In vivo MRS study of intraventricular tumors

Purpose:

To evaluate the role of MR spectroscopy (MRS) as a noninvasive tool for characterization of intraventricular brain tumors.

Materials and Methods:

Twenty‐three intraventricular tumors, all histologically classified (11 central neurocytomas [CNC], 5 meningiomas [Men], other intraventricular tumors [OIV], including 2 anaplastic gliomas [WHO III], 1 tumor each of rhabdoid tumor, glioneuronal hamartoma, GBM, hemangiopericytoma, and subependymoma II), were studied by MRS before surgery using a point‐resolved spectroscopic sequence (PRESS).

Results:

Statistically significant differences (P < 0.03) were observed for NAA/Cr and Cho/Cr between CNCs and OIV. A significant difference (P < 0.01) was observed in the presence of Gly between the CNCs and meningiomas, and CNCs and OIV. In addition, the presence of Ala was also significantly different (P < 0.01) between OIV and meningiomas, and OIV and CNCs.

Conclusion:

The present study has shown that MRS can be useful in characterizing intraventricular tumor and distinguishing CNCs from meningiomas and other intraventricular tumors. Prior information about intraventricular tumor types could be useful to clinicians in planning treatment and resection strategy. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

In vivo proton magnetic resonance spectroscopy of large focal hepatic lesions and metabolite change of hepatocellular carcinoma before and after transcatheter arterial chemoembolization using 3.0-T MR scanner

PURPOSE: To investigate the value of in vivo proton magnetic resonance spectroscopy (MRS) in the assessment of large focal hepatic lesions and to measure the metabolite change of hepatocellular carcinoma (HCC) after transcatheter arterial chemoembolization (TACE) using 3.0-T scanner. MATERIALS AND METHODS: In this prospective study, 43 consecutive patients with large (not less than 3 cm in diameter) hepatic tumors and eight normal volunteer were included. MRS of the lesions in addition to uninvolved liver parenchyma was carried out using a whole-body 3.0-T scanner. Among the patients with proven HCC, eight lesions were evaluated before and two to five days after TACE. The choline-to-lipid (cho/lipid) ratio was measured by dividing the peak area of choline at 3.2 ppm by the peak area of lipid at 1.3 ppm. The sensitivity and specificity profiles of MRS in the diagnosis of malignant hepatic tumors were determined by plotting empirical receiver operating characteristic (ROC) curve. The mean cho/lipid ratios in different groups before and after TACE were also measured. RESULTS: The technical success rate for MRS was 90% (53/59). The ROC curve showed proton MRS has moderate discriminating ability in diagnosing malignant hepatic tumors, although the sensitivity was less than 50% while 1-specificity was less than 20%. The area under the curve was 0.71 (P < 0.05). The mean +/- 1 standard error (SE) of cho/lipid ratios for uninvolved liver (N = 8), benign tumor (N = 8), and malignant tumor (N = 21; 19 HCC, one angiosarcoma, and one lymphoma) were 0.06 +/- 0.02, 0.02 +/- 0.02, and 0.17 +/- 0.05, respectively. A significantly statistical difference (ANOVA planned contrast test, P = 0.01 and Games-Howell procedure, P = 0.03) was achieved in the mean cho/lipid ratio between malignant and benign tumors. The mean cho/lipid ratios were significantly decreased from 0.23 +/- 0.11 before TACE to 0.01 +/- 0.00 after the treatment (t = 2.01, P < 0.05, one-tail paired t-test; z = -2.37, P < 0.05, Wilcoxon Signed Ranks Test). CONCLUSION: In vivo proton MRS is technically feasible for the evaluation of focal hepatic lesions. The technique has potential in the detection of early metabolite change in malignant liver tumors after TACE but limitation still exists in clear differentiation between normal liver and benign and malignant tumor.     

