Low-grade glioma: correlation of short echo time 1H-MR spectroscopy with 23Na MR imaging

BACKGROUND AND PURPOSE: There is considerable variability in the clinical behavior and treatment response of low-grade (WHO grade II) gliomas. The purpose of this work was to characterize the metabolic profile of low-grade gliomas by using short echo time ¹H-MR spectroscopy and to correlate metabolite levels with MR imaging-measured sodium (²³Na) signal intensity. Based on previous studies, we hypothesized decreased N-acetylaspartate (NAA) and increased myo-inositol (mIns), choline (Cho), glutamate (Glu), and ²³Na signal intensity in glioma tissue.MATERIALS AND METHODS: Institutional ethics committee approval and informed consent were obtained for all of the subjects. Proton (¹H-MR) spectroscopy (TR/TE = 2200/46 ms) and sodium (²³Na) MR imaging were performed at 4T in 13 subjects (6 women and 7 men; mean age, 44 years) with suspected low-grade glioma. Absolute metabolite levels were quantified, and relative ²³Na levels were measured in low-grade glioma and compared with the contralateral side in the same patients. Two-sided Student t tests were used to test for statistical significance.RESULTS: Significant decreases were observed for NAA (P < .001) and Glu (P = .004), and increases were observed for mIns (P = .003), Cho (P = .025), and sodium signal intensity (P < .001) in low-grade glioma tissue. Significant correlations (r² > 0.25) were observed between NAA and Glu (P < .05) and between NAA and mIns (P < .01). Significant correlations were also observed between ²³Na signal intensity and NAA (P < .01) and between ²³Na signal intensity and Glu (P < .01). Ratios of NAA/mIns, NAA/²³Na, and NAA/Cho were altered in glioma tissue (P < .001); however based on the t statistic, NAA/²³Na (t = 9.6) was the most significant, followed by NAA/mIns (t = 6.1), and NAA/Cho (t = 5.0).CONCLUSION: Although Glu concentration is reduced and mIns concentration is elevated in low-grade glioma tissue, the NAA/²³Na ratio was the most sensitive indicator of pathologic tissue.

Low-grade (WHO grade II) gliomas, including astrocytoma, oligodendroglioma, and mixed glioma (oligoastrocytoma), account for 10%–20% of primary brain tumors in adults.¹ Although such tumors are more indolent than high-grade gliomas, there is considerable variability in their clinical behavior.² They are capable of malignant transformation and, ultimately, are almost universally fatal. Pathologically, these tumors are diffuse and infiltrative but lack such anaplastic features as necrosis, endothelial proliferation, and mitotic activity.³Tailoring treatment to the individual patient requires a better understanding of the factors that account for the variability in tumor behavior.^{4, 5} Currently, neither the appearance of a low-grade glioma on conventional MR imaging nor tumor pathology can completely predict future tumor behavior or response to treatment. Metabolic profiling of these tumors with MR spectroscopy has the potential to improve our ability to predict the biological behavior and treatment response of low-grade gliomas and to better delineate tumor boundaries. Previous in vitro and in vivo MR spectroscopy studies have identified metabolic markers that help noninvasively discriminate tumor type,^6–8 aid in radiation treatment planning,⁹ or predict survival.¹⁰ Most studies have used long echotime spectroscopy acquisitions (TE ≥ 130 ms), limiting tumor metabolite characterization to the dominant peaks in the ¹H spectrum: N-acetylaspartate (NAA; a putative marker of neuronal viability), total creatine (Cr; involved in energy metabolism), choline-containing compounds (Cho; associated with membrane breakdown/synthesis), and lactate (associated with anaerobic glycolysis). Typically, low-grade glioma is characterized by reduced NAA due to reduced neuronal attenuation, reduced Cr due to a hypermetabolic state, and increased Cho, reflecting increased membrane turnover.^{6, 8} The metabolites glutamate (Glu) and myo-inositol (mIns), measurable by shorter echotime ¹H-MR spectroscopy, may provide additional information about the pathologic state of the neoplasm. A previous study¹¹ has demonstrated that highly malignant tumors may release excess Glu to kill surrounding tissue and promote tumor growth, and increased Glu plus glutamine (Gln) has been measured previously in oligodendroglioma by ¹H-MR spectroscopy.¹² mIns activation of protein kinase C¹³ has also been associated with tumor malignancy. The limited use of short echotime ¹H-MR spectroscopy is due mainly to the difficulty in quantifying metabolites with complicated j-modulated spectral line shapes and the uncertainty introduced by less well-characterized macromolecule resonances beneath the metabolites of interest.Tumors may also be characterized by the local concentration of total sodium, which is sensitive to changes in the tumor microstructure.^14–16 For example, neoplastic cell proliferation and packing, cell death, and necrosis expand the extracellular space in tumors. A defective blood-brain barrier in tumors also permits water, electrolytes, and proteins to enter the extracellular space leading to vasogenic edema. Because both intracellular and extracellular sodium levels may be increased in tumors, ²³Na MR imaging represents a potentially sensitive and noninvasive means of monitoring tissue sodium content related to cancer pathology.^15–18The purpose of this study was to prospectively characterize the metabolic profile of low-grade gliomas by using ¹H-MR spectroscopy and to correlate metabolite levels with MR imaging-measured sodium signal intensity. Based on previous studies, it was hypothesized that levels of NAA would be reduced, and levels of Cho, mIns, Glu, and ²³Na signal intensity would be increased in low-grade glioma compared with normal tissue.     

