Metabolic Changes in the Visual Cortex of Binocular Blindness Macaque Monkeys: A Proton Magnetic Resonance Spectroscopy Study

Purpose

To evaluate proton magnetic resonance spectroscopy (¹H-MRS) in a study of cross-modal plasticity in the visual cortex of binocular blindness macaque monkeys.

Materials and Methods

Four healthy neonatal macaque monkeys were randomly divided into 2 groups, with 2 in each group. Optic nerve transection was performed in both monkeys in the experimental group (group B) to obtain binocular blindness. Two healthy macaque monkeys served as a control group (group A). After sixteen months post-procedure, ¹H-MRS was performed in the visual cortex of all monkeys. We compared the peak areas of NAA, Cr, Cho, Glx and Ins and the ratios of NAA/Cr, Cho/Cr, Glx/Cr and Ins/Cr of each monkey in group B with group A.

Results

The peak area of NAA and the NAA/Cr ratio in the visual cortex of monkey 4 in group B were found to be dramatically decreased, the peak area of NAA slightly decreased and the NAA/Cr ratio clearly decreased in visual cortex of monkey 3 in group B than those in group A. The peak area of Ins and the Ins/Cr ratio in the visual cortex of monkey 4 in group B slightly increased. The peak area of Cho and the Cho/Cr ratio in the visual cortex of all monkeys in group B dramatically increased compared with group A. The peak area of Glx in the visual cortex of all monkeys in group B slightly increased compared with group A.

Conclusions

¹H-MRS could detect biochemical and metabolic changes in the visual cortex and therefore this technique can be used to provide valuable information for investigating the mechanisms of cross-modal plasticity of binocular blindness in a macaque monkey model.     

Design and Evaluation of a Hybrid Radiofrequency Applicator for Magnetic Resonance Imaging and RF Induced Hyperthermia: Electromagnetic Field Simulations up to 14.0 Tesla and Proof-of-Concept at 7.0 Tesla

This work demonstrates the feasibility of a hybrid radiofrequency (RF) applicator that supports magnetic resonance (MR) imaging and MR controlled targeted RF heating at ultrahigh magnetic fields (B₀≥7.0T). For this purpose a virtual and an experimental configuration of an 8-channel transmit/receive (TX/RX) hybrid RF applicator was designed. For TX/RX bow tie antenna electric dipoles were employed. Electromagnetic field simulations (EMF) were performed to study RF heating versus RF wavelength (frequency range: 64 MHz (1.5T) to 600 MHz (14.0T)). The experimental version of the applicator was implemented at B₀ = 7.0T. The applicators feasibility for targeted RF heating was evaluated in EMF simulations and in phantom studies. Temperature co-simulations were conducted in phantoms and in a human voxel model. Our results demonstrate that higher frequencies afford a reduction in the size of specific absorption rate (SAR) hotspots. At 7T (298 MHz) the hybrid applicator yielded a 50% iso-contour SAR (iso-SAR-50%) hotspot with a diameter of 43 mm. At 600 MHz an iso-SAR-50% hotspot of 26 mm in diameter was observed. RF power deposition per RF input power was found to increase with B₀ which makes targeted RF heating more efficient at higher frequencies. The applicator was capable of generating deep-seated temperature hotspots in phantoms. The feasibility of 2D steering of a SAR/temperature hotspot to a target location was demonstrated by the induction of a focal temperature increase (ΔT = 8.1 K) in an off-center region of the phantom. Temperature simulations in the human brain performed at 298 MHz showed a maximum temperature increase to 48.6C for a deep-seated hotspot in the brain with a size of (19×23×32)mm³ iso-temperature-90%. The hybrid applicator provided imaging capabilities that facilitate high spatial resolution brain MRI. To conclude, this study outlines the technical underpinnings and demonstrates the basic feasibility of an 8-channel hybrid TX/RX applicator that supports MR imaging, MR thermometry and targeted RF heating in one device.     