Preliminary observations and diagnostic value of lipid peak in ovarian thecomas/fibrothecomas using in vivo proton MR spectroscopy at 3T

Purpose:

To retrospectively evaluate the significance of lipid peak in in vivo proton magnetic resonance (MR) spectroscopy for the diagnosis of ovarian thecomas/fibrothecomas in patients with solid gynecologic tumors exhibiting totally or partially low signal intensity on T2‐weighted images.

Materials and Methods:

MR spectroscopy was performed in patients with pathologically diagnosed gynecologic tumors at 3T MRI. Single‐voxel MR spectroscopy data were collected from a single square volume of interest that encompassed the gynecologic masses. The lipid concentration level was classified into three classes (high; low; none).

Results:

A total of 20 gynecologic tumors in 20 patients were evaluated in this study. High lipid peak was observed in all seven thecomas/fibrothecomas, whereas low lipid peak was observed in only one fibroma in 13 nonthecomatous tumors (six benign ovarian tumors and seven subserosal uterine leiomyomas). The presence of lipid peak for the diagnosis of thecomas/fibrothecomas had a sensitivity of 100%, specificity of 92%, positive predictive value of 88%, and negative predictive value of 100%.

Conclusion:

The high lipid peak reflecting abundant intracellular lipid contents is considered a specific metabolite concentration for thecomas/fibrothecomas. Demonstration of high lipid peak may contribute to the diagnosis of thecomas/fibrothecomas in distinguishing from other benign ovarian fibrous tumors or subserosal uterine leiomyomas. J. Magn. Reson. Imaging 2012;36:907–911. © 2012 Wiley Periodicals, Inc.     

Detection of elevated glutathione in meningiomas by quantitative in vivo 1H MRS.

Glutathione has major roles in removing free radicals and toxins from normal tissues, but its presence in tumor cells hinders the effectiveness of many anticancer therapies. Analysis of short echo time brain tumor (1)H spectra at 1.5 T using a linear combination of metabolite spectra (LCModel) suggested a significant contribution of glutathione to meningioma spectra. By in vivo MRS (TE = 30 ms, TR = 2020 ms), reduced glutathione was found to be significantly elevated in meningiomas (3.3 +/- 1.5 mM, Mann Whitney, P < 0.005) compared to normal white matter (1.2 +/- 0.15 mM) and low-grade gliomas (1.0 +/- 0.26 mM), in agreement with published histofluorescence studies of tumor biopsies. Glx concentrations were also found to be elevated in meningiomas compared to astrocytomas or normal white matter, indicative of metabolic differences. The ability to noninvasively quantify reduced glutathione in vivo may aid selection of treatment therapies and also provide an indication of tumor aggressiveness.     

Assessment of glutamate and glutamine contribution to in vivo N-acetylaspartate quantification in human brain by (1)H-magnetic resonance spectroscopy.

N-Acetylaspartate (NAA) is one of the most important metabolites detectable by brain (1)H-MRS being considered an index of neuronal integrity. At the low magnetic field used in most clinical settings beta,gamma-glutamate/glutamine (Glx) resonances are very close and partially overlap the methyl-NAA resonance interfering with NAA quantification especially at low TE and in the presence of increased Glx signals. NAA overestimation due to Glx on a set of model solutions containing NAA, glutamate, and glutamine in variable amounts was evaluated and the result tested in vivo in six healthy controls and five age- and sex-matched patients with hepatic encephalopathy (HE), the latter having an increased Glx content. A method to assess in vivo the NAA overestimation caused by Glx is proposed. A perfect match was obtained between the assessment of Glx contamination on the NAA of healthy controls and that obtained on the model solutions. However, a substantial difference in NAA overestimation was found between controls and HE patients that cannot be explained by our model. An interpretative hypothesis is provided.     

