Proton magnetic resonance spectroscopy of brain tumors: an in vitro study

Newer MR imaging techniques for head and neck

Dynamic and functional imaging techniques are being developed to improve the evaluation of various pathologic processes of the head and neck region. These techniques include dynamic contrast-enhanced MR imaging for evaluating soft tissue masses and cervical lymph nodes, the use of ultrasmall superparamagnetic iron oxide contrast agent, and functional techniques such as in vivo and in vitro MR spectroscopy of head and neck cancer and lymph nodes and apparent diffusion coefficient mapping of parotid glands. These techniques can help to differentiate nonmalignant tissue from malignant tumors and lymph nodes and can aid in differentiating residual malignancies from postradiation changes. From methodological development, they are making the critical transition to preclinical and clinical validating methods and eventually to widespread clinical tools.

Differential MRI diagnosis between brain abscesses and necrotic or cystic brain tumors using the apparent diffusion coefficient and normalized diffusion-weighted images

Magnetic Resonance Diffusion-Weighted Imaging (DWI) has been reported to be helpful for the differential diagnosis between abscesses and cystic/necrotic brain tumors. However the number of patients is still limited, and the sensitivity and specificity of the method remain to be confirmed. The primary purpose of this study was to investigate a larger sample of patients, all investigated under the same experimental conditions, in order to obtain statistically significant data. Moreover, there is no consensus about the appropriate values of b required to use to make an accurate diagnosis from DWI. The secondary purpose of this study was to determine the discriminating threshold b values for raw diffusion-weighted images and for normalized diffusion-weighted images. On the basis of 14 abscesses, 10 high-grade gliomas and 2 metastases, we show that the calculation of accurate Apparent Diffusion Coefficient (ADC) values gives a specificity rate of 100%. Without ADC calculation, we show that image normalization is required to make an accurate differential diagnosis, and we highlight the ability of DWI to discriminate between brain abscesses and cystic/necrotic brain tumors using normalized signal intensity at lower b values (503 s/mm(2)) than usual.

1H MR spectroscopy of brain tumours and masses

Accurate diagnosis is essential for optimum management and treatment of patients with brain tumours. Proton magnetic resonance spectroscopy ((1)H MRS) provides information non-invasively on tumour biochemistry and has been shown to provide important additional information to that obtained by conventional radiology. We review the current status of (1)H MRS in classifying brain tumour type and grade, for monitoring response to therapy and progression to higher grade, and as a molecular imaging technique for determining tumour extent for treatment planning.

Utility of proton MR spectroscopy in the diagnosis of radiologically atypical intracranial meningiomas

Our aim was to evaluate the usefulness of proton MR spectroscopy ((1)H MRS) in the diagnosis of radiologically atypical brain meningiomas. We studied 37 patients with intracranial meningiomas with MRI and (1)H MRS (TE 136 ms). Their spectra were quantitatively assessed and compared with those of 93 other intracranial brain neoplasms: 15 low-grade and 14 anaplastic astrocytomas, 30 glioblastomas and 34 metastases. The most characteristic features of meningiomas were the presence of alanine, high relative concentrations of choline and glutamine/glutamate and low concentrations of creatine-containing compounds, N-acetyl-containing compounds and lipids. These resonances were assembled in algorithms for two-way differentiation between meningioma and the other tumours. The performance of the algorithms was tested in the 130 patients using the leave-one-out method, with 94% success in differentiating between meningioma and other tumour. Of the 37 meningiomas, five (14%) were thought atypical on MRI, and in only one of these, found to be malignant on histology, was a diagnosis other than meningioma suggested by the algorithm. The other four were correctly classified. We suggest that (1)H MRS provides information on intracranial meningiomas which may be useful in diagnosis of radiologically atypical cases.

In vivo 3-T MR spectroscopy in the distinction of recurrent glioma versus radiation effects: initial experience

PURPOSE

To determine if 3-T magnetic resonance (MR) spectroscopy allows accurate distinction of recurrent tumor from radiation effects in patients with gliomas of grade II or higher.

MATERIALS AND METHODS

This blinded prospective study included 14 patients who underwent in vivo 3-T MR spectroscopy prior to stereotactic biopsy. All patients received a previous diagnosis of glioma (grade II or higher) and high-dose radiation therapy (>54 Gy). Prior to MR spectroscopy, conventional MR imaging was performed at 1.5 T to identify a gadolinium-enhanced region within the irradiated volume. Diagnosis was assigned by means of histopathologic analysis of the biopsy samples.

