Whole-body MRI System Research Articles

A simple, clinically usable whole-body MRI system of joint assessment in adolescents and young people with juvenile idiopathic arthritis.

To introduce and evaluate a simple method for assessing joint inflammation and structural damage on whole-body MRI (WBMRI) in juvenile idiopathic arthritis (JIA), which is usable in clinical practice. The proposed system utilizes post-contrast Dixon WBMRI scans. Joints are assessed for synovitis (grade 0-2) and structural damage (present/absent) at 81 sites. The synovitis grading is based on features including above-normal intensity synovial enhancement, synovial hypertrophy, joint effusion, subarticular bone marrow oedema and peri-articular soft tissue oedema.This system was evaluated in a prospective study of 60 young people (47 patients with JIA and 13 controls with non-inflammatory musculoskeletal pain) who underwent a WBMRI. Three readers (blinded to diagnosis) independently reviewed all images and re-reviewed 20 individual scans. The intra- and inter-reader overall agreement (OA) and the intra- and inter-reader Gwet's agreement coefficients 2 (GAC2) were measured for the detection of a) participants with ≥1 joint with inflammation or structural damage and b) joint inflammation or structural damage for each joint. The inter-reader OA for detecting patients with ≥1 joint with inflammation, defined as grade 2 synovitis (G2), and ≥1 joint with structural damage were 80% and 73%, respectively. The intra-reader OA for readers 1-3 was 80-90% and 75-90%, respectively. The inter-reader OA and GAC2 for joint inflammation (G2) at each joint were both ≥85% for all joints but were lower if grade 1 synovitis was included as positive. The intra- and inter-reader agreements of this WBMRI assessment system are adequate for assessing objective joint inflammation and damage in JIA.

Investigations on correlations between changes of optical tissue properties and NMR relaxation times

BackgroundAccurate light dosimetry is a complex remaining challenge in interstitial photodynamic therapy (iPDT) for malignant gliomas. The light dosimetry should ideally be based on the tissue morphology and the individual optical tissue properties of each tissue type in the target region. First investigations are reported on using NMR information to estimate changes of individual optical tissue properties. MethodsPorcine brain tissue and optical tissue phantoms were investigated. To the porcine brain, supplements were added to simulate an edema or high blood content. The tissue phantoms were based on agar, Lipoveneous, ink, blood and gadobutrol (Gd-based MRI contrast agent). The concentrations of phantom ingredients and tissue additives are varied to compare concentration-dependent effects on optical and NMR properties. A 3-tesla whole-body MRI system was used to determine T1 and T2 relaxation times. Optical tissue properties, i.e., the spectrally resolved absorption and reduced scattering coefficient, were obtained using a single integrating sphere setup. The observed changes of NMR and optical properties were compared to each other. ResultsBy adjusting the NMR relaxation times and optical tissue properties of the tissue phantoms to literature values, recipes for human brain tumor, white matter and grey matter tissue phantoms were obtained that mimic these brain tissues simultaneously in both properties. For porcine brain tissue, it was observed that with increasing water concentration in the tissue, both NMR-relaxation times increased, while µa decreased and µs’ increased at 635 nm. The addition of blood to porcine brain samples showed a constant T1, while T2 shortened and the absorption coefficient at 635 nm increased. ConclusionsIn this investigation, by changing sample contents, notable changes of both NMR relaxation times and optical tissue properties have been observed and their relations examined. The developed dual NMR/optical tissue phantoms can be used in iPDT research, clinical training and demonstrations.

Safety and function of programmable ventriculo-peritoneal shunt valves: An in vitro 7 Tesla magnetic resonance imaging study.

