Mohammad Sabati

Multivendor implementation and comparison of volumetric whole-brain echo-planar MR spectroscopic imaging

To assess volumetric proton MR spectroscopic imaging (MRSI) of the human brain on multivendor MRI instruments.

Reproducibility and reliability of short-TE whole-brain MR spectroscopic imaging of human brain at 3T

A feasibility study of an echo‐planar spectroscopic imaging (EPSI) using a short echo time (TE) that trades off sensitivity, compared with other short‐TE methods, to achieve whole brain coverage using inversion recovery and spatial oversampling to control lipid bleeding.

Fast and high-resolution quantitative mapping of tissue water content with full brain coverage for clinically-driven studies☆ , ☆☆

An efficient method for obtaining longitudinal relaxation time (T1) maps is based on acquiring two spoiled gradient recalled echo (SPGR) images in steady states with different flip angles, which has also been extended, with additional acquisitions, to obtain a tissue water content (M0) map. Several factors, including inhomogeneities of the radio-frequency (RF) fields and low signal-to-noise ratios may negatively affect the accuracy of this method and produce systematic errors in T1 and M0 estimations. Thus far, these limitations have been addressed by using additional measurements and applying suitable corrections; however, the concomitant increase in scan time is undesirable for clinical studies. In this note, a modified dual-acquisition SPGR method based on an optimization of the sequence formulism is presented for good and reliable M0 mapping with an isotropic spatial resolution of 1×1×1mm(3) that covers the entire human brain in 6:30min. A combined RF transmit/receive map is estimated from one of the SPGR scans and the optimal flip angles for M0 map are found analytically. The method was successfully evaluated in eight healthy subjects producing mean M0 values of 69.8% (in white matter) and 80.1% (in gray matter) that are in good agreement with those found in the literature and with high reproducibility. The mean value of the resultant voxel-based coefficients-of-variation was 3.6%.

Unenhanced MR Angiography of the Renal Arteries with Balanced Steady-State Free Precession Dixon Method

OBJECTIVE The purpose of this study was to evaluate the feasibility of a novel technique for fat-water separation to image the renal arteries without using a contrast agent. CONCLUSION Five healthy volunteers were imaged on a 3-T clinical MR scanner using the balanced steady-state free precession (SSFP) Dixon method. We were able to image the proximal renal arteries with high conspicuity within a 3-minute overall scanning time. The balanced-SSFP Dixon method shows potential for unenhanced MR angiography of the proximal renal arteries.

Impact of reduced k-space acquisition on pathologic detectability for volumetric MR spectroscopic imaging.

To assess the impact of accelerated acquisitions on the spectral quality of volumetric magnetic resonance spectroscopic imaging (MRSI) and to evaluate their ability in detecting metabolic changes with mild injury.

Physiological neuronal decline in healthy aging human brain — An in vivo study with MRI and short echo-time whole-brain 1H MR spectroscopic imaging

Knowledge of physiological aging in healthy human brain is increasingly important for neuroscientific research and clinical diagnosis. To investigate neuronal decline in normal aging brain eighty-one healthy subjects aged between 20 and 70years were studied with MRI and whole-brain (1)H MR spectroscopic imaging. Concentrations of brain metabolites N-acetyl-aspartate (NAA), choline (Cho), total creatine (tCr), myo-inositol (mI), and glutamine+glutamate (Glx) in ratios to internal water, and the fractional volumes of brain tissue were estimated simultaneously in eight cerebral lobes and in cerebellum. Results demonstrated that an age-related decrease in gray matter volume was the largest contribution to changes in brain volume. Both lobar NAA and the fractional volume of gray matter (FVGM) decreased with age in all cerebral lobes, indicating that the decreased NAA was predominantly associated with decreased gray matter volume and neuronal density or metabolic activity. In cerebral white matter Cho, tCr, and mI increased with age in association with increased fractional volume, showing altered cellular membrane turn-over, energy metabolism, and glial activity in human aging white matter. In cerebellum tCr increased while brain tissue volume decreased with age, showing difference to cerebral aging. The observed age-related metabolic and microstructural variations suggest that physiological neuronal decline in aging human brain is associated with a reduction of gray matter volume and neuronal density, in combination with cellular aging in white matter indicated by microstructural alterations and altered energy metabolism in the cerebellum.

A statistical method for characterizing the noise in nonlinearly reconstructed images from undersampled MR data: The POCS example☆

The projection-onto-convex-sets (POCS) algorithm is a powerful tool for reconstructing high-resolution images from undersampled k-space data. It is a nonlinear iterative method that attempts to estimate values for missing data. The convergence of the algorithm and its other deterministic properties are well established, but relatively little is known about how noise in the source data influences noise in the final reconstructed image. In this paper, we present an experimental treatment of the statistical properties in POCS and investigate 12 stochastic models for its noise distribution beside its nonlinear point spread functions. Statistical results show that as the ratio of the missing k-space data increases, the noise distribution in POCS images is no longer Rayleigh as with conventional linear Fourier reconstruction. Instead, the probability density function for the noise is well approximated by a lognormal distribution. For small missing data ratios, however, the noise remains Rayleigh distributed. Preliminary results show that in the presence of noise, POCS images are often dominated by POCS-enhanced noise rather than POCS-induced artifacts. Implicit in this work is the presentation of a general statistical method that can be used to assess the noise properties in other nonlinear reconstruction algorithms.

Magnetization evolution in balanced steady-state free precession with continuously moving table

Diagnostic imaging of systemic disorders, such as peripheral vascular diseases, requires a field-of-view (FOV) larger than the local FOV available on clinical MR scanners. The continuously moving table (CMT) method acquires large FOV images in a single acquisition. Balanced steady-state free precession (bSSFP) is an attractive candidate for the CMT method due to its short repetition time and high signal-to-noise ratio. However, introducing table motion during data acquisition perturbs the magnetization evolution towards steady state. In this paper, a computer model was developed to simulate the bSSFP magnetization evolution in the presence of table motion. From these simulations, predictions were made about the maximum table velocities that would allow the magnetizations of specific tissues to evolve to the theoretical steady-state values. These predicted maximum table velocities were then successfully verified in vivo with bSSFP CMT acquisitions. For an imaging FOV <or= 35 cm, table velocities of less than 2 cm s(-1) were found to produce satisfactory CMT images.

Reproducibility and reliability of short-TE whole-brain MR spectroscopic imaging of human brain at 3T: Short-TE Whole Brain MR Spectroscopic Imaging

A feasibility study of an echo‐planar spectroscopic imaging (EPSI) using a short echo time (TE) that trades off sensitivity, compared with other short‐TE methods, to achieve whole brain coverage using inversion recovery and spatial oversampling to control lipid bleeding.

Erratum: Impact of reduced k-space acquisition on pathologic detectability for volumetric MR spectroscopic imaging (Journal of Magnetic Resonance Imaging (2014) 39 (224-234))

To assess the impact of accelerated acquisitions on the spectral quality of volumetric magnetic resonance spectroscopic imaging (MRSI) and to evaluate their ability in detecting metabolic changes with mild injury.