重复时间对MR氢质子波谱定量脑组织代谢物浓度的影响

目的 探讨在体单体素氢质子MR波谱(1H-MRS)重复时间(TR)对定位测量脑组织代谢物绝对和相对浓度的影响.方法 正常志愿者30名采用1.5 T超导型MR成像系统行点分辨自旋回波(PRESS)序列单体素1H-MRS扫描,取左侧大脑半球顶枕部白质,体素8 cm3,TR分别为1500和5000 ms.采用线性拟合模型(LCModel)处理原始数据,测量肌酸和磷酸肌酸(tCr)、谷氨酸(Glu)、肌醇(mI)、N-乙酰天冬氨酸(NAA)、甘油磷酸胆碱(GPC)和谷氨酸和谷氨酰胺(Glx)等的绝对浓度和相对浓度,并采用配对t检验对不同TR下各代谢物的浓度进行比较.结果 大脑左顶枕部白质代谢物tCr、Clu、mI、NAA、GPC和Glx在TR为1500 ms时绝对浓度分别为(3.0±0.2)、(4.4±0.7)、(3.0±0.3)、(5.0±0.4)、(1.1±0.1)和(5.9±0.6)mmol/L;TR为5000 ms时分别为(4.2±0.4)、(5.3±0.5)、(3.7±0.5)、(6.7±0.7)、(1.4±0.1)和(6.6±0.6)mmol/L.TR为1500 ms时,Gh、mI、NAA、GPC和Glx的相对浓度分别为1.47±0.27、1.00±0.11、1.69±0.17、0.36±0.05和1.95±0.22;TR为5000 ms时分别为1.25±0.12、0.89±0.09、1.60±0.16、0.33±0.04和1.58±0.17.不同TR时,各代谢物绝对浓度和相对浓度差异均有统计学意义(P值均＜0.05).结论1H-MRS可有效地进行脐组织代谢物绝对浓度和相对浓度的测量,PRESS序列中不同的TR所获得的代谢物绝对和相对浓度均有较大差异,较短的TR可低估代谢物的绝对浓度.     

Detection of glutamate in the human brain at 3 T using optimized constant time point resolved spectroscopy.

A CT-PRESS sequence was implemented on a 3-T MR scanner and optimized for the detection of the C4 resonance of glutamate. By simulating the sequence using the full density matrix it was found that 121 chemical shift encoding steps in t1 with an increment delta t1 = 1.6 ms were sufficient to separate the glutamate C4 resonance. The simulations also showed that the highest signal-to-noise ratio was achieved at an average echo time of 131 ms. When using an eightfold undersampling scheme in f1 in order to reduce the minimum total measurement time, the average echo time was 139 ms with 17 encoding steps (delta t1 = 12.8 ms). The sequence was tested on phantoms containing solutions of various brain metabolites and on healthy human volunteers. Besides resolving glutamate, other resonances detected in vivo comprised N-acetyl aspartate, total creatine, choline containing compounds, and myo-inositol. However, glutamine resonances could not be resolved due to severe signal overlap from glutamate and N-acetyl aspartate.     

Test‐retest reliability and reproducibility of short‐echo‐time spectroscopic imaging of human brain at 3T

