3T MRI Systems Research Articles

Cerebroventricular deformation and vector mapping, a topographic visualizer for surgical interventions in pediatric hydrocephalus.

Hydrocephalus is a challenging neurosurgical condition due to nonspecific symptoms and complex brain-fluid pressure dynamics. Typically, the assessment of hydrocephalus in children requires radiographic or invasive pressure monitoring. There is usually a qualitative focus on the ventricular spaces even though stress and shear forces extend across the brain. Here, the authors present an MRI-based vector approach for voxelwise brain and ventricular deformation visualization and analysis. Twenty pediatric patients (mean age 7.7 years, range 6 months-18 years; 14 males) with acute, newly diagnosed hydrocephalus requiring surgical intervention for symptomatic relief were randomly identified after retrospective chart review. Selection criteria included acquisition of both pre- and posttherapy paired 3D T1-weighted volumetric MRI (3D T1-MRI) performed on 3T MRI systems. Both pre- and posttherapy 3D T1-MRI pairs were aligned using image registration, and subsequently, voxelwise nonlinear transformations were performed to derive two exemplary visualizations of compliance: 1) a whole-brain vector map projecting the resulting deformation field on baseline axial imaging; and 2) a 3D heat map projecting the volumetric changes along ventricular boundaries and the brain periphery. The patients underwent the following interventions for treatment of hydrocephalus: endoscopic third ventriculostomy (n = 6); external ventricular drain placement and/or tumor resection (n = 10); or ventriculoperitoneal shunt placement (n = 4). The mean time between pre- and postoperative imaging was 36.5 days. Following intervention, the ventricular volumes decreased significantly (mean pre- and posttherapy volumes of 151.9 cm3 and 82.0 cm3, respectively; p < 0.001, paired t-test). The largest degree of deformation vector changes occurred along the lateral ventricular spaces, relative to the genu and splenium. There was a significant correlation between change in deformation vector magnitudes within the cortical layer and age (p = 0.011, Pearson), as well as between the ventricle size and age (p = 0.014, Pearson), suggesting higher compliance among infants and younger children. This study highlights an approach for deformation analysis and vector mapping that may serve as a topographic visualizer for therapeutic interventions in patients with hydrocephalus. A future study that correlates the degree of cerebroventricular deformation or compliance with intracranial pressures could clarify the potential role of this technique in noninvasive pressure monitoring or in cases of noncompliant ventricles.

Characterizing Off-center MRI with ZTE

PurposeTo maximize acquisition bandwidth in zero echo time (ZTE) sequences, readout gradients are already switched on during the RF pulse, creating unwanted slice selectivity. The resulting image distortions are amplified especially when the anatomy of interest is not located at the isocenter. We aim to characterize off-center ZTE MRI of extremities such as the shoulder, knee, and hip, adjusting the carrier frequency of the RF pulse excitation for each TR. MethodsIn ZTE MRI, radial encoding schemes are used, where the distorted slice profile due to the finite RF pulse length rotates with the k-space trajectory. To overcome these modulations for objects far away from the magnet isocenter, the frequency of the RF pulse is shifted for each gradient setting so that artifacts do not occur at a given off-center target position. The sharpness of the edges in the images were calculated and the ZTE acquisition with off-center excitation was compared to an acquisition with isocenter excitation both in phantom and in vivo off-center MRI of the shoulder, knee, and hip at 1.5 and 3T MRI systems. ResultsDistortion and blurriness artifacts on the off-center MRI images of the phantom, in vivo shoulder, knee, and hip images were mitigated with off-center excitation without time or noise penalty, at no additional computational cost. ConclusionThe off-center excitation allows ZTE MRI of the shoulder, knee, and hip for high-bandwidth image acquisitions for clinical settings, where positioning at the isocenter is not possible.

Multi-centre and multi-vendor reproducibility of a standardized protocol for quantitative susceptibility Mapping of the human brain at 3T

Quantitative Susceptibility Mapping (QSM) is an MRI-based technique allowing the non-invasive quantification of iron content and myelination in the brain. The RIN – Neuroimaging Network established an optimized and harmonized protocol for QSM across ten sites with 3T MRI systems from three different vendors to enable multicentric studies. The assessment of the reproducibility of this protocol is crucial to establish susceptibility as a quantitative biomarker. In this work, we evaluated cross-vendor reproducibility in a group of six traveling brains. Then, we recruited fifty-one volunteers and measured the variability of QSM values in a cohort of healthy subjects scanned at different sites, simulating a multicentric study. Both voxelwise and Region of Interest (ROI)-based analysis on cortical and subcortical gray matter were performed.The traveling brain study yielded high structural similarity (∼0.8) and excellent reproducibility comparing maps acquired on scanners from two different vendors. Depending on the ROI, we reported a quantification error ranging from 0.001 to 0.017 ppm for the traveling brains. In the cohort of fifty-one healthy subjects scanned at nine different sites, the ROI-dependent variability of susceptibility values, of the order of 0.005–0.025 ppm, was comparable to the result of the traveling brain experiment.The harmonized QSM protocol of the RIN – Neuroimaging Network provides a reliable quantification of susceptibility in both cortical and subcortical gray matter regions and it is ready for multicentric and longitudinal clinical studies in neurological and pychiatric diseases.