磁共振波谱技术在肝脏肿瘤中的研究现状及发展趋势

磁共振波谱(magnatic resonance spectroscopy,MRS)能显示病理组织和正常组织之间不同代谢的差异,能在分子水平上反应病理情况,是目前对人体唯一无创的研究活体组织器官代谢、生化变化及化合物定量分析的方法。随着MRS技术日臻成熟,MRS在临床肿瘤诊断方面起着越来越重要的作用。本文就MRS的基本原理及其在肝脏肿瘤中的应用作一综述。     

Detection of an antioxidant profile in the human brain in vivo via double editing with MEGA-PRESS.

Vitamin C (ascorbate) and glutathione (GSH) are the two most concentrated non-enzymatic antioxidants in the human brain. Double editing with (DEW) MEGA-PRESS at 4T was designed in this study to measure both antioxidants in the same amount of time previously required to measure one. In the occipital lobe of four human subjects, resolved ascorbate (Asc) and GSH resonances were detected repeatedly and simultaneously using DEW MEGA-PRESS. The Asc and GSH concentrations measured using LCModel analysis of DEW MEGA-PRESS spectra were 0.8 +/- 0.1 and 1.0 +/- 0.1 micromol/g (mean +/- SD), with average Cramer-Rao lower bounds (CRLB) of 10% and 7%, respectively. Aside from the effects of J-modulation at a common echo time (TE), double editing did not compromise sensitivity. To determine the extent to which the oxidized forms of Asc and GSH contribute to DEW MEGA-PRESS spectra in vivo, chemical shifts and coupling constants for dehydroascorbate (DHA) and oxidized glutathione (GSSG) were measured at physiologic pH and temperature. DHA does not contribute to the 3.73 ppm DEW MEGA-PRESS Asc resonance. GSSG contributions to the DEW MEGA-PRESS GSH resonance (3.0 ppm) are negligible under physiologic conditions, and would be evidenced by a distinct GSSG resonance (3.3 ppm) at exceptionally high concentrations.     

中枢神经细胞瘤的CT、MRI及1H-MRS诊断(附7例报告并文献综述)

目的探讨中枢神经细胞瘤的CT、MRI及1H-MRS诊断特点.方法回顾性分析经手术病理证实的中枢神经细胞瘤7例,结合文献对其影像学特点进行复习.2例行CT、MRI及MRS检查,2例仅行MRI检查,3例仅行CT检查.结果肿瘤均位于侧脑室,侧脑室示不同程度的脑积水;CT表现为混杂密度,内有低密度囊变坏死区,并可见点条状及团块状钙化灶,增强扫描病灶均呈不均一强化.MRI呈等低T1、等高T2混杂信号;增强扫描均呈不均一强化.在体1H-MRS表现为Cho峰明显升高,NAA明显降低.结论青年人位于脑室内尤其是透明隔区的肿瘤,应考虑中枢神经细胞瘤的可能.CT、MRI及1H-MRS有助于诊断.     

In vivo spatially localized high resolution 1H MRS via intermolecular single‐quantum coherence of rat brain at 7 T

Purpose:

To compare the conventional localized point‐resolved spectroscopy (PRESS) with localized 2D intermolecular single‐quantum coherence (iSQC) magnetic resonance spectroscopy (MRS) and obtain in vivo MRS spectrum of rat brain using the latter technique.

Materials and Methods:

A brain phantom, an intact pig brain tissue, and mature Sprague–Dawley rat were studied by PRESS, Nano magic‐angle spinning spectroscopy, and iSQC MRS.

Results:

Using PRESS, high‐resolution MRS can be obtained from the brain phantom and pig brain tissue with a small voxel in a relatively homogeneous field. When a large voxel is selected, the field homogeneity is distinctly reduced. No useful information is obtained from the PRESS spectra. However, using the iSQC MRS, high‐resolution spectra can be obtained from the two samples with a relatively large voxel. In the same way, an iSQC MRS spectrum can be obtained from a relatively large voxel of in vivo rat brain with a comparable resolution to the PRESS spectrum with a small voxel.

Conclusion:

Compared to PRESS, the iSQC MRS may be more feasible and promising for detection of strongly structured tissues with relatively large voxels. J. Magn. Reson. Imaging 2013;37:359–364. © 2012 Wiley Periodicals, Inc.     

