Efficacy of proton magnetic resonance spectroscopy in clinical decision making for patients with suspected malignant brain tumors

The Utility of Spectroscopic MRI in Stereotactic Biopsy and Radiotherapy Guidance in Newly Diagnosed Glioblastoma

Current diagnostic and therapeutic approaches for gliomas have limitations hindering survival outcomes. We propose spectroscopic magnetic resonance imaging as an adjunct to standard MRI to bridge these gaps. Spectroscopic MRI is a volumetric MRI technique capable of identifying tumor infiltration based on its elevated choline (Cho) and decreased N-acetylaspartate (NAA). We present the clinical translatability of spectroscopic imaging with a Cho/NAA ≥ 5x threshold for delineating a biopsy target in a patient diagnosed with non-enhancing glioma. Then, we describe the relationship between the undertreated tumor detected with metabolite imaging and overall survival (OS) from a pilot study of newly diagnosed GBM patients treated with belinostat and chemoradiation. Each cohort (control and belinostat) were split into subgroups using the median difference between pre-radiotherapy Cho/NAA ≥ 2x and the treated T1-weighted contrast-enhanced (T1w-CE) volume. We used the Kaplan-Meier estimator to calculate median OS for each subgroup. The median OS was 14.4 months when the difference between Cho/NAA ≥ 2x and T1w-CE volumes was higher than the median compared with 34.3 months when this difference was lower than the median. The T1w-CE volumes were similar in both subgroups. We find that patients who had lower volumes of undertreated tumors detected via spectroscopy had better survival outcomes.

Diagnostic accuracy and added value of qualitative radiological review of 1H-magnetic resonance spectroscopy in evaluation of childhood brain tumors

Background

¹H-magnetic resonance spectroscopy (MRS) facilitates noninvasive diagnosis of pediatric brain tumors by providing metabolite profiles. Prospective studies of diagnostic accuracy and comparisons with conventional MRI are lacking. We aimed to evaluate diagnostic accuracy of MRS for childhood brain tumors and determine added clinical value compared with conventional MRI.

Methods

Children presenting to a tertiary pediatric center with brain lesions from December 2015 through 2017 were included. MRI and single-voxel MRS were acquired on 52 tumors and sequentially interpreted by 3 radiologists, blinded to histopathology. Proportions of correct diagnoses and interrater agreement at each stage were compared. Cases were reviewed to determine added value of qualitative radiological review of MRS through increased certainty of correct diagnosis, reduced number of differentials, or diagnosis following spectroscopist evaluation. Final diagnosis was agreed by the tumor board at study end.

Results

Radiologists' principal MRI diagnosis was correct in 69%, increasing to 77% with MRS. MRI + MRS resulted in significantly more additional correct diagnoses than MRI alone (P = .035). There was a significant increase in interrater agreement when correct with MRS (P = .046). Added value following radiologist interpretation of MRS occurred in 73% of cases, increasing to 83% with additional spectroscopist review. First histopathological diagnosis was available a median of 9.5 days following imaging, with 25% of all patients managed without conclusive histopathology.

Conclusions

MRS can improve the accuracy of noninvasive diagnosis of pediatric brain tumors and add value in the diagnostic pathway. Incorporation into practice has the potential to facilitate early diagnosis, guide treatment planning, and improve patient care.

The value of magnetic resonance spectroscopy as a supplement to MRI of the brain in a clinical setting

BACKGROUND

There are different opinions of the clinical value of MRS of the brain. In selected materials MRS has demonstrated good results for characterisation of both neoplastic and non-neoplastic lesions. The aim of this study was to evaluate the supplemental value of MR spectroscopy (MRS) in a clinical setting.

MATERIAL AND METHODS

MRI and MRS were re-evaluated in 208 cases with a clinically indicated MRS (cases with uncertain or insufficient information on MRI) and a confirmed diagnosis. Both single voxel spectroscopy (SVS) and chemical shift imaging (CSI) were performed in 105 cases, only SVS or CSI in 54 and 49 cases, respectively. Diagnoses were grouped into categories: non-neoplastic disease, low-grade tumour, and high-grade tumour. The clinical value of MRS was considered very beneficial if it provided the correct category or location when MRI did not, beneficial if it ruled out suspected diseases or was more specific than MRI, inconsequential if it provided the same level of information, or misleading if it provided less or incorrect information.

RESULTS

There were 70 non-neoplastic lesions, 43 low-grade tumours, and 95 high-grade tumours. For MRI, the category was correct in 130 cases (62%), indeterminate in 39 cases (19%), and incorrect in 39 cases (19%). Supplemented with MRS, 134 cases (64%) were correct, 23 cases (11%) indeterminate, and 51 (25%) incorrect. Additional information from MRS was beneficial or very beneficial in 31 cases (15%) and misleading in 36 cases (17%).

CONCLUSION

In most cases MRS did not add to the diagnostic value of MRI. In selected cases, MRS may be a valuable supplement to MRI.

Evaluation of the added value of 1H-magnetic resonance spectroscopy for the diagnosis of pediatric brain lesions in clinical practice

Background

Magnetic resonance spectroscopy (MRS) aids noninvasive diagnosis of pediatric brain tumors, but use in clinical practice is not well documented. We aimed to review clinical use of MRS, establish added value in noninvasive diagnosis, and investigate potential impact on patient care.

Methods

Sixty-nine children with lesions imaged using MRS and reviewed by the tumor board from 2014 to 2016 met inclusion criteria. Contemporaneous MRI diagnosis, spectroscopy analysis, histopathology, and clinical information were reviewed. Final diagnosis was agreed on by the tumor board at study end.

Results

Five cases were excluded for lack of documented MRI diagnosis. The principal MRI diagnosis by pediatric radiologists was correct in 59%, increasing to 73% with addition of MRS. Of the 73%, 19.1% (95% CI, 9.1%-33.3%) were incorrectly diagnosed with MRI alone. MRS led to a significant improvement in correct diagnosis over all tumor types (P = .012). Of diagnoses correctly made with MRI, confidence increased by 37% when adding MRS, with no patients incorrectly re-diagnosed. Indolent lesions were diagnosed noninvasively in 85% of cases, with MRS a major contributor to 91% of these diagnoses. Of all patients, 39% were managed without histopathological diagnosis. MRS contributed to diagnosis in 68% of this group, modifying it in 12%. MRS influenced management in 33% of cases, mainly through avoiding and guiding biopsy and aiding tumor characterization.

Conclusion

MRS can improve accuracy and confidence in noninvasive diagnosis of pediatric brain lesions in clinical practice. There is potential to improve outcomes through avoiding biopsy of indolent lesions, aiding tumor characterization, and facilitating earlier family discussions and treatment planning.