RESULTS

Sixteen of 17 biopsy locations could be classified as predominantly tumor or predominantly radiation effect on the basis of the ratio of choline at the biopsy site to normal creatine level by using a value greater than 1.3 as the criterion for tumor. The remaining case, classified as recurrent tumor on the basis of MR spectroscopy results, was diagnosed as predominantly radiation effect on the basis of histopathologic findings. Disease in this patient progressed to biopsy-proven recurrence within 3 months. Overall, the ratio of choline at the biopsy site to normal creatine level was significantly elevated (unpaired two-tailed Student t test, P <.002) in those biopsy samples composed predominantly of tumor (n = 9) compared with those containing predominantly radiation effects (n = 8). The ratio was not significantly different between the two histopathologic groups.

CONCLUSION

In vivo 3-T MR spectroscopy has sufficient spatial resolution and chemical specificity to allow distinction of recurrent tumor from radiation effects in patients with treated gliomas.

Adult primitive neuroectodermal tumor: proton MR spectroscopic findings with possible application for differential diagnosis

PURPOSE

To assess the utility of proton magnetic resonance (MR) spectroscopy in the clinical categorization of primitive neuroectodermal tumors (PNETs) in adults.

MATERIALS AND METHODS

In vivo proton MR spectroscopy was performed with an echo time of 136 msec in nine adults with PNET, and findings were retrospectively compared with spectroscopic findings of 22 meningiomas, 12 low-grade astrocytomas, eight anaplastic astrocytomas, 23 glioblastomas, and 21 metastases. Nine resonances were semiquantitatively evaluated. Statistical analysis was performed by using Kruskal-Wallis and Mann-Whitney U tests. The Hochberg correction was applied for multiple comparisons. Results were prospectively validated in 24 tumors of the six types included in the study.

RESULTS

The resonances of choice for identifying PNET were alanine (P <.001) and glutamate and glutamine (P =.004), both decreased with respect to meningioma; choline increased with respect to low-grade (P <.001) and anaplastic astrocytoma (P =.055); and lipids at 1.30 ppm decreased and choline and other trimethyl-amine-containing compounds increased with respect to glioblastoma (P <.001 and P =.004, respectively) and metastasis (P <.001 and P =.021, respectively). We developed an algorithm for bilateral differential diagnosis between PNET and other tumor types. The leave-one-out method was used to test the five possible differential situations in the retrospective data set, with the following results: PNET versus meningioma, 31/23/5/3 (number of total/correct/unclassifiable/incorrect procedures); PNET versus low-grade astrocytoma, 21/19/2/0; PNET versus anaplastic astrocytoma, 17/6/9/2; PNET versus glioblastoma, 32/28/2/2; and PNET versus metastasis, 30/27/1/2. In total, 131 consecutive procedures produced 103 (79%) correct classifications and nine (7%) misclassifications. Twenty-five (78%) of 32 possible procedures in the prospective independent test set produced correct classifications and four (13%) produced incorrect classifications.

CONCLUSION

In vivo proton MR spectroscopy provides useful information in clinical differentiation between PNETs and common brain tumors in adults.

Quantification of cerebral metabolites in glioma patients with proton MR spectroscopy using T2 relaxation time correction

This study was aimed to investigate the significance of absolute concentration of metabolites in glioma patients using proton MR spectroscopy (MRS) with T2 relaxation time correction using three different echo times. The absolute concentrations of metabolites in 7 normal subjects and in 23 gliomas (10 low-grade, 13 high-grade) were obtained by proton MRS using a tissue water signal as an internal standard. The signal intensities of metabolites and tissue water were corrected by T2 relaxation time. In low-grade glioma, the T2 relaxation time of NAA was shorter, and T2 relaxation time of water was prolonged as compared to normal subjects (p < 0.001). In high-grade glioma, the T2 relaxation time of NAA (p < 0.001) and T2 relaxation time of Cr (p < 0.01) were shorter, and T2 relaxation time of water (p < 0.001) was prolonged as compared to normal subjects. Moreover, high-grade gliomas revealed a shorter T2 relaxation time of Cr than low-grade gliomas (p < 0.05). In glioma, NAA and Cr concentration were decreased, and Cho were increased as compared to normal subjects. Moreover, high-grade glioma revealed a significant lower Cr (p < 0.001) and Cho (p < 0.01) concentration compared to low-grade gliomas. Low Cr concentration is the most reliable indicator of malignancy in glioma. Cho concentration did not correlate with malignancy in gliomas.

Proton MR spectroscopy of craniopharyngiomas

To date, only a few cases of craniopharyngiomas have been studied by magnetic resonance (MR) spectroscopy. We report our spectroscopy experiences with five patients having surgically proven craniopharyngiomas. Proton MR spectroscopy images were obtained using the single-voxel mode with spin-echo point resolved spectroscopy. Very prominent peaks centered at 1-1.5ppm were noted in spectroscopic analysis, which probably corresponded to lipid/cholesterol peaks, correlating with the histological findings revealing high amounts of cholesterol in the cyst fluids.