Study of the features of proton MR spectroscopy (1H‐MRS) on amyotrophic lateral sclerosis

Purpose:

To study the features of proton magnetic resonance spectroscopy (¹H‐MRS) on amyotrophic lateral sclerosis (ALS) and its relation with clinical scale.

Materials and Methods:

Fifteen patients with definite or probable ALS and 15 age‐ and gender‐matched normal controls were enrolled. ¹H‐MRS was performed on a 3.0 Tesla GE imaging system (GE Healthcare, Milwaukee, WI). TE‐averaged Point Resolved Selective Spectroscopy was used. N‐acetylaspartate (NAA), creatine (Cr), Glu, and Glx (glutamate + glutamine) values of the motor cortex and posterior limb of internal capsule were acquired. The t‐test was used to compare differences between groups, and the correlations between the above values and clinical scale were analyzed.

Results:

The motor area and posterior limb of the internal capsule of ALS patients had lower NAA/Cr (1.91 ± 0.34, 1.53 ± 0.17) compared with normal subjects (2.23 ± 0.33, 1.66 ± 0.07), and the differences between groups were statistically significant (P < 0.01, 0.01). ALS patients had higher Glu/Cr (0.34 ± 0.05, 0.29 ± 0.06) and Glx/Cr (0.40 ± 0.04, 0.33 ± 0.06) compared with normal subjects (0.30 ± 0.03, 0.25 ± 0.04) and (0.32 ± 0.05, 0.26 ± 0.03), and the differences between groups were statistically significant (P < 0.01, 0.01). The Norris scale was negatively correlated with Glx/Cr of primary motor cortex by lineal correlation analysis (r = −0.75), and this correlation had statistical significance (F = 16.60; P = 0.001).

Conclusion:

Neuronal loss and Glu+Gln increase can be detected by using proton MRS in ALS patients. ¹H‐MRS is an useful tool in reflecting the characteristic changes of metabolite in ALS. J. Magn. Reson. Imaging 2010; 31: 457–465. © 2010 Wiley‐Liss, Inc.

     

Enhanced neurochemical profile of the rat brain using in vivo 1H NMR spectroscopy at 16.4 T

Single voxel magnetic resonance spectroscopy with ultrashort echo time was implemented at 16.4 T to enhance the neurochemical profile of the rat brain in vivo. A TE of 1.7 msec was achieved by sequence optimization and by using short‐duration asymmetric pulses. Macromolecular signal components were parameterized individually and included in the quantitative analysis, replacing the use of a metabolite‐nulled spectrum. Because of the high spectral dispersion, several signals close to the water line could be detected, and adjacent peaks could be resolved. All 20 metabolites detected in this study were quantified with Cramér‐Rao lower bounds below 20%, implying reliable quantification accuracy. The signal of acetate was detected for the first time in rat brain in vivo with Cramér‐Rao lower bounds of 16% and a concentration of 0.52 μmol/g. The absolute concentrations of most metabolites showed close agreement with values previously measured using in vivo ¹H NMR spectroscopy and in vitro biochemical assay. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Interindividual,repositioning, and time‐of‐day effects on single voxel proton MR spectroscopy of the anterior cingulate cortex

Purpose:

To measure interindividual, repositioning, and time‐of‐day effects of single voxel PRESS (P oint RES olved S pectroscopy) proton magnetic resonance spectroscopy (¹H‐MRS) acquisition of the anterior cingulate cortex (AC) in healthy human subjects.