Creatine CEST MRI for Differentiating Gliomas with Different Degrees of Aggressiveness

PURPOSE

Creatine (Cr) is a major metabolite in the bioenergetic system. Measurement of Cr using conventional MR spectroscopy (MRS) suffers from low spatial resolution and relatively long acquisition times. Creatine chemical exchange saturation transfer (CrCEST) magnetic resonance imaging (MRI) is an emerging molecular imaging method for tissue Cr measurements. Our previous study showed that the CrCEST contrast, obtained through multicomponent Z-spectral fitting, was lower in tumors compared to normal brain, which further reduced with tumor progression. The current study was aimed to investigate if CrCEST MRI can also be useful for differentiating gliomas with different degrees of aggressiveness.

PROCEDURES

Intracranial 9L gliosarcoma and F98 glioma bearing rats with matched tumor size were scanned with a 9.4 T MRI scanner at two time points. CEST Z-spectra were collected using a customized sequence with a frequency-selective rectangular saturation pulse (B1 = 50 Hz, duration = 3 s) followed by a single-shot readout. Z spectral data were fitted pixel-wise with five Lorentzian functions, and maps of CrCEST peak amplitude, linewidth, and integral were produced. For comparison, single-voxel proton MR spectroscopy (1H-MRS) was performed to quantify and compare the total Cr concentration in the tumor.

RESULTS

CrCEST contrasts decreased with tumor progression from weeks 3 to 4 in both 9L and F98 phenotypes. More importantly, F98 tumors had significantly lower CrCEST integral compared to 9L tumors. On the other hand, integrals of other Z-spectral components were unable to differentiate both tumor progression and phenotype with limited sample size.

CONCLUSIONS

Given that F98 is a more aggressive tumor than 9L, this study suggests that CrCEST MRI may help differentiate gliomas with different aggressiveness.

Clinical magnetic resonance spectroscopy of the central nervous system

Proton magnetic resonance spectroscopy (1H MRS) is a noninvasive imaging technique that can easily be added to the conventional magnetic resonance (MR) imaging sequences. Using MRS one can directly compare spectra from pathologic or abnormal tissue and normal tissue. Metabolic changes arising from pathology that can be visualized by MRS may not be apparent from anatomy that can be visualized by conventional MR imaging. In addition, metabolic changes may precede anatomic changes. Thus, MRS is used for diagnostics, to observe disease progression, monitor therapeutic treatments, and to understand the pathogenesis of diseases. MRS may have an important impact on patient management. The purpose of this chapter is to provide practical guidance in the clinical application of MRS of the brain. This chapter provides an overview of MRS-detectable metabolites and their significance. In addition some specific current clinical applications of MRS will be discussed, including brain tumors, inborn errors of metabolism, leukodystrophies, ischemia, epilepsy, and neurodegenerative diseases. The chapter concludes with technical considerations and challenges of clinical MRS.

Combined MRI and MRS improves pre-therapeutic diagnoses of pediatric brain tumors over MRI alone

INTRODUCTION

The specific goal of this study was to determine whether the inclusion of MRS had a measureable and positive impact on the accuracy of pre-surgical MR examinations of untreated pediatric brain tumors over that of MRI alone in clinical practice.

METHODS

Final imaging reports of 120 pediatric patients with newly detected brain tumors who underwent combined MRI/MRS examinations were retrospectively reviewed. Final pathology was available in all cases. Group A comprised 60 subjects studied between June 2001 and January 2005, when MRS was considered exploratory and radiologists utilized only conventional MRI to arrive at a diagnosis. For group B, comprising 60 subjects studied between January 2005 and March 2008, the radiologists utilized information from both MRI and MRS. Furthermore, radiologists revisited group A (blind review, time lapse >4 years) to determine whether the additional information from MRS would have altered their interpretation.

RESULTS

Sixty-three percent of patients in group A were diagnosed correctly, whereas in 10% the report was partially correct with the final tumor type mentioned (but not mentioned as most likely tumor), while in 27% of cases the reports were wrong. For group B, the diagnoses were correct in 87%, partially correct in 5%, and incorrect in 8% of the cases, which is a significant improvement (p < 0.005). Re-review of combined MRI and MRS of group A resulted 87% correct, 7% partially correct, and 7% incorrect diagnoses, which is a significant improvement over the original diagnoses (p < 0.05).

CONCLUSION

Adding MRS to conventional MRI significantly improved diagnostic accuracy in preoperative pediatric patients with untreated brain tumors.

CEST signal at 2ppm (CEST@2ppm) from Z-spectral fitting correlates with creatine distribution in brain tumor

In general, multiple components such as water direct saturation, magnetization transfer (MT), chemical exchange saturation transfer (CEST) and aliphatic nuclear Overhauser effect (NOE) contribute to the Z-spectrum. The conventional CEST quantification method based on asymmetrical analysis may lead to quantification errors due to the semi-solid MT asymmetry and the aliphatic NOE located on a single side of the Z-spectrum. Fitting individual contributors to the Z-spectrum may improve the quantification of each component. In this study, we aim to characterize the multiple exchangeable components from an intracranial tumor model using a simplified Z-spectral fitting method. In this method, the Z-spectrum acquired at low saturation RF amplitude (50 Hz) was modeled as the summation of five Lorentzian functions that correspond to NOE, MT effect, bulk water, amide proton transfer (APT) effect and a CEST peak located at +2 ppm, called CEST@2ppm. With the pixel-wise fitting, the regional variations of these five components in the brain tumor and the normal brain tissue were quantified and summarized. Increased APT effect, decreased NOE and reduced CEST@2ppm were observed in the brain tumor compared with the normal brain tissue. Additionally, CEST@2ppm decreased with tumor progression. CEST@2ppm was found to correlate with the creatine concentration quantified with proton MRS. Based on the correlation curve, the creatine contribution to CEST@2ppm was quantified. The CEST@2ppm signal could be a novel imaging surrogate for in vivo creatine, the important bioenergetics marker. Given its noninvasive nature, this CEST MRI method may have broad applications in cancer bioenergetics.

The use of magnetic resonance spectroscopy in the evaluation of epilepsy

Magnetic resonance spectroscopy (MRS) is indicated in the imaging protocol of the patient with epilepsy to screen for metabolic derangements such as inborn errors of metabolism and to characterize masses that may be equivocal on conventional magnetic resonance imaging for dysplasia versus neoplasia. Single-voxel MRS with echo time of 35 milliseconds may be used for this purpose as a quick screening tool in the epilepsy imaging protocol. MRS is useful in the evaluation of both focal and generalized epilepsy.