Quantitative short echo time 1H-MR spectroscopy of untreated pediatric brain tumors: preoperative diagnosis and characterization

PURPOSE: Our aims were to evaluate the metabolic profiles of pediatric brain tumors with short echo time (TE) MR spectroscopy and absolute quantitation of metabolite concentrations (in mmol/kg of tissue) and to describe metabolic features that distinguish individual tumor types and that may help to improve preoperative diagnosis of specific tumors. METHODS: MR imaging examinations of 60 patients with untreated brain tumors (14 medulloblastomas, 5 anaplastic astrocytomas, 3 low-grade astrocytomas, 17 pilocytic astrocytomas, 4 anaplastic ependymomas, 5 ependymomas, 3 choroid plexus papillomas, 3 choroid plexus carcinomas, and 6 pineal germinomas) were reviewed. Single-voxel proton MR spectroscopy with a TE of 35 ms was performed and absolute metabolite concentrations were determined by using fully automated quantitation. RESULTS: Taurine (Tau) was significantly elevated in medulloblastomas (P < .00001) compared with all other tumors pooled (All Other). Tau was also observed consistently, at lower concentration, in pineal germinomas. Creatine (Cr) was significantly reduced in pilocytic astrocytomas, distinguishing them from All Other (P < .000001). The MR spectra of choroid plexus papillomas exhibited low Cr (P < .01) concentrations; however, myoinositol was elevated (P < .01) and total choline (tCho) (P < .0001) was reduced relative to All Other. Choroid plexus carcinomas had low Cr (P < .01 versus All Other) and the lowest Cr/tCho ratio (P < .0001 versus All Other) among all tumors studied. Guanidinoacetate was reduced in low-grade astrocytomas and anaplastic astrocytomas (P < .00001) versus All Other, whereas ependymoma and anaplastic ependymomas exhibited particularly low N-acetylaspartate (P < .00001 versus All Other). CONCLUSION: Quantitative proton MR spectroscopy reveals features of pediatric brain tumors that are likely to improve preoperative diagnoses.     

Differentiation of metastases from high-grade gliomas using short echo time 1H spectroscopy

