Abstract: BACKGROUND AND PURPOSE: GM is typically affected in HD since the presymptomatic stage. Our aim was to investigate with MT MR imaging the microstructural changes of the residual brain subcortical and cortical GM in carriers of the HD gene and to preliminarily assess their correlation with the clinical features. MATERIALS AND METHODS: Fifteen HD gene carriers with a range of clinical severity and 15 age- and sex-matched healthy controls underwent MT MR imaging on a 1.5T scanner. The MT ratio was measured automatically in several subcortical and cortical GM regions (striatal nuclei; thalami; and the neocortex of the frontal, temporal, parietal, and occipital lobes) by using FLS tools. RESULTS: The MT ratio was significantly (P < .05 with Bonferroni correction for multiple comparison) decreased in all subcortical structures except the putamen and decreased diffusely in the cerebral cortex of HD carriers compared with controls. Close correlation was observed between the subcortical and cortical regional MT ratios and several clinical variables, including disease duration, motor disability, and scores in timed neuropsychological tests. CONCLUSIONS: MT imaging demonstrates degeneration of the subcortical and cortical GM in HD carriers and might serve, along with volumetric assessment, as a surrogate marker in future clinical trials of HD.
Abstract: PURPOSE: Metabolite ratios are the measurements most commonly utilised for clinical applications of brain proton magnetic resonance spectroscopy ((1)H-MRS) [1]. We evaluated the agreement between the metabolite ratios calculated with semiautomatic and automatic software. MATERIALS AND METHODS: Two single-voxel spectra (3.375 ml) localised in the frontal grey matter (GM) and peritrigonal white matter (WM) were obtained in 20 healthy subjects by using a point-resolved proton spectroscopy sequence (PRESS, TE=144 ms). The spectra were processed using the semiautomatic software J-Magnetic Resonance User Interface (JMRUI) and the automatic software SpectroView. Agreement of the N-acetyl-aspartate (NAA)/creatine (Cr), NAA/choline (Cho) and Cho/Cr ratios calculated with the two methods was assessed by estimating the 95% limits of agreement (LAs) of the differences of the values obtained with the two software packages. RESULTS: Mean values and standard deviations of NAA/Cr, Cho/Cr and NAA/Cho (semiautomatic//automatic software) were 1.99+/-0.53//1.73+/-0.36, 1.13+/-0.40//1.04+/-0.33, 1.85+/-0.62//1.89+/-0.69 for the GM and 2.24+/-0.41//2.37+/-0.27, 0.96+/-0.17//1.13+/-0.15, 2.37+/-0.43//2.11+/-0.23 for the WM. The 95% LAs were wider for GM spectra and ranged between -0.51, 0.17 for Cho/Cr in the WM and -1.54, 1.47 for NAA/Cho in the GM. CONCLUSIONS: The difference between brain metabolite ratios calculated with the two software packages is not negligible and reflects spectral quality.
Abstract: PURPOSE: To compare repeatability and reproducibility of four different methods of apparent diffusion coefficient (ADC) evaluation of liver parenchyma. In fact, repeatability and reproducibility assessment is mandatory in quantitative evaluations, however, these have not been accurately investigated in liver MR-diffusion-weighted studies. MATERIALS AND METHODS: Diffusion-weighted sequences, b-value = 0-1000 s/mm(2), were acquired on 30 healthy volunteers by a 1.5T scanner whose reliability has been validated by a phantom study. Four sampling methods, evaluating various parenchyma percentages by different-sized region-of-interests (ROIs), were compared by two observers: 70% and 30% of the volume, 4%-one-ROI-per-segment, and 4%-one-ROI-per-slice in the right-lobe. Ninety-five percent limits of agreement and intraclass correlation coefficient (ICC) were calculated. RESULTS: Complete measurements on the left lobe could be obtained in less than half of patients. The 4%-one-ROI-per-slice and 4%-one-ROI-per-segment yielded lower mean values compared with 30-70% volume methods (1343-1373 versus 1463-1560.10(-6) mm(2)/s, respectively). Repeatability was acceptable (ICCs approximately 0.80) whereas reproducibility was low (ICCs <or= 0.45) for all methods. Averaging at least 3 measurements in middle-lower sections of the right lobe improved both repeatability (ICCs to >or=0.87) and reproducibility (ICCs to 0.82) for 30-70% V methods. CONCLUSION: ADC measurements were repeatable but not reproducible in our study. Reproducibility could be improved by taking averages on the right lobe with large ROI methods. Studies on procedures that standardize ADC measurements using more than two observers are needed.
Abstract: PURPOSE: To investigate the impact of cerebrospinal fluid (CSF) contamination on metabolite evaluation in the superior cerebellar vermis with single-voxel (1)H-MRS in normal subjects and patients with degenerative ataxias. MATERIALS AND METHODS: Twenty-nine healthy volunteers and 38 patients with degenerative ataxias and cerebellar atrophy were examined on a 1.5 Tesla scanner. Proton spectra of a volume of interest placed in the superior vermis were acquired using a four TE PRESS technique. We calculated N-acetyl aspartate (NAA)/creatine (Cr), choline (Cho)/Cr, and NAA/Cho ratios, T(2) relaxation times and concentrations of the same metabolites using the external phantom method. Finally, concentrations were corrected taking into account the proportion of nervous tissue and CSF, that was determined as Volume Fraction (VF). RESULTS: In healthy subjects, a significant difference was observed between metabolite concentrations with and without correction for VF. As compared to controls, patients with ataxias showed significantly reduced NAA/Cr and NAA concentrations, while only corrected Cr concentration was significantly increased. The latter showed an inverse correlation with VF. CONCLUSION: CSF contamination has a not negligible effect on the estimation of brain metabolites. The increase of Cr concentration in patients with cerebellar atrophy presumably reflects the substitutive gliosis which takes place along with loss of neurons.
Abstract: A geometric analysis of the global properties of the energy landscape of a minimalistic model of a polypeptide is presented, which is based on the relation between dynamical trajectories and geodesics of a suitable manifold, whose metric is completely determined by the potential energy. We consider different sequences, some with a definite proteinlike behavior, a unique native state and a folding transition, and others undergoing a hydrophobic collapse with no tendency to a unique native state. The global geometry of the energy landscape appears to contain relevant information on the behavior of the various sequences: in particular, the fluctuations of the curvature of the energy landscape, measured by means of numerical simulations, clearly mark the folding transition and allow the proteinlike sequences to be distinguished from the others.
Abstract: We study the geometric properties of the energy landscape of coarse-grained, off-lattice models of polymers by endowing the configuration space with a suitable metric, depending on the potential energy function, such that the dynamical trajectories are the geodesics of the metric. Using numerical simulations, we show that the fluctuations of the curvature clearly mark the folding transition, and that this quantity allows to distinguish between polymers having a proteinlike behavior (i.e., that fold to a unique configuration) and polymers which undergo a hydrophobic collapse but do not have a folding transition. These geometrical properties are defined by the potential energy without requiring any prior knowledge of the native configuration.
