Proton magnetic resonance spectroscopy of brain-stem lesions.

The imaging findings of brain-stem lesions are often nonspecific and histological diagnosis is limited because of fear of complications associated with biopsy. A noninvasive method for tissue characterization is therefore highly desirable. We undertook a review of proton magnetic resonance spectroscopy (MRS) of patients with solitary brain-stem lesions to determine if MRS could characterize them. We carried out single- or multivoxel proton MRS using long echo times (135 or 270 ms) on 34 patients with solitary brain-stem lesions. We analyzed the following peaks: choline (Cho), creatine (Cr), N-acetylaspartate (NAA), and lipids/lactate (Lip) and calculated peak height ratios for Cho/Cr, NAA/Cr and Lip/Cr. The results were compared with histology in nine patients and with the presumptive diagnosis in 25. We also performed single-voxel proton MRS on the brain stem of five normal volunteers. There were differences in all ratios between controls and the patients with neoplastic and non-neoplastic lesions: Cho/Cr was low in non-neoplastic and high in neoplastic lesions (control: 1.8+/-0.1; non-neoplastic: 1.4+/-0.2; neoplastic: 2.0+/-0.2); NAA/Cr was low in non-neoplastic, and lower in neoplastic lesions (control: 2.3+/-0.1; non-neoplastic: 1.4+/-0.2; neoplastic: 1.2+/-0.1), and Lip/Cr was elevated in both neoplastic and non-neoplastic lesions (control: 0.04+/-0.02; nonneoplastic: 1.9+/-0.7; neoplastic:1.9+/-0.7).

Apparent diffusion coefficients in the evaluation of high-grade cerebral gliomas.

BACKGROUND AND PURPOSE: Preliminary data indicate that apparent diffusion coefficient (ADC) values may be useful in identifying and grading primary cerebral tumors. We tested the hypothesis that ADC values can be used to differentiate tumor, edema, and normal brain tissue. METHODS: Fifteen patients with high-grade cerebral astrocytomas underwent conventional MR imaging, diffusion-weighted MR imaging, and proton MR spectroscopy. We defined tumor as an area containing the highest choline/creatine and choline/N-actetyl aspartate ratios, contrast enhancement, and abnormal T2 signal intensity. Edema was defined as tissue with normal proton MR spectra, no enhancement, and high T2 signal intensity. Normal brain was assumed if tissue had normal proton MR spectra, no enhancement, and normal T2 signal intensity in the hemispheres ipsilateral or contralateral to tumor. ADC maps were calculated and regions of interest were manually placed over areas of tumor, edema, and normal tissue. Comparisons were made by analysis of variance. For post hoc testing, the Tukey method was used to correct for the effect of multiple comparisons, and significance was accepted if P was less than .05. RESULTS: When ADC values were analyzed as a group, significant differences were found between tumor (131 + 45) and normal brain tissue (ipsilateral to tumor, 92 + 22; contralateral to tumor, 78 + 5) but not between tumor and adjacent edema (129 + 45). A plot of individual data points showed considerable overlapping among the three types of tissue sampled. CONCLUSION: As a group, ADC values helped to distinguish high-grade glioma from normal tissue but could not be used to separate high-grade glioma from surrounding edema. Individually, ADC values overlapped considerably and were not useful in our patients. The utility of ADC values (as obtained in this relatively small study) is questionable in patients with high-grade cerebral astrocytomas.

Proton MR spectroscopy in patients with acute temporal lobe seizures.