PURPOSE: To determine if short echo time (TE) (1)H magnetic resonance spectroscopy (MRS) can distinguish between intracranial metastases and glioblastomas. MATERIALS AND METHODS: TE 30-msec spectra were acquired (1.5 T) from voxels entirely within tumors from 23 glioblastoma patients and 24 metastases patients (3 breast carcinomas, 1 bladder carcinoma, 8 lung carcinomas, 3 probable lung carcinomas, 6 melanomas, 1 stomach carcinoma, and 2 undetermined). Spectra were analyzed quantitatively (LCModel) to determine metabolite, lipid, and macromolecule concentrations. All tumors were previously untreated and classified histopathologically. RESULTS: The lipid peak area (LPA) ratio (total peak area at ca. delta1.3 to that at ca. delta0.9) was 2.6 +/- 0.6 (N = 25) for glioblastomas and 3.8 +/- 1.4 (N = 34) for metastases (P < 0.0001). There were no significant differences in metabolite or lipid concentrations between the tumor groups. The LPA ratio provided 80% sensitivity and 80% specificity for discriminating metastases from glioblastomas. CONCLUSION: Lipid and macromolecule (LM) signals can dominate (1)H spectra of high-grade tumors and have characteristics that allow significant discrimination of metastases from glioblastomas. Work is now needed to determine the source and biophysical characteristics of these LM signals to further improve differentiation by optimizing the data acquisition and analysis protocol.     

Very short echo time improves the precision of glutamate detection at 3T in 1H magnetic resonance spectroscopy

Purpose:

To examine the precision of glutamate detection using a very short echo time (TE) phase rotation STEAM (PR‐STEAM) sequence.

Materials and Methods:

Spectrosopic data were acquired from the anterior cingulate gyrus in nine healthy adults using 6.5‐msec TE PR‐STEAM, 40‐msec TE PRESS, 72‐msec TE STEAM, and TE‐Averaging with an effective TE of 105 msec on a clinical 3T magnetic resonance imaging (MRI) system. All data were quantified using LCModel and reported as ratios relative to total creatine.

Results:

Glutamate Cramer‐Rao lower bounds were less than 8% for all sequences. The 6.5‐msec TE PR‐STEAM identified glutamate with the greatest precision (coefficient of variation [CV] of 7.1%), followed by TE‐Averaging (CV of 8.9%), 40‐msec TE PRESS (CV of 11.9%), and 72‐msec TE STEAM (CV of 13.8%).

Conclusion:

In the absence of spectral editing, glutamate is best detected in the human brain at 3T using very short TEs. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

脑胶质瘤周围区的^1H-MRS研究

目的应用多体素氢质子磁共振波谱(1H-MRS)探讨胶质瘤周围区脑代谢改变的特点,评价多体素1H-MRS在胶质瘤周围区的应用价值.方法23例病理证实的脑胶质瘤病人分为低级别组(WHO Ⅰ～Ⅱ级)13例和高级别组(WHOⅢ～Ⅳ级)10例.所有病例术前均行多体素1H-MRS检查,测量肿瘤实质区、周围区及对侧正常脑组织区代谢产物的相对定量,进行统计学比较.结果多体素1H-MRS显示高级别胶质瘤的周围区与实质区NAA/Cr、Cho/Cr、NAA/Cho值差异有统计学意义(P值均为0.00).高级别胶质瘤周围区与对侧正常脑组织区NAA/Cr、Cho/Cr、NAA/Cho、Glx/Cr值差异均有统计学意义(P值均为0.00);低级别胶质瘤周围区与实质区NAA/Cr、Cho/Cr、NAA/Cho值差异均有统计学意义(P值均为0.00);低级别胶质瘤周围区与对侧正常脑组织区Cho/Cr、NAA/Cho值差异均有统计学意义(P值分别为0.02、0.00);高级别与低级别胶质瘤实质区NAA/Cr、NAA/Cho、Cho/Cr、Glx/Cr值差异均有统计学意义(P值分别为0.00、0.00、0.03、0.00);高级别与低级别胶质瘤周嗣区NAA/Cr、NAA/Cho、Cho/Cr、Glx/Cr值差异均有统计学意义(P值均为0.00).结论脑胶质瘤周围区代谢物的改变反映了肿瘤向瘤周组织浸润,对确定胶质瘤的分级及预测侵袭性病变的浸润范围有帮助.     

