Localized proton MR spectroscopy of the human kidney in vivo by means of short echo time STEAM sequences

Identifying disease progression in chronic kidney disease using proton magnetic resonance spectroscopy

Chronic kidney disease (CKD) affects approximately 10% of the world population, higher still in some developing countries, and can cause irreversible kidney damage eventually leading to kidney failure requiring dialysis or kidney transplantation. However, not all patients with CKD will progress to this stage, and it is difficult to distinguish between progressors and non-progressors at the time of diagnosis. Current clinical practice involves monitoring estimated glomerular filtration rate and proteinuria to assess CKD trajectory over time; however, there remains a need for novel, validated methods that differentiate CKD progressors and non-progressors. Nuclear magnetic resonance techniques, including magnetic resonance spectroscopy and magnetic resonance imaging, have the potential to improve our understanding of CKD progression. Herein, we review the application of magnetic resonance spectroscopy both in preclinical and clinical settings to improve the diagnosis and surveillance of patients with CKD.

Multiple breath-hold proton spectroscopy of human liver at 3T: Relaxation times and concentrations of glycogen, choline, and lipids

PURPOSE

To evaluate the feasibility of an expiration multiple breath-hold ¹ H-MRS technique to measure glycogen (Glycg), choline-containing compounds (CCC), and lipid relaxation times T₁ , T₂ , and their concentrations in normal human liver.

MATERIALS AND METHODS

Thirty healthy volunteers were recruited. Experiments were performed at 3T. Multiple expiration breath-hold single-voxel point-resolved spectroscopy (PRESS) technique was used for localization. Water-suppressed spectra were used for the estimation of Glycg, CCC, lipid methylene (CH₂ )_n relaxation times and concentrations. Residual water lines were removed by the Hankel Lanczos singular value decomposition filter. After phase correction and frequency alignment, spectra were averaged and processed by LCModel. Summed signals of Glycg resonances H2H4', H3, and H5 between 3.6 and 4 ppm were used to estimate their apparent relaxation times and concentration. Glycg, CCC, and lipid content were estimated from relaxation corrected spectral intensity ratios to unsuppressed water line.

RESULTS

Relaxation times were measured for liver Glycg (T₁ , 892 ± 126 msec; T₂ , 13 ± 4 msec), CCC (T₁ , 842 ± 75 msec; T₂ , 50 ± 5 msec), lipid (CH₂ )_n (T₁ , 402 ± 19 msec; T₂ , 52 ± 3 msec), and water (T₁ , 990 ± 89 msec; T₂ , 30 ± 2 msec). Mean CCC and lipid concentrations of healthy liver were 7.8 ± 1.3 mM and 15.8 ± 23.6 mM, respectively. Glycg content was found lower in the morning (48 ± 21 mM) compared to the afternoon (145 ± 50 mM).

CONCLUSION

Multiple breath-hold ¹ H-MRS together with dedicated postprocessing is a feasible technique for the quantification of liver Glycg, CCC, and lipid relaxation times and concentrations.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:410-417.

Metabolic imaging of human kidney triglyceride content: reproducibility of proton magnetic resonance spectroscopy

Objective

To assess the feasibility of renal proton magnetic resonance spectroscopy for quantification of triglyceride content and to compare spectral quality and reproducibility without and with respiratory motion compensation in vivo.

Materials and Methods

The Institutional Review Board of our institution approved the study protocol, and written informed consent was obtained. After technical optimization, a total of 20 healthy volunteers underwent renal proton magnetic resonance spectroscopy of the renal cortex both without and with respiratory motion compensation and volume tracking. After the first session the subjects were repositioned and the protocol was repeated to assess reproducibility. Spectral quality (linewidth of the water signal) and triglyceride content were quantified. Bland-Altman analyses and a test by Pitman were performed.

Results

Linewidth changed from 11.5±0.4 Hz to 10.7±0.4 Hz (all data pooled, p<0.05), without and with respiratory motion compensation respectively. Mean % triglyceride content in the first and second session without respiratory motion compensation were respectively 0.58±0.12% and 0.51±0.14% (P = NS). Mean % triglyceride content in the first and second session with respiratory motion compensation were respectively 0.44±0.10% and 0.43±0.10% (P = NS between sessions and P = NS compared to measurements with respiratory motion compensation). Bland-Altman analyses showed narrower limits of agreement and a significant difference in the correlated variances (correlation of −0.59, P<0.05).

