Proton MR spectroscopy in predicting the increase of perfusion MR imaging for WHO grade II gliomas.

PURPOSE: To investigate the correlation between the metabolite ratios obtained from proton magnetic resonance (MR) spectroscopy and those obtained from MR perfusion parameters (relative cerebral blood volume [rCBV]) in a cohort of low-grade glioma (LGG). MATERIALS AND METHODS: Patients underwent prospectively conventional MR, proton magnetic resonance spectroscopy ((1) HMRS), and perfusion-weighted images (PWI). Statistical analyses were performed to determine the correlative and independent predictive factors of rCBVmax and the metabolite ratio thresholds with optimum sensitivity and specificity. RESULTS: Thirty-one patients were included in this study. Linear correlations were observed between the metabolic ratios (lactate [Lac]/creatine [Cr], choline [Cho]/N-acetyl-aspartate [NAA], free-lipids/Cr) and rCBVmax (P < 0.05). These metabolic ratios were determined to be independent predictive factors of rCBVmax (P = 0.027, 0.011 and 0.032, respectively). According to the receiver operating characteristic curves, the cutoff values of the metabolic ratios to discriminate between the two populations of rCBVmax (<1.7 versus = 1.7) were 1.72, 1.54, and 1.40, respectively, with a sensitivity = 75% and a specificity >95% for Lac/Cr. CONCLUSION: This study demonstrated consistent correlations between the data from (1) HMRS and PWI. The Lac/Cr ratio predicts regional hemodynamic changes, which are themselves a useful biomarker of clinical prognosis in patients with LGG. As such, this ratio may provide a new parameter for making improved clinical decisions.

Usefulness of magnetic resonance spectroscopy in urea cycle disorders.

Late-onset urea cycle disorders are characterized by chronic encephalopathy and a risk of hyperammonemic crises triggered by environmental stressors. Reported here is the case of a 30-year-old woman with chronic encephalopathy due to argininosuccinate lyase deficiency. Cerebral proton magnetic resonance spectroscopy showed brain creatine deficiency and its normalization during treatment. These findings are in keeping with recent reports suggesting that creatine deficiency is involved in the neurological dysfunction of urea cycle disorders and demonstrate the usefulness of magnetic resonance spectroscopy in the diagnosis and follow-up of urea cycle disorders.

[Cerebral tumours: which images?]. / Tumeurs cérébrales: quelle imagerie?

Magnetic resonance imaging became the gold standard examination of pretherapeutic planning and post-treatment follow-up of cerebral tumours, even if computed tomography remains useful. During the last years, many new modalities of magnetic resonance examination arose, thus leading to increase its specificity. Then, spectroscopy allows better understanding of tumoural metabolism, whereas perfusion weighted imaging provides informations on its neovascularisation. Functional cortical activation imaging and diffusion tensor imaging allows delineation of tumoural extension towards eloquent areas and fiber bundles. Last, peroperative magnetic resonance imaging may lead to better control tumour resection during operation. However, while numerous and increasing the specificity of magnetic resonance examination, confrontation to pathology data remains necessary.

Characterization and correction of distortions in stereotactic magnetic resonance imaging for bilateral subthalamic stimulation in Parkinson disease.

OBJECT: High-frequency stimulation of the subthalamic nucleus (STN) is effective for treating refractory idiopathic Parkinson disease (PD). In stereotactic conditions magnetic resonance (MR) imaging is used by many teams to perform preoperative targeting of the STN. The goal of this study was to analyze and correct the geometrically observed MR imaging acquisitions used for targeting of the STN. METHODS: A dedicated phantom of known geometry was used. The authors calculated existing shifts between measured points and theoretically defined points on the same T1- and T2-weighted sequences used to target the STN. A shifting volume was built to correct the phantom images and images acquired preoperatively in 13 patients with PD. A quantitative study of the correction was conducted using the phantom images and acquisitions acquired in these patients. To quantify the distortion corrections, the authors segmented the lateral ventricles and calculated the overlap of the corrected and uncorrected values between T1 and T2 segmentation. The authors found that the distortions were greater in the direction of slice selection and frequency encoding and weaker on three-dimensional T1-weighted acquisitions. On T2-weighted acquisitions, the maximum shifts were 2.19 mm in the frequency-encoding direction and 3.81 mm in slice selection. The geometrical distortion was significantly reduced and smaller than pixel size after distortion correction. Assessment of the patients' scans showed that the mean ventricular overlap was 76% before and 94% after correction. CONCLUSIONS: The authors found that significant distortions can be observed on T2-weighted images used to demonstrate the STN. These distortions can be corrected using appropriate software.