Diffusion Microscopist Simulator: A General Monte Carlo Simulation System for Diffusion Magnetic Resonance Imaging

This article describes the development and application of an integrated, generalized, and efficient Monte Carlo simulation system for diffusion magnetic resonance imaging (dMRI), named Diffusion Microscopist Simulator (DMS). DMS comprises a random walk Monte Carlo simulator and an MR image synthesizer. The former has the capacity to perform large-scale simulations of Brownian dynamics in the virtual environments of neural tissues at various levels of complexity, and the latter is flexible enough to synthesize dMRI datasets from a variety of simulated MRI pulse sequences. The aims of DMS are to give insights into the link between the fundamental diffusion process in biological tissues and the features observed in dMRI, as well as to provide appropriate ground-truth information for the development, optimization, and validation of dMRI acquisition schemes for different applications. The validity, efficiency, and potential applications of DMS are evaluated through four benchmark experiments, including the simulated dMRI of white matter fibers, the multiple scattering diffusion imaging, the biophysical modeling of polar cell membranes, and the high angular resolution diffusion imaging and fiber tractography of complex fiber configurations. We expect that this novel software tool would be substantially advantageous to clarify the interrelationship between dMRI and the microscopic characteristics of brain tissues, and to advance the biophysical modeling and the dMRI methodologies.     

Neonatal Brain Metabolite Concentrations: An In Vivo Magnetic Resonance Spectroscopy Study with a Clinical MR System at 3 Tesla

Brain metabolite concentrations change dynamically throughout development, especially during early childhood. The purpose of this study was to investigate the brain metabolite concentrations of neonates (postconceptional age (PCA): 30 to 43 weeks) using single-voxel magnetic resonance spectroscopy (MRS) and to discuss the relationships between the changes in the concentrations of such metabolites and brain development during the neonatal period. A total of 83 neonatal subjects were included using the following criteria: the neonates had to be free of radiological abnormalities, organic illness, and neurological symptoms; the MR spectra had to have signal-to-noise ratios ≥ 4; and the estimated metabolite concentrations had to display Cramér-Rao lower bounds of ≤ 30%. MRS data (echo time/repetition time, 30/5000 ms; 3T) were acquired from the basal ganglia (BG), centrum semiovale (CS), and the cerebellum. The concentrations of five metabolites were measured: creatine, choline, N-acetylaspartate, myo-inositol, and glutamate/glutamine complex (Glx). One hundred and eighty-four MR spectra were obtained (83 BG, 77 CS, and 24 cerebellum spectra). Creatine, N-acetylaspartate, and Glx displayed increases in their concentrations with PCA. Choline was not correlated with PCA in any region. As for myo-inositol, its concentration decreased with PCA in the BG, whereas it increased with PCA in the cerebellum. Quantitative brain metabolite concentrations and their changes during the neonatal period were assessed. Although the observed changes were partly similar to those detected in previous reports, our results are with more subjects (n = 83), and higher magnetic field (3T). The metabolite concentrations examined in this study and their changes are clinically useful indices of neonatal brain development.     

New Cerebral Lesions at Magnetic Resonance Imaging after Carotid Artery Stenting Versus Endarterectomy: An Updated Meta-Analysis

Background

Carotid endarterectomy (CEA) or stenting (CAS) are associated with a relatively low rate of clinical events, but diffusion-weighted imaging (DWI) is increasingly being used to compare the incidence of new ischemic lesions. Therefore, we conducted an updated meta-analysis on the occurrence of post-procedural new DWI lesions after CAS versus CEA.

Methods and Results

MEDLINE, Cochrane, ISI Web of Science and SCOPUS databases were searched and 20 studies (2 randomized and 18 non-randomized) with a total of 2104 procedures (CAS = 989; CEA = 1115) were included. The incidence of new DWI cerebral lesions was significantly greater after CAS than CEA (40.3% vs 12.2%; 20 studies; 2104 patients; odds ratio [OR] 5.17; 95% confidence interval [CI], 3.31-8.06; p<0.00001). Also peri-procedural stroke (17 studies; 1833 patients; OR 2.01; 95% CI, 1.14-3.55; p=0.02) and stroke or TIA (17 studies; 1833 patients; OR 2.40; 95% CI, 1.42-4.08; p=0.001) were significantly increased after CAS. This latter clinical advantage in the CEA group over CAS was tempered when CEA procedures were performed with shunting in all instead of selective shunting or when CAS was performed with only closed cell stents instead of both closed and open cell stents, however, no significant differences between subgroups emerged.

Conclusions

CAS is associated with an increased incidence of post-procedural brain DWI lesions. This greater amount of ischemic burden may also reflect a higher rate of cerebral events after CAS. However, whether recent technical advances mainly for CAS could potentially reduce these ischemic events still remains to be evaluated.     