BACKGROUND AND PURPOSE: Decreases in N-acetyl aspartate (NAA) as seen by proton MR spectroscopy are found in hippocampal sclerosis, and elevated levels of lipids/lactate have been observed after electroconvulsive therapy. Our purpose was to determine whether increased levels of lipids/lactate are found in patients with acute seizures of hippocampal origin. METHODS: Seventeen patients with known temporal lobe epilepsy underwent proton MR spectroscopy of the mesial temporal lobes within 24 hours of their last seizure. Four of them were restudied when they were seizure-free. Five healthy individuals were used as control subjects. All MR spectroscopy studies were obtained using a single-voxel technique with TEs of 135 and 270. The relationship between the presence of lipids/lactate and seizures was tested using Fisher's exact test. Mean and standard deviations for NAA/creatine (Cr) were obtained in the hippocampi in patients with seizures on initial and follow-up studies and these values were compared with those in the control subjects. RESULTS: Seizure lateralization was obtained in 15 patients. Of the 17 seizure locations that involved hippocampi, 16 showed lipids/lactate by proton MR spectroscopy. Of the 13 hippocampi not directly affected by seizures, 10 showed no lipids/lactate and three showed lipids/lactate. The relationship between lipids/lactate and seizure location was confirmed. A comparison of NAA/Cr ratios for the involved hippocampi with those in control subjects showed significant differences on initial MR spectroscopy; however, no significant difference was found between acute and follow-up NAA/Cr ratios in hippocampi affected by seizures. CONCLUSION: Lipids/lactate were present in the hippocampi of patients with acute seizures and decreased when the patients were seizure-free. Thus, lipids/lactate may be a sensitive marker for acute temporal lobe seizures.

Correlation of myo-inositol levels and grading of cerebral astrocytomas.

BACKGROUND AND PURPOSE: In a limited number of patients, the level of myo-inositol (MI), as seen by proton magnetic resonance spectroscopy (HMRS), has been shown to differ for gliomas of different histologic grades. We sought to determine if MI levels correlate with cerebral astrocytoma grade. METHODS: Five control subjects, 14 patients with low-grade astrocytoma, 10 patients with anaplastic astrocytoma, and 10 patients with glioblastoma multiforme (GBM) underwent single-volume HMRS with an echo time of 20 ms. Twenty-five patients had received surgery, chemotherapy, and/or radiation therapy previously. Using the curve-fitting program supplied by the manufacturer, peak areas for n-acetyl aspartate (NAA), choline (Cho), and MI were normalized with respect to the peak area of creatine (Cr). Ratios for MI/Cr, Cho/Cr, and NAA/Cr were obtained for each lesion and retrospectively compared with the histologic grade of the lesion. RESULTS: Levels of MI/Cr were higher (0.82 +/- 0.25) in patients with low-grade astrocytoma, intermediate (0.49 +/- 0.07) in control subjects, and lower in patients with anaplastic astrocytoma (0.33 +/- 0.16) and GBM (0.15 +/- 0.12). CONCLUSION: Our study shows a trend toward lower MI levels in the presence of anaplastic astrocytomas and GBMs compared with those of low-grade astrocytomas. MI levels may have implications in the grading of cerebral astrocytomas.

Colloid cyst of the third ventricle: imaging-pathologic correlation.

Colloid cysts are relatively rare intracranial lesions located in the rostral aspect of the third ventricle. They may produce acute hydrocephalus, brain herniation, and lead to death. Although the clinical and imaging features of colloid cysts are well known, their etiology and the factors responsible for their imaging features continue to be a subject of debate. We present the imaging-pathologic correlation of a patient with a colloid cyst as well as data supporting the fact that the presence of cholesterol is probably responsible for the MR imaging features exhibited by some colloid cysts.

Effects of contrast material on single-volume proton MR spectroscopy.

BACKGROUND AND PURPOSE: Administration of contrast material before proton MR spectroscopy may allow more accurate placement of the volume of interest, particularly in tumors; yet, some data have suggested that contrast material may alter the results of MR spectroscopy. To determine the validity of this contention, we performed pre- and postcontrast MR spectroscopy in patients with brain tumors and compared the results with those obtained from a phantom. METHODS: Ten patients with astrocytomas were examined with single-volume MR spectroscopy before and after administration of contrast material. Voxel placement was identical for all studies. Peak area, peak height, and width at half maximum were measured for N-acetyl aspartate (NAA), creatine (Cr), and choline (Cho) in all studies. A phantom containing a 10 mmol concentration of NAA, Cr, and Cho was prepared in phosphate-buffered saline and mixed with contrast concentrations varying from 0.1 to 1.0 mmol. The phantom was studied by MR spectroscopy with the same parameters as used for the clinical studies. RESULTS: No significant differences were found between the pre- and postcontrast MR spectroscopy studies for the three parameters measured. In phantom studies, there was a significant decline in the Cho peak area and height and an increase in the width at half maximum as the concentration of contrast material increased from 0.1 to 1.0 mmol. NAA and Cr peaks showed no significant changes in peak height or area. CONCLUSION: Contrast material may be administered before clinical MR spectroscopy without affecting its interpretation.