Materials and Methods:

AC ¹H‐MRS measurements were performed in 15 healthy adult volunteers using a short echo PRESS sequence (GE Healthcare 3 Tesla, TE/TR = 30/2500 ms, 192 acquisitions, 6 cm³ voxels). For each individual, a total of eight spectra were obtained during two identical scanning sessions separated by 3.5 h. In each, two consecutive AC spectra were acquired. After the first two scans, the subject left the scanner, then immediately returned for repositioning and acquisition of two more consecutive spectra. The subject then left the imaging centre to return 3.5 h later for a repeated procedure. Spectroscopic postprocessing was done using LCmodel. Interindividual, repositioning and time‐of‐day effects were measured using restricted maximum likelihood (REML) models of variance components analysis, where response variables were levels of creatine/phosphocreatine (Cr), N‐acetyl‐aspartate (NAA), myo‐inositol (mI), choline (Cho), and the glutamate‐glutamine complex (Glx).

Results:

Interindividual effects were markedly higher than time‐of‐day and repositioning effects for all metabolites.

Conclusion:

Our findings show that ¹H‐MRS measurements of the AC are sensitive to interindividual differences, while time of day and repositioning are markedly less important. J. Magn. Reson. Imaging 2010;32:276–282. © 2010 Wiley‐Liss, Inc.     

Quantitative proton MR spectroscopic imaging of the mesial temporal lobe

PURPOSE: To evaluate variations in regional metabolite concentrations in the anterior mesial temporal lobe (ATL), and compare metabolite concentrations between the allocortex and neocortex using quantitative proton MR spectroscopic imaging (MRSI). MATERIALS AND METHODS: Metabolite concentrations and ratios were measured in 20 healthy young subjects with the use of a multislice spin-echo (SE) sequence (TR/TE=2300/280 msec). Quantitation of MRSI data was performed by means of the phantom replacement methodology. RESULTS: The highest choline (Cho) concentration (4.1 +/- 1.1 mM) was found in the ATL (P=0.0015 compared to the middle mesial temporal lobe (MTL), and P=0.0008 compared to the posterior mesial temporal lobe (PTL)). The ATL also had a higher Cho/creatine (Cr) ratio and a lower N-acetyl aspartate (NAA)/Cho ratio compared to other examined regions (P <0.0001 and P < or = 0.052, respectively). In the allocortical regions, the average Cho concentration (3.5 +/- 0.8 mM) was 68% higher, and the NAA concentration (9.5 +/- 1.8 mM) was 13% lower than in the neocortex (P <10(-6) and P <0.008, respectively). Cho/Cr was 64% higher, NAA/Cr 14% lower, and NAA/Cho 47% lower in the allocortex than in the neocortex (P <10(-6), P=0.013, and P <10(-6), respectively). CONCLUSION: The mesial temporal lobe shows high levels of Cho, which presumably reflect a difference in cellular composition between the allocortex and neocortex. Regional metabolite variations must be considered when pathological conditions involving the mesial temporal lobe are evaluated.     

In vivo differentiation of N-acetyl aspartyl glutamate from N-acetyl aspartate at 3 Tesla.

A method is described that allows the in vivo differentiation of N-acetyl aspartate (NAA) from N-acetyl aspartyl glutamate (NAAG) by in vivo MR spectroscopy (MRS) at 3 Tesla (3T). The method, which is based on MEGA-point-resolved spectroscopy (PRESS) editing, selectively targets the aspartyl spin system of one species while deliberately removing the other species from the spectrum. This allows quantitative measurements of NAA and NAAG without the need for fitting of unresolved peaks. White matter concentrations of NAA (6.7 +/- 0.3 mM) and NAAG (2.2 +/- 0.3 mM) were measured in 10 healthy volunteers to demonstrate the method.     

Late stimulation of the sphenopalatine‐ganglion in ischemic rats: Improvement in N‐acetyl‐aspartate levels and diffusion weighted imaging characteristics as seen by MR

Purpose:

To assess, by MR spectroscopy (MRS) and diffusion weighted imaging (DWI), the ability of electrical stimulation of the sphenopalatine ganglion (SPG) to augment stroke recovery in transient middle cerebral artery occluded (t‐MCAO) rats, when treatment is started 18 ± 2 h post‐occlusion.