Investigation of Parallel Radiofrequency Transmission for the Reduction of Heating in Long Conductive Leads in 3 Tesla Magnetic Resonance Imaging

Deep Brain Stimulation (DBS) is increasingly used to treat a variety of brain diseases by sending electrical impulses to deep brain nuclei through long, electrically conductive leads. Magnetic resonance imaging (MRI) of patients pre- and post-implantation is desirable to target and position the implant, to evaluate possible side-effects and to examine DBS patients who have other health conditions. Although MRI is the preferred modality for pre-operative planning, MRI post-implantation is limited due to the risk of high local power deposition, and therefore tissue heating, at the tip of the lead. The localized power deposition arises from currents induced in the leads caused by coupling with the radiofrequency (RF) transmission field during imaging. In the present work, parallel RF transmission (pTx) is used to tailor the RF electric field to suppress coupling effects. Electromagnetic simulations were performed for three pTx coil configurations with 2, 4, and 8-elements, respectively. Optimal input voltages to minimize coupling, while maintaining RF magnetic field homogeneity, were determined for all configurations using a Nelder-Mead optimization algorithm. Resulting electric and magnetic fields were compared to that of a 16-rung birdcage coil. Experimental validation was performed with a custom-built 4-element pTx coil. In simulation, 95-99% reduction of the electric field at the tip of the lead was observed between the various pTx coil configurations and the birdcage coil. Maximal reduction in E-field was obtained with the 8-element pTx coil. Magnetic field homogeneity was comparable to the birdcage coil for the 4- and 8-element pTx configurations. In experiment, a temperature increase of 2±0.15°C was observed at the tip of the wire using the birdcage coil, whereas negligible increase (0.2±0.15°C) was observed with the optimized pTx system. Although further research is required, these initial results suggest that the concept of optimizing pTx to reduce DBS heating effects holds considerable promise.     

Application of 3.0 Tesla Magnetic Resonance Imaging for Diagnosis in the Orthotopic Nude Mouse Model of Pancreatic Cancer

The aim of this study was to successfully establish an orthotopic murine model using two different human pancreatic adenocarcinoma cell lines and to propose a 3.0 tesla MRI protocol for noninvasive characterization of this model. SW1990 and MIAPaca-2 tumor cells were injected into the pancreas of BALB/C nu/nu mice. Tumor growth rate and morphological information were assessed by 3.0 tesla MRI (T1WI, T2WI and DCE-MRI) and immunohistology. Proliferation of SW1990 was significantly faster than that of MIAPaca-2 (P=0.000), but MIAPaca-2 mice had a significantly shorter survival than SW1990 mice (41 days and 44 days respectively, P=0.027). MRI could reliably monitor tumor growth in both cell lines: the tumors exhibiting a spherical growth pattern showed a high-intensity signal, and the SW1990 group developed significantly larger tumors compared with the MIAPaCa-2 group. There were no statistical differences between the two groups in which tumor size was assessed using electronic calipers and an MRI scan (P=0.680). Both tumors showed a slow gradual enhancement pattern. Immunohistochemistry demonstrated tumor tissues showing high expression of Ki-67. This model closely mimics human pancreatic cancer and permits monitoring of tumor growth and morphological information by noninvasive 3.0 tesla MRI studies reducing the number of mice required.     

The Reporting of Observational Clinical Functional Magnetic Resonance Imaging Studies: A Systematic Review

Introduction

Complete reporting assists readers in confirming the methodological rigor and validity of findings and allows replication. The reporting quality of observational functional magnetic resonance imaging (fMRI) studies involving clinical participants is unclear.

Objectives

We sought to determine the quality of reporting in observational fMRI studies involving clinical participants.

Methods

We searched OVID MEDLINE for fMRI studies in six leading journals between January 2010 and December 2011.Three independent reviewers abstracted data from articles using an 83-item checklist adapted from the guidelines proposed by Poldrack et al. (Neuroimage 2008; 40: 409–14). We calculated the percentage of articles reporting each item of the checklist and the percentage of reported items per article.

Results

A random sample of 100 eligible articles was included in the study. Thirty-one items were reported by fewer than 50% of the articles and 13 items were reported by fewer than 20% of the articles. The median percentage of reported items per article was 51% (ranging from 30% to 78%). Although most articles reported statistical methods for within-subject modeling (92%) and for between-subject group modeling (97%), none of the articles reported observed effect sizes for any negative finding (0%). Few articles reported justifications for fixed-effect inferences used for group modeling (3%) and temporal autocorrelations used to account for within-subject variances and correlations (18%). Other under-reported areas included whether and how the task design was optimized for efficiency (22%) and distributions of inter-trial intervals (23%).