Evaluation of female intrapelvic tumors by clinical proton MR spectroscopy

We measured metabolites in large tumors of the female pelvis (23 cases total: 6 malignant cases, 17 benign cases) using single-voxel proton magnetic resonance (MR) spectroscopy and evaluated the clinical significance of this method in the differential diagnosis of female pelvic tumors. The characteristically obtained signal was lactate, which was detected not only in all the malignant tumors but also in some of the benign tumors. However, the lactate signals of the malignant tumors tended to form higher peaks than those of benign tumors, which was a finding consistent with the result of the earlier in vitro study reported in ovarian tumors. The signal of choline-containing compounds (Cho) was found only in solid tumors, and the signal intensity varied among different histological types of tumors, possibly reflecting metabolic activity of the cell membrane. We considered that proton MR spectroscopy (MRS) of intrapelvic tumors would be useful for the diagnosis of the nature of female intrapelvic tumors. J. Magn. Reson. Imaging 2001;13:912-917.

Magnetic resonance spectroscopy of brain hemangiopericytomas: high myoinositol concentrations and discrimination from meningiomas

OBJECT

Hemangiopericytomas are a rare type of brain tumor that are very similar to meningiomas in appearance and symptoms but require different treatment. It is not normally possible to distinguish between them by using magnetic resonance (MR) imaging and computerized tomography studies. However, discrimination may be possible by using in vivo MR spectroscopy (MRS) because the biochemical composition of these two lesions is different. The goal of this study was to describe the use of MRS in discriminating between these similar tumor types.

METHODS

In vivo MRS spectra were acquired in 27 patients (three with hemangiopericytomas and 24 with meningiomas) by using a single-voxel proton brain examination system at 1.5 teslas with short- (20-msec) and long- (135-msec) echo times. In addition, brain biopsy specimens obtained by open craniotomy were frozen within 5 minutes of resection and stored in liquid nitrogen until they were used. The specimens were powdered, extracted with perchloric acid, redissolved in 2H2O2 and high-resolution in vitro MRS was used at 9.4 teslas to record their spectra.

CONCLUSIONS

In this study the authors show that hemangiopericytomas could be clearly distinguished from meningiomas because they have a larger peak at 3.56 ppm. Measurements of extracts of the tumors and comparison of spectra acquired with MRS at long- (135-msec) and short- (20-msec) echo times established that this was due to the much higher levels of myoinositol in the hemangiopericytomas.

MR spectroscopy: a powerful tool for investigating brain function and neurological diseases

Magnetic resonance spectroscopy (MRS) has attracted much attention in recent years and has become an important tool to study in vivo particular biochemical aspects of brain disorders. Since the proton is the most sensitive stable nucleus for MRS, and since almost all metabolites contain hydrogen atoms, investigation by in vivo 1H MRS provides chemical information on tissue metabolites, thus enabling a non-invasive assessment of changes in brain metabolism underlying several brain diseases. In this review a brief description of the basic principles of MRS is given. Moreover, we provide some explanations on the techniques and technical problems related to the use of 1H MRS in vivo including water suppression, localization, editing, quantitation and interpretation of 1H spectra. Finally, we discuss the more recent advancement in three major areas of neurological diseases: brain tumors, multiple sclerosis, and inborn errors of metabolism.

Proton NMR chemical shifts and coupling constants for brain metabolites

Proton NMR chemical shift and J-coupling values are presented for 35 metabolites that can be detected by in vivo or in vitro NMR studies of mammalian brain. Measurements were obtained using high-field NMR spectra of metabolites in solution, under conditions typical for normal physiological temperature and pH. This information is presented with an accuracy that is suitable for computer simulation of metabolite spectra to be used as basis functions of a parametric spectral analysis procedure. This procedure is verified by the analysis of a rat brain extract spectrum, using the measured spectral parameters. In addition, the metabolite structures and example spectra are presented, and clinical applications and MR spectroscopic measurements of these metabolites are reviewed.

