Statistically significant differences were found between metabolite ratios (/Cr) of HIV-infected youing adults and healthy control subjects in the occipital gray N-acetylaspartate, right basal ganglia glutamine/glutamate, left anterior insular cortex choline, and left posterior insular cortex. Selected metabolite ratios with respect to Cr were detected bilaterally in the basal ganglia, anterior insular cortex, posterior insular cortex, frontal white and occipital/frontal gray regions of the two groups. The presented method was demonstrated in two-dimensional (2-D) MRSI measurements under the large frequency drift induced by a fMRI experiment.ĭensity Weighted Concentric Circle Trajectories for Brain MRSI at 7TĪ recently implemented 5D echo-planar J-resolved spectroscopic sequence using 8x acceleration and compressed sensing reconstruction was evaluated in 7 perinatally infected and 8 healthy youths. Meanwhile, a precise measurement of the frequency drift and the effective correction is achieved. The new method utilizes the outer volume suppression-localized navigator, termed OVS-localized navigator, resulting in no perturbations of metabolite signals and thus no saturation-induced SNR losses. In this study, a new prospective frequency correction method is introduced. Nonetheless, the SNR loss remains unavoidable and becomes notable when the imperfect refocusing pulses or a short repetition time (TR) are used in MRSI. A small excitation flip angle (10-20°) is used for the PRESS-IRS navigator to reduce the saturation-induced SNR loss on metabolite signals. The prospective frequency correction is typically achieved by incorporating a PRESS-based interleaved reference scan (PRESS-IRS) as a navigator, termed as PRESS-IRS navigator. However, in MRSI measurements, these effects can only be mitigated using the prospective frequency correction, because each spectrum is phase-encoded. These effects can be mitigated retrospectively and prospectively. The frequency drift causes broad and distorted spectral lineshapes, reduced SNR, and quantification errors. However, frequency drifts occur over time even in advanced MR systems and become larger when high shim currents or rapidly switched gradients are applied. During the prolonged scan time, maintaining a constant static magnetic field (B0) is important for a robust MRSI measurement. Prior-Knowledge Quantitation of Glutamate, Glutamine, GABA, and Glutathione using Covariance J-resolved spectroscopyĭata acquisitions for magnetic resonance spectroscopic imaging (MRSI) require a long scan time to increase SNR and for spatial encoding. Therefore, this valuable MR tool can be used in examining the cerebral energy metabolism across different brain regions, and the same approach could be employed to other spin applications. From an engineering perspective, this new approach provides a cost-effective solution for in vivo 31P MRS study of multiple brain regions with a conventional single-channel transmitter-receiver configuration. By successfully implementing this method, we are able to obtain high quality in vivo 31P MR spectra from both frontal and occipital lobes within the same amount of time as the traditional method covering one brain region. In this work, we present a novel design of the dual-channel 31P MRS system for simultaneous measurements of cerebral high-energy phosphate metabolism from two brain regions of interest by incorporating a new pulse sequence and two separated RF surface coils with a transistor-transistor logic (TTL) controller.
Functional/metabolic changes in different brain regions of interest are of importance for better understanding of the pathophysiological mechanism underlying the human brain diseases.