Proton MR spectroscopy in children with bipolar affective disorder: preliminary observations.

BACKGROUND AND PURPOSE: Bipolar affective disorder (BPAD) can have its onset during childhood, but the diagnosis may be difficult to establish on the basis of clinical findings alone. Our purpose was to determine whether proton MR spectroscopy can be used to identify abnormalities in the brain of children with BPAD. METHODS: Ten children, ages 6 to 12 years, underwent clinical testing to establish the diagnosis of BPAD. After a drug washout period, all patients underwent MR spectroscopy in which a TE of 135 was used along with a single-voxel placement in both frontal and temporal lobes during a single session. Peaks from N-acetylaspartate (NAA), choline (Cho), glutamate/ glutamine (Glu/Gln), and lipids were normalized with respect to the creatine (Cr) peak to obtain ratios of values of peak areas. These data were compared with those obtained in 10 non-age-matched control subjects. To corroborate our data, five children with BPAD also underwent 2D MR spectroscopic studies of the frontal lobes with parameters similar to those used in the single-volume studies. RESULTS: All children with BPAD had elevated levels of Glu/Gln in both frontal lobes and basal ganglia relative to the control group. Children with BPAD had elevated lipid levels in the frontal lobes but not in the temporal lobes. Levels of NAA and Cho were similar for all locations in both groups. Two-dimensional MR spectroscopic studies in five children with BPAD confirmed the presence of elevated lipids in the frontal lobes. CONCLUSION: Our preliminary observations suggest that MR spectroscopy may show abnormalities in children with BPAD not found in unaffected control subjects. It remains to be established whether these abnormalities are a signature of the disease and can be used as a screening test.

Sydenham's chorea: MRI and proton spectroscopy.

We present the MRI and proton spectroscopy findings in a child with clinical diagnosis of Sydenham's chorea. MRI showed high signal in the caudate nuclei and putamina on T2-weighted images. We believe that the spectra showed an abnormality in the number and/or function of neurons, lipids from cellular breakdown (cytolytic effect of antibodies), aminoacids (related to the presence of antibodies in the neostriatum), and sugars (also related to the presence of antibodies). The spectroscopy features correlate well with the histopathology and biochemistry of this rare disorder.

Localized MR spectroscopy: basic principles.

Radiologic techniques such as positron-emission tomography and single-photon emission tomography have been used for many years to determine metabolic changes in disease processes. Because of increased radiation exposure, these techniques are normally not used to perform extended serial studies to monitor disease processes. This article discusses the basics of MR spectroscopy, various techniques, and terminology used in clinical MR spectroscopy.

Proton MR spectroscopy of common brain tumors.

Proton MR spectroscopy allows differentiation of normal tissues from pathologic ones. There is now evidence that this technique may be able to distinguish different histological grades of tumors. The proton MR spectroscopic changes due to treatment of brain tumors is discussed in this article.

Proton MR spectroscopy in psychiatric and neurodevelopmental childhood disorders: early experience.

Variations in brain morphology are increasingly being found in patients with psychiatric disorders. There is early evidence that some metabolic abnormalities may also be present in these patients. In many patients with psychiatric disorders, the diagnosis is not straight forward and may be confounded by co-morbid processes. Establishing the correct diagnosis is important as it leads to institution of appropriate therapies. Descriptions of the authors early experience using proton MR spectroscopy in the evaluation of children with bipolar affective disorder, attention deficit hyperactivity disorder, neurodevelopmental abnormalities in patients with neurofibromatosis type 1, and the effects of certain types of treatment used for these disorders are discussed.

Usefulness of proton MR spectroscopy in the evaluation of temporal lobe epilepsy.