Conclusions

This study indicates that substantial improvement in the reporting of observational clinical fMRI studies is required. Poldrack et al.''s guidelines provide a means of improving overall reporting quality. Nonetheless, these guidelines are lengthy and may be at odds with strict word limits for publication; creation of a shortened-version of Poldrack''s checklist that contains the most relevant items may be useful in this regard.     

Gadoxetic Acid Disodium-Enhanced Magnetic Resonance Imaging for the Detection of Hepatocellular Carcinoma: A Meta-Analysis

Objective

To determine the accuracy of MR imaging with gadoxetic acid disodium (Gd-EOB-DTPA) for the detection of hepatocelluar carcinoma (HCC).

Materials and Methods

A systematic search was performed in PUBMED, EMBASE, Web of Science, Cochrane Library and the Chinese Biomedical Literature Database up to March 2013 to identify studies about evaluation of Gd-EOB-DTPA enhanced MR imaging in patients suspected of having HCC. The data were extracted to perform heterogeneity test and threshold effect test and to calculate sensitivity, specificity, diagnostic odds ratio, predictive value, and areas under summary receiver operating characteristic curve (AUC).

Results

From 601 citations, 10 were included in the meta-analysis. The methodological quality of the 10 studies was good. Overall HCC: There was significant heterogeneity in the pooled analysis (I² = 69.4%, P = 0.0005), and the pooled weighted values were determined to be sensitivity: 0.91 (95% confidence interval (CI): 0.89, 0. 93); specificity: 0.95 (95% CI: 0.94, 0.96); diagnostic odds ratio: 169.94 (95% CI: 108.84, 265.36); positive likelihood ratio: 15.75 (95% CI: 7.45, 33.31); negative likelihood ratio: 0.10 (95% CI: 0.06, 0.15). The AUC was 0.9778. HCC in cirrhosis: The estimates were to be sensitivity: 0.91 (95% CI: 0.88, 0.93); specificity: 0.93 (95% CI: 0.89, 0.95); diagnostic odds ratio: 234.24 (95% CI: 33.47, 1639.25); positive likelihood ratio: 15.08 (95% CI: 2.20, 103.40); negative likelihood ratio: 0.08 (95% CI: 0.03, 0.21). The AUC was 0.9814. ≤20 mm HCC: The AUC was 0.9936. There was no notable publication bias.

Conclusions

This meta-analysis suggests that MR imaging with Gd-EOB-DTPA has high diagnostic accuracy for the detection of HCC, especially for ≤20 mm HCC. This technique shows good prospect in diagnosis of HCC.     

Fast Diffusion Tensor Magnetic Resonance Imaging of the Mouse Brain at Ultrahigh-Field: Aiming at Cohort Studies

Introduction

In-vivo high resolution diffusion tensor imaging (DTI) of the mouse brain is often limited by the low signal to noise ratio (SNR) resulting from the required small voxel sizes. Recently, cryogenically cooled resonators (CCR) have demonstrated significant increase of the effective SNR. It is the objective of this study to enable fast DTI of the mouse brain. In this context, CCRs appear attractive for SNR improvement.

Methods

Three mice underwent a DTI examination at 156²×250 µm³ spatial resolution with a CCR at ultrahigh field (11.7T). Diffusion images were acquired along 30 gradient directions plus 5 references without diffusion encoding, resulting in a total acquisition time of 35 minutes. For comparison, mice additionally underwent a standardized 110 minutes acquisition protocol published earlier. Fractional anisotropy (FA) and fiber tracking (FT) results including quantitative tractwise fractional anisotropy statistics (TFAS) were qualitatively and quantitatively compared.

Results

Qualitative and quantitative assessment of the calculated fractional anisotropy maps and fibre tracking results showed coinciding outcome comparing 35 minute scans to the standardized 110 minute scan. Coefficients of variation for ROI-based FA-comparison as well as for TFAS revealed comparable results for the different scanning protocols.

Conclusion

Mouse DTI at 11.7 T was performed with an acquisition time of approximately 30 minutes, which is considered feasible for cohort studies. The rapid acquisition protocol reveals reliable and reproducible FA-values and FT reconstructions, thus allowing an experimental setup for in-vivo large scale whole brain murine DTI cohort studies.     