Diffeomorphic registration for retinotopic maps of multiple visual regions.

Retinotopic map, the mapping between visual inputs on the retina and neuronal responses on the cortical surface, is one of the central topics in vision science. Typically, human retinotopic maps are constructed by analyzing functional magnetic resonance responses to designed visual stimuli on the cortical surface. Although it is widely used in visual neuroscience, retinotopic maps are limited by the signal-to-noise ratio and spatial resolution of fMRI. One promising approach to improve the quality of retinotopic maps is to register individual subject's retinotopic maps to a retinotopic template. However, none of the existing retinotopic registration methods has explicitly quantified the diffeomorphic condition, that is, retinotopic mapsshall be aligned by stretching/compressing without tearing up the cortical surface. Here, we developed Diffeomorphic Registration for Retinotopic Maps (DRRM) to simultaneously align retinotopic maps in multiple visual regions under the diffeomorphic condition. Specifically, we used the Beltrami coefficient to model the diffeomorphic condition and performed surface registration based on retinotopic coordinates. The overall framework preserves the topological condition defined in the template. We further developed a unique evaluation protocol and compared the performance of the new method with several existing registration methods on both synthetic and real datasets. The results showed that DRRM is superior to the existing methods in achieving diffeomorphic registration in synthetic and empirical data from 3T and 7T MRI systems. DRRM may improve the interpretation of low-quality retinotopic maps and facilitate applications of retinotopic maps in clinical settings.

MULTI‐TISSUE ASSESSMENT AND 24‐MONTH PROGRESSION OF SEMI‐QUANTITATIVE MRI BIOMARKERS OF KNEE OSTEOARTHRITIS IN THE IMI‐APPROACH COHORT