The diagnostic role of diffusion tensor imaging in multifocal inflammatory leukoencephalopathy

Multifocal inflammatory leukoencephalopathy (MIL) is a rare syndrome that can occur in patients with colon cancer after chemotherapy with 5-fluorouracil (5-FU) and levamisole. Histologic diagnosis by brain biopsy is most effective, but there can be high surgical risks and technical limitations. Therefore, we introduce a noninvasive diagnostic technique using diffusion tensor imaging (DTI) for patients suspected to have MIL. A 45-year-old woman had been treated for 12 weeks with levamisole and 5-FU for adenocarcinoma of the cecum, when she complained of ataxia, diplopia and left ptosis. Brain MRI showed a nodular enhancing lesion in the left midbrain, using gadolinium enhanced T1-weighted imaging, and scattered multiple white matter lesions throughout the cerebral hemisphere. Instead of a brain biopsy, DTI was performed that revealed reduced fractional anisotropy (FA) and increased radial diffusivity (RD) in the left midbrain lesion compared with the right midbrain denoting demyelination. Levamisole and 5-FU were discontinued, and she received intravenously 1 g of methylprednisolone daily for 5 d. After five weeks, follow-up DTI showed an increased FA and decreased RD, signifying the reversibility. DTI therefore may provide valuable information on diagnosing MIL and assessing the treatment response.

Preoperative magnetic resonance spectroscopy improves diagnostic accuracy in a series of neurosurgical dilemmas

OBJECT

The purpose of this study was to evaluate the usefulness of preoperative magnetic resonance spectroscopy (MRS) in neurosurgical patients with diagnostically challenging intracranial lesions.

METHODS

Included in this study are twenty-three consecutive patients presenting to the neurosurgery service with diagnostically challenging intracranial lesions and who were investigated by conventional MR imaging and proton ((1)H) MRS, followed by surgery with subsequent histopathological diagnosis. An experienced neuroradiologist (RJ) blinded to the final histopathology evaluated the imaging studies retrospectively. Provisional diagnoses based on preoperative clinical and conventional MR data versus preoperative MRS data were compared with definitive histopathological diagnoses.

RESULTS

Compared with preoperative clinical and conventional MR data, (1)H MRS improved the accuracy of MR imaging from 60.9% to 83%. We found (1)H MRS reliably distinguished between abscess and high-grade tumour, and between high-grade glioma and low-grade glioma, but was not able to reliably distinguish between recurrent glioma and radiation necrosis. In 12/23 cases (52%) the (1)H MRS findings positively altered our clinical management. Two representative cases are presented.

CONCLUSIONS

Our study supports a beneficial role for (1)H MRS in certain diagnostic intracranial dilemmas presenting to neurosurgeons. The information gleaned from preoperative (1)H MRS can be a useful adjunct to clinical and conventional MR imaging data in guiding the management of patients with intracranial pathologies, particularly high-grade tumour versus abscess, and high-grade versus low-grade glioma. Further larger prospective studies are needed to clearly define the utility of (1)H MRS in diagnostically challenging intracranial lesions in neurosurgery.

Algorithms for characterizing brain metabolites in two-dimensional in vivo MR correlation spectroscopy

Traditional analyses of in vivo 1D MR spectroscopy of brain metabolites have been limited to the inspection of one-dimensional free induction decay (FID) signals from which only a limited number of metabolites are clearly observable. In this article we introduce a novel set of algorithms to process and characterize two-dimensional in vivo MR correlation spectroscopy (2D COSY) signals. 2D COSY data was collected from phantom solutions of topical metabolites found in the brain, namely glutamine, glutamate, and creatine. A statistical peak-detection and object segmentation algorithm is adapted for 2D COSY signals and applied to phantom solutions containing varied concentrations of glutamine and glutamate. Additionally, quantitative features are derived from peak and object structures, and we show that these measures are correlated with known phantom metabolite concentrations. These results are encouraging for future studies focusing on neurological disorders that induce subtle changes in brain metabolite concentrations and for which accurate quantitation is important.

Metabolic response of glioblastoma to superselective intra-arterial cerebral infusion of bevacizumab: a proton MR spectroscopic imaging study

BACKGROUND AND PURPOSE

SIACI of bevacizumab has emerged as a promising novel therapy in the treatment of recurrent GB. This study assessed the potential of (1)H-MRS as an adjunctive technique in detecting metabolic changes reflective of antiproliferative effects of targeted infusion of bevacizumab in the treatment of GB.

MATERIALS AND METHODS

Eighteen patients enrolled in a phase I/II study of SIACI of bevacizumab for treatment of recurrent GB were included. Concurrent MR imaging and (1)H-MRS scans were performed before and after treatment. Five distinct morphologic ROIs were evaluated for structural and metabolic changes on MR imaging and (1)H-MRS, which included enhancing, nonenhancing T2 hyperintense signal abnormality, and multiple control regions. Pre- and post-SIACI of bevacizumab peak areas for NAA, tCho, tCr, as well as tCho/tCr and tCho/NAA ratios, were derived for all 5 ROIs and compared using the Wilcoxon signed-rank test.

RESULTS

A significant median decrease of 25.99% (range -55.76 to 123.94; P = .006) in tCho/NAA was found post-SIACI of bevacizumab relative to pretreatment values in regions of enhancing disease. A trend-level significant median decrease of 6.45% (range -23.71 to 37.67; P = .06) was noted in tCho/NAA posttreatment in regions of nonenhancing T2-hyperintense signal abnormality.

CONCLUSIONS

The results of this (1)H-MRS analysis suggest that GB treatment with SIACI of bevacizumab may be associated with a direct antiproliferative effect, as demonstrated by significant reductions of tCho/NAA after the intervention.

Spatial characteristics of newly diagnosed grade 3 glioma assessed by magnetic resonance metabolic and diffusion tensor imaging

The spatial heterogeneity in magnetic resonance (MR) metabolic and diffusion parameters and their relationship were studied for patients with treatment-naive grade 3 gliomas. MR data were evaluated from 51 patients with newly diagnosed grade 3 gliomas. Anatomic, diffusion, and metabolic imaging data were considered. Variations in metabolite levels, apparent diffusion coefficient (ADC), and fractional anisotropy (FA) were evaluated in regions of gadolinium enhancement and T2 hyperintensity as well as regions with abnormal metabolic signatures. Contrast enhancement was present in only 21 of the 51 patients. When present, the enhancing component of the lesion had higher choline-to-N-acetylaspartate index (CNI), higher choline, lower N-acetylaspartate, similar creatine, similar ADC and FA, and higher lactate/lipid than the nonenhancing lesion. Regions with CNI ≥ 4 had higher choline, lower N-acetylaspartate, higher lactate/lipid, higher ADC, and lower FA than normal-appearing white matter and regions with intermediate CNI values. For lesions that exhibited gadolinium enhancement, the metabolite levels and diffusion parameters in the region of enhancement were consistent with it corresponding to the most abnormal portion of the tumor. For nonenhancing lesions, areas with CNI ≥ 4 were the most abnormal in metabolic and diffusion parameters. This suggests that the region with the highest CNI might provide a good target for biopsies for nonenhancing lesions to obtain a representative histologic diagnosis of its degree of malignancy. Metabolic and diffusion parameter levels may be of interest not only for directing tissue sampling but also for defining the targets for focal therapy and assessing response to therapy.