Automatic Localization of the Left Ventricle from Cardiac Cine Magnetic Resonance Imaging: A New Spectrum-Based Computer-Aided Tool

Traditionally, cardiac image analysis is done manually. Automatic image processing can help with the repetitive tasks, and also deal with huge amounts of data, a task which would be humanly tedious. This study aims to develop a spectrum-based computer-aided tool to locate the left ventricle using images obtained via cardiac magnetic resonance imaging. Discrete Fourier Transform was conducted pixelwise on the image sequence. Harmonic images of all frequencies were analyzed visually and quantitatively to determine different patterns of the left and right ventricles on spectrum. The first and fifth harmonic images were selected to perform an anisotropic weighted circle Hough detection. This tool was then tested in ten volunteers. Our tool was able to locate the left ventricle in all cases and had a significantly higher cropping ratio of 0.165 than did earlier studies. In conclusion, a new spectrum-based computer aided tool has been proposed and developed for automatic left ventricle localization. The development of this technique, which will enable the automatic location and further segmentation of the left ventricle, will have a significant impact in research and in diagnostic settings. We envisage that this automated method could be used by radiographers and cardiologists to diagnose and assess ventricular function in patients with diverse heart diseases.     

Involvement of the Extrageniculate System in the Perception of Optical Illusions: A Functional Magnetic Resonance Imaging Study

Research on the neural processing of optical illusions can provide clues for understanding the neural mechanisms underlying visual perception. Previous studies have shown that some visual areas contribute to the perception of optical illusions such as the Kanizsa triangle and Müller-Lyer figure; however, the neural mechanisms underlying the processing of these and other optical illusions have not been clearly identified. Using functional magnetic resonance imaging (fMRI), we determined which brain regions are active during the perception of optical illusions. For our study, we enrolled 18 participants. The illusory optical stimuli consisted of many kana letters, which are Japanese phonograms. During the shape task, participants stated aloud whether they perceived the shapes of two optical illusions as being the same or not. During the word task, participants read aloud the kana letters in the stimuli. A direct comparison between the shape and word tasks showed activation of the right inferior frontal gyrus, left medial frontal gyrus, and right pulvinar. It is well known that there are two visual pathways, the geniculate and extrageniculate systems, which belong to the higher-level and primary visual systems, respectively. The pulvinar belongs to the latter system, and the findings of the present study suggest that the extrageniculate system is involved in the cognitive processing of optical illusions.     

Differentiating Laryngeal Carcinomas from Precursor Lesions by Diffusion-Weighted Magnetic Resonance Imaging at 3.0 T: A Preliminary Study

Background

Diffusion-weighted magnetic resonance imaging (DWI) has been introduced in head and neck cancers. Due to limitations in the performance of laryngeal DWI, including the complex anatomical structure of the larynx leading to susceptibility effects, the value of DWI in differentiating benign from malignant laryngeal lesions has largely been ignored. We assessed whether a threshold for the apparent diffusion coefficient (ADC) was useful in differentiating preoperative laryngeal carcinomas from precursor lesions by turbo spin-echo (TSE) DWI and 3.0-T magnetic resonance.

Methods

We evaluated DWI and the ADC value in 33 pathologically proven laryngeal carcinomas and 17 precancerous lesions.

Results

The sensitivity, specificity, and accuracy were 81.8%, 64.7%, 76.0% by laryngostroboscopy, respectively. The sensitivity, specificity, and accuracy of conventional magnetic resonance imaging were 90.9%, 76.5%, 86.0%, respectively. Qualitative DWI analysis produced sensitivity, specificity, and accuracy values of 100.0, 88.2, and 96.0%, respectively. The ADC values were lower for patients with laryngeal carcinoma (mean 1.195±0.32×10⁻³ mm²/s) versus those with laryngeal precancerous lesions (mean 1.780±0.32×10⁻³ mm²/s; P<0.001). ROC analysis showed that the area under the curve was 0.956 and the optimum threshold for the ADC was 1.455×10⁻³ mm²/s, resulting in a sensitivity of 94.1%, a specificity of 90.9%, and an accuracy of 92.9%.

Conclusions

Despite some limitations, including the small number of laryngeal carcinomas included, DWI may detect changes in tumor size and shape before they are visible by laryngostroboscopy. The ADC values were lower for patients with laryngeal carcinoma than for those with laryngeal precancerous lesions. The proposed cutoff for the ADC may help distinguish laryngeal carcinomas from laryngeal precancerous lesions.     