A ¹H magnetic resonance spectroscopic imaging study at 3T and short echo time was conducted to evaluate both the reproducibility, as measured by the interscan coefficient of variation (CV), and test‐retest reliability, as measured by the intraclass correlation coefficient (ICC), of measurements of glutamate (Glu), combined glutamate and glutamine (Glx), myo‐inositol (mI), N‐acetylaspartate, creatine, and choline in 21 healthy subjects. The effect of partial volume correction on these measures and the relationship of reproducibility and reliability to data quality were also examined. A ¹H magnetic resonance spectroscopic imaging slice was prescribed above the lateral ventricles and single repeat scans were performed within 30 min to minimize physiologic variability. Interscan CVs based on all the voxels varied from 0.05 to 0.07 for N‐acetylaspartate, creatine, and choline to 0.10–0.13 for mI, Glu, and Glx. Findings on the reproducibility of gray and white matter estimates of N‐acetylaspartate, creatine, and choline are consistent with previous studies using longer echo times, with CVs in the range of 0.02–0.04 and ICC in the range of 0.65–0.90. CVs for Glu, Glx, and mI are much lower than reported in previous studies at 1.5T, while white matter mI (CV = 0.04, ICC = 0.93) and gray matter Glx (CV = 0.04, ICC = 0.68) demonstrated both high reproducibility and test‐retest reliability. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Measurement of brain glutamate using TE-averaged PRESS at 3T.

A method is introduced that provides improved in vivo spectroscopic measurements of glutamate (Glu), glutamine (Gln), choline (Cho), creatine (Cre), N-acetyl compounds (NAtot, NAA + NAAG), and the inositols (mI and sI). It was found that at 3T, TE averaging, the f1 = 0 slice of a 2D J-resolved spectrum, yielded unobstructed signals for Glu, Glu + Gln (Glx), mI, NA(tot), Cre, and Cho. The C4 protons of Glu at 2.35 ppm, and the C2 protons of Glx at 3.75 ppm were well resolved and yielded reliable measures of Glu/Gln stasis. Apparent T1/T2 values were obtained from the raw data, and metabolite tissue levels were determined relative to a readily available standard. A repeatibility error of <5%, and a coefficient of variation (CV) of <10% were observed for brain Glu levels in a study of six normal volunteers.     

Measurement of glycine in the human brain in vivo by 1H‐MRS at 3 T: application in brain tumors

Glycine is a key metabolic intermediate required for the synthesis of proteins, nucleic acids, and other molecules, and its detection in cancer could, therefore, provide biologically relevant information about the growth of the tumor. Here, we report measurement of glycine in human brain and gliomas by an optimized point‐resolved spectroscopy sequence at 3 T. Echo time dependence of the major obstacle, myo‐inositol (mI) multiplet, was investigated with numerical simulations, incorporating the 3D volume localization. The simulations indicated that a subecho pair (TE₁, TE₂) = (60, 100) ms permits detection of both glycine and mI with optimum selectivity. In vivo validation of the optimized point‐resolved spectroscopy was conducted on the right parietal cortex of five healthy volunteers. Metabolite signals estimated from LCModel were normalized with respect to the brain water signal, and the concentrations were evaluated assuming the total creatine concentration at 8 mM. The glycine concentration was estimated as 0.6 ± 0.1 mM (mean ± SD, n = 5), with a mean Cramér‐Rao lower bound of 9 ± 1%. The point‐resolved spectroscopy sequence was applied to measure the glycine levels in patients with glioblastoma multiforme. Metabolite concentrations were obtained using the water signal from the tumor mass. The study revealed that a subset of human gliomas contains glycine levels elevated 1.5–8 fold relative to normal. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Accelerated proton echo planar spectroscopic imaging (PEPSI) using GRAPPA with a 32-channel phased-array coil.

Parallel imaging has been demonstrated to reduce the encoding time of MR spectroscopic imaging (MRSI). Here we investigate up to 5-fold acceleration of 2D proton echo planar spectroscopic imaging (PEPSI) at 3T using generalized autocalibrating partial parallel acquisition (GRAPPA) with a 32-channel coil array, 1.5 cm(3) voxel size, TR/TE of 15/2000 ms, and 2.1 Hz spectral resolution. Compared to an 8-channel array, the smaller RF coil elements in this 32-channel array provided a 3.1-fold and 2.8-fold increase in signal-to-noise ratio (SNR) in the peripheral region and the central region, respectively, and more spatial modulated information. Comparison of sensitivity-encoding (SENSE) and GRAPPA reconstruction using an 8-channel array showed that both methods yielded similar quantitative metabolite measures (P > 0.1). Concentration values of N-acetyl-aspartate (NAA), total creatine (tCr), choline (Cho), myo-inositol (mI), and the sum of glutamate and glutamine (Glx) for both methods were consistent with previous studies. Using the 32-channel array coil the mean Cramer-Rao lower bounds (CRLB) were less than 8% for NAA, tCr, and Cho and less than 15% for mI and Glx at 2-fold acceleration. At 4-fold acceleration the mean CRLB for NAA, tCr, and Cho was less than 11%. In conclusion, the use of a 32-channel coil array and GRAPPA reconstruction can significantly reduce the measurement time for mapping brain metabolites.     