MR spectroscopy using normalized and non-normalized metabolite ratios for differentiating recurrent brain tumor from radiation injury

RATIONALE AND OBJECTIVES

To compare the ability of normalized versus non-normalized metabolite ratios to differentiate recurrent brain tumor from radiation injury using magnetic resonance spectroscopy (MRS) in previously treated patients.

MATERIALS AND METHODS

Twenty-five patients with previous diagnosis of primary intracranial neoplasm confirmed with biopsy/resection, previously treated with radiation therapy (range, 54-70 Gy) with or without chemotherapy and new contrast enhancing lesion on a 1.5 T magnetic resonance imaging at the site of the primary neoplasm participated in this retrospective study. After MRS, clinical, radiological, and histopathology data were used to classify new contrast-enhancing lesions as either recurrent neoplasm or radiation injury. Volume of interest included both the lesion and normal-appearing brain on the contralateral side. Non-normalized metabolic ratios were calculated from choline (Cho), creatine (Cr), and N-acetylaspartate (NAA) spectroscopic values obtained within the contrast-enhancing lesion: Cho/Cr, NAA/Cr, and Cho/NAA. Normalized ratios were calculated using the metabolic values from the contralateral normal side: Cho/normal creatinine (nCr), Cho/normal N-acetylaspartate (nNAA), Cho/normal choline, NAA/nNAA, NAA/nCr, and Cr/nCr. Results were correlated with the final diagnosis by Wilcoxon rank-sum analysis.

RESULTS

Two of three non-normalized ratios, Cho/NAA (sensitivity 86%, specificity 90%) and NAA/Cr (sensitivity 93%, specificity 70%) significantly associated with tumor recurrence even after correcting for multiple comparisons. Of the six normalized ratios, only Cho/nNAA significantly correlated with tumor recurrence (sensitivity 73%, specificity 40%), but did not remain significant after correcting for multiple comparisons.

CONCLUSION

Cho/NAA and NAA/Cr were the two ratios with the best discriminating ability and both had better discriminating ability than their corresponding normalized ratios (Area under the curve = 0.92 versus 0.77, AUC= 0.85 vs. 0.66), respectively.

Treatment monitoring in gliomas: comparison of dynamic susceptibility-weighted contrast-enhanced and spectroscopic MRI techniques for identifying treatment failure

OBJECTIVE

To evaluate whether dynamic susceptibility-weighted contrast-enhanced (DSC), dynamic contrast-enhanced (DCE), and proton spectroscopic imaging ((1)H-MRSI) can identify progression and predict treatment failure during follow-up before tumor size changes, contrast agent uptake, or when new lesions become obvious. The aim was also to find out which of the aforementioned techniques had the best diagnostic performance compared with each other and standard magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Thirty-seven patients with gliomas (21 women, 16 men; mean age at inclusion, 48 ± 14 years [standard deviation]) were assessed prospectively by (1)H-MRSI (point-resolved spectroscopy), DCE, and DSC perfusion MRI, each after a single dose of gadobenate dimeglumine during follow-up. Histology was available in all cases (resection, N = 18; biopsy, N = 19). All patients with low-grade gliomas (n = 20) did not receive any radio- or chemotherapy after partial resection (n = 7) or biopsy (n = 13), whereas 17 patients with high-grade gliomas had received adjuvant radiotherapy immediately after surgery. Tumor progression (progressive disease, PD) was defined as increase in longest glioma diameter by at least 20% (Response Evaluation Criteria in Solid Tumors), appearance of new lesions, or new contrast-enhancement. DSC, DCE, and MRSI image analyses comprised a detailed semiquantitative region of interest (ROI) analysis of the different parameters. Wilcoxon signed-rank test, Wilcoxon rank sum test, and Cox regression were used for statistical analysis.

RESULTS

The median follow-up time was 607 days. Twenty patients showed PD (54%), 8 of 20 with low-grade (40%) and 12 of 17 with high-grade gliomas (71%). In PD, significant positive differences between log2-transformed ROI ratios at the last measurement in comparison to the first measurement (baseline) could be detected for tumor blood flow (P < 0.006) and volume (P < 0.001) derived from DSC and for maximum choline within tumor tissue (P = 0.0029) and Cho/Cr (P = 0.032) but not choline/N-acetyl-aspartate (P = 0.37) derived from MRSI. In contrast, these parameters were not significantly higher at last measurement in stable disease. Also, the differences between last value and baseline were significantly different between PD and stable disease for tumor blood flow (P < 0.004) and volume (P < 0.002) as well as for maximum choline within tumor tissue (P = 0.0011). The best prognostic parameter for PD at Cox analysis was time-dependent difference to baseline of log2 of relative regional cerebral blood flow normalized on gray matter (hazard ratio, 2.67; 95% confidence interval, 1.25-6.08; P = 0.01), while a prognostic value of MRS parameters could not be demonstrated.

CONCLUSION

DSC perfusion imaging can identify progression and can predict treatment failure during follow-up of gliomas with the best diagnostic performance.

Use of in vivo two-dimensional MR spectroscopy to compare the biochemistry of the human brain to that of glioblastoma

PURPOSE

To develop an in vivo two-dimensional localized correlation spectroscopy technique with which to monitor the biochemistry of the human brain and the pathologic characteristics of diseases in a clinically applicable time, including ascertainment of appropriate postprocessing parameters with which to allow diagnostic and prognostic molecules to be measured, and to investigate how much of the chemical information, known to be available from malignant cultured cells, could be recorded in vivo from human brain.

MATERIALS AND METHODS

The study was approved by the institutional review board and was compliant with HIPAA. With use of a 3.0-T clinical magnetic resonance (MR) unit and a 32-channel head coil, localized correlation spectroscopy was performed in six healthy control subjects and six patients with glioblastoma multiforme (GBM) with an acquisition time of 11 minutes. Two-dimensional spectra were processed and analyzed and peak volume ratios were tabulated. The data used were proved to be normally distributed by passing the Shapiro-Wilk normality test. The first row of the spectra was extracted to examine diagnostic features. The pathologic characteristics and grade of each GBM were determined after biopsy or surgery. Statistically significant differences were assessed by using a t test.

RESULTS

The localized correlation spectroscopy method assigned biochemical species from the healthy human brain. The correlation spectra of GBM were of sufficiently high quality that many of the cross peaks, recorded previously from malignant cell models in vitro, were observed, demonstrating a statistically significant difference (P < .05) between the cross peak volumes measured for healthy subjects and those with GBM (which include lipid, alanine, N-acetylaspartate, γ-aminobutyric acid, glutamine and glutamate, glutathione, aspartate, lysine, threonine, total choline, glycerophosphorylcholine, myo-inositol, imidazole, uridine diphosphate glucose, isocitrate, lactate, and fucose). The first row of the spectra was found to contain diagnostic features.