Evaluation of a Quantitative Magnetic Resonance Imaging System for Whole Body Composition Analysis in Rodents

We evaluated the EchoMRI‐900 combination rat and mouse quantitative magnetic resonance (QMR) body composition method in comparison to traditional whole‐body chemical carcass composition analysis (CCA) for measurements of fat and fat‐free mass in rodents. Live and postmortem (PM) QMR fat and lean mass measurements were obtained for lean, obese and outbred strains of rats and mice, and compared with measurements obtained using CCA. A second group of rats was measured before and after 18 h food or water deprivation. Significant positive correlations between QMR and CCA fat and lean mass measurements were shown for rats and mice. Although all live QMR fat and lean measurements were more precise than CCA for rats, values obtained for mice significantly differed from CCA for lean mass only. QMR performed PM slightly overestimated fat and lean values relative to live QMR but did not show lower precision than live QMR. Food deprivation reduced values for both fat and lean mass; water deprivation reduced estimates of lean mass only. In summary, all measurements using this QMR system were comparable to those obtained by CCA, but with higher overall precision, similar to previous reports for the murine QMR system. However, PM QMR measurements slightly overestimated live QMR values, and lean and fat mass measurements in this QMR system are influenced by hydration status and animal size, respectively. Despite these caveats, we conclude that the EchoMRI QMR system offers a fast in vivo method of body composition analysis, well correlated to but with greater overall precision than CCA.     

Functional Imaging of Plants: A Nuclear Magnetic Resonance Study of a Cucumber Plant

Functional magnetic resonance imaging was used to study transients of biophysical parameters in a cucumber plant in response to environmental changes. Detailed flow imaging experiments showed the location of xylem and phloem in the stem and the response of the following flow characteristics to the imposed environmental changes: the total amount of water, the amount of stationary and flowing water, the linear velocity of the flowing water, and the volume flow. The total measured volume flow through the plant stem was in good agreement with the independently measured water uptake by the roots. A separate analysis of the flow characteristics for two vascular bundles revealed that changes in volume flow of the xylem sap were accounted for by a change in linear-flow velocities in the xylem vessels. Multiple-spin echo experiments revealed two water fractions for different tissues in the plant stem; the spin-spin relaxation time of the larger fraction of parenchyma tissue in the center of the stem and the vascular tissue was down by 17% in the period after cooling the roots of the plant. This could point to an increased water permeability of the tonoplast membrane of the observed cells in this period of quick recovery from severe water loss.     

High Spatial Resolution and Temporally Resolved T2 * Mapping of Normal Human Myocardium at 7.0 Tesla: An Ultrahigh Field Magnetic Resonance Feasibility Study

Myocardial tissue characterization using T₂ ^* relaxation mapping techniques is an emerging application of (pre)clinical cardiovascular magnetic resonance imaging. The increase in microscopic susceptibility at higher magnetic field strengths renders myocardial T₂ ^* mapping at ultrahigh magnetic fields conceptually appealing. This work demonstrates the feasibility of myocardial T₂ ^* imaging at 7.0 T and examines the applicability of temporally-resolved and high spatial resolution myocardial T₂ ^* mapping. In phantom experiments single cardiac phase and dynamic (CINE) gradient echo imaging techniques provided similar T₂ ^* maps. In vivo studies showed that the peak-to-peak B₀ difference following volume selective shimming was reduced to approximately 80 Hz for the four chamber view and mid-ventricular short axis view of the heart and to 65 Hz for the left ventricle. No severe susceptibility artifacts were detected in the septum and in the lateral wall for T₂ ^* weighting ranging from TE = 2.04 ms to TE = 10.2 ms. For TE >7 ms, a susceptibility weighting induced signal void was observed within the anterior and inferior myocardial segments. The longest T₂ ^* values were found for anterior (T₂ ^* = 14.0 ms), anteroseptal (T₂ ^* = 17.2 ms) and inferoseptal (T₂ ^* = 16.5 ms) myocardial segments. Shorter T₂ ^* values were observed for inferior (T₂ ^* = 10.6 ms) and inferolateral (T₂ ^* = 11.4 ms) segments. A significant difference (p = 0.002) in T₂ ^* values was observed between end-diastole and end-systole with T₂ ^* changes of up to approximately 27% over the cardiac cycle which were pronounced in the septum. To conclude, these results underscore the challenges of myocardial T₂ ^* mapping at 7.0 T but demonstrate that these issues can be offset by using tailored shimming techniques and dedicated acquisition schemes.     