Metabolic profiles of human brain tumors using quantitative in vivo 1H magnetic resonance spectroscopy.

Proton spectroscopy can noninvasively provide useful information on brain tumor type and grade. Short- (30 ms) and long- (136 ms) echo time (TE) (1)H spectra were acquired from normal white matter (NWM), meningiomas, grade II astrocytomas, anaplastic astrocytomas, glioblastomas, and metastases. Very low myo-Inositol ([mI]) and creatine ([Cr]) were characteristic of meningiomas, and high [mI] characteristic of grade II astrocytomas. Tumor choline ([Cho]) was greater than NWM and increased with grade for grade II and anaplastic astrocytomas, but was highly variable for glioblastomas. Higher [Cho] and [Cr] correlated with low lipid and lactate (P < 0.05), indicating a dilution of metabolite concentrations due to necrosis in high-grade tumors. Metabolite peak area ratios showed no correlation with lipids and mI/Cho (at TE = 30 ms), and Cr/Cho (at TE = 136 ms) best correlated with tumor grade. The quantified lipid, macromolecule, and lactate levels increased with grade of tumor, consistent with progression from hypoxia to necrosis. Quantification of lipids and macromolecules at short TE provided a good marker for tumor grade, and a scatter plot of the sum of alanine, lactate, and delta 1.3 lipid signals vs. mI/Cho provided a simple way to separate most tumors by type and grade.     

T2 measurement and quantification of glutamate in human brain in vivo.

The proton NMR transverse relaxation time T(2) of glutamate (Glu) in human brain was measured by means of spectrally selective refocusing at 3.0 T in vivo. An 81.4-ms-long dual-band Gaussian 180 degrees RF pulse, designed for refocusing at 2.35 and 3.03 ppm, was employed within point-resolved spectroscopy (PRESS) to generate the Glu C4-proton target multiplet and the total creatine (tCr) singlet. Six optimal echo times (TEs) between 128 and 380 ms were selected from numerical analysis of the filtering performance for effective detection of the Glu signal with minimal contamination from glutamine (Gln), N-acetylaspartate (NAA), and glutathione (GSH). The magnetization of Glu and tCr was extracted from spectral fitting of experimental and calculated spectra. Apparent T(2) values of Glu and tCr were estimated as 201 +/- 18 and 164 +/- 12 ms for the medial prefrontal (PF) cortex, and 198 +/- 22 and 169 +/- 15 ms (mean +/- SD, N = 5) for the left frontal (LF) cortex, respectively. With water segmentation data, the magnetization values of Glu and tCr of the two adjacent voxels, calculated from the T(2) values and spectra following the thermal equilibrium magnetization, were combined to give the Glu and tCr concentrations as 10.37 +/- 1.06 and 8.87 +/- 0.56 mM for gray matter (GM), and 5.06 +/- 0.57 and 5.16 +/- 0.45 mM (mean +/- SD, N = 5) for white matter (WM), respectively.     

Three-dimensional J-resolved H-1 magnetic resonance spectroscopic imaging of volunteers and patients with brain tumors at 3T.