Conclusion

Metabolic imaging of the human kidney using renal proton magnetic resonance spectroscopy is a feasible tool to assess cortical triglyceride content in humans in vivo and the use of respiratory motion compensation significantly improves spectral quality and reproducibility. Therefore, respiratory motion compensation seems a necessity for metabolic imaging of renal triglyceride content in vivo.

High dynamic-range magnetic resonance spectroscopy (MRS) time-domain signal analysis

In the absence of water signal suppression, the proton magnetic resonance spectroscopy ((1)H MRS) in vivo water resonance signal-to-noise ratio (SNR) is orders of magnitude larger than the SNR of all the other resonances. In this case, because the high-SNR water resonance dominates the data, it is difficult to obtain reliable parameter estimates for the low SNR resonances. Herein, a new model is described that offers a solution to this problem. In this model, the time-domain signal for the low SNR resonances is represented as the conventional sum of exponentially decaying complex sinusoids. However, the time-domain signal for the high SNR water resonance is assumed to be a complex sinusoid whose amplitude is slowly varying from pure exponential decay and whose phase is slowly varying from a constant frequency. Thus, the water resonance has only an instantaneous amplitude and frequency. The water signal is neither filtered nor subtracted from the data. Instead, Bayesian probability theory is used to simultaneously estimate the frequencies, decay-rate constants, and amplitudes for all the low SNR resonances, along with the water resonance's time-dependent amplitude and phase. While computationally intensive, this approach models all of the resonances, including the water and the metabolites of interest, to within the noise level.

In vivo monitoring response to chemotherapy of human diffuse large B-cell lymphoma xenografts in SCID mice by 1H and 31P MRS

RATIONALE AND OBJECTIVES

A reliable noninvasive method for in vivo detection of early therapeutic response of non-Hodgkin's lymphoma (NHL) patients would be of great clinical value. This study evaluates the feasibility of (1)H and (31)P magnetic resonance spectroscopy (MRS) for in vivo detection of response to combination chemotherapy of human diffuse large B-cell lymphoma (DLCL2) xenografts in severe combined immunodeficient (SCID) mice.

MATERIALS AND METHODS

Combination chemotherapy with cyclophosphamide, hydroxy doxorubicin, Oncovin, prednisone, and bryostatin 1 (CHOPB) was administered to tumor-bearing SCID mice weekly for up to four cycles. Spectroscopic studies were performed before the initiation of treatment and after each cycle of the CHOPB. Proton MRS for detection of lactate and total choline was performed using a selective multiple-quantum-coherence-transfer (Sel-MQC) and a spin-echo-enhanced Sel-MQC (SEE-Sel-MQC) pulse sequence, respectively. Phosphorus-31 MRS using a nonlocalized, single-pulse sequence without proton decoupling was also performed on these animals.

RESULTS

Significant decreases in lactate and total choline were detected in the DLCL2 tumors after one cycle of CHOPB chemotherapy. The ratio of phosphomonoesters to beta-nucleoside triphosphate (PME/betaNTP, measured by (31)P MRS) significantly decreased in the CHOPB-treated tumors after two cycles of CHOPB. The control tumors did not exhibit any significant changes in either of these metabolites.

CONCLUSIONS

This study demonstrates that (1)H and (31)P MRS can detect in vivo therapeutic response of NHL tumors and that lactate and choline offer a number of advantages over PMEs as markers of early therapeutic response.

On restoring motion-induced signal loss in single-voxel magnetic resonance spectra

Destructive interference from phase fluctuations caused by motion during (1)H magnetic resonance spectroscopy (MRS) stimulated-echo acquisition mode (STEAM) and point-resolved spectroscopy (PRESS) acquisitions can significantly diminish the traditional radicalN-gain in signal-to-noise ratio (SNR) afforded by averaging N signals, especially in the torso. The SNR loss is highly variable among individuals, even when identical acquisition protocols are used. This paper presents a theory for the SNR loss, assuming that the phase fluctuates randomly. It is shown that SNR in conventional averaging is reduced by the factor sinc(sigma(phi) radical3/pi), where sigma(phi) is the standard deviation (SD) of the phase. "Constructive averaging," whereby each individual acquisition is phase-corrected using the phase of a high-SNR peak before averaging, reverses the SNR loss from motion-induced dephasing, resulting in a {1/sinc(sigma(phi) radical3/pi)}-fold SNR improvement. It is also shown that basing phase corrections on an average of radicalN adjacent points both improves correction accuracy and effectively eliminates false signal artifacts when corrections are based on low-SNR peaks. The theory is validated over a sevenfold range of variation in signal loss due to motion observed in (1)H STEAM and PRESS data acquired from 17 human subjects (heart: N = 16; leg: N = 1). Constructive averaging should be incorporated as a routine tool for in vivo (1)H MRS.