The quantity of ultra-high field MRI neuroimaging studies has rapidly increased. This study tests function, safety, and image artifacts of two frequently implanted programmable ventriculo-peritoneal (VP) shunt valves in a 7T MRI system. All tests were performed using a whole-body 7T MRI system. Three proGAV 2.0 and 3 CODMAN CERTAS® Plus programmable VP-shunt valves were tested in three steps. 1) Deflection angle tests close to the bore opening at the location of a static magnetic field gradient of 3-5 T/m. 2) Valves were fixed on a spherical phantom in 3 positions (a. lateral, b. cranial, c. cranial with 22.5° tilt anteriorly) and assessed for keeping the programmed pressure setting and reprogrammability. 3) Valves were fixed on the phantom and positioned lateral in a radiofrequency head coil. MRI scans were performed for both models, including MPRAGE, GRE and SE sequences. Deflection angles were moderate (13°, 14°, 13°) for the proGAV valves and close to critical (43°, 43°, 41°) for the CODMAN valves at the test location. Taking a scaling factor of 2-3 for the maximum spatial magnetic field gradient accessible to a patient within the magnet bore into account renders both valves MR unsafe regarding ferromagnetic attraction. The proGAV valves kept the pressure settings in all positions and were reprogrammable in positions a. and b. In position c., reprogrammability was lost. The CODMAN valves changed their pressure setting and reprogrammability was lost in all positions. MR image signal homogeneity was unaltered in the phantom center, artifacts limit the assessability of structures in close vicinity to the valves. Both tested programmable VP-shunt valves are MR unsafe for 7T systems. Novel programming mechanisms using permanent magnets with sufficient magnetic coercivity or magnet-free mechanisms may allow the development of programmable VP-shunt valves that are conditional for 7T MR systems.

Human prostate MRI at ultrahigh-performance gradient: A feasibility study.

To demonstrate the technical feasibility and the value of ultrahigh-performance gradient in imaging the prostate in a 3T MRI system. In this local institutional review board-approved study, prostate MRI was performed on 4 healthy men. Each subject was scanned in a prototype 3T MRI system with a 42-cm inner-diameter gradient coil that achieves a maximum gradient amplitude of 200 mT/m and slew rate of 500 T/m/s. PI-RADS V2.1-compliant axial T2 -weighted anatomical imaging and single-shot echo planar DWI at standard gradient of 70 mT/m and 150 T/m/s were obtained, followed by DWI at maximum performance (i.e., 200 mT/m and 500 T/m/s). In comparison to state-of-the-art clinical whole-body MRI systems, the high slew rate improved echo spacing from 1020 to 596 μs and, together with a high gradient amplitude for diffusion encoding, TE was reduced from 55 to 36 ms. In all 4 subjects (waist circumference = 81-91 cm, age = 45-65 years), no peripheral nerve stimulation sensation was reported during DWI. Reduced image distortion in the posterior peripheral zone prostate gland and higher signal intensity, such as in the surrounding muscle of high-gradient DWI, werenoted. Human prostate MRI at simultaneously high gradient amplitude of 200 mT/m and slew rate of 500 T/m/s is feasible, demonstrating that improved gradient performance can address image distortion and T2 decay-induced SNR issues for in vivo prostate imaging.

Motion-corrected 23 Na MRI of the human brain using interleaved 1 H 3D navigator images.

To evaluate the feasibility of motion correction for sodium (23 Na) MRI based on interleaved acquired 3D proton (1 H) navigator images. A 3D radial density-adapted sequence for interleaved 23 Na/1 H MRI was implemented on a 7 Tesla whole-body MRI system. The 1 H data obtained during the 23 Na acquisition were used to reconstruct 140 navigator image volumes with a nominal spatial resolution of (2.5 mm)3 and a temporal resolution of 6 s. The motion information received from co-registration was then used to correct the 23 Na image dataset, which also had a nominal spatial resolution of (2.5 mm)3 . The approach was evaluated on six healthy volunteers, whose motion during the scans had different intensities and characteristics. Interleaved acquisition of two nuclei did not show any relevant influence on image quality (SNR of 13.0 for interleaved versus 13.2 for standard 23 Na MRI and 176.4 for interleaved versus 178.0 for standard 1 H MRI). The applied motion correction increased the consistency between two consecutive scans for all examined volunteers and improved the image quality for all kinds of motion. The SD of the differences ranged between 2.30% and 6.96% for the uncorrected and between 2.13% and 2.67% for the corrected images. The feasibility of interleaved acquired 1 H navigator images to be used for retrospective motion correction of 23 Na images was successfully demonstrated. The approach neither affected the 23 Na image quality nor elongated the scan time and can therefore be an important tool to improve the accuracy of quantitative 23 Na MRI.