CONCLUSION

Localized correlation spectroscopy of the human brain at 3.0 T with use of a 32-channel head coil was performed in 11 minutes and provided information about neurotransmitters, metabolites, lipids, and macromolecules. The method was able to help differentiate healthy brain from the biochemical signature of GBM in vivo. This method may, in the future, reduce the need for biopsy and is now applicable for the study of selected neurologic diseases.

Combined use of neuroradiology and 1H-MR spectroscopy may provide an intervention limiting diagnosis of glioblastoma multiforme

PURPOSE

To evaluate the accuracy of (1)H-MR spectroscopy ((1)H-MRS) as an intervention limiting diagnostic tool for glioblastoma multiforme. GBM is the most common and aggressive primary brain tumor, with mean survival under a year. Oncological practice currently requires histopathological diagnosis before radiotherapy.

MATERIALS AND METHODS

Eighty-nine patients had clinical computed tomography (CT) and MR imaging and 1.5T SV SE (1)H-MRS with PRESS localization for neuroradiological diagnosis and tumor classification with spectroscopic and automated pattern recognition analysis (TE 30 ms, TR 2000 ms, spectral width 2500 Hz and 2048 data points, 128-256 signal averages were acquired, depending on voxel size (8 cm(3) to 4 cm(3)). Eighteen patients from a cohort of 89 underwent stereotactic biopsy.

RESULTS

The 18 stereotactic biopsies revealed 14 GBM, 2 grade II astrocytomas, 1 lymphoma, and 1 anaplastic astrocytoma. All 14 biopsied GBMs were diagnosed as GBM by a protocol combining an individual radiologist and an automated spectral pattern recognition program.

CONCLUSION

In patients undergoing stereotactic biopsy combined neuroradiological and spectroscopic evaluation diagnoses GBM with accuracy that could replace the need for biopsy. We do not advocate the replacement of biopsy in all patients; instead our data suggest a specific intervention limiting role for the use of (1)H-MRS in brain tumor diagnosis.

MR spectroscopy in radiation injury

Detecting a new area of contrast enhancement in or in the vicinity of a previously treated brain tumor always causes concern for both the patient and the physician. The question that immediately arises is whether this new lesion is recurrent tumor or a treatment effect. The differentiation of recurrent tumor or progressive tumor from radiation injury after radiation therapy is often a radiologic dilemma regardless the technique used, CT or MR imaging. The purpose of this article was to review the utility of one of the newer MR imaging techniques, MR spectroscopy, to distinguish recurrent tumor from radiation necrosis or radiation injury.

Proton MR spectroscopy improves discrimination between tumor and pseudotumoral lesion in solid brain masses

BACKGROUND AND PURPOSE

Differentiating between tumors and pseudotumoral lesions by conventional MR imaging may be a challenging question. This study aims to evaluate the potential usefulness and the added value that single-voxel proton MR spectroscopy could provide on this discrimination.

MATERIALS AND METHODS

A total of 84 solid brain lesions were retrospectively included in the study (68 glial tumors and 16 pseudotumoral lesions). Single-voxel spectra at TE 30 ms (short TE) and 136 ms (long TE) were available in all cases. Two groups were defined: "training-set" (56 cases) and "test-set" (28 cases). Tumors and pseudotumors were compared in the training-set with the Mann-Whitney U test. Ratios between resonances were defined as classifiers for new cases, and thresholds were selected with receiver operating characteristic (ROC) curves. The added value of spectroscopy was evaluated by 5 neuroradiologists and assessed with the Wilcoxon signed-rank test.

RESULTS

Differences between tumors and pseudotumors were found in myo-inositol (mIns); P < .01) at short TE, and N-acetylaspartate (NAA; P < .001), glutamine (Glx; P < .01), and choline (CHO; P < .05) at long TE. Classifiers suggested tumor when mIns/NAA ratio was more than 0.9 at short TE and also when CHO/NAA ratio was more than 1.9 at long TE. Classifier accuracy was tested in the test-set with the following results: short TE, 82% (23/28); long TE, 79% (22/28). The neuroradiologists' confidence rating of the test-cases on a 5-point scale (0-4) improved between 5% (from 2.86-3) and 27% (from 2.25-2.86) with spectroscopy (mean, 17%; P < .01).

CONCLUSIONS

The proposed ratios of mIns/NAA at short TE and CHO/NAA at long TE provide valuable information to discriminate between brain tumor and pseudotumor by improving neuroradiologists' accuracy and confidence.

Magnetic resonance spectroscopy of the brain: review of metabolites and clinical applications

Magnetic resonance imaging (MRI) provides anatomic images and morphometric characterization of disease, whereas magnetic resonance spectroscopy (MRS) provides metabolite/biochemical information about tissues non-invasively in vivo. MRS has been used clinically for more than two decades. The major applications of this advanced MRI tool are in the investigation of neurological and neurosurgical disorders. MRS has also been used in the evaluation of the prostate gland and muscle tissue, but these applications will not be addressed in this review. The aim of this review is to attempt to introduce the technique, review the metabolites and literature, as well as briefly describe our clinical experience.

Apparent T(2) relaxation times of lipid and macromolecules: a study of high-grade tumor spectra

PURPOSE

To determine T(2) relaxation times of lipid and macromolecules (Lip/MMs) observed by (1)H magnetic resonance spectroscopy ((1)H MRS) of metastases (MET) and glioblastomas (GBM), so that they may be better characterized.

MATERIALS AND METHODS

(1)H spectra were acquired at multiple echo times from brain lesions using point-resolved spectroscopy sequence (PRESS) at TE = 30 msec either with metabolite-nulling (six GBM and 11 MET), or without metabolite-nulling (four MET and one mucocele). All lesions were previously untreated and had subsequent histopathological classification.

RESULTS

The T(2) of the 1.3-ppm Lip/MM peak was concentration-dependent, but at high concentrations it was significantly different (P = 0.015) between GBM (42 +/- 6 msec) and MET (63 +/- 18 msec). The broad 2.05-ppm and 0.09-ppm Lip/MM peaks had similar T(2)s in MET and GBM. The T(2) of the narrow 2.05-ppm Lip/MM peak sometimes observed had a T(2) of 100 +/- 17 msec in MET and 75 msec in the mucocele.

CONCLUSION

We observed significantly higher T(2) of the 1.3-ppm Lip/MM peak in MET compared with GBM at high 1.3-ppm proton concentrations, in agreement with a higher 1.3/0.9-ppm peak ratio found in MET. The relatively long T(2) of the 2.05-ppm Lip/MM peak sometimes observed in MET may cause it to be confused with N-acetyl aspartate (NAA).

The use of short-echo-time 1H MRS for childhood cerebellar tumours prior to histopathological diagnosis

BACKGROUND

Proton magnetic resonance spectroscopy (MRS) measures concentrations of metabolites in vivo and provides a powerful method for identifying tumours. MRS has not entered routine clinical use partly due to the difficulty of analysing the spectra.