T1, T2 and proton density measurements in the grading of cerebral gliomas

The possibility that cerebral tumours may be graded by measuring T1 or T2 with magnetic resonance (MR) imaging was studied. A consecutive series of patients with subsequently verified gliomas was enrolled, and studied with MR. Patients who had prior surgical, chemotherapeutic or steroid treatment were excluded. Single slice multiple saturation recovery and multiple spin echo techniques were used to measure T1, T2 and proton density in the tumour. In 33 patients with cerebral gliomas there were 5 grade I, 12 grade II, 7 grade III and 9 grade IV. T1 and T2 values tended to be smaller in grade I gliomas than in grades II, III and IV gliomas. Relaxation parameters overlapped considerably in tumours with different grades. Proton density values did not show much change between different grades of gliomas. Relaxation parameters cannot be used to determine tumour grade reliably. Correspondence to: S. Newman     

对比剂对3T氢质子MR波谱的影响

目的 用高场MR仪研究对比剂是否会影响氢质子MR波谱(1H-MRS)的结果.方法 对22例颅内肿瘤患者分别于增强扫描前后行1H-MRS检查,比较扫描前后2次胆碱复合物(Cho)、肌酸(Cr)、N-乙酰天门冬氨酸(NAA)的峰下面积及Cho/Cr、Cho/NAA比值.结果 增强后Cho、Cr、NAA峰下面积分别为增强前的(86.7±27.3)%、(94.6±40.8)%、(113.8±74.5)%,NAA、Cr峰下面积增强前后差异无统计学意义(Z值分别为-0.601、-1.640,P值均＞0.05),Cho峰下面积较增强前明显缩小,差异有统计学意义(Z值为-2.520,P值＜0.05).Cho/Cr增强前为2.4±1.6、增强后为2.3±1.3,Cho/NAA增强前为2.5±1.8、增强后为2.1±1.5,增强前后差异均无统计学意义(Z值分别为-0.179、-1.408,P值均＞0.05).结论 对比剂不会影响1H-MRS的结果分析.     

Diagnostic potential of short echo time MR spectroscopy of gliomas with single-voxel and point-resolved spatially localised proton spectroscopy of brain

Accurate neuroimaging grading of gliomas is useful for management, but techniques such as MRI and CT are not sufficiently reliable. Necrosis is a consistent, decisive prognostic factor and the key diagnostic criterion for glioblastoma multiforme. MR spectroscopy (MRS) allows noninvasive measurement of metabolites in brain tumours and mobile lipids reflect necrosis. However, short echo-time (TE) spectroscopy has been required for reliable assessment of lipids, since their relaxation times are very short. Recent advances have made it possible to perform short-TE MRS. We attempted to evaluate the significance of short TE spectroscopy as part of routine imaging for diagnosis and grading of gliomas. We performed TE 30 ms MRS in 25 patients with gliomas (grade II six; grade III three; grade IV, 16) and in 19 areas of healthy white matter using proton brain examination/single voxel (PROBE/SV) and point-resolved spatially localised spectroscopy (PRESS). With short-TE spectroscopy, lipid signals were detected in all 16 tumours of grade IV, one grade II (P = 0.0002) and none of grade III (P = 0.001). TE 136 ms MRS, carried out in 20 of these cases, showed lipid signals in only four of 14 grade IV tumours and in none of the other six. N-acetylaspartate/choline (NAA/Cho) ratios were always more than 1.0 in healthy tissues and less than 1.0 in all but one of the gliomas. The mean creatine (Cr)/Cho ratio in each tumour grade was significantly lower than in the healthy tissues. The mean Cr/Cho ratio was also significantly lower in grade IV than in grade II tumours (P < .0005). Considerable overlap in Cr/Cho ratio was observed between grade II and grades III and IV gliomas at long but less so at short-TE MRS. We conclude that short-TE MRS with PROBE/SV and PRESS is of value in grading gliomas. Received: 25 June 2000 Accepted: 1 September 2000     