P2260Impacts of hippocampal blood flow on cardiac remodeling in patients with chronic heart failure

Abstract Background Chronic heart failure (CHF) patients have a high prevalence of depression. Increased mortality and hospitalization are noted in depressive CHF patients. We have previously demonstrated that cerebral blood flow in the hippocampus, which is the important brain area for emotion and memory, is associated with depressive symptoms in CHF patients (Brain Assessment and Investigation in Heart Failure Trial (B-HeFT), UMINehz748.073808584). Purpose To test our hypothesis that blood flow in the hippocampus (green areas, Figure A, B) is associated with cardiac remodeling in CHF patients. Methods We enrolled 80 CHF patients aged 45–90 years from August 2012 to April 2013. We measured hippocampal blood flow, psychological test scores, and echocardiographic parameters as baseline values within 6 months after enrollment. Among them, echocardiography was repeated in 70 patients (65.0±10.0 [SD] yrs, 71.4% men) at 3.1±0.5 years after the baseline evaluation in B-HeFT2 (UMINehz748.073820355). Hippocampal blood flow was measured with pseudocontinuous arterial spin labeling perfusion images acquired with a 1.5-T whole-body MRI system. The patients underwent the 15-item Geriatric Depression Scale (GDS) test, where existence of depressive symptoms was defined as 5 or more in the GDS score. To test our hypothesis, we conducted a voxel-wise multiple regression analysis, using blood flow at each voxel in the hippocampus as independent variable and differences in echocardiographic parameters between the 2 time points as dependent variable adjusted for age and sex. Results Consistent with our hypothesis, baseline blood flow in the hippocampus was significantly associated with the changes in left-ventricular posterior wall thickness (LVPWT). Anterior hippocampal blood flow was negatively correlated with changes in LVPWT (blue areas, Figure A, B), while positive correlations of posterior hippocampal blood flow were found (red areas, Figure A, B) (P<0.05 uncorrected for multiple comparisons). The negative correlations in limited areas of the anterior hippocampus survived at a significance threshold of P<0.05 with family-wise error corrections (yellow areas, Figure A, B). A correlation coefficient between baseline anterior hippocampal blood flow and changes in LVPWT was –0.452 (P<0.001, Figure C). Existence of depressive symptoms was positively correlated with baseline anterior hippocampal blood flow and negatively with changes in LVPWT (P<0.05, both). A structural equation model showed that, apart from a direct effect [standardized estimate 0.344 (95% CI 0.564, 0.124), P=0.002], the association between baseline anterior hippocampal blood flow and LVPWT thinning was mediated by existence of depressive symptoms [standardized estimate 0.111 (95% CI 0.213, 0.002), P=0.046] (Figure D). Figure 1 Conclusions These results provide the first evidence that hippocampal blood flow is associated with cardiac remodeling, which is mediated, at least partly, by existence of depressive symptoms. Acknowledgement/Funding Japan Society for the Promotion of Science

Remotely controllable phantom rotation system for ultra-high field MRI to improve Cross Calibration

Abstract Optical tracking systems, such as the Moiré Phase Tracking system (MPT), can be used to correct motion prospectively especially during magnetic resonance imaging (MRI, MR) in neurologic application. For that an MRI safe camera is mounted in the MRI bore to detect motion by tracking a specific MPT marker, which is rigidly attached on the subject’s head. To enable prospective updates of the imaging volume´s position and orientation, and therefore to correct motion from the subject, the motion information captured from the camera need to be transformed from the camera into the MR coordinate system. The process of finding the transformation between both coordinate systems is called cross calibration and is essential for the overall motion correction performance. For the procedure of the cross calibration, an MR visible phantom with an attached MPT-marker is measured simultaneously with MRI and the MPT camera in multiple specific alignment positions. To reduce cross calibration errors, it is essential to move the phantom precisely into specified alignment positions. Due to the long and narrow bore design of ultra-high field systems (tunnel length > 3 m), the phantom can not be moved simply from a person leaning inside the scanner bore. Thus, to rotate it after each measurement step, either a technician must work inside the tunnel during the complete period of the cross calibration or the table must be moved in and out of the bore multiple times. To improve this currently established cross calibration procedure, we have developed an MRI safe phantom rotation system, which can be controlled remotely and precisely from outside the MRI bore. Even for ultra-high field imaging, the rotation system is fully MRI compatible. Initial tests were performed at a 7T whole-body MRI system and have proven the benefit of our rotation system.