OBJECTIVE

To create a straightforward method for interpreting short-echo-time MRS of childhood cerebellar tumours.

MATERIALS AND METHODS

Single-voxel MRS (1.5-T Siemens Symphony NUM4, TR/TE 1,500/30 ms) was performed at presentation in 30 children with cerebellar tumours. The MRS results were analysed for comparison with histological diagnosis. Peak heights for N-acetyl aspartate (NAA), creatine (Cr), choline (Cho) and myo-inositol (mIns) were determined and receiver operator characteristic curves used to select ratios that best discriminated between the tumour types. The method was implemented by a group of clinicians and scientists, blinded to the results.

RESULTS

A total of 27 MRS studies met the quality control criteria. NAA/Cr >4.0 distinguished all but one of the astrocytomas from the other tumours. A combination of Cr/Cho <0.75 and mIns/NAA <2.1 separated all the medulloblastomas from the ependymomas.

CONCLUSION

Peak height ratios from short-echo-time MRS can accurately predict the histopathology of childhood cerebellar tumours.

Technology Assessment in Radiology: Putting the Evidence in Evidence-based Radiology

In this review, which is part of a larger series on evidence-based practice in radiology, the relationship between technology assessment (TA) and the practice of evidence-based radiology (EBR) is discussed. TA guides researchers in the methods required to be reliable providers of unbiased and relevant evidence. Meanwhile, EBR equips radiologists with the skills needed to be discerning consumers of that evidence. Both paradigms aim to improve the effectiveness of health care spending. In this review, it is argued that EBR can be only as good as the TA on which it is based. However, TA is particularly complex in regard to diagnostic radiology because of the many links in the chain between the interim objective (to make the correct diagnosis) and the ultimate goal (to improve patient health). In this article, the development of TA in medicine in general and, more specifically, the TA hierarchy for the evaluation of diagnostic imaging are described. Some of the improvements in the pool of evidence during the past 30 years are documented, and some of the remaining tensions between TA and EBR are highlighted.

Brain tumor imaging and cancer management: the neuro-oncologists perspective

Brain tumors remain a significant cause of morbidity and mortality and are often refractory to treatment. Neuroimaging, in particular magnetic resonance imaging (MRI) and associated techniques, has become an important tool for the neuro-oncologist in the management of brain tumors. Magnetic resonance imaging is the most sensitive method to demonstrate the presence of a mass in the brain and can often narrow the differential diagnosis with nonneoplastic lesions such as cerebral abscess and subacute infarction. Once the diagnosis has been confirmed, MRI is essential for initial treatment planning, including surgical resection and radiation therapy. In selected patients, serial MRI will also be necessary to evaluate for response during adjuvant chemotherapy and to monitor for treatment-induced toxicity. New magnetic resonance techniques such as magnetic resonance spectroscopy, diffusion-weighted imaging, and perfusion-based imaging methods will also be discussed where applicable.

The clinical value of proton magnetic resonance spectroscopy in adult brain tumours

Proton magnetic resonance spectroscopy (1H MRS) non-invasively provides information on the biochemical profile (typically including up to nine metabolites and mobile lipids) of brain tissue, which varies according to the underlying disease process. A number of studies have assessed its accuracy in the diagnosis of adult brain tumours. This article describes the basic principles of 1H MRS, the metabolic profiles of different brain tumours, and practical points to aid interpretation of spectra. The literature is reviewed regarding the role of 1H MRS in the diagnosis of brain tumours and more specifically where it has proven to be of additional benefit over conventional magnetic resonance imaging.

Automated analysis of 1H magnetic resonance metabolic imaging data as an aid to clinical decision-making in the evaluation of intracranial lesions

Proton magnetic resonance spectroscopic imaging (1H MRSI) is a noninvasive metabolic imaging technique that has emerged as a potentially powerful tool for complementing structural magnetic resonance imaging (MRI) in the clinical evaluation of neurological disorders and diagnostic decision-making. However, the relative complexity of methods that are currently available for analyzing the derived multi-dimensional metabolic imaging data has slowed incorporation of the technique into routine clinical practice. This paper discusses this impediment to widespread clinical use of 1H MRSI and then describes an automated data analysis approach that promises to facilitate use of the technique in the evaluation of intracranial lesions, with the potential to enhance the specificity of MRI and improve clinical decision-making.

Impact of evidence-based medicine on magnetic resonance spectroscopy

Magnetic resonance spectroscopy (MRS) is a robust, non-invasive means of defining aspects of human neurochemistry. After more than two decades, it is clear that in addition to its scientific interest, MRS has diagnostic value in tumor diagnosis, prognosis, therapeutic outcome, dementia diagnosis and prognosis, multiple sclerosis, infections, trauma, development, stroke, perinatal ischemia, xenobiotics and inborn errors (as determined from a meta-analysis included in this paper). However, in many healthcare systems, a new radiological technique requires evidence-based medicine (EBM) before it is recommended for reimbursement. Much of the reason why MRS is thought to be non-reimbursable in the USA is due to recent announcements that this 15-year-old technique is still considered 'investigational' by these EBM assessments. An analysis is presented of the technology assessments that brought about this situation. Based on the conclusions of the EBM assessments, strategies are suggested that involve all entities responsible for spectroscopy including the scientists' role in ensuring the future for clinical spectroscopy.

In vivo optical spectroscopy detects radiation damage in brain tissue

OBJECTIVE

Magnetic resonance imaging abnormalities in malignant brain tumors after irradiation may represent either recurrent tumor or radiation injury. Optical spectroscopy may represent a novel technique to identify radiation damage in brain tissues and to differentiate contrast-enhancing lesions from recurrent tumor.

METHODS

Fluorescence and diffuse reflectance spectra were acquired from 90 patients: 15 undergoing surgical resection for presumed recurrent tumor after radiation therapy, 15 with epilepsy and hippocampal sclerosis, and 60 with tumors who had not received irradiation. Optical spectra were acquired from 6 to 10 sites and were compared with a biopsy obtained from beneath the optical spectroscopy probe; the data then were classified by a neuropathologist blinded to the spectroscopy data. A probe for the intraoperative collection of diffuse reflectance and fluorescence spectra was used.

RESULTS

Thirteen of 15 patients (29 of 129 spectra) with previous irradiation showed a unique spectral feature characterized by a fluorescence peak centered at 500 nm (F500). All biopsy specimens showing histopathological signs of radiation injury had the F500 on their corresponding spectra (18 of 18). The F500 was identified in another 10% (11 of 111 spectra) of samples with previous irradiation but no histologically identifiable signs of radiation damage. The F500 was never seen in the normal temporal lobe of epilepsy patients with hippocampal sclerosis (0 of 105) and was seen in only 1.5% of tumor patients who did not undergo previous irradiation (6 of 433).

CONCLUSION

Optical spectroscopy detects radiation damage in brain tissues. The F500 spectral peak may allow accurate selection of tissues for biopsy in evaluating patients with new, contrast-enhancing lesions in the setting of previous irradiation.

