile signal caused the impairment in motion correction. The new tools were shown to perform much better, achieving substantial motion correction and distortion correction of the muscle EPI images. [ABSTRACT FROM AUTHOR]

Purpose: To explore the effect of diffusion tensor imaging (DTI) acquisition parameters on principal and minor eigenvector stability within human lower leg skeletal muscles.Materials and Methods: Lower leg muscles were evaluated in seven healthy subjects at 3T using an 8-channel transmit/receive coil. Diffusion-encoding was performed with nine signal averages (NSA) using 6, 15, and 25 directions (NDD). Individual DTI volumes were combined into aggregate volumes of 3, 2, and 1 NSA according to number of directions. Tensor eigenvalues (λ1 , λ2 , λ3 ), eigenvectors (ε1 , ε2 , ε3 ), and DTI metrics (fractional anisotropy [FA] and mean diffusivity [MD]) were calculated for each combination of NSA and NDD. Spatial maps of signal-to-noise ratio (SNR), λ3 :λ2 ratio, and zenith angle were also calculated for region of interest (ROI) analysis of vector orientation consistency.Results: ε1 variability was only moderately related to ε2 variability (r = 0.4045). Variation of ε1 was affected by NDD, not NSA (P < 0.0002), while variation of ε2 was affected by NSA, not NDD (P < 0.0003). In terms of tensor shape, vector variability was weakly related to FA (ε1 :r = -0.1854, ε2 : ns), but had a stronger relation to the λ3 :λ2 ratio (ε1 :r = -0.5221, ε2 :r = -0.1771). Vector variability was also weakly related to SNR (ε1 :r = -0.2873, ε2 :r = -0.3483). Zenith angle was found to be strongly associated with variability of ε1 (r = 0.8048) but only weakly with that of ε2 (r = 0.2135).Conclusion: The second eigenvector (ε2 ) displayed higher directional variability relative to ε1 , and was only marginally affected by experimental conditions that impacted ε1 variability. [ABSTRACT FROM AUTHOR]

Abstract: Objective: The objective of the study was to investigate the cerebrovascular hemodynamic response of cervical spine positions including rotation and cervical spine manipulation in vivo using magnetic resonance imaging technology on the vertebral artery (VA). Methods: This pilot study was conducted as a blinded examiner cohort with 4 randomized clinical tasks. Ten healthy male participants aged 24 to 30 years (mean, 26.8 years) volunteered to participate in the study. None of the participants had a history of disabling neck, arm, or headache pain within the last 6 months. They did not have any current or history of neurologic symptoms. In a neutral head position, physiologic measures of VA blood flow and velocity at the C1-2 spinal level were obtained using phase-contrast magnetic resonance imaging after 3 different head positions and a chiropractic upper cervical spinal manipulation. A total of 30 flow-encoded phase-contrast images were collected over the cardiac cycle, in each of the 4 conditions, and were used to provide a blood flow profile for one complete cardiac cycle. Differences between flow (in milliliters per second) and velocity (in centimeters per second) variables were evaluated using repeated-measures analysis of variance. Results: The side-to-side difference between ipsilateral and contralateral VA velocities was not significant for either velocities (P = .14) or flows (P = .19) throughout the conditions. There were no other interactions or trends toward a difference for any of the other blood flow or velocity variables. Conclusions: There were no significant changes in blood flow or velocity in the vertebral arteries of healthy young male adults after various head positions and cervical spine manipulations. [Copyright &y& Elsevier]