Is the subthalamic nucleus hypointense on T2-weighted images? A correlation study using MR imaging and stereotactic atlas data.

BACKGROUND AND PURPOSE: Although the subthalamic nucleus is the most frequently used target for surgical treatment of Parkinson's disease, the criteria on which it can be identified on T2-weighted images have never been clearly defined. This study was conducted to characterize the precise anatomic distribution of T2-weighted hyposignal in the subthalamic region and to correlate this hyposignal with iron content in the subthalamic nucleus. METHODS: The T2-weighted MR imaging acquisitions of 15 patients with Parkinson's disease were fused with a digitized version of the Schaltenbrand and Wahren anatomic atlas. The MR signal intensity within the anatomic limits of the subthalamic nucleus was evaluated. An anatomic specimen obtained at autopsy was used to evaluate iron content. RESULTS: In all patients, the subthalamic nucleus was hypointense on both sides in the anterior half of the nucleus. At more posterior levels of the nucleus, hypointensity was less frequently observed (20-80%). Hypointensity was never observed at the most posterior pole. Iron was present in the anteromedial part of the nucleus but absent at the most posterior levels. CONCLUSION: The hypointense signal intensity located lateral to the red nucleus and dorsolateral to the substantia nigra correlates with the presence of iron and corresponds anatomically to the subthalamic nucleus. It can therefore be used as a landmark for electrode implantation in patients with Parkinson's disease. It should, however, be emphasized that although hypointensity was always present in the anterior half of the subthalamic nucleus, the posterior part of the nucleus was not visible in most cases.

Mathematical modeling of energy metabolism and hemodynamics of WHO grade II gliomas using in vivo MR data.

Therapeutic management of low-grade gliomas (LGG) is a challenge because they have undergone anaplastic transformation with variable delay. Today, only progressive volume growth on successive MRI allows an in vivo monitoring of this evolution. On the other hand, multinuclear spectroscopy and perfusion available during MRI may also provide assessment of metabolic changes underlying morphological modifications. To overcome this drawback, we developed a mathematical model of the metabolism and the hemodynamic of gliomas, based on a physiological model previously published, and including the MR parameters. This allows us to suggest that some specific profiles of metabolic and hemodynamic changes would be good indicators of potential anaplastic transformation.

Brain lymphoma: usefulness of the magnetic resonance spectroscopy.

The diagnosis of primary central nervous system lymphoma (PCNSL) should always be considered as an emergency because of the therapeutic consequences it implies. In immunocompetent patients, it relies on stereotactic biopsy. Unfortunately, clinical and radiological features may be misleading and delay the diagnostic procedure. The case we report here illustrates the contribution of magnetic resonance spectroscopy in the diagnostic approach of a very atypical PCNSL.

Proton magnetic resonance spectroscopy predicts proliferative activity in diffuse low-grade gliomas.

The aim of the study was to investigate the ability of (1)HMRS to reflect proliferative activity of diffuse low-grade gliomas (WHO grade II). Between November 2002 and March 2007, a prospective study was performed on consecutive patients with suspected supratentorial hemispheric diffuse low-grade tumors. All the patients underwent MR examination using uniform procedures, and then surgical resection or biopsy within 2 weeks of the MR examination. Proliferative activity of the tumors was assessed by Ki-67 immunochemistry (Mb-1) on paraffin embedded tumor sections. Spectroscopic data was compared with Ki-67 labeling index and other histologic data such as histological subtype, cellular atypia, cellular density using univariate and multivariate analysis. 82 of 97 consecutive patients had histologically confirmed WHO grade 2 gliomas. Ki-67 proliferation index (PI) was correlated with specific spectral patterns: (1) low PI (<4%) was associated with increased Cho/Cr and absence of both free lipids or lactates; (2) intermediate PI (4-8%) was associated with resonance of lactates; and (3) high PI (>8%) was characterized by a resonance of free lipids. On multivariate analysis, resonance of lactates and resonance of free lipids appeared as independent predictors of intermediate PI (P < 0.001) and high PI (P < 0.001), respectively; moreover, free lipids resonance was correlated with cellular atypia (P < 0.05). This study suggests that (1)HMRS is a reliable tool to evaluate the proliferation activity of WHO grade 2 glioma and to identify potentially more aggressive clinical behavior.