Corrections of myocardial tissue sodium concentration measurements in human cardiac 23Na MRI at 7 Tesla

To quantify the tissue sodium concentration (TSC) in cardiac 23 Na MRI. To evaluate the influence of different correction methods on the measured myocardial TSC. 23 Na MRI of four healthy subjects was conducted at a whole-body 7T MRI system using an oval-shaped 23 Na birdcage coil. Data acquisition was performed with a density-adapted 3D radial pulse sequence using a golden angle projection scheme. 1 H MRI data were acquired at a 3T MRI system to generate a myocardial mask. Retrospective cardiac and respiratory gating were used to reconstruct 23 Na MRI data in the diastolic phase and exhaled state. B0 and B1 inhomogeneity and partial volume (PV) effects were corrected. Relaxation times and TSC of ex vivo blood samples and calf muscle were determined. These values were used in the PV correction to estimate myocardial TSC, which was compared with the measured TSC of calf muscle. Without any correction the measured myocardial TSC was (54 ± 5) mM. The applied correction methods reduced these values by (48 ± 5)% to (29 ± 3) mM, where PV correction had the largest effect (reduction of (34 ± 1)%). Respiratory and cardiac motion gating decreased the concentrations by (11 ± 1)%. With the applied setup, the corrections of B0 and B1 inhomogeneity (reduction of (3 ± 2)%) had negligible influences on TSC values. The resulting myocardial TSC was approximately 1.4-fold higher than the measured TSC of calf muscle tissue of the same healthy subjects ((20 ± 3) mM). For quantitative human cardiac 23 Na MRI several corrections are needed and ranked for our setup: PV correction, respiratory and cardiac gating, correction for B1 inhomogeneity effects.

Study of kinetics of 19F-MRI using a fluorinated imaging agent (19FIT) on a 3T clinical MRI system.

To use 19F imaging tracer (19FIT-27) to evaluate kinetics in major organs. Kinetics studies using proton MRI are difficult because of low concentration of 19FIT-27 protons relative to background water protons. Because there is no background source of 19F NMR in a biological body, 19F may be an ideal nucleus to directly trace 19FIT-27. However, there are several challenges for reliable 19F MR imaging and spectroscopy, particularly with clinical whole-body MRI systems, which include low concentrations and long 19F T1. We performed a dynamic 19F MRI study on mice at a 3T whole-body MRI system using a homemade transmit/receive (Tx/Rx) switch and a Tx/Rx volume RF coil. We used a newly developed fluorine imaging agent, which has 27 identical fluorine atoms with identical chemical shift, a relatively short T1, and high hydrophilicity. Basic kinetics parameters were estimated from the 19F signal-time curve. Resultant fluorine images show fairly high spatial (3 × 3 × 3mm3) and temporal resolutions. Biodistribution and kinetics of 19FIT-27 are obtained via 19F images for major uptake organs. Whole-body dynamic 19F MRI of newly developed 19FIT-27 in mice was obtained with fairly high spatial and temporal resolutions on a 3T clinical MRI system. The present study demonstrates the feasibility of 19F MRI using our newly developed compound to investigate major organ kinetics.

Ultra-High Field NMR and MRI—The Role of Magnet Technology to Increase Sensitivity and Specificity