OBJECTIVE: The purpose of our study was to compare the ability of MR spectroscopy with that of standard presurgical methods to accurately lateralize the abnormal hippocampus in a group of patients with complex partial seizures. SUBJECTS AND METHODS: Ten healthy volunteers (five male, five female) without a history of seizures, significant head trauma, or other neurologic abnormalities were chosen to participate in the study. Twelve consecutive patients (three male, nine female) having intractable temporal lobe epilepsy and undergoing presurgical evaluation for temporal lobectomy were chosen to participate in the study. The condition of all patients was refractory to medications. All patients underwent presurgical examination with interictal and video ictal electroencephalography, ictal single-photon emission computed tomography, interictal positron emission tomography, MR imaging, and neuropsychologic testing. When noninvasive data were inconclusive, depth or grid recordings were performed. The results of MR spectroscopy were also compared with postsurgical seizure control as defined by the Engel classification. RESULTS: Nine (90%) of 10 control subjects showed no significant difference in N-acetyl aspartate. One control subject showed 16% asymmetry in N-acetyl aspartate between sides. The control group showed no statistically significant differences in ratios of N-acetyl aspartate:creatine, N-acetyl aspartate:choline, or creatine:choline when comparing sides (p < .05). All 12 patients showed clearly lateralizing values identified by the index of asymmetry in N-acetyl aspartate (range, 24-93%), with a mean difference of 51% (SD, 22) (p = .01). Additionally, as a group, statistically significant indexes of asymmetry (p = .01) were seen in ratios of N-acetyl aspartate:choline (mean, 42; SD, 22%), N-acetyl aspartate:creatine (mean, 41; SD, 27), and N-acetyl aspartate:creatine + choline (mean, 42; SD, 22). Using an N-acetyl aspartate index of asymmetry of greater than 15%, which represents the mean index of asymmetry of the control subjects +/- two SDs, as our cutoff level for lateralization, the correct side was identified in all patients. When comparing both hippocampi using an asymmetry index of 15% for N-acetyl aspartate:choline + creatine, 11 (92%) of 12 were correctly lateralized. When comparing the unaffected temporal lobes between patients and control subjects, no statistically significant differences were detected in any metabolites or ratios. CONCLUSION: Our study agrees with others in showing decreased N-acetyl aspartate in the hippocampus of seizure patients when compared with control subjects. Using N-acetyl aspartate, N-acetyl aspartate:creatine, N-acetyl aspartate:choline, and N-acetyl aspartate:creatine + choline as our parameters, patients with mesial temporal lobe epilepsy were correctly lateralized with MR spectroscopy when compared with clinical consensus criteria. We consider MR spectroscopy to be complementary to MR imaging. Both studies can be performed as a single integrated examination.

Proton MR spectroscopy in neoplastic and non-neoplastic brain disorders.

The basic principles of proton MR spectroscopy as well as newer and more advanced related techniques are reviewed. Spectroscopy is capable of differentiating normal from pathologic brain and provides tissue specificity greater than that of imaging in many instances. Spectroscopic mapping allows for the visualization of the concentration of different metabolites and their distribution within a lesion. This article emphasizes the utility of proton MR spectroscopy in the diagnosis of brain tumors, postradiation therapy changes, infections, degenerative brain disorders, hepatic encephalopathy, ischemia, and demyelination.

MR spectroscopy in the evaluation of epilepsy.

MR spectroscopy may be a helpful, reliable, noninvasive test with which to lateralize the seizure focus in patients with partial complex seizures. MR spectroscopy is complementary to other studies, especially MR imaging, and both may be performed in a single integrated examination and result in improved surgical management and outcome.

Extraneous lipid contamination in single-volume proton MR spectroscopy: phantom and human studies.