Distinction between normal and renal cell carcinoma kidney cortical biopsy samples using pattern recognition of (1)H magic angle spinning (MAS) NMR spectra

The technique of magic angle spinning (MAS) high resolution (1)H NMR spectroscopy applied to intact tissues provides excellent peak resolution and thus much biochemical information. The use of computer-based pattern recognition techniques to classify human renal cortex tissue samples as normal or tumour based on their (1)H MAS NMR spectra has been investigated. In this preliminary study of 22 paired control and tumour samples, exploratory data analysis using principal components based on NMR spectral intensities showed clear separation of the two classes. Furthermore, using the supervised method of linear discriminant analysis, based on individual data point intensities or on integrated spectral regions, it was possible to distinguish between the normal and tumour kidney cortex tissue with 100% accuracy, including a single example of a metastatic tumour from a primary lung carcinoma. A tumour sample from the collecting duct of the kidney showed a different NMR spectral profile, and pattern recognition indicated that this sample did not classify with the cortical tumours.

In vivo proton magnetic resonance spectroscopy of central neurocytomas

OBJECTIVE

The authors report on the metabolic features of central neurocytomas observed during in vivo single-voxel proton magnetic resonance spectroscopy.

METHODS

Volume-selective single-voxel proton magnetic resonance spectroscopy was performed with a 1.5-T unit using a point-resolved spectroscopy sequence (TR/TE = 2000 ms/135 and 270 ms) to obtain spectra of a single 8-cc voxel. The subjects were five patients in the Department of Neurosurgery of Seoul National University Hospital whose central neurocytomas had been diagnosed histologically. The peak intensities of compounds containing choline (Cho), N-acetylaspartate, creatine/phosphocreatine, and lactate were analyzed.

RESULTS

The ratios of Cho to creatine/phosphocreatine and Cho to N-acetylaspartate were significantly higher than ratios in normal brains. A lactate signal was present, and an unidentified signal was also observed at 3.55 ppm, which might have been produced by inositol or glycine.

CONCLUSION

A combination of the signal at 3.55 ppm and a prominent Cho peak seems to be a characteristic feature of central neurocytomas. Volume-selective single-voxel proton magnetic resonance spectroscopy could provide additional information to aid in diagnosing this condition.

Noninvasive evaluation of the malignant potential of intracranial meningiomas performed using proton magnetic resonance spectroscopy

OBJECT

Controversy exists about correlations between histological tumor grade and magnetic resonance (MR) spectroscopy data. The authors studied single-voxel proton MR spectroscopy as a noninvasive way to evaluate grade of malignancy in intracranial meningiomas.

METHODS

The authors compared the results of MR spectroscopy with those derived by the MIB-1 staining index (SI) in 29 meningiomas. Proton MR spectroscopy was performed using stimulated echo acquisition and volume-localized solvent-attenuated proton nuclear MR sequences before surgery or other therapy. Twenty-four tumors were histologically benign (13 meningothelial, three fibrous, four transitional, three angiomatous, and one chordoid); four were atypical (Grade II), and one was papillary (Grade III). The mean MIB-1 SI in the benign group was significantly lower than those in the other groups (p = 0.0041). The mean choline-containing compound (Cho)/ creatine and phosphocreatine (Cr) ratios in the benign and nonbenign groups were 2.56+/-1.26 and 7.85+/-3.23, respectively (p = 0.0002). A significant linear correlation was observed between the Cho/Cr ratio and the MIB-1 SI (r0.05 = 0.74, p<0.001). Necrosis was present histologically in four of the five meningiomas classified either as atypical or papillary. Magnetic resonance spectroscopy revealed a methylene signal in these meningiomas that was not detected in benign meningiomas. Of the five meningiomas in which only a lactate signal was observed, two were benign and the MIB-1 SI in these two benign meningiomas was higher than the mean value for the benign group. Alanine, detected in 12 of 30 meningiomas, did not correlate with either tumor grade or Cho/Cr ratio.

CONCLUSIONS

Proton MR spectroscopy is a useful diagnostic method for determining the proliferative or malignant potential of meningiomas according to the Cho/Cr ratio. A lactate and/or methylene signal suggests a high-grade tumor.

High-performance liquid chromatographic analysis of physiological amino acids in human brain tumors by pre-column derivatization with phenylisothiocyanate

A reversed-phase high-performance liquid chromatographic technique for the determination of free amino acids in five biopsies of human brain tumors (two meningiomas, one glioblastoma and two oligodendrogliomas) is described. The frozen tissues were homogenized, deproteinized with perchloric acid and neutralized with potassium hydroxide. Aliquots of the supernatant containing the physiological amino acids are used for pre-column derivatization with phenylisothiocyanate. The derivatized PTC-amino acids (phenylthiocarbamyl derivatives) are stable for a five day period if stored as a powder at -20 degrees C in an inert atmosphere and they can be analyzed on a reversed-phase column (PicoTag) using a gradient of two eluents with absorption detection at a wavelength of 254 nm. Good resolution of several amino acids (>30) is achieved within ca. 60 min. For most amino acids this method is suitable for an accurate measurement over a wide range of physiological concentrations (50-400 pmol) starting from a very small amount of sample.