The IMI-APPROACH (Applied Public-Private Research enabling OsteoArthritis Clinical Headway) study is an exploratory, European, 5-centre, 2-year prospective follow-up cohort project. IMI-APPROACH was designed to prospectively describe pre-identified progressor phenotypes of patients with symptomatic and/or structural knee OA by use of conventional and novel clinical, imaging, and biochemical biomarkers, and to validate and refine a predictive model for progressor phenotypes based on these markers. The recruitment for IMI-APPROACH was based on rankings produced by machine-learning models that were trained using data from existing cohorts to estimate the likelihood of joint space width loss and/or increased or sustained knee pain over the course of the study from demographic data, pain scores, and radiographic features. To describe baseline multi-tissue semiquantitative MRI evaluation of index knees and to describe change for different MRI features based on number of subregion-approaches and change in maximum grades over a 24-month period. MRIs were acquired using 1.5T or 3T MRI systems and assessed using the semi-quantitative MRI OA Knee Scoring (MOAKS) system. MRIs were read at baseline and 24-months for cartilage damage, bone marrow lesions (BML), osteophytes, meniscal damage and extrusion, and Hoffa- and effusion-synovitis. In descriptive fashion, the frequencies of MRI features at baseline and change in these biomarkers over time are presented for the entire sample in a subregional and maximum score approach for most features. Differences between knees without and with structural radiographic (R) OA are analyzed in addition. 289 participants had a readable baseline scan. Participants were on average 66.6±7.1 years old and had a BMI of 28.1±5.3 kg/m². The majority (55.3%) of the knees had definite signs of radiographic OA. Any change in total cartilage MOAKS score was seen in 53.1% considering only full-grade changes and in 73.9% including full-grade and within-grade changes. Any medial cartilage progression was seen in 23.9% and any lateral progression in 22.1%. While for the medial and lateral compartments numbers of subregions with improvement and worsening of BMLs were very similar, for the PFJ more improvement was observed compared to worsening (15.5% vs. 9.0%). Including within grade changes, the number of knees showing BML worsening increased from 42.2% to 55.6%. While for some features 24-months change was rare, frequency of change was much more common in the ROA- compared to the non-ROA subgroup (e.g. worsening of total MOAKS score cartilage in 68.4% of ROA knees vs. 36.7% of no-ROA knees, and 60.7% vs. 21.8% for an increase in maximum BML score per knee). A wide range of MRI-detected structural pathologies was present in the IMI-APPROACH cohort. Baseline prevalence and change of features was significantly more common in the ROA subgroup compared to the knees without ROA. This work was supported by the Innovative Medicines Initiative Joint Undertaking under grant agreement no 115770, resources of which are composed of financial contribution from the European Union's Seventh Framework Programme (FP7/2007-2013) and EFPIA companies’ in kind contribution. See www.imi.europa.eu and www.approachproject.eu . FWR is shareholder of Boston Imaging Core Lab. (BICL),LLC. And is consultant to Calibr and Grünenthal (in thals t 36 months) CL reports other from Merck KGaA, during the conduct of the study; MK reports grants from IMI-APPROACH, grants from Dutch Arthritis Association, during the conduct of the study; other from GlaxoSmithKline, Pfizer, Merck-Serono, Kiniksa, Abbvie, outside the submitted work; FJB reports grants from Gebro Pharma, grants from BIOIBERICA, grants from AB Science, grants from Abbvie, grants from Ablynx N.V., grants from Amgen, grants from Archigen Biotech Limited, grants from Boehringer, grants from Bristol-Myers, grants from Celgene Int., grants from Eli Lilly and Company, grants from F. Hoffmann- La Roche, grants from Galapagos, grants from Gedeon, grants from Genentech, grants from Gideal Sciences, NC, grants from Glaxosmithkline, grants from Hospira, grants from INC Research UK, grants from Inventiv Health Clinical, grants from Janssen, grants from Lilly, grants from Nichi-IKO Pharmaceutical, grants from Novartis, grants from ONO Pharma, grants from Pfizer, grants from Pharmaceutical Research, grants from Regeneron, grants from Roche, grants from SA UCB Pharma, grants from Sanofi, grants from TRB Chemedica, grants from UCB Biosciences GMBH, outside the submitted work; IKH reports personal fees from AbbVie, grants from Pfizer, outside the submitted work; FB reports personal fees from Boehringer, Bone Therapeutics, Expanscience, Galapagos, Gilead, GSK, Merck Sereno, MSD, Nordic, Novartis, Pfizer, Regulaxis, Roche, Sandoz, Sanofi, Servier, UCB, Peptinov, TRB Chemedica, 4P Pharma CORRESPONDENCE ADDRESS: frank.roemer@uk-erlangen.de .

Effects of patient orientations, landmark positions, and device positions on the MRI RF-induced heating for modular external fixation devices.

This paper studies the RF-induced heating for modular external fixation devices applied on the leg regions of the human bodies. Through numerical investigations of RF-induced heating related to different patient orientations, landmark positions, and device positions under 1.5T and 3T MRI systems, simple and practical methods to reduce RF-induced heating are recommended. Numerical simulations using a full-wave electromagnetic solver based on the finite-difference time-domain method were performed to characterize the effects of patient orientations (head-first/feet-first), landmark positions (the scanning area of the patient), and device positions (device on left or right leg) on the RF-induced heating of the external fixation devices. The G32 coil design and three anatomical human models (Duke model, Ella model, and Fats model) were adopted to model the MRI RF coil and the patients. The relative positions of the patient, device, and coil can significantly affect the RF-induced heating. With other conditions remaining the same, changing the device position or patient orientation can lead to a peak 1-g averaged spatial absorption ratio variation of a factor around four. By changing the landmark position and the patient orientation, the RF-induced heating can be reduced from 1323.6 W/kg to 217.5 W/kg for the specific scanning situations studied. Patient orientations, landmark positions, and device positions influence the RF-induced heating of modular external fixation devices at 1.5 T and 3 T. These features can be used to reduce the RF-induced heating during MRI simply and practically.

Genetic algorithm search for the worst-case MRI RF exposure for a multiconfiguration implantable fixation system modeled using artificial neural networks.

This paper presents a method to search for the worst-case configuration leading to the highest RF exposure for a multiconfiguration implantable fixation system under MRI. A two-step method combining an artificial neural network and a genetic algorithm is developed to achieve this purpose. In the first step, the level of RF exposure in terms of peak 1-g and/or 10-g averaged specific absorption rate (SAR1g/10g ), related to the multiconfiguration system, is predicted using an artificial neural network. A genetic algorithm is then used to search for the worst-case configuration of this multidimensional nonlinear problem within both the enumerated discrete sample space and generalized continuous sample space. As an example, a generic plate system with a total of 576 configurations is used for both 1.5T and 3T MRI systems. The presented method can effectively identify the worst-case configuration and accurately predict the SAR1g/10g with no more than 20% of the samples in the studied discrete sample space, and can even predict the worst case in the generalized continuous sample space. The worst-case prediction error in the generalized continuous sample space is less than 1.6% for SAR1g and less than 1.3% for SAR10g compared with the simulation results. The combination of an artificial neural network with genetic algorithm is a robust technique to determine the worst-case RF exposure level for a multiconfiguration system, and only needs a small amount of training data from the entire system.

