RESUMEN
The objective of the current study was to quantify the degree of white matter (WM) abnormalities in chronic and virally suppressed HIV-infected (HIV+) persons while carefully taking into account demographic and disease factors. Diffusion tensor imaging (DTI) was conducted in 40 HIV- and 82 HIV+ men with comparable demographics and life style factors. The HIV+ sample was clinically stable with successful viral control. Diffusion was measured across 32 non-colinear directions with a b-value of 1000 s/mm2; fractional anisotropy (FA) and mean diffusivity (MD) maps were quantified with Itrack IDL. Using the ENIGMA DTI protocol, FA and MD values were extracted for each participant and in 11 skeleton regions of interest (SROI) from standard labels in the JHU ICBM-81 atlas covering major striato-frontal and parietal tracks. We found no major differences in FA and MD values across the 11 SROI between study groups. Within the HIV+ sample, we found that a higher CNS penetrating antiretroviral treatment, higher current CD4+ T cell count, and immune recovery from the nadir CD4+ T cell count were associated with increased FA and decreased MD (p < 0.05-0.006), while HIV duration, symptomatic, and asymptomatic cognitive impairment were associated with decreased FA and increased MD (p < 0.01-0.004). Stability of HIV treatment and antiretroviral CNS penetration efficiency in addition to current and historical immune recovery were related to higher FA and lower MD (p = 0.04-p < 0.01). In conclusion, WM DTI measures are near normal except for patients with neurocognitive impairment and longer HIV disease duration.
Asunto(s)
Fármacos Anti-VIH/uso terapéutico , Encéfalo/diagnóstico por imagen , Disfunción Cognitiva/diagnóstico por imagen , Infecciones por VIH/diagnóstico por imagen , Sustancia Blanca/diagnóstico por imagen , Anciano , Anisotropía , Terapia Antirretroviral Altamente Activa , Encéfalo/inmunología , Encéfalo/virología , Mapeo Encefálico , Linfocitos T CD4-Positivos/inmunología , Linfocitos T CD4-Positivos/virología , Disfunción Cognitiva/tratamiento farmacológico , Disfunción Cognitiva/inmunología , Disfunción Cognitiva/virología , Imagen de Difusión Tensora , Infecciones por VIH/tratamiento farmacológico , Infecciones por VIH/inmunología , Infecciones por VIH/virología , VIH-1/efectos de los fármacos , VIH-1/fisiología , Homosexualidad Masculina , Humanos , Masculino , Persona de Mediana Edad , Estudios Prospectivos , Factores de Tiempo , Carga Viral/efectos de los fármacos , Sustancia Blanca/inmunología , Sustancia Blanca/virologíaRESUMEN
Measuring the geometry or morphology of sulcal folds has recently become an important approach to investigating neuroanatomy. However, relationships between cortical sulci and other brain structures are poorly understood. The present study investigates how age-related changes in sulcal width are associated with age-related changes in traditional indices of brain structure such as cortical thickness, and cortical gray matter (GM), white matter (WM), subcortical, and white matter hyperintensity (WMH) volumes. These indices and sulcal width were measured at baseline and at two-year follow up in 185 community-dwelling individuals (91 men) aged 70-89 years. There were significant increases in sulcal width and WMH volume, and significant decreases in all other indices between baseline and follow-up. Sulcal widening was associated with decreases in cortical GM, subcortical and WM volumes. A further association between sulcal width and cortical thickness became non-significant when cortical GM volume was controlled for. Our findings give insights into the mechanisms responsible for cortical sulcal morphology. The relationships between sulcal morphology and other common measures suggest that it could be a more comprehensive measure for clinical classifications than traditional neuroimaging metrics, such as cortical thickness.
Asunto(s)
Envejecimiento/patología , Puntos Anatómicos de Referencia/patología , Corteza Cerebral/patología , Sustancia Gris/patología , Imagen por Resonancia Magnética , Neuroimagen , Sustancia Blanca/patología , Anciano , Anciano de 80 o más Años , Atrofia/patología , Femenino , Humanos , Estudios Longitudinales , Masculino , Tamaño de los Órganos , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
PURPOSE: To investigate the anisotropic elasticity of soft tissues using MR elastography (MRE) combined with diffusion tensor imaging (DTI). MATERIALS AND METHODS: The storage moduli parallel (µ(â)) and perpendicular (µ(â¥)) to the local fiber orientation were calculated assuming a transversely isotropic model. The local fiber orientation was provided by DTI. The proposed technique was validated against rheometry using anisotropic viscoelastic phantoms with various fiber volume fractions (V(f) = 0%, 15%, and 35%) and bovine skeletal muscle samples. RESULTS: The anisotropic ratio (µ(â)/µ(â¥)) as measured by MRE correlated well with rheometry for all samples (R(2) = 0.809). The combined MRE/DTI technique was also able to differentiate different levels of mechanical anisotropy with the mechanical anisotropy (µ(â)/µ(â¥)) of the V(f) = 35% phantoms being significantly higher than the V(f) = 15% and the isotropic (V(f) = 0%) phantoms. The bovine muscle samples showed significantly higher mechanical anisotropy than all phantoms. CONCLUSION: This study has demonstrated the feasibility of the proposed imaging technique for characterizing mechanical anisotropy of anisotropic materials and biological tissues, and validated the mechanical anisotropy results.
Asunto(s)
Imagen de Difusión por Resonancia Magnética/métodos , Diagnóstico por Imagen de Elasticidad/métodos , Imagen por Resonancia Magnética/métodos , Algoritmos , Animales , Anisotropía , Bovinos , Elasticidad , Diseño de Equipo , Procesamiento de Imagen Asistido por Computador , Modelos Estadísticos , Músculo Esquelético/patología , Fantasmas de Imagen , Reología , Estrés Mecánico , ViscosidadRESUMEN
White matter in the brain exhibits strong anisotropic conductivity. Modeling studies on electroencephalography have found that such anisotropic conductivity greatly influences the estimated dipole source. In this study, we made a detailed comparison of the effects of conductivity anisotropy using a computational model of electroconvulsive therapy (ECT). The human head model was a high resolution finite element model generated from MRI scans, implemented with tissue heterogeneity and an excitable neural model incorporated in the brain. Results showed that anisotropy in conductivity had minimal effects on the location of the brain region that was maximally activated, but it had relatively large effects on deep brain structures.
Asunto(s)
Potenciales de Acción/fisiología , Encéfalo/fisiología , Terapia Electroconvulsiva/métodos , Modelos Neurológicos , Fibras Nerviosas Mielínicas/fisiología , Terapia Asistida por Computador/métodos , Anisotropía , Simulación por Computador , HumanosRESUMEN
Understanding the biomechanical mechanisms by which the cerebral cortex folds is a fundamental problem in neuroscience. Current mathematical models of cortical folding do not include three dimensional geometry or measurement of cortical growth in developing brains extracted from experimental data. We present two biomechanical models of cortical folding which integrate 3D geometry and information taken from MRI scans of fetal sheep brains at a number of key developmental stages. The first model utilises diffusion tensor imaging (DTI) measurements of white matter fibre orientation in the fetal sheep brains as a cue to the tension forces that may regulate folding. In the second model, tangential cortical growth is modelled by osmotic expansion of the tissue and regulated by inhomogeneous white matter rigidity as a biomechanism of cortical folding. This is based on quantitative analysis of cortical growth and inhomogeneous white matter anisotropy measured from the MRI data. We demonstrate that structural and diffusion tensor MRI can be combined with finite element modelling and an explicit growth mechanism of the cortex to create biologically meaningful models of the cortical folding process common to higher order mammals.