Application of new imaging techniques for the evaluation of squamous cell carcinoma of the head and neck

The past several years have seen dramatic changes in imaging of the head and neck. Technical improvements in CT and MRI coupled with their widespread availability have made cross-sectional imaging an important adjunct in evaluation of patients with disease of the extracranial head and neck. The most recent advances in head and neck imaging are from new metabolic and functional imaging techniques. The intent of this report is to provide an update on the potential role of positron emission tomography, new MRI agents, and magnetic resonance spectroscopy for evaluating squamous cell carcinoma of the extracranial head and neck.

Serial evaluation of patients with brain tumors using volume MRI and 3D 1H MRSI

Patients with brain tumors are routinely monitored for tumor progression and response to therapy using magnetic resonance imaging (MRI). Although serial changes in gadolinium enhancing lesions provide valuable information for making treatment decisions, they do not address the fate of non-enhancing lesions and are unable to distinguish treatment induced necrosis from residual or recurrent tumor. The introduction of a non-invasive methodology, which could identify an active tumor more reliably, would have a major impact upon patient care and evaluation of new therapies. There is now compelling evidence that magnetic resonance spectroscopic imaging (MRSI) can provide such information as an add-on to a conventional MRI examination. We discuss data acquisition and analysis procedures which are required to perform such serial MRI-MRSI examinations and compare their results with data from histology, contrast enhanced MRI, MR cerebral blood volume imaging and FDG-PET. Applications to the serial assessment of response to therapy are illustrated by considering populations of patients being treated with brachytherapy and gamma knife radiosurgery.

Characterization of choline compounds with in vitro 1H magnetic resonance spectroscopy for the discrimination of primary brain tumors

RATIONALE AND OBJECTIVES

The authors sought to compare 1H magnetic resonance spectroscopy (MRS) spectra from extracts of low-grade and high-grade gliomas, especially with respect to the signals of choline-containing compounds.

METHODS

Perchloric acid extracts of six high-grade and six low-grade gliomas were analyzed by 1H MRS at 9.4 Tesla.

RESULTS

The signals of glycerophosphocholine (GPC) at 3.23 ppm, phosphocholine (PC) at 3.22 ppm, and choline (Cho) at 3.21 ppm were identified in both types of tumors. The absolute concentrations of all Cho-containing compounds (GPC + PC + Cho) in high-grade and low-grade gliomas were significantly different. The relative contributions of each of the Cho-containing compounds to the total choline signal were also statistically different. For high-grade gliomas, the choline signal is composed of GPC, PC, and Cho in a well-balanced contribution, whereas in low-grade gliomas, the signal is largely due to GPC with a small involvement of PC and Cho.

CONCLUSIONS

The differences in the concentration and the repartition of Cho-containing compounds seem to be a marker of high-grade gliomas. They could also help to discriminate between high- and low-grade gliomas in some difficult cases, especially if there is histologic uncertainty between anaplastic astrocytomas and low-grade oligodendrogliomas.

Differential diagnosis of sellar masses

The differential diagnosis of nonpituitary sellar masses is broad; differentiating among potential etiologies may not always be straightforward because many of these lesions, tumorous and nontumorous, may mimic the clinical, endocrinologic, and radiologic presentations of pituitary adenomas. This article provides an overview of the clinical and radiographic characteristics of both pituitary tumors and the nonpituitary lesions found in the sellar/parasellar region and discusses, in detail, the specific nonpituitary origins of the sellar masses.

Pediatric low-grade gliomas: prognosis with proton magnetic resonance spectroscopic imaging

OBJECTIVE

Our aim was to assess the correlation between the low-grade glioma (LGG) metabolic profile and tumor progression. Using in vivo proton magnetic resonance spectroscopic imaging, we specifically asked whether and which metabolic features are associated with tumor regrowth or recurrence.

METHODS

Eleven pediatric patients with histologically proven partially resected (<20% resection) midline LGG were treated and followed up for a period of 2 years. All patients underwent proton magnetic resonance spectroscopic imaging studies before any management was determined. Tumor progression was defined as radiological evidence of mass enlargement (>25%) during the follow-up period. Proton magnetic resonance spectroscopic imaging was performed using a PRESS-CSI sequence on a General Electric 1.5-tesla scanner (General Electric Medical System, Waukesha, WI). The signal intensities of N-acetylaspartate, choline (CHO), and creatine from the tumor and the normal brain were used to calculate normalized metabolite intensities and metabolite ratios.