Simulations of a birdcage coil B1+ field on a human body model for designing a 3T multichannel TMS/MRI head coil array.

This article considers a new type of integrated multichannel Transcranial Magnetic Stimulator and Magnetic Resonance Imaging (TMS/MRI) system at 3T that is currently being designed. The system will enable unprecedented spatiotemporal control of the TMS-induced electric fields (Efields) with simultaneous rapid whole-head MRI acquisition to record the brain activity. A critical design question is how TMS coil elements interact with the transmit field (${\mathrm B}_{1}^{+}$) of the volume coil integrated in 3T MRI systems. In general, the TMS coils are not designed to have any resonant characteristics at the MRI frequency, they may potentially disturb the RF field due to the eddy currents induced. This is especially a concern with a multichannel TMS setup where the subject's head will be largely covered with the stimulation coils. Therefore, we investigated this problem by computational simulations with realistic TMS coil geometries and a birdcage transmit coil in conjunction with a human body model. We compared the ${\mathrm B}_{1}^{+}$ interaction effects of a commercially available MR-compatible TMS coil with our coil prototype. In both cases, the results show small local changes in the transmit field ${\mathrm B}_{1}^{+}$of the birdcage coil. Maximal Average Specific Absorption Rate (SAR) values over 1g tissue were found to be slightly lower when the TMS elements were present. We conclude that it should be feasible and safe to use the conventional body transmit coil even when an array of TMS coils is used.

Quantitative susceptibility mapping (QSM) minimizes interference from cellular pathology in R2* estimation of liver iron concentration.

A challenge for R2 and R2* methods in measuring liver iron concentration (LIC) is that fibrosis, fat, and other hepatic cellular pathology contribute to R2 and R2* and interfere with LIC estimation. To examine the interfering effects of fibrosis, fat, and other lesions on R2* LIC estimation and to use quantitative susceptibility mapping (QSM) to reduce these distortions. Prospective. Water phantoms with various concentrations of gadolinium (Gd), collagen (Cl, modeling fibrosis), and fat; nine healthy controls with no known hepatic disease, nine patients with known or suspected hepatic iron overload, and nine patients with focal liver lesions. The phantoms and human subjects were imaged using a 3D multiecho gradient-echo on clinical 1.5T and 3T MRI systems. QSM and R2* images were postprocessed from the same gradient-echo data. Fat contributions to susceptibility and R2* were corrected in signal models for LIC estimation. Polynomial regression analyses were performed to examine relations among susceptibility, R2* and true [Gd] and [Cl] in phantoms, and among susceptibility and R2* in patient livers. In phantoms, R2* had a strong nonlinear dependency on [Cl], [fat], and [Gd], while susceptibility was linearly dependent (R2 > 0.98). In patients, R2* was highly sensitive to liver pathological changes, including fat, fibrosis, and tumors, while QSM was relatively insensitive to these abnormalities (P = 0.015). With moderate iron overload, liver susceptibility and R2* were not linearly correlated over a common R2* range [0, 100] sec-1 (P = 0.35). R2* estimation of LIC is prone to substantial nonlinear interference from fat, fibrosis, and other lesions. QSM processing of the same gradient echo MRI data can effectively minimize the effects of cellular pathology. 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;48:1069-1079.

Integration of routine QA data into mega-analysis may improve quality and sensitivity of multisite diffusion tensor imaging studies.

