RESUMO
Conventional MR imaging does not discriminate basal ganglia and thalamic internal anatomy well. Radiology reports describe anatomic locations but not specific functional structures. Functional neurosurgery uses indirect targeting based on commissural coordinates or atlases that do not fully account for individual variability. We describe innovative MR imaging sequences that improve the visualization of normal anatomy in this complex brain region and may increase our understanding of basal ganglia and thalamic function. Better visualization also may improve treatments for movement disorders and other emerging functional neurosurgery targets. We aim to provide an accessible review of the most clinically-relevant neuroanatomy within the thalamus and basal ganglia.
Assuntos
Gânglios da Base , Tálamo , Gânglios da Base/anatomia & histologia , Gânglios da Base/diagnóstico por imagem , Encéfalo , Humanos , Imageamento por Ressonância Magnética/métodos , Procedimentos Neurocirúrgicos/métodos , Tálamo/anatomia & histologia , Tálamo/diagnóstico por imagemRESUMO
At very low diffusion weighting the diffusion MRI signal is affected by intravoxel incoherent motion (IVIM) caused by dephasing of magnetization due to incoherent blood flow in capillaries or other sources of microcirculation. While IVIM measurements at low diffusion weightings have been frequently used to investigate perfusion in the body as well as in malignant tissue, the effect and origin of IVIM in normal brain tissue is not completely established. We investigated the IVIM effect on the brain diffusion MRI signal in a cohort of 137 radiologically-normal patients (62 male; mean ageâ¯=â¯50.2⯱â¯17.8, rangeâ¯=â¯18 to 94). We compared the diffusion tensor parameters estimated from a mono-exponential fit at bâ¯=â¯0 and 1000â¯s/mm2 versus at bâ¯=â¯250 and 1000â¯s/mm2. The asymptotic fitting method allowed for quantitative assessment of the IVIM signal fraction f* in specific brain tissue and regions. Our results show a mean (median) percent difference in the mean diffusivity of about 4.5 (4.9)% in white matter (WM), about 7.8 (8.7)% in cortical gray matter (GM), and 4.3 (4.2)% in thalamus. Corresponding perfusion fraction f* was estimated to be 0.033 (0.032) in WM, 0.066 (0.065) in cortical GM, and 0.033 (0.030) in the thalamus. The effect of f* with respect to age was found to be significant in cortical GM (Pearson correlation ρ â= â0.35, p â= â3*10-5) and the thalamus (Pearson correlation ρâ¯=â¯0.20, pâ¯=â¯0.022) with an average increase in f* of 5.17*10-4/year and 3.61*10-4/year, respectively. Significant correlations between f* and age were not observed for WM, and corollary analysis revealed no effect of gender on f*. Possible origins of the IVIM effect in normal brain tissue are discussed.
Assuntos
Córtex Cerebral/diagnóstico por imagem , Imagem de Difusão por Ressonância Magnética/normas , Substância Cinzenta/diagnóstico por imagem , Microcirculação , Neuroimagem/normas , Tálamo/diagnóstico por imagem , Substância Branca/diagnóstico por imagem , Adolescente , Adulto , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Córtex Cerebral/irrigação sanguínea , Imagem de Difusão por Ressonância Magnética/métodos , Feminino , Substância Cinzenta/irrigação sanguínea , Humanos , Masculino , Microcirculação/fisiologia , Pessoa de Meia-Idade , Movimento (Física) , Neuroimagem/métodos , Fatores Sexuais , Tálamo/irrigação sanguínea , Substância Branca/irrigação sanguínea , Adulto JovemRESUMO
Functional neurosurgery is a rapidly growing field with exciting future potential applications. This article describes currently used implanted electronic devices for neurologic stimulation and monitoring. The devices to be reviewed include invasive EEG electrodes, deep brain stimulator, motor cortex stimulator, responsive neurostimulation, osteo-integrated hearing aid, middle ear implant, cochlear implant, auditory brainstem implant, vagal nerve stimulator and spinal cord stimulator. Emphasis is placed on the normal components, function, positioning, potential complications and MRI safety of these devices. Understanding the motivations and appropriate use of these implantable devices is critical for clinical neuroradiologists to provide relevant imaging interpretation and protocols for patients and referring physicians.