Bayesian modeling of Dynamic Contrast Enhanced MRI data in cerebral glioma patients improves the diagnostic quality of hemodynamic parameter maps.

PURPOSE: The purpose of this work is to investigate if the curve-fitting algorithm in Dynamic Contrast Enhanced (DCE) MRI experiments influences the diagnostic quality of calculated parameter maps. MATERIAL AND METHODS: We compared the Levenberg-Marquardt (LM) and a Bayesian method (BM) in DCE data of 42 glioma patients, using two compartmental models (extended Toft's and 2-compartment-exchange model). Logistic regression and an ordinal linear mixed model were used to investigate if the image quality differed between the curve-fitting algorithms and to quantify if image quality was affected for different parameters and algorithms. The diagnostic performance to discriminate between high-grade and low-grade gliomas was compared by applying a Wilcoxon signed-rank test (statistical significance p>0.05). Two neuroradiologists assessed different qualitative imaging features. RESULTS: Parameter maps based on BM, particularly those describing the blood-brain barrier, were superior those based on LM. The image quality was found to be significantly improved (p<0.001) for BM when assessed through independent clinical scores. In addition, given a set of clinical scores, the generating algorithm could be predicted with high accuracy (area under the receiver operating characteristic curve between 0.91 and 1). Using linear mixed models, image quality was found to be improved when applying the 2-compartment-exchange model compared to the extended Toft's model, regardless of the underlying fitting algorithm. Tumor grades were only differentiated reliably on plasma volume maps when applying BM. The curve-fitting algorithm had, however, no influence on grading when using parameter maps describing the blood-brain barrier. CONCLUSION: The Bayesian method has the potential to increase the diagnostic reliability of Dynamic Contrast Enhanced parameter maps in brain tumors. In our data, images based on the 2-compartment-exchange model were superior to those based on the extended Toft's model.

The role of the microcirculation in delayed cerebral ischemia and chronic degenerative changes after subarachnoid hemorrhage.

The mortality after aneurysmal subarachnoid hemorrhage (SAH) is 50%, and most survivors suffer severe functional and cognitive deficits. Half of SAH patients deteriorate 5 to 14 days after the initial bleeding, so-called delayed cerebral ischemia (DCI). Although often attributed to vasospasms, DCI may develop in the absence of angiographic vasospasms, and therapeutic reversal of angiographic vasospasms fails to improve patient outcome. The etiology of chronic neurodegenerative changes after SAH remains poorly understood. Brain oxygenation depends on both cerebral blood flow (CBF) and its microscopic distribution, the so-called capillary transit time heterogeneity (CTH). In theory, increased CTH can therefore lead to tissue hypoxia in the absence of severe CBF reductions, whereas reductions in CBF, paradoxically, improve brain oxygenation if CTH is critically elevated. We review potential sources of elevated CTH after SAH. Pericyte constrictions in relation to the initial ischemic episode and subsequent oxidative stress, nitric oxide depletion during the pericapillary clearance of oxyhemoglobin, vasogenic edema, leukocytosis, and astrocytic endfeet swelling are identified as potential sources of elevated CTH, and hence of metabolic derangement, after SAH. Irreversible changes in capillary morphology and function are predicted to contribute to long-term relative tissue hypoxia, inflammation, and neurodegeneration. We discuss diagnostic and therapeutic implications of these predictions.

[Diffusion-weighted imaging can differentiate cerebral abscesses from tumours of the brain]. / Diffusionsvægtet magnetisk resonans-skanning kan skelne abscesser fra tumorer i hjernen.

Early diagnosis of cerebral abscess, which is decisive for the prognosis, is often complicated by the lack of clinical signs. Conventional computed tomography and magnetic resonance imaging cannot always differentiate a cystic or necrotic tumor from an abscess. An abscess is therefore sometimes misdiagnosed as e.g. a glioblastoma or metastasis. Unfortunately, this is sometimes seen at our department and could maybe have been prevented. Diffusion-weighted imaging and apparent diffusion coefficient facilitate differentiation between cerebral tumor and abscess with a sensitivity of 95.2% (76.2-99.9%) and a specificity of 95.7% (78.1-99.9%).

Atrophy of foot muscles in diabetic patients can be detected with ultrasonography.

OBJECTIVE: To establish a bedside test with ultrasonography for evaluation of foot muscle atrophy in diabetic patients. RESEARCH DESIGN AND METHODS: Thickness and cross-sectional area (CSA) of the extensor digitorum brevis muscle (EDB) and of the muscles of the first interstitium (MILs) were determined in 26 diabetic patients and in 26 matched control subjects using ultrasonography. To estimate the validity, findings were related to the total volume of all foot muscles determined at magnetic resonance imaging (MRI-FM(vol)). Furthermore, the relations of ultrasonographic estimates to nerve conduction, sensory perception thresholds, and clinical condition were established. RESULTS: In diabetic patients, the ultrasonographic thickness of EDB (U-EDB(t)) was (means +/- SD) 6.4 +/- 2.1 vs. 9.0 +/- 1.0 mm in control subjects (P < 0.001), the thickness of MIL (U-MIL(t)) was 29.6 +/- 8.3 vs. 40.2 +/- 3.6 mm in control subjects (P < 0.001), and the CSA of EDB (U-EDB(CSA)) was 116 +/- 65 vs. 214 +/- 38 mm(2) in control subjects (P < 0.001). The MRI-FM(vol) was directly related to U-EDB(t) (r = 0.77), U-MIL(t) (r = 0.71), and U-EDB(CSA) (r = 0.74). U-EDB(t) and U-MIL(t) were thinner in neuropathic than in nonneuropathic diabetic patients (5.8 +/- 2.1 vs. 7.5 +/- 1.7 mm [P < 0.05] and 28.3 +/- 8.8 vs. 35.6 +/- 4.3 mm [P < 0.03], respectively). CONCLUSIONS: Atrophy of intrinsic foot muscles determined at ultrasonography is directly related to foot muscle volume determined by MRI and to various measures of diabetic neuropathy. Ultrasonography seems to be useful for detection of foot muscle atrophy in diabetes.