A novel mega-analytical approach that reduced methodological variance was evaluated using a multisite diffusion tensor imaging (DTI) fractional anisotropy (FA) data by comparing white matter integrity in people with schizophrenia to controls. Methodological variance was reduced through regression of variance captured from quality assurance (QA) and by using Marchenko-Pastur Principal Component Analysis (MP-PCA) denoising. N = 192 (119 patients/73 controls) data sets were collected at three sites equipped with 3T MRI systems: GE MR750, GE HDx, and Siemens Trio. DTI protocol included five b = 0 and 60 diffusion-sensitized gradient directions (b = 1,000 s/mm2 ). In-house DTI QA protocol data was acquired weekly using a uniform phantom; factor analysis was used to distil into two orthogonal QA factors related to: SNR and FA. They were used as site-specific covariates to perform mega-analytic data aggregation. The effect size of patient-control differences was compared to these reported by the enhancing neuro imaging genetics meta-analysis (ENIGMA) consortium before and after regressing QA variance. Impact of MP-PCA filtering was evaluated likewise. QA-factors explained ∼3-4% variance in the whole-brain average FA values per site. Regression of QA factors improved the effect size of schizophrenia on whole brain average FA values-from Cohen's d = .53 to .57-and improved the agreement between the regional pattern of FA differences observed in this study versus ENIGMA from r = .54 to .70. Application of MP-PCA-denoising further improved the agreement to r = .81. Regression of methodological variances captured by routine QA and advanced denoising that led to a better agreement with a large mega-analytic study.

基于表面的形态测量学：3T与7T高分辨磁共振结构成像受试者内比较

ObjectiveHigh resolution structural MR imaging can reveal structural characteristics of cerebral cortex and provide an insight into normal brain development and neuropsychological diseases. The aim of this study was to compare cortical structural characteristics of normal human brain between 3T and 7T MRI systems using surface-based morphometry based on high resolution structural MR imaging. Methods Twelve healthy volunteers were scanned by both 3T with 3D T1-weighted fast spoiled gradient recalled echo (3D T1-FSPGR) sequence and 7T with 3D T1-weighted magnetization-prepared rapid gradient echo (3D T1-MPRAGE) sequence. MRI data were processed with FreeSurfer. The cortical thickness, white and gray matter surface area, convexity, and curvature from data of 3T and 7T were measured and compared by paired t-test. Results Measurements of mean cortical thickness, total white matter surface area and gray matter surface area of 3T were larger than those of 7T (left hemisphere: P=0.000, 0.006, 0.020 respectively; right hemisphere: P=0.000, 0.000, 0.000 respectively). Surface-based morphometry over the whole brain demonstrated both reduced and increased measurements of cortical thickness, white and gray surface area, convexity, and curvature at 7T compared to 3T. Conclusions Inconsistency of brain structural attribute between 3T and 7T was confirmed, and researchers should be cautious about data when using ultrahigh field MR system to investigate brain structural changes.

SU‐F‐J‐171: Robust Atlas Based Segmentation of the Prostate and Peripheral Zone Regions On MRI Utilizing Multiple MRI System Vendors

Purpose:Automatically generated prostate MRI contours can be used to aid in image registration with CT or ultrasound and to reduce the burden of contouring for radiation treatment planning. In addition, prostate and zonal contours can assist to automate quantitative imaging features extraction and the analyses of longitudinal MRI studies. These potential gains are limited if the solutions are not compatible across different MRI vendors. The goal of this study is to characterize an atlas based automatic segmentation procedure of the prostate collected on MRI systems from multiple vendors.Methods:The prostate and peripheral zone (PZ) were manually contoured by an expert radiation oncologist on T2‐weighted scans acquired on both GE (n=31) and Siemens (n=33) 3T MRI systems. A leave‐one‐out approach was utilized where the target subject is removed from the atlas before the segmentation algorithm is initiated. The atlas‐segmentation method finds the best nine matched atlas subjects and then performs a normalized intensity‐based free‐form deformable registration of these subjects to the target subject. These nine contours are then merged into a single contour using Simultaneous Truth and Performance Level Estimation (STAPLE). Contour comparisons were made using Dice similarity coefficients (DSC) and Hausdorff distances.Results:Using the T2 FatSat (FS) GE datasets the atlas generated contours resulted in an average DSC of 0.83±0.06 for prostate, 0.57±0.12 for PZ and 0.75±0.09 for CG. Similar results were found when using the Siemens data with a DSC of 0.79±0.14 for prostate, 0.54±0.16 and 0.70±0.9. Contrast between prostate and surrounding anatomy and between the PZ and CG contours for both vendors demonstrated superior contrast separation; significance was found for all comparisons p‐value &lt; 0.0001.Conclusion:Atlas‐based segmentation yielded promising results for all contours compared to expertly defined contours in both Siemens and GE 3T systems providing fast and automatic segmentation of the prostate.Funding Support, Disclosures, and Conflict of Interest: AS Nelson is a partial owner of MIM Software, Inc. AS Nelson, and A Swallen are current employees at MIM Software, Inc.