History, of course, is difficult to write, if for no other reason, than that it has so many players and so many authors. – P. J. Keating (former Australian Prime Minister) Starting with post-war developments in nuclear magnetic resonance (NMR) a race for stronger and stronger magnetic fields has begun in the 1950s to overcome the inherently low sensitivity of this promising method. Further challenges were larger magnet bores to accommodate small animals and eventually humans. Initially, resistive electromagnets with small pole distances, or sample volumes, and field strengths up to 2.35 T (or 100 MHz 1H frequency) were used in applications in physics, chemistry, and material science. This was followed by stronger and more stable (NbTi based) superconducting magnet technology typically implemented first for small-bore systems in analytical chemistry, biochemistry and structural biology, and eventually allowing larger horizontal-bore magnets with diameters large enough to fit small laboratory animals. By the end of the 1970s, first low-field resistive magnets big enough to accommodate humans were developed and superconducting whole-body systems followed. Currently, cutting-edge analytical NMR systems are available at proton frequencies up to 1 GHz (23.5 T) based on Nb3Sn at 1.9 K. A new 1.2 GHz system (28 T) at 1.9 K, operating in persistent mode but using a combination of low and high temperature multi-filament superconductors is to be released. Preclinical instruments range from small-bore animal systems with typically 600 - 800 MHz (14.1 - 18.8 T) up to 900 MHz (21 T) at 1.9 K. Human whole-body MRI systems currently operate up to 10.5 T. Hybrid combined superconducting and resistive electromagnets with even higher field strength of 45 T dc and 100 T pulsed, are available for material research, of course with smaller free bore diameters. This rather costly development towards higher and higher field strength is a consequence of the inherently low and, thus, urgently needed sensitivity in all NMR experiments. This review particularly describes and compares the developments in superconducting magnet technology and, thus, sensitivity in three fields of research: analytical NMR, biomedical and preclinical research, and human MRI and MRS, highlighting important steps and

Three-dimensional MRI study of the relationship between eye dimensions, retinal shape and myopia.

We investigated changes in eye dimensions and retinal shape with degree of myopia, gender and race. There were 58 young adult emmetropes and myopes (range -1.25D to -8.25D), with 30 East-Asians (21 female/9 male), 23 Caucasians (16/7) and 5 South-Asians (1/4). Three-dimensional magnetic resonance imaging was undertaken with a 3.0 Tesla whole-body clinical MRI system using a 4.0 cm receive-only surface coil positioned over the eye. Automated methods determined eye length, width and height, and curve fitting procedures determined asymmetric and symmetric ellipsoid shapes to 75%, 55% and 35% of the retina. With myopia increase, eye dimensions increased in all directions such that increase in length was considerably greater than increases in width and height. Emmetropic retinas were oblate (steepening away from the vertex) but oblateness decreased with the increase in myopia, so that retinas were approximately spherical at 7 to 8D myopia. Asymmetry of eyes about the best fit visual axis was generally small, with small differences between the vertex radii of curvature and between asphericities in the axial and sagittal planes. Females had smaller eyes than males, with overall dimensions being about 0.5mm less for the former. Race appeared not to have a systematic effect.

The Design of Decoupled Even-Order Zonal Superconducting Shim Coils for a 9.4 T Whole-Body MRI

A novel active shimming method is proposed for the correction of magnetic field nonuniformity of superconducting (SC) magnet for magnetic resonance imaging. Active shimming utilizes several coils to correct specific field harmonic components appear in the inhomogeneous field, and each coil is usually designed independently to the others, and also takes no account of the presence of the main magnet coil blocks. However, the magnetic coupling among these SC shim coils exists, and also the interaction between those zonal even-order shim coils and the main magnet are particularly significant. This coupling/interaction can lead to the drift of main field and even a possible destruction of shim coils by quench due to tremendous energy transferred from the main magnet. In this paper, we attempt to develop magnetic decoupling technologies for the reduction of magnetic interactions between the shim coil and main magnet. Specifically, a hybrid optimization algorithm, including linear and nonlinear programming, is proposed to design a set of decoupled even-order zonal shim coils. The linear programming determines the globally optimal topology and preliminary position of the shim coils. Then, the nonlinear programming is applied to further optimize the position and the turn number of the shim coils, ensuring the designed coils are capable of correcting the unwanted field deviation. Taking the example of Z2 shim coil, compared with the conventional Z2 shim coil, the proposed method significantly reduces the mutual inductance between the Z2 shim coil and the main magnet. For the same field deviation in the tested case, the mutual inductance has been decreased from 83 to 2.3 H. We also further analyze the influence of system parameters and main magnet structure on the optimal topology of decoupled Z2 shim coil. Z4 and Z6 shim coils are also designed with excellent decoupling effect. In our future work, a whole set of active shim coils decoupled from each other and also the main magnet and will be designed and tested in the 9.4 T whole-body MRI system.