RESULTS

Tumors that progressed during a 2-year period displayed higher normalized CHO than those that remained stable (Mann-Whitney test, P < 0.03). The majority (five of six) of the rapidly growing LGG showed values of normalized CHO of at least 1, whereas the nonprogressors had a normalized CHO value of less than 1.

CONCLUSION

In association with pediatric LGG, high normalized CHO values seem to herald the potential for rapid tumor growth. These observations may be valuable for defining subsets of patients with LGG who may benefit from early therapeutic interventions.

Pattern recognition analysis of 1H NMR spectra from perchloric acid extracts of human brain tumor biopsies

Pattern recognition techniques (factor analysis and neural networks) were used to investigate and classify human brain tumors based on the 1H NMR spectra of chemically extracted biopsies (n = 118). After removing information from lactate (because of variable ischemia times), unsupervised learning suggested that the spectra separated naturally into two groups: meningiomas and other tumors. Principal component analysis reduced the dimensionality of the data. A back-propagation neural network using the first 30 principal components gave 85% correct classification of meningiomas and nonmeningiomas. Simplification by vector rotation gave vectors that could be assigned to various metabolites, making it possible to use or to reject their information for neural network classification. Using scores calculated from the four rotated vectors due to creatine and glutamine gave the best classification into meningiomas and nonmeningiomas (89% correct). Classification of gliomas (n = 47) gave 62% correct within one grade. Only inositol showed a significant correlation with glioma grade.

Using pattern analysis of in vivo proton MRSI data to improve the diagnosis and surgical management of patients with brain tumors

We have used pattern analysis of proton magnetic resonance spectroscopic imaging (1H MRSI) data in a variety of situations related to the clinical management of patients with brain tumors and other cerebral space-occupying lesions (SOLs). Here, we review how 'leave-one-out' linear discriminant analyses (LDAs) of in vivo 1H MRSI spectral patterns have enabled us to quickly, accurately, and non-invasively: (1) discriminate amongst tissue arising from the five most common types of supratentorial tumors found in adults, and (2) use the metabolic heterogeneity of cerebral SOLs to predict certain pathological characteristics that are useful in guiding stereotaxic biopsy and selective tumor resection. These findings suggest that pattern analysis of 1H MRSI data can significantly improve the diagnostic specificity and surgical management of patients with certain cerebral SOLs.

Serial proton magnetic resonance spectroscopy imaging of glioblastoma multiforme after brachytherapy

The utility of three-dimensional (3-D) proton magnetic resonance spectroscopy (1H-MRS) imaging for detecting metabolic changes after brain tumor therapy was assessed in a serial study of 58 total examinations of 12 patients with glioblastoma multiforme (GBM) who received brachytherapy. Individual proton spectra from the 3-D array of spectra encompassing the lesion showed dramatic differences in spectral patterns indicative of radiation necrosis, recurrent or residual tumor, or normal brain. The 1H-MRS imaging data demonstrated significant differences between suspected residual or recurrent tumor and contrast-enhancing radiation-induced necrosis. Regions of abnormally high choline (Cho) levels, consistent with viable tumor, were detected beyond the regions of contrast enhancement for all 12 gliomas. Changes in the serial 1H-MRS imaging data were observed, reflecting an altered metabolism following treatment. These changes included the significant reduction in Cho levels after therapy, indicating the transformation of tumor to necrotic tissue. For patients who demonstrated subsequent clinical progression, an increase in Cho levels was observed in regions that previously appeared either normal or necrotic. Several patients showed regional variations in response to brachytherapy as evaluated by 1H-MRS imaging. This study demonstrates the potential of noninvasive 3-D 1H-MRS imaging to discriminate between the formation of contrast-enhancing radiation necrosis and residual or recurrent tumor following brachytherapy. This modality may also allow better definition of tumor extent prior to brachytherapy by detecting the presence of abnormnal metabolite levels in nonenhancing regions of solid tumor.

Proton spectroscopy of suprasellar tumors in pediatric patients

OBJECTIVE

Magnetic resonance imaging and computed tomography provide good anatomic detail of suprasellar tumors in pediatric patients but are not able to predict histology in many cases. Proton magnetic resonance spectroscopy provides metabolic data that may add to diagnostic specificity. We preoperatively performed localized proton magnetic resonance spectroscopy on pediatric patients with suprasellar tumors and correlated the results with the histological findings. Cyst fluid obtained from patients with craniopharyngiomas was studied with high-resolution magnetic resonance spectroscopy to better understand the in vivo data.