Materials and Methods:

¹H‐MRS imaging (¹H‐MRSI) and DWI were used to evaluate ischemic brain tissue after SPG stimulation in rats subjected to 2 h of t‐MCAO. Rats were examined by ¹H‐MRSI, DWI, and behavioral tests at 16 ± 2 h, 8 days, and 28 days post‐MCAO.

Results:

N‐Acetyl‐aspartate (NAA) levels of the stimulated and control rats were the same 16 ± 2 h post‐MCAO (0.52 ± 0.03, 0.54 ± 0.03). At 28 days post‐occlusion, NAA levels were significantly higher in the treated group (0.60 ± 0.04) compared with those of the untreated animals (0.50 ± 0.04; P < 0.05). This effect was more pronounced for regions with low NAA values (0.16 ± 0.03) that changed to 0.32 ± 0.03 (P = 0.04) for the treated group and to 0.10 ± 0.03 (P = 0.20) for the controls. DWI data showed better ischemic tissue condition for the treated rats, but the measured parameters showed only a trend of improvement. The MR results were corroborated by behavioral examinations.

Conclusion:

Our findings suggest that SPG stimulation may ameliorate MR tissue characteristics following t‐MCAO even if treatment is started 18 h post‐occlusion. J. Magn. Reson. Imaging 2010;31:1355–1363. © 2010 Wiley‐Liss, Inc.     

In vivo tumor lactate relaxation measurements by selective multiple‐quantum‐coherence (Sel‐MQC) transfer

The frequency‐selective multiple‐quantum‐coherence (Sel‐MQC) lactate (Lac) filter offers complete lipid and water suppression in a single scan for robust in vivo detection of tumor Lac, even in the presence of abundant lipids. Conversion of the detected signal into accurate tissue concentrations of Lac requires knowledge of in vivo Lac T₁ and T₂ relaxation times. This work reports modifications to the Sel‐MQC pulse sequence, T₁‐ and T₂‐Sel‐MQC, that facilitate relaxation measurements of Lac. The T₁‐Sel‐MQC sequence combines an inversion prepulse with the Sel‐MQC filter. The T₂‐Sel‐MQC sequence incorporates a CH₃‐selective 180° pulse during the MQ preparation period to overcome the J‐modulation effects and allow the insertion of variable echo delays. The performance of these sequences was evaluated with the use of phantoms and subcutaneous murine tumor models in vivo. The present approach will allow investigators to correct for the relaxation‐induced Lac signal loss in Sel‐MQC experiments for the quantitative mapping of in vivo tumor Lac distribution. Magn Reson Med 52:902–906, 2004. © 2004 Wiley‐Liss, Inc.     

Limits on activation-induced temperature and metabolic changes in the human primary visual cortex.

Changes in cerebral blood flow (CBF) and metabolism are now widely used to map and quantify neural activity, although the underlying mechanism for these changes is still incompletely understood. Magnetic resonance spectroscopy (MRS) at 3T, synchronized with a 32-s block design visual stimulation paradigm, was employed to investigate activation-induced changes in temperature and metabolism in the human primary visual cortex. A marginally significant increase in the local temperature of the visual cortex was found (0.1 degrees C, P = 0.09), excluding the possibility of a temperature decrease (95% confidence interval (CI) = 0.0-0.2 degrees C), which was previously suggested. A comparison with models of thermal equilibrium in the presence of blood flow suggests that an increase in heat production during activation, greater than or at least equal to that produced by the complete oxidative metabolism of the elevated glucose (Glc) utilization accompanying activation, would be required to offset the cooling effects of the increased blood flow. The total pools of glutamate (Glu), glutamine (Gln), myo-Inositol (mI), N-acetylaspartate (NAA), choline (Cho), and lactate (Lac) were not significantly affected by activation. Limits on Lac concentration changes were too weak to constrain theories of the metabolic use of elevated Glc consumption during stimulation, and emphasize the challenges of measuring even large Lac changes accompanying stimulation.