Efficacy of proton magnetic resonance spectroscopy in neurological diagnosis and neurotherapeutic decision making

Anatomic and functional neuroimaging with magnetic resonance imaging (MRI) includes the technology more widely known as magnetic resonance spectroscopy (MRS). Now a routine automated "add-on" to all clinical magnetic resonance scanners, MRS, which assays regional neurochemical health and disease, is therefore the most accessible diagnostic tool for clinical management of neurometabolic disorders. Furthermore, the noninvasive nature of this technique makes it an ideal tool for therapeutic monitoring of disease and neurotherapeutic decision making. Among the more than 100 brain disorders that fall within this broad category, MRS contributes decisively to clinical decision making in a smaller but growing number. In this review, we will cover how MRS provides therapeutic impact in brain tumors, metabolic disorders such as adrenoleukodystrophy and Canavan's disease, Alzheimer's disease, hypoxia, secondary to trauma or ischemia, human immunodeficiency virus dementia and lesions, as well as systemic disease such as hepatic and renal failure. Together, these eight indications for MRS apply to a majority of all cases seen. This review, which examines the role of MRS in enhancing routine neurological practice and treatment concludes: 1) there is added value from MRS where MRI is positive; 2) there is unique decision-making information in MRS when MRI is negative; and 3) MRS usefully informs decision making in neurotherapeutics. Additional efficacy studies could extend the range of this capability.

MR spectroscopy of brain tumors

MR Spectroscopy provides a means to characterize the metabolite profiles of tumoral and non-tumoral lesions in the brain. This article aims to provide tools to increase our sensitivity and specificity of neurodiagnosis, particularly in combination with other advanced MRI techniques such as perfusion MR imaging.

Gliomatosis cerebri: a review of 22 cases

OBJECTIVE

Gliomatosis cerebri is an enigmatic diffuse brain neoplasm whose prognosis is grim. We reviewed data for patients with gliomatosis who were treated at the University of California, San Francisco, during a 10-year period. Our focus was on presentation, radiological and pathological features, and outcomes.

METHODS

We reviewed hospital and clinic records and magnetic resonance imaging scans for 22 patients with gliomatosis. The diagnosis was based on magnetic resonance imaging findings and tissue confirmation for all patients. Seven patients also underwent magnetic resonance spectroscopy. Eleven patients were male (50%), and the median age at presentation was 49 years (range, 7-79 yr).

RESULTS

Kaplan-Meier analysis demonstrated median lengths of survival as follows: no treatment, 1 month (n = 4); radiotherapy alone, 28 months (95% confidence interval, 5-51 mo; n = 13); radiotherapy followed by chemotherapy, two patients, alive at 28 and 104 months; radiotherapy and chemotherapy simultaneously, three patients, one alive at 18 months and the others dead at 7 and 9 months. There was no significant difference between radiotherapy alone and radiotherapy combined with chemotherapy (P = 0.69). Karnofsky Performance Scale scores of >/=70 and grade were both significantly related to length of survival in univariate analyses (P < 0.05); these correlations were confirmed in the multivariate analysis, although the small numbers of patients and deaths precluded reliable interpretation.

CONCLUSION

Although the small number of patients in our study and its retrospective nature preclude definitive conclusions regarding the utility of treatment, our findings suggest that biopsies are useful not only for diagnosis but also for prediction of the length of survival.

Preoperative proton-MR spectroscopy of gliomas--correlation with quantitative nuclear morphology in surgical specimen

A comparison between data from proton-MR spectroscopy (1HMRS) and quantitative histomorphology of tumor cell nuclei in gliomas has not been reported up to now. Therefore, the question must be answered, if there are any significant correlations between histomorphology of gliomas and quantitative data from 1HMRS concerning tissue metabolites. Surgical glioma specimen (glioblastomas, astrocytomas, oligodendrogliomas) from 46 patients with tumor grades II-IV according to WHO have been evaluated by means of a digital image analysis system using Ki-67-immunostained paraffin sections. Nuclear density, Ki-67-proliferation index, nuclear area and shape variables (roundness factor, Fourier-amplitudes) have been determined from 200 randomly selected tumor cell nuclei in each tumor specimen. These data have been correlated with preoperative data from 1HMRS. A positive correlation between Fourier-amplitudes, choline peak and lipide peak was observed, as well as a negative correlation between these variables and the nuclear roundness factor. This result indicates higher choline and lipide peaks with increasing irregularity of nuclear outlines. Proliferation index Ki-67 was positively correlated with the lipide peak, nuclear density showed a positive correlation with the choline peak. Glioblastomas (n = 29) showed an additional positive correlation between mean nuclear size and total creatine. Anaplastic gliomas (n = 12) showed a positive correlation between lactate peak and the standard deviation of the nuclear roundness factor. Further multivariate analyses have shown, that for the present collective of 46 cases, histometric variables have a higher significance than spectroscopic data for the differentiation of the different tumor grades. These results verify a significant correlation between preoperative data from 1HMRS and histomorphology of tumor cell nuclei in gliomas, supporting the biological significance of both histomorphometry and 1HMRS for the evaluation of these tumors.

Cerebral radiation necrosis

BACKGROUND

Brain radiation necrosis has been recognized as a potential complication of radiation therapy for cancer for at least five decades. Advances in neuro-radiology and histopathology have helped characterize this problem more fully and some therapeutic interventions may help prevent progression of this pathology. This is important in achieving one of the most important goals of cancer care-maintaining quality of life.

REVIEW SUMMARY

This review discusses the evolution of our understanding of radiation necrosis, from the first "autopsy-dependent" reports to the current characterization of these lesions with magnetic resonance (MR) and functional imaging. The review is presented in two parts; Part I deals with the definition, incidence and presumed pathogenesis of radiation necrosis. Part II includes diagnosis on the basis of imaging characteristics, (including functional imaging) and biopsy results. Management options are also explored.

CONCLUSIONS

Radiation necrosis is a very significant complication of radiation treatment of brain cancers and may have a tremendous impact on a patient's quality of life. The early diagnosis of radiation necrosis in patients receiving radiation therapy to the brain has improved with current neuro-imaging modalities and better understanding of its pathophysiology. The development of treatment modalities has been slower, but is nonetheless promising.

Potential role of magnetic resonance spectroscopy in assessment of tumour response in childhood cancer

This brief review considers to what extent Magnetic Resonance Spectroscopy (MRS) can play a role in monitoring early tumour response with examples of preclinical studies and selected clinical studies in tumours of children and young adults. An early non-invasive indicator of tumour response to therapy would provide useful information regarding the effectiveness of therapy. This might be a relevant prognostic factor in new patients and in phase II studies could facilitate recommendations at an early stage as to whether to continue treatment. This review suggests that several markers and ratios are emerging as potential prognostic markers, but larger prospective studies are needed before translating this into clinical practice.

