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A two-dimensional (2D) chemical shift correlated MR spectroscopic (COSY) sequence integrated into a new volume localization technique (90°-180°-90°) is proposed for whole-body MR spectroscopy (MRS).Due to the recent improvements in the design of B 0 gradient and RF coils, 1 H MR spectra have been recorded in human brain with excellent water suppression using short TE, as short as 15 ms, and several cerebral metabolites have been identified (1-4). During the past decade alterations in several metabolites, namely, N-acetylaspartate (NAA), glutamate/glutamine (Glx), choline (Ch), creatine (Cr), myo-inositol (mI), and ␥-aminobutyrate (GABA) have been reported in different pathologic states involving the central nervous system (CNS) (5-10). Absolute quantitation of cerebral metabolites in vivo has also been reported for only a few metabolites, albeit with limited success (11-13). Due to severe overlap of these metabolites, an unambiguous assignment of J-coupled metabolite multiplets is severely hindered at 1.5 T field strength.One-dimensional (1D) MR spectral editing techniques to unravel the overlapping resonances rely on J-coupled proton metabolites that have well-separated multiplets. A technique based on subtraction methodology is very sensitive to motion artifacts leading to subtraction errors. An additional drawback is that only one metabolite can be identified at a time. Successful attempts in editing GABA and glutamate using whole-body MRI/MRS scanners have been presented by other researchers (13,14). Single-shotbased multiple-quantum filtered MR spectroscopic sequences have also been implemented on whole-body scanners, but a severe signal loss associated with various coherence transfer pathways made it less attractive to human applications (15)(16)(17).A localized version of a two-dimensional (2D) J-resolved MR spectroscopic (JPRESS) sequence using the PRESS sequence for volume localization was recently proposed (18 -20). Even though the JPRESS sequence retains 100% of the magnetization from a localized volume of interest (VOI), the strong coupling effect inherent at 1.5 T field strength resulted in a complex 2D cross-peak pattern for NAA, glutamate/glutamine, GABA, and other cerebral metabolites (19). Also, some of the 2D cross-peaks were heavily T 2 -weighted during the long incremental delays necessitated by the second dimension of the JPRESS spectrum. An oversampled J-resolved sequence has also been proposed recently (21).Compared to the 2D J-resolved spectra, a COSY spectrum produces a better dispersion of J-cross-peaks, although it requires a larger spectral window to be sampled during the evolution period (22). Different versions of the localized COSY sequence have been implemented by other researchers (23-33). McKinnon and Bosiger (23) proposed a conventional COSY sequence with hard RF pulses (90°-t 1 -90°) followed by three volume selective 180°RF pulses. Haase et al. (24) implemented a COSY combined with an outer volume suppressing sequence, namely, LOCUS. Many previous attempts to develop localiz...

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Purpose: To quantify the changes in brain water diffusivity in hepatic encephalopathy (HE) associated with cirrhosis using diffusion tensor imaging (DTI) and to correlate with neuropsychological (NP) scores. Materials and Methods: DTI was performed in 14 patients with low-grade HE and age/gender-comparable 16 healthy controls. Whole brain mean diffusivity (MD) and fractional anisotropy (FA) maps were calculated, normalized to common space, smoothed, and compared voxel-by-voxel between groups using analysis of covariance with age included as a covariate. The average MD and FA values were also calculated from individual subjects for selected brain regions and correlated with the neuropsychological scores. Results:Patients with HE showed increased MD in the cortical gray and white matter and the internal capsule. Less extensive brain regions with decreased FA were observed in the bilateral frontal and occipital white matter. MD values from the corpus callosum correlated inversely with several NP scores among HE patients and controls. Positive correlations were observed with FA values and cognitive scores. LOW-GRADE CEREBRAL EDEMA is considered to be responsible for the neuropsychological abnormalities in cirrhotic patients with chronic hepatic encephalopathy (HE) (1). The brain water changes result in enlargement of astrocytes, a feature interpreted differently by various groups using electron microscopy. Kimelberg (2) described these changes as astrogliosis due to astrocyte hypertrophy resulting in increased cell size without an increase in intracellular water; others have interpreted these changes as astrocyte swelling (1). The changes in the astrocyte are brought about by the chronic hyperammonemia in patients with HE. ConclusionHE is potentially reversible at each stage, provided the precipitating factors responsible for this condition are eliminated. Low-grade HE is associated with poor quality of life and increased work disability; both improve after hepatic transplantation. Patients with HE may appear overtly normal because mental changes are slight and do not necessarily affect their basic life activities. However, neurocognitive changes in patients with HE are observable with testing and include executive dysfunction, reduced psychomotor speed and attention, with a relative sparing of short-term, delayed, and procedural memories that could affect daily routine activities (3).A majority of patients with HE show no visible abnormalities on conventional magnetic resonance imaging (MRI), except for hyperintensities on T 1 -weighted images in the deep gray matter due to the deposition of manganese in varying proportions (4). Currently, a number of MR techniques are available to quantify brain water noninvasively including proton MR spectroscopy (5-7), magnetization transfer (MT) (8), diffusion-weighted imaging (DWI) (9,10), diffusion tensor imaging (DTI) (11), and T 1 -weighted imaging (12). Results from these techniques suggest that increased brain water content correlates with some neuropsycho-