Improved two-dimensional J-resolved spectroscopy

Localised two-dimensional J-resolved spectroscopy (JPRESS) is optimised for the in vivo detection of J-coupled metabolites using magnetic resonance spectroscopy at 3 T. The acquisition of echo signals starts as early as possible (i.e. maximum-echo sampling). This sampling scheme increases sensitivity and decreases overlap of peak tails, hence alleviating baseline problems. Reconstruction issues are discussed and the sensitivity is compared analytically with that of 1D PRESS. The qualitative behaviour of eddy currents in JPRESS is outlined and a 2D eddy current correction procedure based on the 1D phase deconvolution method is proposed.

Decreases in free cholesterol and fatty acid unsaturation in renal cell carcinoma demonstrated by breath-hold magnetic resonance spectroscopy

Increased utilization of cross-sectional imaging has resulted in increased detection of incidental renal tumors. The noninvasive characterization of renal tissue has important implications for the diagnosis of renal malignancies and treatment monitoring. Recently, multiple breath-hold averaged proton magnetic resonance spectroscopy (1H-MRS) performed at high field has enabled the use of this noninvasive metabolic profiling technique for the investigation of the abdomen. Multiple breath-hold averaged 1H-MRS at high field (3T) was obtained in the kidneys of 10 healthy volunteers and in renal cell carcinoma tumors of 14 patients. The spectra of normal kidneys showed four main groups of resonances: 1) at 5.4–5.6 ppm, attributed to C6 of cholesterol and the unsaturated parts of the olefinic region of fatty acids; 2) at 4.7 ppm, attributed to the residual water signal; 3) at 3.2 ppm, attributed to trimethylamine moiety of choline metabolites; and 4) at 1.3 and 0.9 ppm, attributed to the methylenes and terminal methyls of lipids. The ratio of the signal at 5.4 ppm to that of 1.3 ppm was 19-fold lower in renal cell carcinomas than in healthy kidneys, tied P = 0.0003 Mann-Whitney U-test, suggesting a decrease in both free cholesterol and the degree of unsaturation of fatty acids in the malignant tissue. This metabolic shift is in agreement with previous ex vivo studies of human renal cell carcinoma. The ability to detect renal metabolic shifts noninvasively may improve the specificity of preoperative renal tissue characterization and may provide a new modality for treatment monitoring.

Localized in vivo human 1H MRS at very short echo times

A new point-resolved spectroscopy (PRESS) sequence was developed that allows localized human proton MR spectra to be acquired at echo times (TEs) of 10 ms or less. The method was implemented on a 4 Tesla Varian research console and a clinical 3 Tesla Siemens Trio scanner. Human brain spectra acquired in vivo from the prefrontal cortex at TE=8 ms showed improved signals from coupled resonances (such as glutamate, glutamine, and myo-inositol) compared to spectra acquired at TE=30 ms. These improvements should result in more accurate quantitation of these metabolites.

Measurement and correction of respiration-inducedB0 variations in breast1H MRS at 4 Tesla

Respiratory motion is well known to cause artifacts in magnetic resonance spectroscopy (MRS). In MRS of the breast, the dominant artifact is not due to motion of the breast itself, but rather it is produced by B0 field distortions associated with respiratory motion of tissues in the chest and abdomen. This susceptibility artifact has been reported to occur in the brain, but it is more apparent in the breast due to the anatomic proximity of the lungs. In the breast, these B0 distortions cause shot-to-shot frequency shifts, which vary an average of 24 Hz during a typical 1H MRS scan at 4 T. This variation can be corrected retrospectively by frequency shifting individual spectra prior to averaging. If not corrected, these shifts reduce spectral resolution and increase peak fitting errors. This work demonstrates the artifact, describes a method for correcting it, and evaluates its impact on quantitative spectroscopy. When the artifact is not corrected, quantification errors increase by an average of 28%, which dramatically impacts the ability to measure metabolite resonances at low signal-to-noise ratios.