Reproducibility of localized 2D correlated MR spectroscopy

The test-retest reliability of two-dimensional (2D) correlated spectroscopy (COSY) was studied on a whole-body 1.5T MRI scanner. Single-voxel localized 2D proton spectra were recorded in vitro as well as in vivo using a recently implemented localized chemical shift correlated spectroscopic (L-COSY) sequence. A total of 40 in vitro and 40 human brain (10 volunteers, four times each) 2D L-COSY spectra were recorded. The coefficients of variation (CVs) of selected brain metabolites (raw volume integrals) recorded in 10 healthy volunteers were less than 9% for creatine, choline, and N-acetyl aspartate, and less than 17% for myo-inositol, glutamine/glutamate, aspartate, and threonine/lactate. The 2D metabolite ratios and the raw volume integrals of 2D diagonal and cross peaks in healthy human brain were very well reproduced. The intraclass correlation coefficients were greater than 0.4 (P < 0.05) for the major metabolites, indicating that the 2D peak volumes were stable enough within individuals to detect reliable differences between normal subjects.

Analysis of the spatial characteristics of metabolic abnormalities in newly diagnosed glioma patients

PURPOSE

To evaluate the role of 3D MR spectroscopic imaging (MRSI) as a tool for characterizing heterogeneity within a lesion in glioma patients.

MATERIALS AND METHODS

Forty-nine patients with newly diagnosed glioma were studied with 3D water-suppressed proton (1-H) MRSI. Signal intensities from choline (Cho), creatine (Cr), N-acytel aspartate (NAA), and lactate/lipid (LL) were estimated from the spectra. Regions of interest (ROIs) corresponding to the metabolic abnormalities were defined and compared with the anatomic lesions.

RESULTS

This study showed that the tumor burden measured with either the volumes of the metabolic abnormalities or the metabolic levels in the most abnormal voxels was correlated with the degree of malignancy of the tumor. The volumes of elevated Cho and decreased NAA were useful for distinguishing low-grade from high-grade lesions. The volume of abnormal LL was correlated with the existence of necrosis and with the volume of contrast-enhancing lesions in high-grade lesions. The differences in the volume of abnormal LL were also statistically significant between patients in each grade.

CONCLUSION

These 3D-MRSI data provide important additional information to conventional MRI for evaluating and characterizing gliomas.

Imaging changes after stereotactic radiosurgery of primary and secondary malignant brain tumors

After radiosurgery of malignant tumors, it can be difficult to discriminate between transient treatment effects, radiation necrosis, and tumor progression on post-treatment imaging. Misinterpretation of an enlarging lesion may lead to inappropriate treatment and contribute to disagreements about treatment efficacy. In an effort to clarify this problem, we reviewed our experience with interpreting post-radiosurgical imaging in patients with malignant primary and secondary brain tumors. We reviewed results of radiosurgery of 30 malignant gliomas and 35 metastatic brain tumors with minimum follow up of 1 year or until death. Of 30 gliomas, 73% were larger a mean of 13 weeks after radiosurgery. Of 35 metatstatic tumors, 22% were larger a mean of 10 weeks after radiosurgery. Eleven had 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) of enlarging lesions. Eight showed increased activity with respect to brain; three decreased activity. Of the eight, six predicted incorrectly based upon the patients' subsequent courses (all alive, mean follow up of 27 months), and two correctly, with the patients dying from the imaged lesions 8 and 13 months later. Of the three with FDG uptake less than brain, one patient was alive with 32 weeks of follow up, and two patients died from the imaged lesion 13 and 21 months later. Radiographic enlargement after radiosurgery is common, especially for gliomas. Physicians caring for these patients should be aware of this phenomenon and be cautious in interpreting post-treatment images. MRI appearance may be useful for metastases. FDG-PET seems unreliable. Further evaluation of Tl-201 and HMPAO SPECT or MRS is warranted.

Short-echo time proton MR spectroscopy in the presence of gadolinium

PURPOSE

The purpose of this work was to quantify the impact of contrast agents on short-TE single-voxel 1H MR spectroscopy (MRS) diagnosis of recurrent brain tumors.

METHOD

Short-TE 1H MRS was performed in 49 patients with biopsy-proven brain tumors and 14 control subjects. Eight patients (nine paired exams) were examined before and after administration of Gd-DTPA (interval approximately 5-7 min).

RESULTS

Tumor spectra showed increased choline/creatine ratio (Cho/Cr; p < 0.009) and Cho concentrations (p < 0.02). Receiver operator characteristic for Cho/Cr = 0.93 differentiated 100% of tumors from control in the absence or presence of contrast agent. Repeated 1H MRS varied <3%. Cho T2 was significantly longer than Cr T2 (p < 0.02).

CONCLUSION

Proton MRS with TE of 30 ms may safely be used in combined contrast-enhanced MRI/MRS protocols. Further study is required with long-TE MRS because of the prolonged T2 of Cho.

MR-spectroscopy guided target delineation for high-grade gliomas

PURPOSE

Functional/metabolic information provided by MR-spectroscopy (MRSI) suggests MRI may not be a reliable indicator of active and microscopic disease in malignant brain tumors. We assessed the impact MRSI might have on the target volumes used for radiation therapy treatment planning for high-grade gliomas.

METHODS AND MATERIALS

Thirty-four patients (22 Grade III; 12 Grade IV astrocytomas) were evaluated; each had undergone MRI and MRSI studies before surgery. MRI data sets were contoured for T1 region of contrast enhancement (T1), region of necrosis, and T2 region of hyperintensity (T2). The three-dimensional MRSI peak parameters for choline (Cho) and N-acetylaspartate (NAA), acquired by a multivoxel technique, were categorized based on an abnormality index (AI), a quantitative assessment of tissue metabolite levels. The AI data were aligned to the MRI and displayed as three-dimensional contours. AI vs. T conjoint and disjoint volumes were compared.

RESULTS

For both grades, although T2 estimated the region at risk of microscopic disease as being as much as 50% greater than by MRSI, metabolically active tumor still extended outside the T2 region in 88% of patients by as many as 28 mm. In addition, T1 suggested a lesser volume and different location of active disease compared to MRSI.

CONCLUSION

The use of MRSI to define target volumes for RT treatment planning would increase, and change the location of, the volume receiving a boost dose as well as reduce the volume receiving a standard dose. Incorporation of MRSI into the treatment-planning process may have the potential to improve control while reducing complications.

Imaging of low- and intermediate-grade gliomas

Imaging plays a crucial role in the diagnosis and management of low- and intermediate-grade gliomas. In this article, the traditional role of imaging studies in glioma patients and the appearance of some of the more common glial tumors on conventional computed tomography (CT) and magnetic resonance (MR) examinations are reviewed. The impact that MR spectroscopy and MR perfusion imaging have made on the evaluation patients after therapy for glial tumors also is reviewed.