Fast-Field Cycling MRI: A new tool for enhanced diagnosis

Fast Field-Cycling MRI (FFC MRI) is a major shift in MRI technology. It aims to explore how relaxation rates change with the magnetic field strength, an idea that has been successfully exploited in NMR for more than half a century and which is known to provide unique structural information on materials, non-invasively. Scaling up FFC NMR to whole-body MRI systems is a difficult technical challenge that has maintained a lock on this area of research for many years. Our research group has successfully lifted this lock and developed two whole-body FFC MRI scanners: one with a field range of 0.1 mT to 59 mT that has been used in clinical trials for several years and the other with a range of 20 uT to 0.2 T still under development. Our pilot studies, which use both FFC MRI and FFC NMR, have discovered new biomarkers in a range of diseases such as osteoarthritis, breast carcinoma, musculoskeletal sarcoma, obesity, liver fibrosis, thrombosis and others. These FFC MRI biomarkers can differentiate tissues that appear similar on conventional MRI devices thanks, in part, to the greater endogenous contrast present at lower magnetic fields but also due to patterns that emerge from the overall relaxation dispersion curves of these tissues. The latter provides unique insight into the structure of materials and is, we believe, a promising tool to characterise tissue remodelling. This presentation will focus on FFC MRI technology, how it differs from conventional MRI and the results obtained so far from our pilot studies. Fast Field-Cycling MRI (FFC MRI) is a major shift in MRI technology. It aims to explore how relaxation rates change with the magnetic field strength, an idea that has been successfully exploited in NMR for more than half a century and which is known to provide unique structural information on materials, non-invasively. Scaling up FFC NMR to whole-body MRI systems is a difficult technical challenge that has maintained a lock on this area of research for many years. Our research group has successfully lifted this lock and developed two whole-body FFC MRI scanners: one with a field range of 0.1 mT to 59 mT that has been used in clinical trials for several years and the other with a range of 20 uT to 0.2 T still under development. Our pilot studies, which use both FFC MRI and FFC NMR, have discovered new biomarkers in a range of diseases such as osteoarthritis, breast carcinoma, musculoskeletal sarcoma, obesity, liver fibrosis, thrombosis and others. These FFC MRI biomarkers can differentiate tissues that appear similar on conventional MRI devices thanks, in part, to the greater endogenous contrast present at lower magnetic fields but also due to patterns that emerge from the overall relaxation dispersion curves of these tissues. The latter provides unique insight into the structure of materials and is, we believe, a promising tool to characterise tissue remodelling. This presentation will focus on FFC MRI technology, how it differs from conventional MRI and the results obtained so far from our pilot studies.

Regional homogeneity changes between heroin relapse and non-relapse patients under methadone maintenance treatment: a resting-state fMRI study.

BackgroundMethadone maintenance treatment (MMT) is recognized as one of the most effective treatments for heroin addiction but its effect is dimmed by the high incidence of heroin relapse. However, underlying neurobiology mechanism of heroin relapse under MMT is still largely unknown. Here, we took advantage of a resting-state fMRI technique by analysis of regional homogeneity (ReHo), and tried to explore the difference of brain function between heroin relapsers and non-relapsers in MMT.MethodsForty MMT patients were included and received a 12-month follow-up. All patients were given baseline resting-state fMRI scans by using a 3.0 T GE Signa Excite HD whole-body MRI system. Monthly self-report and urine test were used to assess heroin relapse or non-relapse. Subjective craving was measured with visual analog scale. The correlation between ReHo and the degree of heroin relapse was analyzed.ResultsCompared with the non-relapsers, ReHo values were increased in the bilateral medial orbitofrontal cortex, right caudate, and right cerebellum of the heroin relapsers while those in the left parahippocampal gyrus, left middle temporal gyrus, right lingual gyrus, and precuneus were decreased in heroin relapsers. Importantly, altered ReHo in the right caudate were positively correlated with heroin relapse rates or subjective craving response.ConclusionsUsing the resting-state fMRI technique by analysis of ReHo, we provided the first resting-state fMRI evidence that right caudate may serve as a potential biomarker for heroin relapse prediction and also as a promising target for reducing relapse risk.