脑胶质瘤周围区的~1H-MRS研究

目的应用多体素氢质子磁共振波谱(1H-MRS)探讨胶质瘤周围区脑代谢改变的特点,评价多体素1H-MRS在胶质瘤周围区的应用价值。方法23例病理证实的脑胶质瘤病人分为低级别组(WHOⅠ～Ⅱ级)13例和高级别组(WHOⅢ～Ⅳ级)10例,所有病例术前均行多体素1H-MRS检查,测量肿瘤实质区、周围区及对侧正常脑组织区代谢产物的相对定量,进行统计学比较。结果多体素1H-MRS显示高级别胶质瘤的周围区与实质区NAA/Cr、Cho/Cr、NAA/Cho值差异有统计学意义(P值均为0.00)。高级别胶质瘤周围区与对侧正常脑组织区NAA/Cr、Cho/Cr、NAA/Cho、Glx/Cr值差异均有统计学意义(P值均为0.00);低级别胶质瘤周围区与实质区NAA/Cr、Cho/Cr、NAA/Cho值差异均有统计学意义(P值均为0.00);低级别胶质瘤周围区与对侧正常脑组织区Cho/Cr、NAA/Cho值差异均有统计学意义(P值分别为0.02、0.00);高级别与低级别胶质瘤实质区NAA/Cr、NAA/Cho、Cho/Cr、Glx/Cr值差异均有统计学意义(P值分别为0.00、0.00、0.03、0.00);高级别与低级别胶质瘤周...     

Metabolic findings on 3T 1H-MR spectroscopy in peritumoral brain edema

BACKGROUND AND PURPOSE: Little is known about the metabolic properties of brain edema associated with tumors. This work was conducted on the basis of the assumption that, in the presence of intra-axial and extra-axial brain tumors, the white matter involved by the edema is a site of metabolic change that involves the structure of the myelin sheath. MATERIALS AND METHODS: Thirteen patients comprised our cohort affected by intra-axial and extra-axial cerebral tumors with a peritumoral T2-weighted MR signal hyperintensity as a result of edema, where MR spectroscopy showed no increase in choline-containing compounds. Measurements on proton MR spectroscopy (1H-MR spectroscopy) were performed with a 3T whole-body scanner with use of a point-resolved spectroscopy sequence for localization (TR, 2000 ms; TE, 35 ms), and the metabolites were quantified with the SAGE method. Peak intensities of the main metabolites were expressed as ratios of one another and were compared with values obtained in the white matter of the left frontal region in a control group of 16 healthy volunteers. RESULTS: Choline-to-creatine (Cho/Cr) and myo-inositol-to-creatine (mIns/Cr) signal intensity ratios were normal in all patients. N-acetylaspartate-to-creatine (NAA/Cr) and N-acetylaspartate-to-choline (NAA/Cho) ratios decreased in 4 patients. Glutamate plus glutamine-to-creatine (Glx/Cr) was increased in 10 patients. A resonance peak at 3.44 ppm, strongly suggesting the presence of glucose, was detected in all but 1 patient. Lactate was detected in 12 patients and lipids in 5. Moreover, the resonances that pertained to the aliphatic amino acids valine, leucine, and isoleucine were present in 12 patients. CONCLUSIONS: Our findings on MR spectroscopy confirmed the hypothesis that in the edema surrounding brain tumors, an energy-linked metabolic alteration was associated with injury to the myelin sheath.     

Proton MR spectroscopy in children with acute brain injury: comparison of short and long echo time acquisitions

The aim of this study was to evaluate comparatively the information given by proton magnetic resonance spectroscopy (MRS) with short echo time (TE 20 msec) stimulated echo acquisition mode and long TE (270 msec) point-resolved spectroscopy in predicting long-term outcome in children suffering from acute brain injury. At 1.5 T, we performed single-voxel proton MRS with both methods in occipital gray matter of 70 children. A linear discriminant analysis used to predict outcomes based on MRS variables was compared with actual neurologic outcome assigned at least 6 months after injury by a pediatric neurologist. Using peak area metabolite ratios and lactate presence, the short and long TE methods were equally predictive in children over 1 month of age. In neonates less than 1 month of age, the long TE method produced a higher percentage of correct outcome predictions (91%) than the short TE method (79%). The long TE method detected lactate more often in all age groups.     

