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We analyzed the properties of the logarithm of the Rician distribution leading to a full characterization of the probability law of the errors in the linearized diffusion tensor model. An almost complete lack of bias, a simple relation between the variance and the signal-to-noise ratio in the original complex data, and a close approximation to normality facilitated estimation of the tensor components by an iterative weighted least squares algorithm. The theory of the linear model has also been used to derive the distribution of mean diffusivity, to develop an informative statistical test for relative lack of fit of the ellipsoidal (or spherical) model compared to an unrestricted linear model in which no specific shape is assumed for the diffusion process, and to estimate the signal-to-noise ratios in the original data. The false discovery rate (FDR) has been used to control thresholds for statistical significance in the context of multiple comparisons at voxel level. The methods are illustrated by application to three diffusion tensor imaging (DTI) datasets of clinical interest: a healthy volunteer, a patient with acute brain injury, and a patient with hydrocephalus. Interestingly, some salient features, such as a region normally comprising the basal ganglia and internal capsule, and areas of edema in patients with brain injury and hydrocephalus, had patterns of error largely independent from their mean diffusivities. These observations were made in brain regions with sufficiently large signal-to-noise ratios (>2) to justify the assumptions of the log Rician probability model. The combination of diffusivity and its error may provide added value in diagnostic DTI of acute pathologic expansion of the extracellular fluid compartment in brain parenchymal tissue. Hum. Brain Mapping 24:144-155, 2005. © 2004 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Objetivo: El trastorno obsesivo-compulsivo (TOC) es un trastorno neuropsiquiátrico frecuente, hereditario, hipotéticamente provocado por alteraciones en la conexión de numerosos sistemas cerebrales. Se desconoce la amplitud de las alteraciones en la sustancia blanca en el TOC y se conocen pocos datos acerca de las bases genéticas del trastorno. Los autores utilizaron una técnica de resonancia magnética, la neuroimagen por tensor de difusión, para examinar las alteraciones en la sustancia blanca de la estructura cerebral a través de la cuantificación de la difusión de agua, y confirmar si existen alteraciones en la sustancia blanca en el TOC. También exploraron si tales anomalías se presentan en los familiares de primer grado sanos, lo que indicaría la posible existencia de endofenotipos que representen un riesgo genético aumentado para el TOC. Método: Los autores utilizaron las imágenes por tensor de difusión para medir la anisotropía fraccional de la sustancia blanca en 30 pacientes con TOC, 30 familiares de primer grado no afectados y 30 individuos sanos de comparación apareados. Mediante pruebas de permutación se identificaron las regiones de anisotropía fraccional anormal significativa en los pacientes, comparados con los individuos sanos de control. Los autores evaluaron si estas anormalidades eran evidentes también en los familiares de primer grado. Se practicó un análisis secundario de regiones de interés para evaluar el alcance de la reproducción entre nuestros datos y las publicaciones relevantes previas. Resultados: Los pacientes con TOC presentaron una reducción significativa de la anisotropía fraccional en una amplia región de la sustancia blanca parietal derecha y un aumento significativo de la anisotropía fraccional en la región frontal media derecha. Los familiares también presentaron alteraciones significativas en la anisotropía fraccional en estas regiones. Conclusiones: Estos hallazgos indican que el TOC está asociado con alteraciones en la sustancia blanca en las regiones frontal y parietal. Alteraciones similares en familiares de primer grado no enfermos sugieren que podría tratarse de endofenotipos del TOC en la sustancia blanca. [ABSTRACT FROM AUTHOR]

Objective: To explore the possibilities of radioligands against the mitochondrial outer membrane translocator protein (TSPO) as biomarkers for mitochondrial disease, we performed brain PET-MRI with [ 11 C]PK11195 in 14 patients with genetically confirmed mitochondrial disease and 33 matched controls., Methods: Case-control study of brain PET-MRI with the TSPO radioligand [ 11 C]PK11195., Results: Forty-six percent of symptomatic patients had volumes of abnormal radiotracer binding greater than the 95th percentile in controls. [ 11 C]PK11195 binding was generally greater in gray matter and significantly decreased in white matter. This was most striking in patients with nuclear TYMP or mitochondrial m.3243A>G MT-TL 1 mutations, in keeping with differences in mitochondrial density seen postmortem. Some regional binding patterns corresponded to clinical presentation and underlying mutation, even in the absence of structural changes on MRI. This was most obvious for the cerebellum, where patients with ataxia had decreased binding in the cerebellar cortex, but not necessarily volume loss. Overall, there was a positive correlation between aberrant [ 11 C]PK11195 binding and clinical severity., Conclusion: These findings endorse the use of PET imaging with TSPO radioligands as a noninvasive in vivo biomarker of mitochondrial pathology., Classification of Evidence: This study provides Class III evidence that brain PET-MRI with TSPO radioligands identifies mitochondrial pathology., (Copyright © 2021 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.)