Chimpanzee (Pan troglodytes) Precentral Corticospinal System Asymmetry and Handedness: A Diffusion Magnetic Resonance Imaging Study

Background

Most humans are right handed, and most humans exhibit left-right asymmetries of the precentral corticospinal system. Recent studies indicate that chimpanzees also show a population-level right-handed bias, although it is less strong than in humans.

Methodology/Principal Findings

We used in vivo diffusion-weighted and T1-weighted magnetic resonance imaging (MRI) to study the relationship between the corticospinal tract (CST) and handedness in 36 adult female chimpanzees. Chimpanzees exhibited a hemispheric bias in fractional anisotropy (FA, left>right) and mean diffusivity (MD, right>left) of the CST, and the left CST was centered more posteriorly than the right. Handedness correlated with central sulcus depth, but not with FA or MD.

Conclusions/Significance

These anatomical results are qualitatively similar to those reported in humans, despite the differences in handedness. The existence of a left>right FA, right>left MD bias in the corticospinal tract that does not correlate with handedness, a result also reported in some human studies, suggests that at least some of the structural asymmetries of the corticospinal system are not exclusively related to laterality of hand preference.     

Characterization of Phase-Based Methods Used for Transmission Field Uniformity Mapping: A Magnetic Resonance Study at 3.0 T and 7.0 T

Knowledge of the transmission field (B₁ ⁺) of radio-frequency coils is crucial for high field (B₀ = 3.0 T) and ultrahigh field (B₀≥7.0 T) magnetic resonance applications to overcome constraints dictated by electrodynamics in the short wavelength regime with the ultimate goal to improve the image quality. For this purpose B₁ ⁺ mapping methods are used, which are commonly magnitude-based. In this study an analysis of five phase-based methods for three-dimensional mapping of the B₁ ⁺ field is presented. The five methods are implemented in a 3D gradient-echo technique. Each method makes use of different RF-pulses (composite or off-resonance pulses) to encode the effective intensity of the B₁ ⁺ field into the phase of the magnetization. The different RF-pulses result in different trajectories of the magnetization, different use of the transverse magnetization and different sensitivities to B₁ ⁺ inhomogeneities and frequency offsets, as demonstrated by numerical simulations. The characterization of the five methods also includes phantom experiments and in vivo studies of the human brain at 3.0 T and at 7.0 T. It is shown how the characteristics of each method affect the quality of the B₁ ⁺ maps. Implications for in vivo B₁ ⁺ mapping at 3.0 T and 7.0 T are discussed.     

Neural Correlates of Emotional Personality: A Structural and Functional Magnetic Resonance Imaging Study

Studies addressing brain correlates of emotional personality have remained sparse, despite the involvement of emotional personality in health and well-being. This study investigates structural and functional brain correlates of psychological and physiological measures related to emotional personality. Psychological measures included neuroticism, extraversion, and agreeableness scores, as assessed using a standard personality questionnaire. As a physiological measure we used a cardiac amplitude signature, the so-called E_κ value (computed from the electrocardiogram) which has previously been related to tender emotionality. Questionnaire scores and E_κ values were related to both functional (eigenvector centrality mapping, ECM) and structural (voxel-based morphometry, VBM) neuroimaging data. Functional magnetic resonance imaging (fMRI) data were obtained from 22 individuals (12 females) while listening to music (joy, fear, or neutral music). ECM results showed that agreeableness scores correlated with centrality values in the dorsolateral prefrontal cortex, the anterior cingulate cortex, and the ventral striatum (nucleus accumbens). Individuals with higher E_κ values (indexing higher tender emotionality) showed higher centrality values in the subiculum of the right hippocampal formation. Structural MRI data from an independent sample of 59 individuals (34 females) showed that neuroticism scores correlated with volume of the left amygdaloid complex. In addition, individuals with higher E_κ showed larger gray matter volume in the same portion of the subiculum in which individuals with higher E_κ showed higher centrality values. Our results highlight a role of the amygdala in neuroticism. Moreover, they indicate that a cardiac signature related to emotionality (E_κ) correlates with both function (increased network centrality) and structure (grey matter volume) of the subiculum of the hippocampal formation, suggesting a role of the hippocampal formation for emotional personality. Results are the first to show personality-related differences using eigenvector centrality mapping, and the first to show structural brain differences for a physiological measure associated with personality.