Metabolite concentrations in human term placentae and their changes due to delayed collection after delivery

The present study was designed to quantify the major cellular metabolites in human placentae and their changes due to the confounding effect of time and subsequent hypoxia during sample collection using magnetic resonance spectroscopy ((1)H-and (31)P-MRS). The absolute placental concentrations of lactate, glucose, major amino acids and cellular volume/osmo-regulators, glutathione, high-energy phosphates, fatty acids, phospholipids, triglycerols, and cholesterol are reported. There were no spatial differences in metabolism or protein expression throughout the placenta. The most significant temporal changes, due to the collection time (from 1 to 25 min after delivery), were increased concentrations of lactate (r=0.996, statistically significant P< 0.01 after 11 min) and decreased concentration of glucose and ATP (r=-0.963 and -0.97, respectively, P< 0.01 after 11 min). The placental samples from the later collection groups (16-24 min) had also significantly lower level of NAD(+) (r=-0.95, P< 0.01). Only the latest collection group (21-24 min) had increased lipid peroxidation and changes in lipid metabolites (P< 0.01). We conclude that the optimal window for collecting placental tissue without incurring metabolic artifacts due to hypoxic conditions is within 9 min of placental delivery.

Proton magnetic resonance spectroscopy of the kidney in renal stone disease

Previous studies of renal stone disease (RSD) in Thailand indicated abnormal urinary aggregator and inhibitor composition among farmers with excessive sweat loss. Our aim was to compare the proton MR spectra obtained from the kidneys of 32 proven cases of RSD (aged 38 to 65 yrs) with nine age-matched normal control subjects. We used the STEAM sequence with TE = 15 ms and TR = 2,000 ms. The spectra at 3.25, 3.6 and 3.9 ppm were analyzed. The results showed a correlation between the three peaks (p < 0.001), however, there was no significant difference between the RSD group and the normal control subjects. We therefore concluded that there was no overloading of these osmolytes among the renal stone patients.

Magnetic resonance spectroscopy of renal and other retroperitoneal tumors

PURPOSE OF REVIEW

This paper focuses on demonstrating the power of magnetic resonance spectroscopy when used as a clinical tool in the medical sciences. The main goal is to illustrate the potential of proton magnetic resonance spectroscopy in renal oncology.

RECENT FINDINGS

The broad application of spectroscopy to the study of tumors in human brain, breast and prostate is well documented in the literature; however, the method is not yet widely utilized in the study of renal tumors. The analysis of the in-vitro high-resolution magnetic resonance spectroscopy of specimens removed during surgery shows promise for identifying biochemical profiles characteristic of benign renal tumors and renal cancers of different grades. In particular, resonances of creatine, acetate, choline compounds, and lipid components seem to vary between benign and malignant tissue.

SUMMARY

The identification of specific metabolites that differentiate benign from malignant tissue in vivo would spare the patient with a solid renal mass from unnecessary biopsies prior to surgery, or from surgery when a lesion would best be treated medically.

Implications of respiratory motion for the quantification of 2D MR spectroscopic imaging data in the abdomen

Magnetic resonance spectroscopic imaging (MRSI) studies in the abdomen or breast are acquired in the presence of respiratory motion. This modifies the point spread function (PSF) and hence the reconstructed spectra. We evaluated the quantitative effects of both periodic and aperiodic motion on spectra localized by MRSI. Artefactual signal changes, both the modification of native to a voxel and spurious signals arising elsewhere, depend primarily upon the motion amplitude relative to the voxel dimension. A similar dependence on motion amplitude was observed for simple harmonic motion (SHM), quasi-periodic motion and random displacements. No systematic dependence upon the period or initial phase of SHM or on the array size was found. There was also no significant variation with motion direction relative to the internal and external phase-encoding directions. In measured excursion ranges of 20 breast and abdominal tumours, 70% moved < or = 5 mm, while 30% moved 6-23 mm. The diaphragm and fatty tissues in the gut typically moved approximately 15-20 mm. While tumour/organ excursions less than half the voxel dimension do not substantially affect native signals, the bleeding in of strong lipid signals will be problematic in 1H studies. MRSI studies in the abdomen, even of relatively well-anchored tumours, are thus likely to benefit from the addition of respiratory triggering or other motion compensation strategies.

Motion correction and lipid suppression for 1H magnetic resonance spectroscopy

Spectral/spatial spin-echo pulses with asymmetric excitation profiles were incorporated into a PRESS-based localization sequence to provide lipid suppression while retaining a sufficient amount of water to allow for correction of motion-induced shot-to-shot phase variations. 1H magnetic resonance spectroscopy data were acquired at 1.5 Tesla from a motion phantom and in vivo from the human liver, kidney, and breast. The results demonstrated that lipids in the chemical shift stopband were completely suppressed and that full metabolite signal intensity was maintained after implementation of a regularization algorithm based on phasing the residual water signal. Liver and kidney spectra contained a large resonance at 3.2 ppm that was ascribed to trimethylammonium moieties (betaine plus choline) and a weaker signal at 3.7 ppm that may result from glycogen. A breast spectrum from a histologically proven invasive ductal carcinoma displayed a highly elevated choline signal (3.2 ppm) relative to that from a normal volunteer.