A method that combines two-dimensional (2D) J-resolved spectroscopy with three spatial dimension magnetic resonance spectroscopic imaging (MRSI) is introduced to measure J-coupled metabolites of glutamate (Glu), glutamine (Gln), myo-Inositol (mI), and lactate (Lac) in the brain and to simultaneously obtain T(2) values of choline (Cho), creatine (Cr), and N-acetyl aspartate (NAA). Relatively few points in the t(1) dimension (six echo times) and a flyback echo-planar trajectory were incorporated in the acquisition to speed up the total acquisition time so that it was within a clinically feasible range (23 min). Data obtained using GAMMA software simulations and from phantoms have shown that the (4)CH(2) resonances of Glu can be separated from Gln at 2.35 ppm in TE-averaged spectra. Results from phantoms, six normal volunteers, and four patients demonstrated good signal-to-noise ratio (SNR). The J cross-peaks from the methyl group of Lac were visualized in the 2D spectra from the phantom and the glioma patient, and could be quantified from the spectra at J = +/-4.17 Hz. This technique also enables the evaluation of the changes in metabolite T(2). Compared with the values in normal white matter, the T(2) values of Cho and Cr were statistically significantly increased in regions of glioma.     

In vivo detection of brain glycine with echo-time-averaged (1)H magnetic resonance spectroscopy at 4.0 T.

A single-voxel proton magnetic resonance spectroscopy ((1)H-MRS) method is described that enables the in vivo measurement of endogenous brain glycine (Gly) levels in human subjects. At 4.0 T, TE-averaging (1)H-MRS dramatically attenuates the overlapping myo-inositol (mI) resonances at 3.52 ppm, permitting a more reliable measure of the Gly singlet peak. This methodology initially is described and tested in phantoms. The phantom data infers that the 3.55-ppm peak predominantly is Gly with a smaller contribution from mI. The composite resonance thus is differentiated from pure Gly and mI and is labeled Gly*. The mI contribution was calculated as <2% of the total Gly* signal for a 1:1 mI/Gly mixture. The technique subsequently was used to acquire TE-averaged (1)H-MRS data from the occipital cortex of healthy control subjects. The resultant spectra closely resembled experimental phantom data. LC-model analysis provided a means for quantifying TE-averaged (1)H-MRS spectra and a mean test-retest variability measure of 15% was established for brain Gly* levels in studies of six healthy subjects.     

Acquisition-weighted stack of spirals for fast high-resolution three-dimensional ultra-short echo time MR imaging.

Ultra-short echo time (UTE) MRI requires both short excitation ( approximately 0.5 ms) and short acquisition delay (<0.2 ms) to minimize T(2)-induced signal decay. These requirements currently lead to low acquisition efficiency when high resolution (<1 mm) is pursued. A novel pulse sequence, acquisition-weighted stack of spirals (AWSOS), is proposed here to acquire high-resolution three-dimensional (3D) UTE images with short scan time ( approximately 72 s). The AWSOS sequence uses variable-duration slice encoding to minimize T(2) decay, separates slice thickness from in-plane resolution to reduce the number of slice encodings, and uses spiral trajectories to accelerate in-plane data collections. T(2)- and off-resonance induced slice widening and image blurring were calculated from 1.5 to 7 Tesla (T) through point spread function. Computer simulations were performed to optimize spiral interleaves and readout times. Phantom scans and in vivo experiments on human heads were implemented on a clinical 1.5T scanner (G(max) = 40 mT/m, S(max) = 150 T/m/s). Accounting for the limits on B(1) maximum, specific absorption rate (SAR), and the lowered amplitude of slab-select gradient, a sinc radiofrequency (RF) pulse of 0.8ms duration and 1.5 cycles was found to produce a flat slab profile. High in-plane resolution (0.86 mm) images were obtained for the human head using echo time (TE) = 0.608 ms and total shots = 720 (30 slice-encodings x 24 spirals). Compared with long-TE (10 ms) images, the ultrashort-TE AWSOS images provided clear visualization of short-T(2) tissues such as the nose cartilage, the eye optic nerve, and the brain meninges and parenchyma.     