Combined 3T diffusion tensor tractography and 1H-MR spectroscopy in motor neuron disease

BACKGROUND AND PURPOSE: Diagnostic confidence in motor neuron disease may be improved by the use of advanced MR imaging techniques. Our aim was to assess the accuracy (sensitivity/specificity) and agreement of combined ¹H-MR spectroscopy (proton MR spectroscopy) and diffusion tensor imaging (DTI) at 3T in patients with suspected motor neuron disease regarding detection of upper motor neuron (UMN) dysfunction.MATERIALS AND METHODS: Eighteen patients with suspected motor neuron disease were studied with MR spectroscopy/DTI and clinically rated according to the El-Escorial and ALSFRS-R scales. For MR spectroscopy, absolute N-acetylaspartate (NAA), choline (Cho), and phosphocreatine (PCr) concentrations and relative NAA/Cho and NAA/PCr ratios of corresponding volumes of interest within the primary motor cortex were calculated. For DTI, fractional anisotropy (FA) and mean diffusivity (MD) were measured bilaterally at the level of the precentral gyrus, corona radiata, internal capsule, cerebral peduncles, pons, and pyramid. FA and MD statistics were averaged on the corticospinal tracts (CSTs) as a whole to account for a region-independent analysis.RESULTS: MR spectroscopy indicated NAA reduction beyond the double SD of controls in 6 of 8 patients with clinical evidence for UMN involvement. Congruently, the mean FA of these patients was significantly lower in the upper 3 regions of measurements (P < .01). Overall, MR spectroscopy and DTI were concordant in all except 3 cases: 1 was correctly excluded from motor neuron disease by DTI (genetically proved Kennedy syndrome), whereas MR spectroscopy indicated CST involvement. MR spectroscopy and DTI each were false-positive for CST affection in 1 patient with lower motor neuron involvement only.CONCLUSION: Combined MR spectroscopy/DTI at 3T effectively adds to the detection of motor neuron disease with a high degree of accordance.

Amyotrophic lateral sclerosis (ALS), Lou Gehrig syndrome or Charcot disease, is the most common progressive motor neuron disease.¹ Classic ALS affects the upper (UMN) and lower motor neurons (LMN), but cases with predominant UMN or LMN involvement also occur. It is still debated whether primary lateral sclerosis (PLS) and ALS are distinct disorders or manifestations of a single disorder, and a classification into ALS, UMN–dominant ALS, and PLS has been proposed to systematize future trials,² hence the correctness of UMN assessment is crucial.In addition to traditional diagnostic steps, such as electromyography, transcranial magnetic stimulation,^3,4 and assessment according to established clinical rating scales (eg, El-Escorial [EE]⁵ or ALS Functional Rating Scale-Revised [ALSFRS-R⁶]), recent promising attempts to improve diagnostic confidence of UMN assessment used advanced MR imaging techniques: ¹H-MR spectroscopy (proton MR spectroscopy),^7–11 diffusion tensor imaging (DTI),^12–19 diffusion tensor tractography (DTT),²⁰ or combinations thereof.^21,22 However, systematic evaluation of their concordance in the same patients is still rare.^21,23To obtain a definite diagnosis early in the disease is important for therapeutic intervention,^21,24 quality of life,^17,25,26 and monitoring therapeutic trials.^16,22 Cervical myelopathy, Kennedy syndrome (spinobulbar muscle atrophy, [SBMA]), peripheral nerve lesions, and multifocal polyneuropathy are, among others, differential diagnoses that have to be excluded. The clinical diagnosis is especially difficult when UMN involvement remains unclear. The previously mentioned techniques not only hold the promise of a more specific and potentially objective MR imaging measure but may even lead to a biomarker of disease severity.In contrast, most characteristics observed on structural MR imaging, such as corticospinal tract (CST) hyperintensities in T2-weighted, proton density, and fluid-attenuated inversion recovery (FLAIR) imaging^27–32; hypointense precentral gyrus changes^33,34; or marked frontal or callosal atrophy,³⁵ are rather uncertain.^31,32 CST hyperintensities are frequently found in healthy individuals, whereas the hypointense precentral gyrus sign apparently is motor neuron disease–specific according to Ishikawa et al³³ but occurs only in a minority of patients with ALS. To our knowledge, none of these signs have yet been studied at 3T. The principal aim of the present study was to evaluate the diagnostic accuracy of combined MR spectroscopy and DTI at 3T as an additional diagnostic tool in patients with suggested motor neuron disease and to provide an estimate of their concordance when applied to the same patients.     