PURPOSE: To determine the degree of extraneous lipid contamination in defined volumes of interest studied with single-volume proton MR spectroscopy. METHODS: Single-volume proton MR spectroscopy was performed on a fat/water phantom and in three volunteers using the stimulated-echo acquisition mode (STEAM) and point-resolved spectroscopy (PRESS) localization methods. Three different volumes of interest (8, 27, and 64 cm3) were examined at echo times of 20, 135, and 270 for the STEAM sequences and 135 and 270 for the PRESS acquisitions in both the phantom and the volunteers (volumes of interest were placed adjacent to but not encompassing fat-containing structures, such as the scalp and retroorbital fat). The degree of lipid contamination was then correlated with measurements of the section profiles. RESULTS: The PRESS method resulted in less extraneous lipid contamination in both phantom and volunteer studies. The STEAM method had the highest level of lipid contamination signal in phantom and human studies. In the volunteers, volumes of interest abutting fat-containing structures obtained with PRESS or STEAM sequences showed no lipid contamination. However, the STEAM sequences showed lipid signal in the volume of interest adjacent to orbital fat whereas the PRESS sequences did not. These observations are supported by the section profile studies, which showed that the actual volume excited by the STEAM sequence was 7% to 32% larger than that originally selected, while with PRESS the actual excited volume was 12% to 16% smaller than that originally selected. CONCLUSION: In our MR unit, short-echo-time STEAM sequences (< or = 135 milliseconds) resulted in extraneous lipid contamination in phantom and human studies adjacent to the orbits. PRESS sequences showed no lipid contamination in volumes abutting fat structures in phantoms or humans. These results correlated closely with the configuration of the section profiles. Although these findings might be dependent on the MR unit used, our study could help determine extraneous lipid contamination for other MR units.

Proton MR spectroscopy of squamous cell carcinoma of the extracranial head and neck: in vitro and in vivo studies.

PURPOSE: To determine the ability of in vitro one-dimensional and two-dimensional proton MR spectroscopy to help differentiate squamous cell carcinoma of the extracranial head and neck from normal tissues and to correlate the in vitro observations with clinical studies. METHODS: In vitro 1-D and 2-D correlated proton MR spectroscopy (11 T) was performed in tissue specimens of squamous cell carcinoma of the head and neck (n = 19), in normal tissue (n = 13), in metastatic cervical lymph nodes (n = 3), and in a squamous cell carcinoma cell line. In vivo 1-D proton MR spectroscopy (1.5 T) was performed in patients with squamous cell carcinoma (n = 7) and in healthy volunteers (n = 7). The ratio of the areas under the choline (Cho) and creatine (Cr) resonances were calculated for 1-D proton MR spectra for the in vitro tissue studies and correlated with the in vivo studies. Data from in vitro 2-D correlated spectroscopy were analyzed for differences in the presence or absence of various metabolites in samples of tumor and normal tissue. Statistical analysis consisted of 2 x 2 factorial repeated measures analysis of variance (ANOVA), discriminate analysis, and chi2 test. RESULTS: The mean in vitro 1-D proton MR spectroscopic Cho/Cr ratio was significantly higher in tumor than in normal tissue. The difference between the mean ratios appeared to increase with increasing echo time. All in vivo tumor Cho/Cr ratios were greater than the calculated mean in vitro tumor ratio, whereas six of the seven volunteers had no detectable Cho and Cr resonances. Two-dimensional correlated MR spectroscopic data revealed that a variety of amino acids have a significantly greater likelihood of being detected in tumor than in normal tissues. CONCLUSIONS: One-dimensional and 2-D proton MR spectroscopy can help differentiate primary squamous cell carcinoma and nodal metastases containing squamous cell carcinoma from normal tissue both in vitro and in vivo. In addition, 2-D spectroscopy can help identify the presence of certain amino acids in squamous cell carcinoma that are not detected in normal tissue.

Postmortem MR imaging of the brains of patients with AIDS.

Forty-two postmortem formalin-fixed brains of known patients with AIDS were examined with T2-weighted MR imaging before brain cutting. The gross and microscopic brain findings were correlated with the T2 signal changes in the postmortem MR imaging. The brains included examples of progressive multifocal leukoencephalopathy with involvement of the central brain and cerebellum. The authors also encountered the coexistence of progressive multifocal leukoencephalopathy and HIV encephalitis, and the T2 signal changes for each were compared. The T2 signal changes of leptomeningeal and perivascular space cryptococcal infection and CMV ependymitis are documented. Several expressions of primary cerebral lymphoma, including large nodules, choroid plexus infiltration, and diffuse microscopic sites of tumor also are assessed.

Proton MR spectroscopy in Coats disease.

We describe a case of acute left-sided visual loss in a 4-year-old boy. CT showed hyperdense retinal detachment with a tiny calcification, and MR imaging showed subretinal hyperintensity on both T1- and T2-weighted images. Proton MR spectroscopy showed a large peak between 1 and 1.6 ppm that we believe corresponds mainly to lipids, which are characteristic of the exudate present in Coats disease.