Magnetic resonance coronary angiography with vasovist™: in-vivo T 1 estimation to improve image quality of navigator and breath-hold techniques

The purpose of the study was to estimate T ₁ values of blood and myocardium after a single injection of Vasovist™ and to assess Vasovist™ for magnetic resonance coronary angiography (MRCA). For all exams 0.05 mmol/kg of Vasovist™ was injected. T ₁ values of blood and myocardium were estimated over 30 min after injection. Twelve volunteers were examined on a 1.5-T Siemens system using a SSFP sequence with incrementally increasing inversion times for T ₁-estimation and a breath-hold 3D IR-FLASH sequence for MRCA. Eleven examinations were performed on 1.5-T Philips system using the Look-Locker approach for T ₁ estimation and a whole-heart inversion-prepared, 3D SSFP sequence for MRCA. SNR, CNR and image quality were assessed. T ₁ values of blood (5 min: 230 ms vs. 30 min: 275 ms) and myocardium (5 min: 99 ms vs. 30 min: 130 ms) increased over time. Whereas the blood SNR (1 min: 23.6 vs. 30 min: 21.2) showed no significant differences, the blood-to-myocardium CNR (1 min: 18.1 vs. 30 min: 13.8) and the image quality (1 min: 2.9 vs. 30 min: 3.8) degraded over time. Due to long plasma half-time the T1-shortening effect of Vasovist™ remains effective over 30 min, which allows for multiple breath-hold or high-resolution MRCA.     

Measurement of glycine in human brain by triple refocusing 1H-MRS in vivo at 3.0T.

A new (1)H-MRS filtering strategy for selective measurement of glycine (Gly) in human brain in vivo at 3.0T is proposed. Investigation of multiple refocusing following a 90 degrees excitation pulse indicated that triple refocusing is most effective for suppression of the strongly coupled resonances of myo-inositol (mI) at the Gly 3.55-ppm resonance. The echo times of the triple refocusing were optimized, with numerical analysis of the filtering performance, as {TE(1), TE(2), TE(3)} = {67, 62, 69} ms. Compared with the 90 degrees -acquired mI signal the mI suppression ratios of the filter were 170 and 1000, in terms of peak amplitude and area, respectively, between 3.51 and 3.59 ppm. From LCModel analyses, using density-matrix calculated spectra as basis functions, the concentration of Gly in parieto-occipital cortex of healthy adults was estimated to be 0.5 +/- 0.1 mM (mean +/- SD, n = 6), with reference to creatine at 8 mM.     

Proton echo-planar spectroscopic imaging of J-coupled resonances in human brain at 3 and 4 Tesla.

In this multicenter study, 2D spatial mapping of J-coupled resonances at 3T and 4T was performed using short-TE (15 ms) proton echo-planar spectroscopic imaging (PEPSI). Water-suppressed (WS) data were acquired in 8.5 min with 1-cm(3) spatial resolution from a supraventricular axial slice. Optimized outer volume suppression (OVS) enabled mapping in close proximity to peripheral scalp regions. Constrained spectral fitting in reference to a non-WS (NWS) scan was performed with LCModel using correction for relaxation attenuation and partial-volume effects. The concentrations of total choline (tCho), creatine + phosphocreatine (Cr+PCr), glutamate (Glu), glutamate + glutamine (Glu+Gln), myo-inositol (Ins), NAA, NAA+NAAG, and two macromolecular resonances at 0.9 and 2.0 ppm were mapped with mean Cramer-Rao lower bounds (CRLBs) between 6% and 18% and approximately 150-cm(3) sensitive volumes. Aspartate, GABA, glutamine (Gln), glutathione (GSH), phosphoethanolamine (PE), and macromolecules (MMs) at 1.2 ppm were also mapped, although with larger mean CRLBs between 30% and 44%. The CRLBs at 4T were 19% lower on average as compared to 3T, consistent with a higher signal-to-noise ratio (SNR) and increased spectral resolution. Metabolite concentrations were in the ranges reported in previous studies. Glu concentration was significantly higher in gray matter (GM) compared to white matter (WM), as anticipated. The short acquisition time makes this methodology suitable for clinical studies.     