Cortical and medullary betaine-GPC modulated by osmolality independently of oxygen in the intact kidney

Renal osmolyte concentrations are reduced during reflow following ischemia. Osmolyte decreases may follow oxygen depletion or loss of extracellular osmolality in the medulla. Image-guided volume-localized magnetic resonance (MR) microspectroscopy was used to monitor regional osmolytes during hyposmotic shock and hypoxia in the intact rat kidney. Alternate spectra were acquired from 24-microl voxels in cortex and medulla of the isolated perfused kidney. There was a progressive decrease in the combined betaine-glycerophosphorylcholine (GPC) peak intensity of 21% in cortex and 35% in medulla of normoxic kidneys between 60 and 160 min after commencing perfusion. Hypoxia had no significant effect on the betaine-GPC peak intensity in cortex or medulla, despite a dramatic reduction in tubular sodium, potassium, and water reabsorption. The results suggest that cortical and medullary intracellular osmolyte concentrations depend on osmotically regulated channels that are insensitive to oxygen and dissociated from the oxygen-dependent parameters of renal function, the fractional excretion of sodium, the fractional excretion of potassium, and urine-to-plasma inulin concentration ratio.

In vivo 1H NMR spectroscopy of rat brain at 1 ms echo time

Using optimized, asymmetric radiofrequency (RF) pulses for slice selection, the authors demonstrate that stimulated echo acquisition mode (STEAM) localization with ultra-short echo time (1 ms) is possible. Water suppression was designed to minimize sensitivity to B1 inhomogeneity using a combination of 7 variable power RF pulses with optimized relaxation delays (VAPOR). Residual water signal was well below the level of most observable metabolites. Contamination by the signals arising from outside the volume of interest was minimized by outer volume saturation using a series of hyperbolic secant RF pulses, resulting in a sharp volume definition. In conjunction with FASTMAP shimming (Gruetter Magn Reson Med 1993;29: 804-811), the short echo time of 1 msec resulted in highly resolved in vivo 1H nuclear magnetic resonance spectra. In rat brain the water linewidths of 11-13 Hz and metabolite singlet linewidths of 8-10 Hz were measured in 65 microl volumes. Very broad intense signals (delta v(1/2) > 1 kHz), as expected from membranes, for example, were not observed, suggesting that their proton T2 are well below 1 msec. The entire chemical shift range of 1H spectrum was observable, including resolved resonances from alanine, aspartate, choline group, creatine, GABA, glucose, glutamate, glutamine, myo-inositol, lactate, N-acetylaspartate, N-acetylaspartylglutamate, phosphocreatine, and taurine. At 9.4 T, peaks close to the water were observed, including the H-1 of alpha-D-glucose at 5.23 ppm and a tentative H-1 resonance of glycogen at 5.35 ppm.

Feasibility study of lactate imaging of head and neck tumors

A proton spectroscopic imaging sequence was used to investigate the feasibility of lactate imaging in head and neck tumors. The sequence employs a two-shot lactate editing method with inversion recovery for additional lipid suppression, and a restricted field of view to suppress motion artifacts. Variations in acquisition parameters and two different receive coils were investigated on twelve patients. Elevated lactate was detected in three patients, no lactate was observed in seven patients, and two studies were inconclusive because of severe motion or inhomogeneity artifacts. Best results were obtained with an anterior/posterior neck coil at a 288 ms echo time (TE).