脑转移瘤MR T1WI自旋回波与反转恢复序列的比较

T1WI常用于显示人体解剖结构,在脑转移瘤的诊断中,增强T1WI通过肿瘤的强化,可更清楚地显示肿瘤的边界,并有助于发现更多的转移灶.T1WI一般多采用自旋回波(SE)序列(T1 WSE),而反转恢复(IR)序列的T1WI(T1WIR)具有较高的组织分辨率,但成像时间长[1-2].     

MR氢质子波谱成像在神经上皮组织肿瘤分级中的应用

目的研究MR氢质子波谱（^1H-MRS）成像在神经上皮组织肿瘤分级中的价值。方法52例颅内神经上皮组织肿瘤患者，低级别29例，高级别23例，均行MRI及^1H-MRS检查。结果52例中，Ⅱ级9例，Ⅲ级11例，Ⅳ级12例，将Ⅱ级列为低级别组，Ⅲ级、Ⅳ级为高级别组，脂质（Lip）[乳酸（Lac）]／肌酸（Cr）、Lip（Lac）／N-乙酰天门冬氨酸（NAA）、Lip（Lac）／胆碱化合物（Cho），Lip（Lac）在组间差异有统计学意义，低级别组各代谢物比值中位数分别为0．14、0．16、0．09、0．32，高级别组各代谢物中位数分别为1．64、1．24、0．87、1．68。Lip（Lac）／Cr≤0．425为低级别肿瘤，Lip（1ac）／Cr＞0．425为高级别肿瘤，诊断敏感度、特异度、阳性予测值、阴性预测值分别为87．0％、96．6％、95.2％、90．3％。常规MR图像诊断肿瘤级别敏感度、特异度、阳性予测值、阴性预测值分别为87．0％、82．8％、80．0％、88．9％。结论^1H-MRS在神经上皮组织肿瘤分级中有一定的价值，常规MR图像结合MRS可明显提高诊断准确率。     

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

In order to obtain proton magnetic resonance spectra from the normal human kidney in vivo, we employed a STEAM sequence with delay times TE= 10 ms and TM = 30 ms. Signals are attenuated during STEAM sequences by J-coupling effects and by macroscopic movement of the sample. The combination of short echo times and respiratory triggering ensured that the kidney was stationary during the pulse sequence, and allowed us to detect strongly coupled resonances between 3 and 4.2 ppm. Analysis of spectra of extracts of bovine kidneys suggested that the renal MR-visible metabolites could include the osmolytes betaine, myo-inositol, and glycerophosphocholine. Four volunteers were subjected to overnight dehydration followed by rehydration, and we found that these signals increased significantly after dehydration, and decreased significantly 4 h after rehydration, thus supporting the assignment of the resonances as osmotically active metabolites.     

Short echo time MR spectroscopy of brain tumors: Grading of cerebral gliomas by correlation analysis of normalized spectral amplitudes

Purpose:

To process single voxel spectra of low‐ and high‐grade gliomas. To propose correlation analysis of the scatter plots of normalized spectral amplitudes as a pattern recognition tool for the classification (grading) of brain tumors. To propose a spectrum processing approach that improves the differentiation of proton spectra with dominating macromolecule and lipid peaks.

Materials and Methods:

LCModel was used to process spectra. Mean metabolite concentrations and mean normalized spectra were obtained for normal white matter and for gliomas. The mean spectra of macromolecules and lipids (ML) in the range 1.4–0.9 ppm, and mean difference spectra (DS) without ML and lactate were computed. Correlation analysis of the scatter plot of the patient and mean normalized spectral amplitudes and dispersion of the scatter plot points were used for classification and grading of tumors.

Results:

It was found advantageous to perform the classifications using DS spectra. The shape of ML spectrum and concentration of tCr seem to be a good markers for glioma grade.

Conclusion:

Combining a qualitative comparison of the patient and mean DS spectra of the tumors using correlation analysis of normalized spectra amplitudes with a quantitative comparison of metabolite concentrations is a powerful tool in studying brain lesions. J. Magn. Reson. Imaging 2010;31:39–45. © 2009 Wiley‐Liss, Inc.     