Myoinositol content in the human brain is modified by transcranial direct current stimulation in a matter of minutes: A 1H‐MRS study

Brain content of myoinositol (mI) has been shown to be altered in several neuropsychiatric conditions. Likewise, various forms of electric currents have been applied to the human brain for therapeutic purposes in neuropsychiatric diseases. In this study we aimed to depict the effects of low‐power transcranial direct current stimulation (tDCS) on brain mI by proton magnetic resonance spectroscopy (¹H‐MRS). We studied two groups of five healthy subjects by ¹H‐MRS: the first group was studied before and after both anodal and sham (placebo) tDCS over the right frontal lobe, and the second group was studied at the same intervals without undergoing either sham or anodal tDCS. Anodal tDCS induced a significant increase of mI content at 30 min after stimulation offset (141.5 ± 16.7%, P < 0.001) below the stimulating electrode but not in distant regions, such as the visual cortex, whereas sham tDCS failed to induce changes in mI. Neither N‐acetyl‐aspartate (NAA) nor the other metabolite contents changed after anodal or sham stimulation. ¹H‐MRS represents a powerful tool to follow the regional effects of tDCS on brain mI and, possibly, on the related phosphoinositide system. Magn Reson Med 60:782–789, 2008. © 2008 Wiley‐Liss, Inc.     

脑卒中后抑郁患者的波谱研究

目的：探讨M RS定量测定在预测梗塞后抑郁中的价值。方法对51例首发脑卒中且预后良好的患者和15例健康志愿者进行1 H‐M RS。根据DSM‐IV抑郁性疾患诊断标准和 HDRS评分,将所有脑卒中患者分为3组,然后分析卒中后抑郁患者与未受梗塞灶累及的额叶（前扣带回）1 H‐MRS数据之间的关系。采用单体素 MRS来评价额叶 NAA／Cr ,Glu／Cr ,Cho／Cr和mI／Cr的值。结果共11例患者（21．5％）符合抑郁症的诊断标准,9例（17．6％）患者的 HDRS评分＞14、但不符合抑郁症的诊断标准,这两组例患者的Glu／Cr值都高于 HDRS评分＜14的卒中患者和健康志愿者（ P＜0．001）。但是NAA／Cr、Cho／Cr和mI／Cr的值在卒中后各组之间无明显统计学差异。结论研究表明卒中后抑郁症的患者其额叶Glu的水平发生了变化。     

High-resolution T1 and T2 mapping of the brain in a clinically acceptable time with DESPOT1 and DESPOT2.

Variations in the intrinsic T(1) and T(2) relaxation times have been implicated in numerous neurologic conditions. Unfortunately, the low resolution and long imaging time associated with conventional methods have prevented T(1) and T(2) mapping from becoming part of routine clinical evaluation. In this study, the clinical applicability of the DESPOT1 and DESPOT2 imaging methods for high-resolution, whole-brain, T(1) and T(2) mapping was investigated. In vivo, 1-mm(3) isotropic whole-brain T(1) and T(2) maps of six healthy volunteers were acquired at 1.5 T with an imaging time of <17 min each. Isotropic maps (0.34 mm(3)) of one volunteer were also acquired (time <21 min). Average signal-to-noise within the 1-mm(3) T(1) and T(2) maps was approximately 20 and approximately 14, respectively, with average repeatability standard deviations of 46.7 ms and 6.7 ms. These results demonstrate the clinical feasibility of the methods in the study of neurologic disease.     