SU‐F‐I‐27: Measurement of SAR and Temperature Elevation During MRI Scans

Purpose:The poor reliability and repeatability of the manufacturer‐reported SAR values on clinical MRI systems have been acknowledged. The purpose of this study is to not only measure SAR values, but also RF‐induced temperature elevation at 1.5 and 3T MRI systems.Methods:SAR measurement experiment was performed at 1.5 and 3T. Three MRI RF sequences (T1w TSE, T1w inversion recovery, and T2w TSE) with imaging parameters were selected. A hydroxyl‐ethylcelluose (HEC) gelled saline phantom mimicking human body tissue was made. Human torso phantom were constructed, based on Korean adult standard anthropometric reference data (Fig.1). FDTD method was utilized to calculate the SAR distribution using Sim4Life software. Based on the results of the simulation, 4 electrical field (E‐field) sensors were located inside the phantom. 55 Fiber Bragg Grating (FBG) temperature sensors (27 sensors in upper and lower cover lids, and one sensor located in the center as a reference) were located inside the phantom to measure temperature change during MRI scan (Fig.2).Results:Simulation shows that SAR value is 0.4 W/kg in the periphery and 0.001 W/kg in the center (Fig.2). One 1.5T and one of two 3T MRI systems represent that the measured SAR values were lower than MRI scanner‐reported SAR values. However, the other 3T MRI scanner shows that the averaged SAR values measured by probe 2, 3, and 4 are 6.83, 7.59, and 6.01 W/kg, compared to MRI scanner‐reported whole body SAR value (&lt;1.5 W/kg) for T2w TSE (Table 1). The temperature elevation measured by FBG sensors is 5.2°C in the lateral shoulder, 5.1°C in the underarm, 4.7°C in the anterior axilla, 4.8°C in the posterior axilla, and 4.8°C in the lateral waist for T2w TSE (Fig.3).Conclusion:It is essential to assess the safety of MRI system for patient by measuring accurate SAR deposited in the body during clinical MRI.

Rapid volumetric T1 mapping of the abdomen using three-dimensional through-time spiral GRAPPA.

To develop an ultrafast T1 mapping method for high-resolution, volumetric T1 measurements in the abdomen. The Look-Locker method was combined with a stack-of-spirals acquisition accelerated using three-dimensional (3D) through-time spiral GRAPPA reconstruction for fast data acquisition. A segmented k-space acquisition scheme was proposed and the time delay between segments for the recovery of longitudinal magnetization was optimized using Bloch equation simulations. The accuracy of this method was validated in a phantom experiment and in vivo T1 measurements were performed with 35 asymptomatic subjects on both 1.5 Tesla (T) and 3T MRI systems. Phantom experiments yielded close agreement between the proposed method and gold standard measurements for a large range of T1 values (200 to 1600 ms). The in vivo results further demonstrate that high-resolution T1 maps (2 × 2 × 4 mm(3)) for 32 slices can be achieved in a single clinically feasible breath-hold of approximately 20 s. The T1 values for multiple organs and tissues in the abdomen are in agreement with the published literature. A high-resolution 3D abdominal T1 mapping technique was developed, which allows fast and accurate T1 mapping of multiple abdominal organs and tissues in a single breath-hold.

Advances in pediatric neuroimaging.

Conventional MRI protocols are an integral part of routine clinical imaging in pediatric patients. The advent of several newer MRI techniques provides crucial insight into the structural integrity and functional aspects of the developing brain, especially with the introduction of 3T MRI systems in clinical practice. The field of pediatric neuroimaging continues to evolve, with greater emphasis on high spatial resolution, faster scan time, as well as a quest for visualization of the functional aspects of the human brain. MR vendors are increasingly focusing on optimizing MR technology to make it suitable for children, in whom as compared to adults the head size is usually smaller and demonstrates inherent neuroanatomical differences relating to brain development. The eventual goal of these advances would be to evolve as potential biomarkers for predicting neurodevelopment outcomes and prognostication, in addition to their utility in routine diagnostic and therapeutic decision-making. Advanced MR techniques like diffusion tensor imaging, functional MRI, MR perfusion, spectroscopy, volumetric imaging and arterial spin labeling add to our understanding of normal brain development and pathophysiology of various neurological disease processes. This review is primarily focused on outlining advanced MR techniques and their current and potential pediatric neuroimaging applications as well as providing a brief overview of advances in hardware and machine design.