TH-CD-207-11: Gradient Nonlinearity Calibration and Correction for Head-Only Asymmetric Gradient System

Purpose: Due to engineering limitations, the gradient fields in clinical MRI inevitably contain high-order, nonlinear components. The presence of gradient nonlinearity (GNL) causes image geometrical distortion. Standard correction methods are based on parameterization of the simulated gradient fields with spherical harmonic polynomials. Conventional whole-body gradient systems typically employ symmetric designs, and the GNL for such systems usually contains only odd-order terms (up to 5th-order). Recently, a high-performance, head-only gradient system was developed. Due to asymmetric design, this new system exhibits more complex GNL profiles. Here, we demonstrate measurement-based high-order(N>5) GNL-correction on this new system using a fiducial phantom and iterative model-fitting procedure. Methods: The Alzheimer’s Disease Neuroimaging Initiative (ADNI) phantom was scanned with a 3D IR-FSPGR sequence (sagittal acquisition plane, Nx=Ny=256, Nz=196, x= y=1.05mm, z=1.3mm, BW=125kHz) on the head-only gradient system operating at 80mT/m, 500T/m/s. This phantom contains 160 fiducial spheres (diameter=1.0 or 1.5cm) that are distributed within a diameter=20cm spherical shell. The spatial positions of the fiducials were then measured from the distorted images and fit using a spherical harmonic polynomial model and iterative fitting procedure. The model order was increased from 1 to 10 step-by-step to test the effects of including high-order terms (N>5). Then, the coefficients were used to correct distortion. The residual root-mean-square-error (RMSE) was calculated from fiducial positions tracked from GNL-corrected images. Results: The RMSE analysis shows that GNL-distortion is reduced from 3.93 to 0.39mm by using correction terms up to 7th-order including both even-and odd-order terms. The addition of higher orders (N>7) provides negligible benefit. Conclusion: The GNL of a high-performance, head-only gradient system was successfully measured. The use of up to 7th-order correction terms was found to be sufficient for correcting GNL-distortion in a typical brain scan. These techniques could also improve geometric accuracy for whole-body MRI systems used for radiation therapy planning.

Evolution of aortic wall thickness: long-term follow up from the Multi-Ethnic Study of Atherosclerosis (MESA)

Background A number of studies have been published over the years concerning the relationship between the thickened intima of human arteries and atherogenesis. Increased arterial wall thickness is associated with the prevalence and incidence of cardiovascular disease. Age-related increases of aortic wall thickness have been reported in several crosssectional community-based studies. However, longitudinal changes of these measurements have not yet been documented. The purpose of this study is to characterize ageand sex-specific aortic wall thickness (AWT) distributions and yearly rates of change in older adults. Methods 371 longitudinal and 426 cross sectional studies with AWT images by MRI were analyzed. MRI was performed at first in MESA1 (baseline, 2000-2001), and then in MESA5 (ten-year follow-up, 2010-2011). Both exams used 1.5-T whole-body MRI systems. Images were obtained using a double inversion recovery blackblood fast spin-echo sequence with ECG gating. Axial images of the descending thoracic aorta were obtained at the level of the right pulmonary artery. The thickness of the midthoracic descending aortic wall was measured using electronic calipers at 4 standard positions: 12, 3, 6,

902 – A combined fMRI and VBM study to show motor deficits in schizophrenic versus control subjects during a simple motor task

Schizophrenia is one of the psychotic mental disorders, characterized by social problems and disorders of thought, behaviour, motor and cognitive functions such as long-term memory, verbal memory, executive functioning and vigilance etc. However, the relation between structural and functional alterations in schizophrenia remains unclear. Therefore, the present study sought to investigate whether functional alterations in schizophrenia are also associated with structural brain aberrations directly in related brain regions or in anatomically closely connected areas. The current study was conducted to investigate the possible relationship between functional and structural changes for a simple motor task in schizophrenics. 16 controls and 16 schizophrenic patients were chosen for the study. The structural and functional MRI scans were acquired using 3 Tesla whole-body MRI system with a 16 channel head array coil. For fMRI, a block paradigm with alternating blocks of motor task (right finger tapping; 120 taps/min) and rest was carried out. Pre-processing and post-processing of MRI scans were performed using SPM8 software. The fMRI study showed relatively less activation in the left precentral and postcentral gyrus and right cerebellum in schizophrenic patients as compared to controls during finger tapping task. Voxel-based morphometry (VBM) revealed grey matter decreases in the left precentral and postcentral gyrus and left middle frontal gyrus while white matter decreases in the right cerebellum and right inferior temporal gyrus of schizophrenics as compared to controls. The present study provides strong evidence for an association between motor functional deficits and structural alterations in schizophrenic patients as compared to controls.