METHODS

Nineteen patients aged 1 to 21 years underwent spectroscopy. Surgical pathological samples were obtained from 14 patients. In each of five patients, the presence of a solid chiasmatic mass in addition to clinical evidence of neurofibromatosis Type I allowed the presumptive diagnosis of chiasmatic astrocytoma. Thus, the study population included 6 patients with craniopharyngiomas, 10 with chiasmatic/hypothalamic astrocytomas, and 3 with pituitary adenomas. The data obtained were compared with those of healthy brain from age-matched participants.

RESULTS

Spectroscopy was specific for the diagnosis. All craniopharyngiomas showed a dominant peak at 1 to 2 ppm, consistent with lactate or lipids, with trace amounts of other metabolites. This was confirmed using high-resolution spectroscopy. Chiasmatic gliomas showed a profile of choline, N-acetylaspartate, and creatine, and the choline:N-acetylaspartate ratio was 2.6 +/- 1.3, compared with 0.7 +/- 0.3 for samples of healthy brain (t test, P = 0.0003). Pituitary adenomas showed only a choline peak or no metabolites at all.

CONCLUSION

Proton spectroscopy may be helpful in supplementing standard imaging for the preoperative diagnosis of three types of suprasellar tumors that are common in pediatric patients.

Diagnosis of brain abscess by magnetic resonance spectroscopy. Report of two cases

Two cases of brain abscess were diagnosed by combining magnetic resonance spectroscopy (MRS) and magnetic resonance (MR) imaging. The resonances observed in vivo were assigned by means of an in vitro MRS study of the exudates extracted during surgical aspiration of the abscesses. The technique of MRS was demonstrated to be very powerful in the differential diagnosis of brain abscesses from other brain pathologies such as neoplasms. Amino acids, probably originating from extracellular proteolysis, and other compounds, such as acetate, arising from bacterial metabolism, were visible in the MRS spectra of the abscess, whereas they are not present in spectra of neoplasms. In this sense, MRS complemented the information provided by MR imaging to achieve a correct diagnosis of brain abscesses and could be added to routine MR examinations with only a small increase in cost and time.

Potential role of in vitro 1H magnetic resonance spectroscopy in the definition of malignancy grading of human neuroepithelial brain tumours

The increasing sensitivity of neuro-imaging in the diagnosis of brain expanding lesions is not directly related to biopathological specificity and new technological approaches are under study. In particular Magnetic Resonance Spectroscopy (MRS) allows evaluation of some biochemical pathways whose metabolic alterations may be correlated with the nature and malignancy grading of primary brain tumours. In the present study the author performed an in vitro high field 1H MRS (9.4 and 14.1 T) analysis of specimens obtained from stereotactic biopsy or microsurgical removal of primary brain tumours. Different samples derived from heterogeneous areas and/or infiltrated perilesional regions were examined. This study was principally focused on malignancy grading of gliomas and its correlation with the ratio (R) between the resonance band arising from choline containing compounds (between 3.14 and 3.35 ppm) and the total creatine signal (3.0 ppm). Analyses allowed significant discrimination between astrocytomas (R = 2.4 +/- 0.6) and glioblastoma (GBM) (R = 4.4 +/- 1.3) [p < 0.002]; however the results did not allow discrimination between differentiated and anaplastic astrocytomas. The GBM showed the largest spread of values corresponding to their higher level of tissue heterogeneity and de-differentiation. Studies on non astrocytic brain tumours indicated that even higher R values were exhibited by oligodendrogliomas, even in well differentiated forms (p < 0.02 with respect to GBM). Moreover, preliminary observations indicated that signals arising from other metabolites may also contribute to a differential diagnosis of different oncotypes. Among these glycine appears particularly relevant, since higher levels were measured for this amino acid in GBM with respect to both astrocytomas and oligodendrogliomas.

Histological heterogeneity of neuroradiologically suspected adult low grade gliomas detected by Xenon enhanced computerized tomography (CT)

Xenon-enhanced computerized tomography (XeCT) was performed on 14 consecutive adult patients presenting with seizures showing supratentorial non-enhancing radiologically uniform appearing low grade gliomas on CT/MR images. Pre-operative XeCT patterns were compared with postoperative histological diagnosis, grading and Ki67 proliferation indices (PI). After gross-total, subtotal resection or biopsy, 11 astrocytomas, 2 oligodendrogliomas and 1 oligo-astrocytoma were diagnosed and graded: Grade I: 2 patients (Ki67-PI = 0.5-0.8), Grade I-II: 4 patients (Ki67-PI = 0.3-1.5), Grade II: 3 patients (Ki67-PI = 0.5-3.5), Grade II-III: 4 patients (Ki67-PI = 3.8-6.8) and Grade III: 1 patient (Ki67-PI = 5.2), (Kernohan Classification). Xenon CT studies revealed different flow patterns, correlating with the postoperative histological diagnosis, grading and proliferation indices: A tumour group with well defined, delayed, only minimally enhancing tumour area (5 patients, Grade I, I-II or II), a second group with less well defined low-flow-area borders and inhomogenous, strong enhancement within the tumour (4 patients, Grade II-III, III) and a third group with fast enhancing tumours was identified. The third pattern was exclusively shown in the 2 oligodendrogliomas (Grade I and II-III) and 1 oligo-astrocytoma (Grade II). The preliminary report identifies the Xenon enhance CT as a beneficial pre-operative investigation for patients with radiologically uniform appearing suspected adult supratentorial low-grade gliomas, which may give information about the presence of anaplastic foci or oligodendroglial components.