Comments on "Ensuring safety of implanted devices under MRI using reversed polarization"

A 3‐T study is presented, comparing the ability of two ¹H spectroscopy pulse sequences, Carr–Purcell point resolved spectroscopy (CPRESS; TE = 45 msec), and conventional PRESS (TE = 35 msec), to separate between groups of 20 normal control (NC) and 20 mild cognitive impairment (MCI) subjects. Both sequences showed higher myo‐inositol (mI) and mI/N‐acetyl‐aspartate (NAA) levels in the posterior cingulate gyrus of the MCI subjects. The increased intrasubject repeatability of mI and mI/NAA CPRESS measurements (～6% vs. 9% for PRESS) translated into decreased intraclass variability. A 22% intraclass mI PRESS variability was reduced to 16% for CPRESS, and an 18% intraclass mI/NAA PRESS variability was reduced to 12% for CPRESS for the group of NC subjects. Similar results were observed for the MCI subjects. Decreased intraclass variability led to improved separation between NC and MCI subjects (P = 0.017 for PRESS and P < 0.0001 for CPRESS mI/NAA, the best NC/MCI discriminant for each method). Seventy‐five percent sensitivity at eighty percent specificity was demonstrated by mI/NAA CPRESS measurements in separating NC from MCI subjects. High correlations were also observed between subject performance on a number of neuropsychological tests (probing verbal memory, visuoconstruction performance, and visual motor integration) and the mI/NAA ratio; higher correlation coefficients (with stronger statistical significance) were consistently evident for CPRESS than for PRESS data. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Reproducibility of short echo time proton magnetic resonance spectroscopy using point-resolved spatially localized spectroscopy sequence in normal human brains.

The reproducibility of short echo time proton MR spectroscopy (1H-MRS) in normal human brains was examined. Thirteen healthy volunteers were studied, and each underwent three MRS examinations. Second and third measurements were done on the same day, about two months after the first measurement, and interday and intraday reproducibility were evaluated. MRS was performed with proton brain examination/single voxel (PROBE/SV) and point-resolved spatially localized spectroscopy (PRESS) (repetition time = 2000 ms, echo time = 30 ms). Five metabolite ratios were computed; N-acetyl-aspartate (NAA)/creatine (Cr), choline (Cho)/Cr, myo-inositol (mI)/Cr, NAA/(NAA + Cr + Cho), and NAA/Cho. Their normal range and reproducibility were measured. For each metabolite ratio, there was no significant difference between interday difference and intraday difference, suggesting that the interval of two months has minimal effect on MRS measurements. MRS may be utilized for the observation of central nervous system diseases.     

Proton MR spectroscopy in Rett syndrome.

Seven patients (mean age 7.7yr) with Rett syndrome, a condition with progressive regression of psychomotor development are included in this study. Proton MR spectroscopy images were obtained with the multivoxel chemical-shift imaging mode (TR=1500ms, TE=40ms). Spectra from 224 voxels in the brain parenchyma were studied. N-acetyl aspartate (NAA), creatine (Cr), choline (Cho), and myoinositol (mI) peaks were quantitatively evaluated, and NAA/Cr, NAA/Cho, and Cho/Cr, mI/Cr ratios were calculated. Five age-matched normal cases were available as controls. In three patients with Rett syndrome spectroscopy findings were normal, and the metabolite ratios were similar to control cases. In the remaining four patients with the syndrome prominent decrease of the NAA peak was the main finding resulting in decreases in NAA/Cr (1.14+/-17), and NAA/Cho (1.08+/-27) ratios (p<0.0001). Cho/Cr ratios (0.93+/-26), and mI/Cr ratios (0.88+/-36) were normal compared to controls. There was no correlation between spectroscopic changes and clinical status of the patients. The findings suggested that not only reduced neuronal-dendritic arborizations but also decreased neuronal function could contribute to spectroscopy changes in Rett syndrome.