Summary: Diffusion-tensor MR imaging of the brain is an objective method that can measure diffusion of water in tissue noninvasively. Five adult volunteers participated in this study that was performed to evaluate the potential of gradient-and spin-echo readout for diffusion-tensor imaging by comparing it with single-shot spin-echo echo-planar imaging. Gradient-and spin-echo readout provides comparable measures of water diffusion to single-shot spinecho echo-planar readout with significantly less geometrical distortion at the expense of a longer imaging time.Diffusion-tensor MR imaging of the brain has been proposed as a noninvasive technique that provides microstructural and physiological information regarding brain tissue in vivo by measuring the diffusion of water (1, 2). Most current applications of diffusion-tensor MR imaging implement ultrafast single-shot echo-planar readouts, which effectively freeze physiological effects (3-5) despite severe geometrical distortions caused by local magnetic field inhomogeneity. Gradient-and spinecho (GRASE) MR imaging has less distortion compared with single-shot echo-planar imaging because the multiple refocusing RF pulses implemented in GRASE MR imaging are responsible for reducing errors originating from static field inhomogeneity (6). For this technical note, we compared the signal-to-noise ratio (SNR), isotropic apparent diffusion coefficient (ADCi), fractional anisotropy (FA), and geometrical distortions from diffusion-tensor MR imaging by use of GRASE and echo-planar readout techniques. Description of the Technique MR Imaging and Data ProcessingMR imaging studies were performed on a 1.5-T MR system (ACS-NT; Philips Medical Systems, Best, The Netherlands) using a quadrature head coil operating in receive mode. The ᭧ American Society of Neuroradiology whole-brain MR imaging protocol included axial T1-weighted spin-echo 517/14/2 (TR/TE/excitations) imaging and axial diffusion-tensor imaging using peripheral gating. The diffusion tensor MR imaging was performed using single-shot spin-echo echo-planar and GRASE readouts. Diffusion sensitization was applied sequentially in six different non-colinear directions (G xx , G yy , G zz , G xy , G xz , G yz ). The parameters for single-shot spin-echo echo-planar diffusion-tensor imaging were 3429-5538/96/4 (TR/effective TE/excitations), with a b value of 600 s·mm Ϫ2 . The parameters for GRASE diffusion-tensor imaging with four spin echoes each comprising five gradient echoes were 4000-4615/119 (TR/TE eff ), with a b value of 600 s·mm Ϫ2 . To eliminate phase errors that originated during the diffusion preparation period, a dephasing gradient and a 90-degree RF pulse before the GRASE readout were used (7). The T1-weighted spin-echo sequence and both the diffusiontensor sequences were matched for total brain coverage (number of sections, 18; section thickness, 5 mm; intersection gap, 1 mm; field of view, 23 cm). The GRASE experiment was performed twice, once with four excitations (4-GRASE) and once with 10 excitations (10-GRASE)....

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The Shy-Drager syndrome (SDS) is a form of progressive autonomic nervous system failure (PAF) with orthostatic hypotension and associated extrapyramidal involvement that is often mistaken for Parkinson disease. SDS includes olivopontocerebellar atrophy and striatonigral degeneration which is attended by PAF. Eight patients with SDS were studied on a 0.5-T superconducting system utilizing T1-weighted inversion recovery (IR) and T2-weighted spin-echo pulse sequences and also on a 1.5-T system using spin-echo sequences. With IR sequences, atrophy of the putamina was demonstrated in patients with SDS that is consistent with findings of neuronal loss in these nuclei reported on postmortem examinations. An abnormal decrease in signal intensity of the putamina, particularly along their lateral and posterior portions, was also detected, predominantly on T2-weighted sequences, and in three cases on T1-weighted spin-echo sequences. Abnormalities were detected on both imagers but were shown with greater clarity on the 1.5-T device. SDS is the first disease in which convincing basal ganglia changes have been shown in vivo exclusively by MR imaging.

Twenty cases of surgically verified pituitary microadenoma (17 with Cushing disease and three with acromegaly) were studied with positron emission tomography (PET) with use of fluorine-18-2-fluorodeoxyglucose (FDG). The diagnostic results were compared with those of other modalities, namely, computed tomography (CT), magnetic resonance (MR) imaging, and, in the cases of Cushing disease, simultaneous bilateral inferior petrosal sinus sampling (SIPS). The PET results showed 12 positive readings and one questionable reading, compared with seven positive readings and one questionable reading for CT (18 cases studied) and 13 positive and two questionable MR imaging readings. PET complemented MR imaging, in the sense that five of the positive PET readings were negative or questionable at MR imaging. PET studies of 20 healthy control subjects showed no false-positive cases, whereas other studies of healthy subjects with contrast material-enhanced CT and MR imaging have yielded, respectively, 20% and 15% positive readings, with findings suggestive of silent or occult adenomas.