P184: Activity and functional connectivity of the premotor-parietal network modulate intrinsic power changes of mu rhythms: an EEG-fMRI study

P185 – Figure 1. A. Brain regions more activated when using tools compared to neutral objects (bars) in fMRI study with healthy controls. B. Statistical map of the voxels associated with tool use scoring in LBD patients in lesion analyse study using VLSM. acquired brain activity from fifteen healthy participants (age range 21-35), by combining 32-channel MRI-compatible EEG and Siemens 3T-MRI systems. During data acquisition, the participants were awake and not engaged in any tasks with their eyes closed. BOLD-based fMRI signals and surface EEG data were recorded simultaneously for 20 min. Power of mu rhythms was calculated from EEG data at C3 and C4 electrodes within a 3-second time bin, corresponding to a single scan of MRI data (400 data points in total). Using SPM software, voxel-based general linear model analyses were performed in the whole brain to find regions correlated with spontaneous fluctuations of mu rhythm power physically at rest. We found that greater BOLD activities in the IPL and PMv were linked with suppression of mu rhythm power. Furthermore, we discovered that the functional connectivity between IPL and PMv was decreased when the power of mu rhythms was suppressed. We did not find any brain regions showing greater activities or functional connectivity in association with increases of mu rhythm power. We conclude that greater activity but reduced functional connectivity of IPL and PMv are correlated with spontaneous suppression of mu rhythm amplitudes at rest. Our results may provide new insight into mechanisms of spontaneous fluctuations of brain activity or connectivity in a resting state. P185 Investigation of the neural correlates of tool use with activation studies in healthy subjects and lesion studies in brain damaged patients E. Salazar-Lopez1, M.L. Brandi1, G. Goldenberg2, A. Wohlschlaeger3, L. Johannsen1, J. Hermsdoerfer1 1Technische Universitaet Muenchen, Lehrstuhl fuer Bewegungswissenschaft, Muenchen, Germany; 2Klinikum Bogenhausen, Klinik fuer Neuropsychologie, Muenchen, Germany; 3Technische Universitaet Muenchen, Klinikum rechts der Isar, Diagnostische und Interventionelle Neuroradiologie. Neuro-Kopf-Zentrum, Muenchen, Germany Question: Results from brain activation studies in healthy subjects and lesion analyses in brain damage patients are expected to reveal a correspondence between areas activated by task performance with lesioned areas in case of deficits. We are planning to directly compare both approaches to study the neural network of tool use in as similar as possible and as realistic as possible conditions: On the other hand we examined tool use in healthy elderly subjects, during the realization of fMRI. On the other hand we plan to correlate the execution in this task in chronic stroke patients – with apraxia – with their damaged brain areas. Methods: Both experiments used a tool carousel for controlled tool presentation (12 tools of daily life). The fMRI-data was analyzed with SPM8 in a factorial design (object and task) during the planningand action-phase. In the lesion analyze study we score the execution according to an apraxic errors scale and use the voxel based lesion symptom mapping (VLSM), a method that includes mapping the lesion manually, normalizing brain image using cost function masking with SPM8 and making a voxelwise statistical analysis of neurological lesions to define the relationship between tissue damaged and behavior. Results: Besides a clear left-sided lateralization, a wide spread network can be identified with the fMRI analysis (see figure). This is specific to planning tool use and includes parietal cortex (superior and inferior parietal lobule and intraparietal sulcus), frontal cortex (dorsal and ventral premotor cortex

Determinants of iron accumulation in deep grey matter of multiple sclerosis patients

Background: Iron accumulation in deep grey matter (GM) structures is a consistent finding in multiple sclerosis (MS) patients. This study focused on the identification of independent determinants of iron accumulation using R2* mapping. Subjects and methods: Ninety-seven MS patients and 81 healthy controls were included in this multicentre study. R2* mapping was performed on 3T MRI systems. R2*in deep GM was corrected for age and was related to disease duration, disability, T2 lesion load and brain volume. Results: Compared to controls, R2* was increased in all deep GM regions of MS patients except the globus pallidus and the substantia nigra. R2* increase was most pronounced in the progressive stage of the disease and independently predicted by disease duration and disability. Reduced cortical volume was not associated with iron accumulation in the deep GM with the exception of the substantia nigra and the red nucleus. In lesions, R2* was inversely correlated with disease duration and higher total lesion load. Conclusion: Iron accumulation in deep GM of MS patients is most strongly and independently associated with duration and severity of the disease. Additional associations between cortical GM atrophy and deep GM iron accumulation appear to exist in a region specific manner.