Objective: Multiple sclerosis (MS) is a chronic neurodegenerative disease of the CNS. Recently a controversial vascular hypothesis for MS, termed chronic cerebrospinal venous insufficiency (CCSVI), has been advanced. The objective of this study was to evaluate the relative prevalence of the venous abnormalities that define CCSVI. Methods: A case-control study was conducted in which 100 MS patients aged between 18–65 y meeting the revised McDonald criteria were randomly selected and stratified into one of four MS subtypes: relapsing/remitting, secondary progressive, primary progressive and benign. Control subjects (16–70 y) with no known history of MS or other neurological condition were matched with the MS cases. All cases and controls underwent ultrasound imaging of the veins of the neck plus the deep cerebral veins, and magnetic resonance imaging of the neck veins and brain. These procedures were performed on each participant on the same day. Results: On ultrasound we found no evidence of reflux, stenosis or blockage in the internal jugular veins (IJV) or vertebral veins (VV) in any study participant. Similarly, there was no evidence of either reflux or cessation of flow in the deep cerebral veins in any subject. Flow was detected in the IJV and VV in all study participants. Amongst 199 participants there was one MS subject who fulfilled the minimum two ultrasound criteria for CCSVI. Using MRI we found no significant differences in either the intra- or extra-cranial venous flow velocity or venous architecture between cases and controls. Conclusion: This case-control study provides compelling evidence against the involvement of CCSVI in multiple sclerosis. [ABSTRACT FROM AUTHOR]

Introduction: Structural evidence of exercise-induced muscle disruption has traditionally involved histological analysis of muscle tissue obtained by needle biopsy, however, there are multiple limitations with this technique. Recently, diffusion tensor magnetic resonance imaging (DT-MRI) has been successfully demonstrated to noninvasively assess skeletal muscle abnormalities induced by traumatic injury. Methods: To determine the potential for DT-MRI to detect musculoskeletal changes after a bout of eccentric exercise, 10 healthy men performed 300 eccentric actions on an isokinetic dynamometer. DT-MRI measurements and muscle biopsies from the vastus lateralis were obtained before and 24 h post-exercise. Results: Z-band streaming was higher 24 h post-exercise compared with baseline ( P < 0.05). The histological indices of damage coincided with changes in DT-MRI parameters of fractional anisotropy (FA) and apparent diffusion coefficient; reflecting altered skeletal muscle geometry ( P < 0.05). Z-band streaming quantified per fiber correlated with FA (r = −0.512; P < 0.05). Conclusions: DT-MRI can detect changes in human skeletal muscle structure following eccentric exercise. Muscle Nerve 46: 42-50, 2012 [ABSTRACT FROM AUTHOR]

MRI phase and magnitude images provide information about local magnetic field variation (ΔB0), which can consequently be used to understand tissue properties. Often, phase information is discarded. However, corrected phase images are able to produce contrast as a result of magnetic susceptibility differences and local field inhomogeneities due to the presence of diamagnetic and paramagnetic substances. Three-dimensional (3D) susceptibility weighted imaging (SWI) can be used to probe changes in MRI phase evolution and, subsequently, result in an alternate form of contrast between tissues. For example, SWI has been useful in the assessment of negative phase induced ΔB0 modulation due to the presence of paramagnetic substances such as iron. Very little, however, has been done to assess positive phase induced contrast changes resulting from the presence of diamagnetic substances such as precipitated calcium. As ductal carcinoma in situ, which is the precursor of invasive ductal cancer, is often associated with breast microcalcification, the authors proposed using SWI as a possible visualization technique. In this study, breast phantoms containing calcifications (0.4–1.5 mm) were imaged using mammography, computed tomography (CT), and SWI. Corrected phase and magnitude images acquired using SWI allowed identification and correlation of all calcifications seen on CT. As the approach is a 3D technique, it could potentially allow for more accurate localization and biopsy and maybe even reduce the use of gadolinium contrast. Furthermore, the approach may be beneficial to women with dense breast tissue where the ability to detect microcalcification with mammography is reduced. [ABSTRACT FROM AUTHOR]

Specifying the boundary of tissues or an organ is one of the most frequently required tasks for a radiologist. It is a first step for further processing, such as comparing two serial images in time, volume measurements. In the present work, we use genetic algorithms (GA) and where necessary apply a "dynamic genetic algorithm" (dGA) procedure, which (we believe) is a unique application, to assess different values for finding an optimal set of parameters that characterize the level set method, a geometric active contour, for use as a boundary detection method. Four quantitative measures are used in calculating geometric differences between the object boundaries, as determined by the level set method, and the desired object boundaries. A semi-automated method is also developed to find the desired boundary for the object. A two-step method requires the user to manipulate the object boundaries obtained by applying an edge detection method based on the Canny filter. By setting the level set method parameters using the output of the GA we obtain accurate boundaries of organs automatically and rapidly. [ABSTRACT FROM AUTHOR]