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...
Type 2 diabetes and major depression are disorders that are mutual risk factors and may share similar pathophysiological mechanisms. To further understand these shared mechanisms, the purpose of our study was to examine the biochemical basis of depression in patients with type 2 diabetes using proton MRS. Patients with type 2 diabetes and major depression (n ¼ 20) were scanned along with patients with diabetes alone (n ¼ 24) and healthy controls (n ¼ 21) on a 1.5 T MRI/MRS scanner. Voxels were placed bilaterally in dorsolateral white matter and the subcortical nuclei region, both areas important in the circuitry of late-life depression. Absolute values of myoinositol, creatine, N-acetyl aspartate, glutamate, glutamine, and choline corrected for CSF were measured using the LC-Model algorithm. Glutamine and glutamate concentrations in depressed diabetic patients were significantly lower (po0.001) in the subcortical regions as compared to healthy and diabetic control subjects. Myo-inositol concentrations were significantly increased (po0.05) in diabetic control subjects and depressed diabetic patients in frontal white matter as compared to healthy controls. These findings have broad implications and suggest that alterations in glutamate and glutamine levels in subcortical regions along with white matter changes in myo-inositol provide important neurobiological substrates of mood disorders.
The test-retest reliability of two-dimensional (2D) correlated spectroscopy (COSY) was studied on a whole-body 1.5T MRI scanner. Single-voxel localized 2D proton spectra were recorded in vitro as well as in vivo using a recently implemented localized chemical shift correlated spectroscopic (L-COSY) sequence. A total of 40 in vitro and 40 human brain (10 volunteers, four times each) 2D L-COSY spectra were recorded. The coefficients of variation (CVs) of selected brain metabolites (raw volume integrals) recorded in 10 healthy volunteers were less than 9% for creatine, choline, and N-acetyl aspartate, and less than 17% for myo-inositol, glutamine/glutamate, aspartate, and threonine/lactate. The 2D metabolite ratios and the raw volume integrals of 2D diagonal and cross peaks in healthy human brain were very well reproduced. The intraclass correlation coefficients were greater than 0.4 (P < 0.05) for the major metabolites, indicating that the 2D peak volumes were stable enough within individuals to detect reliable differences between normal subjects. In the past decade, MR spectroscopy (MRS) has become a reliable clinical tool for the diagnosis of selected diseases (1-7). An important feature of any diagnostic tool is its reproducibility. Many studies on the reproducibility of one-dimensional (1D) 1 H MRS have reported the ratios and absolute concentrations of the metabolites (8 -13). Although these studies have shown small errors (3-6%) in the measurement of metabolites in vitro (8,9), the in vivo studies showed higher coefficients of variation (7-26%) in a maximum of only five metabolites (9 -13). Severe overlap of brain metabolites is a major hindrance in 1D MRS.Localized and nonlocalized versions of 2D MRS were reported a decade ago (14 -18); however, only recently have 2D proton spectra been recorded in healthy human subjects and patients with brain tumors (19 -25). Compared to 1D MRS, 2D MR spectra allow less ambiguous assignment of several metabolite resonances in human brain and prostate (25)(26)(27). In a previous study (25), the resonances caused by glutamine/glutamate (Glx) were clearly separated from the dominant singlet resulting from N-acetyl aspartate (NAA) and myo-inositol (mI) in the human brain. Even though identification of "free" aspartate (Asp) was not possible with 1D MRS, the peaks were separated from NAA in 2D MRS (25). 2D cross peaks caused by phosphoethanolamine and ethanolamine (PE), phosphoryl choline (PCh), threonine and lactate (Thr/Lac), and ␥-aminobutyric acid (GABA) were also identified in the 2D L-COSY spectra of the brain. However, to date there has been no report on the reproducibility of 2D MRS. The goal of this work was to investigate the reproducibility of 2D peak volumes and 2D metabolite ratios recorded in phantom solutions and healthy brain using the L-COSY sequence (25). MATERIALS AND METHODS A 1.5 T GE Horizon (5.8) MRI/MRS scanner (GE MedicalSystems, Waukesha, WI) with echo-speed gradients was used with a body coil for transmission and a 3-inch surface coil for reception. ...
Purpose To develop a simultaneous T1, T2, and ADC mapping method that provides co‐registered, distortion‐free images and enables multiparametric quantification of 3D brain coverage in a clinically feasible scan time with the MR Multitasking framework. Methods The T1/T2/diffusion weighting was generated by a series of T2 preparations and diffusion preparations. The underlying multidimensional image containing 3 spatial dimensions, 1 T1 weighting dimension, 1 T2‐preparation duration dimension, 1 b‐value dimension, and 1 diffusion direction dimension was modeled as a 5‐way low‐rank tensor. A separate real‐time low‐rank model incorporating time‐resolved phase correction was also used to compensate for both inter‐shot and intra‐shot phase inconsistency induced by physiological motion. The proposed method was validated on both phantom and 16 healthy subjects. The quantification of T1/T2/ADC was evaluated for each case. Three post‐surgery brain tumor patients were scanned for demonstration of clinical feasibility. Results Multitasking T1/T2/ADC maps were perfectly co‐registered and free from image distortion. Phantom studies showed substantial quantitative agreement (R2=0.999) with reference protocols for T1/T2/ADC. In vivo studies showed nonsignificant T1 (P = .248), T2 (P = .97), ADC (P = .328) differences among the frontal, parietal, and occipital regions. Although Multitasking showed significant differences of T1 (P = .03), T2 (P < .001), and ADC (P = .001) biases against the references, the mean bias estimates were small (ΔT1% < 5%, ΔT2% < 7%, ΔADC% < 5%), with all intraclass correlation coefficients greater than 0.82 indicating “excellent” agreement. Patient studies showed that Multitasking T1/T2/ADC maps were consistent with the clinical qualitative images. Conclusion The Multitasking approach simultaneously quantifies T1/T2/ADC with substantial agreement with the references and is promising for clinical applications.
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