Brain morphometry reproducibility in multi-center 3 T MRI studies: A comparison of cross-sectional and longitudinal segmentations

Large-scale longitudinal multi-site MRI brain morphometry studies are becoming increasingly crucial to characterize both normal and clinical population groups using fully automated segmentation tools. The test–retest reproducibility of morphometry data acquired across multiple scanning sessions, and for different MR vendors, is an important reliability indicator since it defines the sensitivity of a protocol to detect longitudinal effects in a consortium. There is very limited knowledge about how across-session reliability of morphometry estimates might be affected by different 3T MRI systems. Moreover, there is a need for optimal acquisition and analysis protocols in order to reduce sample sizes. A recent study has shown that the longitudinal FreeSurfer segmentation offers improved within session test–retest reproducibility relative to the cross-sectional segmentation at one 3T site using a nonstandard multi-echo MPRAGE sequence. In this study we implement a multi-site 3T MRI morphometry protocol based on vendor provided T1 structural sequences from different vendors (3D MPRAGE on Siemens and Philips, 3D IR-SPGR on GE) implemented in 8 sites located in 4 European countries. The protocols used mild acceleration factors (1.5–2) when possible. We acquired across-session test–retest structural data of a group of healthy elderly subjects (5 subjects per site) and compared the across-session reproducibility of two full-brain automated segmentation methods based on either longitudinal or cross-sectional FreeSurfer processing. The segmentations include cortical thickness, intracranial, ventricle and subcortical volumes. Reproducibility is evaluated as absolute changes relative to the mean (%), Dice coefficient for volume overlap and intraclass correlation coefficients across two sessions. We found that this acquisition and analysis protocol gives comparable reproducibility results to previous studies that used longer acquisitions without acceleration. We also show that the longitudinal processing is systematically more reliable across sites regardless of MRI system differences. The reproducibility errors of the longitudinal segmentations are on average approximately half of those obtained with the cross sectional analysis for all volume segmentations and for entorhinal cortical thickness. No significant differences in reliability are found between the segmentation methods for the other cortical thickness estimates. The average of two MPRAGE volumes acquired within each test–retest session did not systematically improve the across-session reproducibility of morphometry estimates. Our results extend those from previous studies that showed improved reliability of the longitudinal analysis at single sites and/or with non-standard acquisition methods. The multi-site acquisition and analysis protocol presented here is promising for clinical applications since it allows for smaller sample sizes per MRI site or shorter trials in studies evaluating the role of potential biomarkers to predict disease progression or treatment effects.

Correlation of the R1 and R2 values of gadolinium-based MRI contrast media with the ΔHounsfield unit of CT contrast media of identical concentration

The optimal volume of contrast medium must be injected into the patient who emits the maximum signal intensity in an ROI. This study was investigated four different type MRI and one CT contrast agent in vitro and sought to establish relations between concentration, MRI relaxivity, CT Hounsfield unites selected kVp and different MRI T1 sequences. Using a CT contrast medium and four different MRI T1 contrast media, we developed five different phantom series. The MRI contrast media phantom was imaged on 1.5T and 3T MRI systems and measured the R1 and R2 value. A CT scanner was used to obtain images of the Iopromide 370 phantom with the quality of radiation to obtain images. The Pearson's correlation coefficient analyses were conducted between MRI CM phantom series with Iopromide 370 phantom. The non-parametric statistical analyses were performed for the values of kVp. The ΔHU of the test solution of the CT contrast media was produced in the same amount as the exponentially increased concentration of the MRI contrast media according to the increase in the dilution concentration, and was influenced by the quality of the X-ray. Through the results of this experiment that considered the two aforementioned factors, an image with a high diagnosis value can be acquired from the information on the concentration of the MRI T1 contrast media.

Feasibility of cerebral magnetic resonance imaging in patients with externalised spinal cord stimulator

ObjectSpinal cord stimulation (SCS) is a well-known treatment option for intractable neuropathic pain after spinal surgery, but its pathophysiological mechanisms are poorly stated. The goal of this study is to analyse the feasibility of using brain MRI, functional MRI (fMRI) and Magnetic Resonance Spectroscopy (MRS) as tools to analyse these mechanisms in patients with externalised neurostimulators during trial period. MethodsThe authors conducted in an in vitro and in vivo study analysing safety issues when performing brain MRI, fMRI and MRS investigations in human subjects with externalised SCS. Temperature measurements in vitro were performed simulating SCS during MRI sequences using head transmit-receive coils in 1.5 and 3T MRI systems. 40 Patients with externalised SCS were included in the in vivo study. 20 patients underwent brain MRI, fMRI and another 20 patients underwent brain MRI and MRS. ResultsA maximal temperature increase of 0.2°C was measured and neither electrode displacements nor hardware failures were observed. None of the patients undergoing the MRS sequences at the 1.5 or 3T MRI scanners described any discomfort or unusual sensations. ConclusionWe can conclude that brain MRI, fMRI and MRS studies performed in patients with externalised SCS can be safely executed.