Proton magnetic resonance spectroscopy and intracranial tumours: clinical perspectives

Proton magnetic resonance spectroscopy (1H-MRS) was applied to characterize intracranial tumours of different hystological types. Seventy patients with intracranial neoplasms were studied before receiving surgery, radiotherapy or chemotherapy. All tumours were characterized by reduced or absent N-acetylasparate and increased signal from choline-containing compounds. Distinctive patterns were observed only for primitive brain neoplasms; high-grade gliomas were differentiated from low-grade ones by higher levels of choline-containing compounds. The metabolic aspects of metastatic lesions were similar to high-grade gliomas. These results, together with the limitations of 1H-MRS and future applications are reviewed.

Proton chemical shift imaging, metabolic maps, and single voxel spectroscopy of glial brain tumors

Seventeen patients with presumed glial brain tumors were examined with proton chemical shift imaging and single voxel spectroscopy that used different echo times. Metabolite resonances were evaluated by metabolic ratios and absolutely by correcting for coil load and comparison to phantom measurements. Metabolic images were created to visualize the metabolic changes. All patients showed spectra that were different from those measured in healthy control subjects. Spectral changes were also present in normal-appearing matter (NAM) that was distant from lesions. The resonance at 3.55 ppm which is usually assigned to both myo-inositol and glycine, was the only one to allow a discrimination between healthy volunteers, astrocytoma grade II, and glioblastoma multiforme (GBM) (p < 0.02). From the different echo times used we conclude that an increase in this resonance has to be assigned to glycine rather than myo-inositol. This resonance might be used to grade human gliomas more reliably. Total creatine (Cr) decreased more drastically with malignancy than N-acetylated metabolites (NA). This led to a higher NA/Cr ratio in GBM compared to astrocytoma grade II. NA/Cr was thus pseudonormal in GBM due to a change in both nominator and denominator. This study reveals the importance of comparing magnetic resonance spectroscopy data of lesions to spectra measured in identical localizations in healthy control subjects instead of NAM and the importance of quantifying single metabolic peaks instead of creating metabolic ratios in clinical magnetic resonance spectroscopy.

Proton magnetic resonance spectroscopy in patients with glial tumors: a multicenter study

The authors represent a cooperative group of 15 institutions that examined the feasibility of using metabolic features observed in vivo with 1H-magnetic resonance (MR) spectroscopy to characterize brain tumors of the glial type. The institutions provided blinded, centralized MR spectroscopy data processing long with independent central review of MR spectroscopy voxel placement, composition and contamination by brain, histopathological typing using current World Health Organization criteria, and clinical data. Proton 1H-MR spectroscopy was performed using a spin-echo technique to obtain spectra from 8-cc voxels in the tumor and when feasible in the contralateral brain. Eighty-six cases were assessable, 41 of which had contralateral brain spectra. Glial tumors had significantly elevated intensities of choline signals, decreased intensities of creatine signals, and decreased intensities of N-acetylaspartate compared to brain. Choline signal intensities were highest in astrocytomas and anaplastic astrocytomas, and creatine signal intensities were lowest in glioblastomas. However, whether expressed relative to brain or as intratumoral ratios, these metabolic characteristics exhibited large variations within each subtype of glial tumor. The resulting overlaps precluded diagnostic accuracy in the distinction of low-and high-grade tumors. Although the extent of contamination of the 1H-MR spectroscopy voxel by brain had a marked effect on metabolite concentrations and ratios, selection of cases with minimal contamination did not reduce these overlaps. Thus, each type and grade of tumor is a metabolically hetero-geneous group. Lactate occurred infrequently and in all grades. Mobile lipids, on the other hand, occurred in 41% of high-grade tumors with higher mean amounts found in glioblastomas. This result, coupled with the recent demonstration that intratumoral mobile lipids correlate with microscopic tumor cell necrosis, leads to the hypothesis that mobile lipids observed in vivo in 1H-MR spectroscopy may correlate independently with prognosis of individual patients.