Soy protein modification of rat polycystic kidney disease

We undertook a study to determine whether soy protein feeding would ameliorate renal injury in the Han:SPRD-cy rat model of polycystic kidney disease (PKD). Male offspring of Han:SPRD-cy heterozygotes received isocaloric diets based on 20% casein or 20% heat-treated soy protein at weaning ad libitum for 8 wk. Soy-fed animals demonstrated lower serum creatinine (66 vs. 125 mumol/l; P = 0.002), lower urinary ammonium excretion (0.080 vs. 0.173 mmol/kg; P = 0.01), reduced renal cysts (0.98 vs. 4.92 ml/kg body wt, P < 0.0001), renal fibrosis (0.79 vs. 1.4 ml/kg; P = 0.016), macrophage infiltration, renal tubular cell proliferation, and apoptosis. Proton nuclear magnetic resonance (1H-NMR) studies of urine demonstrated that soy diet was associated with increased losses of citric acid cycle organic anions. 1H-NMR of perchloric acid-extracted tissue found that levels of succinate were not depleted in soy-fed animals, despite increased urinary losses. Soy-fed animals had marked elevation of tissue betaine (P < 0.001), with reduced taurine and cholines, compared with casein-fed animals (P < 0.001). Soy feeding dramatically reduces both tubular and interstitial pathology in the Han:SPRD-cy rat model of PKD, through mechanisms that remain to be determined.

1H MRS of liver and brain in a patient with AL amyloidosis

A patient with AL (amyloid light chain) amyloidosis was investigated in liver and brain by localized magnetic resonance spectroscopy. Liver spectra of the patient were characterized by small line widths, a striking increase of trimethylammonium compounds, and the presence of a further resonance at 3.8 ppm. None of the healthy control subjects showed trimethylammonium levels of comparable intensity. In the brain, the intensities of amino acids was relatively increased in white matter, whereas the concentration of choline, creatine, and N-acetyl-aspartate were reduced.

Regional proton nuclear magnetic resonance spectroscopy differentiates cortex and medulla in the isolated perfused rat kidney

Volume-localized proton nuclear magnetic resonance spectroscopy was used as an assay of regional biochemistry in the isolated perfused rat kidney. This model eliminated artifacts caused by respiratory and cardiac motion experienced in vivo. Immersion of the kidney under its venous effluent reduced the susceptibility artifacts evoked by tissue-air interfaces. The rapid acquisition with relaxation enhancement imaging sequence was used for scout imaging. This gave excellent spatial resolution of the cortex, outer medulla, and inner medulla. Spectra were then acquired in 10 minutes using the volume-selective multipulse spectroscopy sequence from voxels with a volume of approximately 24 microL located within the cortical or medullary regions. Spectral peaks were assigned by the addition of known compounds to the perfusion medium and by comparison with spectra of protein-free extracts of cortex and medulla. The medullary region spectra were characterized by signals from the osmolytes betaine, glycerophosphorylcholine, and inositol. The spectra from the cortex were more complex and contained lesser contributions from osmolytes.

On the use of two-dimensional-J NMR measurements for in vivo proton MRS: measurement of homonuclear decoupled spectra without the need for short echo times

The potential of two-dimensional (2D)-J NMR for in vivo proton MRS is examined. Single voxel measurements on the rat brain were performed at 4.7 T using point-resolved spectrocopy localization with a voxel size of 64 microliter and total measuring times of 10-15 min. It is shown that a series of measurements with only 16 or fewer different echo times (TE) enables good signal localization in the f1 axis corresponding to the coupling patterns. For data evaluation, the 2D-J NMR spectrum as well as cross-sections at given f1 values and projections onto the f2 axis are used. A comparison between cross-section spectra taken at different f1 values may help to solve problems of peak assignment. The projection of the 2D magnitude spectrum onto the f2 axis corresponds to a homonuclear decoupled 1D proton spectrum. Because the T2 relaxation times of several coupled resonances (e.g., myo-inositol and glutamate) are rather long, only minor losses in the quality of the projection spectra occur if the measurements with short TE (< or = 50 ms) are not used for data processing. Thus, homonuclear decoupled proton spectra detecting uncoupled and several coupled resonances can be measured with high quality in vivo, even on MR systems that are not equipped with actively shielded gradients, prohibiting data acquisition with TEs of 50 ms or less.

In vivo localized proton NMR spectroscopy of thiamine-deficient rat brain

Thiamine deficiency (TD) in rats produces lesions similar to those found in humans suffering from Wernicke's encephalopathy, an organic mental disorder associated with alcoholism. Male Sprague-Dawley rats (n = 29) were deprived of thiamine via a regimen of thiamine-deficient chow and daily intraperitoneal injections of the thiamine antagonist pyrithiamine hydrobromide. Spectra were obtained by using the STEAM sequence. No significant change occurred in the ratio of Cr/NAA, while the ratio of Cho/NAA declined significantly (60 +/- 11%) on Day 14. Eleven rats received intraperitoneal injections of thiamine hydrochloride at the end of 12 days, and dose-dependent recovery in Cho/NAA was observed.