Improved correction for gradient nonlinearity effects in diffusion‐weighted imaging

To provide an improved correction for gradient nonlinearity (GN) effects in diffusion-weighted imaging (DWI). These effects produce spatially varying apparent diffusion coefficient (ADC), a result that will be significant in large field-of-view imaging, and may be confounded by distortion and concomitant fields related to the DWI acquisition. The effect of more accurate gradient field maps on GN correction (GNC) of ADC was evaluated. A simulation compared GN effects in commonly imaged anatomy. A temperature-controlled phantom was imaged at positions 0 cm and 11 cm from isocenter and in two whole-body MRI systems at 1.5T with different patient bore diameters (55 cm and 60 cm). Varying correction methods were applied to determine the errors from spatial variance and interscanner reproducibility. As compared to conventional fifth-order spherical harmonics, a seventh-order GNC improved ADC accuracy by 1%. The combination of GNC with a dual-spin-echo pulse sequence and a retrospective concomitant field correction reduced ADC error due to spatial variance from 9.5% to 1.8% (55 cm bore) and from 4.2% to 1.8% (60 cm bore). The error in ADC attributed to interscanner reproducibility was reduced from 5.8% to 0.15% (at isocenter) and from 10% to 0.63% (11 cm from isocenter). GNC in DWI improved spatial accuracy and interscanner reproducibility of ADC.

Visualization and characterization of pure and coupled modes in water-based dielectric resonators on a human 7T scanner

MRI represents a unique method to visualize directly different resonant modes of arbitrarily-shaped dielectric resonators in the radiofrequency spectrum via construction of resonators filled with distilled, deionized water which has a low conductivity and high relative permittivity. The required dimensions, particularly for higher order modes, are large and so a high field whole-body MRI system is needed to visualize these modes. In this study, using a simple cylindrical geometry, many higher order modes were identified and confirmed using electromagnetic simulations. In addition, coupled modes between more than one resonator were investigated, with possible future applications including direct visualization of fields in metamaterials.

Baseline memory performance as a predictor of neurocognitive outcome of first-episode late-onset depression

There is high comorbidity of depression and cognitive impairment in the elderly, and it would be important to explore the relationship between cognitive decline and late-life depression. This study was designed to prospectively explore the neurocognitive outcome of first-episode late-onset depression (LOD) at 6-month follow-up interval, and to explore the potential predictors of cognitive decline. Forty-nine LOD patients were recruited at Dementia Care & Research Center, Peking University Institute of Mental Health. Thirty-one with remission completed the neurocognitive examination at 6-month follow-up. A comprehensive neuropsychological test was administered at baseline and follow-up, including general cognitive function (measured with mini-mental state examination (MMSE) and cognitive abilities screening instrument (CASI)), memory (immediate object memory, 5-min delayed recall of objects, 30-min delayed recall of objects, logical memory, visual copy and recall), and executive function (verbal fluency, trail making test-A). The severity of depression was rated with geriatric depression scale (GDS-30). Subjects were imaged with a 3.0-Tesla whole-body MRI system and FLAIR images were acquired for the measurement of white matter hyper intensity (WMH). The polymorphism of ApoE gene was derived with PCR-RFLP. According to the GDS and MMSE score at follow-up the subjects were classified into cognitively stable group (GDS < 9, MMSE > 26, n=18) and cognitively progressive group (GDS < 9, MMSE < 26, n=13). The score of MMSE and total score of CASI of cognitively progressive group were significantly lower than cognitively stable group (P < 0.05). Relative to cognitively stable group, the performance of immediate object memory, 5-min delayed recall of objects, 30-min delayed recall of objects, visual copy and recall were significantly poorer in cognitively progressive group (P < 0.05). In the multivariate model, the score of immediate object memory test at baseline was inversely associated with the cognitive progression among late-onset depression (OR=0.31, 95% CI=0.13-0.70). Late-onset depressive patients with poorer immediate memory performance may be at greater risk of cognitive decline.