Elimination of artifacts in short echo time 1H MR spectroscopy of the frontal lobe

Localized ¹H spectra from the frontal part of the human brain are often distorted by “ghost” artifacts, especially with short echo time PRESS sequences. These artifacts are caused by insufficient dephasing of unwanted coherences involving magnetization in the sinuses and the mouth. Because the various unwanted coherences of a PRESS sequence are dephased differently, the order of the slice gradients has a pronounced effect on the spectral quality. For frontal voxels, the last slice gradient has to be applied in the axial direction. With this slice order, the major metabolites can be quantified with an interindividual variability of about 10%.     

Improved initial value estimation for short echo time magnetic resonance spectroscopy spectral analysis using short T2 signal attenuation

Robust spectral analysis of magnetic resonance spectroscopy data frequently uses a spectral model with prior metabolite signal information within a nonlinear least squares optimization algorithm. Starting values for the spectral model greatly influence the final results. Short echo time magnetic resonance spectroscopy contains broad signals that overlap with metabolite signals, complicating the estimation of starting values. We describe a method for more robust initial value estimation using a filter to attenuate short T₂ signal contributions (e.g., macromolecules or residual lipids). The method attenuates signals by truncating early points in the data set. Metabolite peak estimation is simplified by the removal of broad, short T₂ signals, and corrections for metabolite signal truncation are described. Short echo time simulated Monte Carlo data and in vivo data were used to validate the method. Areas for metabolite signals in the Monte Carlo data with singlet (N‐acetylaspartate, creatine, choline) and singlet‐like (myo‐inositol) resonances were estimated within 10% of actual value for various metabolite line widths, signal‐to‐noise ratios, and underlying broad signal contributions. Initial value estimates of in vivo magnetic resonance spectroscopy data were within 14% of metabolite area ratios relative to the creatine peak fitted using established magnetic resonance spectroscopy spectral analysis software. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.     

Assessment of malignancy in gliomas by 3T 1H MR spectroscopy

The purpose of this study was to assess clinical 1H MR spectroscopy (MRS) as a noninvasive method for evaluating brain tumor malignancy at 3T high-field system. Using 3T MRI/MRS system, localized water-suppressed single-voxel technique in patients with brain tumor (i.e., gliomas) was employed to evaluate spectra with peaks of N-acetyl aspartate (NAA), choline-containing compounds (Cho), creatine/phosphocreatine (Cr) and lactate. On the basis of Cr, these peak areas were quantitated as a relative ratio. The variation of metabolite measurements of the designated region in 10 normal volunteers was less than 10%. Normal ranges of NAA/Cr and Cho/Cr ratios were 1.67+/-018 and 1.16+/-0.15, respectively. NAA/Cr ratio of gliomas was significantly lower than that of the normal tissues (P= .005), but Cho/Cr ratio of gliomas was significantly higher (P= .001). Cho/Cr ratio of high-grade gliomas was significantly higher than that of low-grade gliomas. The present study demonstrated that the neuronal degradation or loss was observed in all gliomas. Higher-grade glioma was correlated with higher Cho/Cr ratio, indicating a significant dependence of Cho levels on malignancy of gliomas. Our results suggest that clinical 1H MR spectroscopy could be useful to predict tumor malignancy.     

Metabolic and neurological patterns in chronic cerebral infarction: a single-voxel 1H-MR spectroscopy study

The details of brain metabolism in chronic cerebral infarcts have not been clarified. Using proton MR spectroscopy (¹H-MRS) at 1.5 T, we measured biochemical changes in 16 patients with large infarcts involving the motor cortex in the chronic phase (median 293.9 days) and related the findings to clinical data. Localised spectra were obtained using point-resolved spectroscopy, with an echo time of 270 ms. Regions of interest were placed on the frontal lobe, including the precentral gyrus and central sulcus. Motor function was assessed by the manual muscle power test at the time of the ¹H-MRS study. Only three patients with severe paresis had no signal in the lesions and a lactate signal was obtained in 13 cases. N -acetyl aspartate (NAA) was observed in 4 cases with recanalisation of an occluded vessel. Motor function correlated strongly with the NAA/choline-containing compounds (Cho) ratio (P < 0.01) and lactate/Cho ratio (P < 0.01). We found various metabolic patterns, reflecting residual neurological function. Received: 19 August 1996 Addressed: 26 September 1996