No abstract

Nonmonoexponential MR diffusion decay behavior has been observed at high diffusion-weighting strengths for cell aggregates and tissues, including the myocardium; however, implications for myocardial MR diffusion tensor imaging are largely unknown. In this study, a slow-exchange-limit, two-component diffusion tensor model was fitted to diffusion-weighted images obtained in isolated, perfused rat hearts. Results indicate that there are at least two distinct components of anisotropic diffusion, characterized by a "fast" component whose principal diffusivity is comparable to that of the perfusate, and a highly anisotropic "slow" component. It is speculated that the two components correspond to tissue compartments and have a general agreement with the orientations of anisotropy, or fiber orientations, in the myocardium. Moreover, consideration of previous studies of myocardial diffusion suggests that the presently observed fast component may likely be dominated by diffusion in the vascular space, whereas the slow component may include the intracellular and interstitial compartments. The proton MR signal is sensitive to the molecular dynamics of water. In the presence of applied magnetic field gradients, such as the classic Stejskal-Tanner pulsed gradient spin echo (PGSE) pair (1), information regarding the translational Brownian motion (i.e., self-diffusion, or simply diffusion) of water can be quantitatively characterized from the induced signal attenuation. Furthermore, because molecular movements are strongly influenced by the organization and geometry of the microscopic environment, diffusion-weighted MRI has emerged as a useful tool to probe the microstructure of materials and biological tissues.One class of diffusion-weighted MRI for characterizing anisotropic diffusion is diffusion tensor imaging (DTI) (2). In 3D space, the generalized diffusion tensor is a symmetric, 3 ϫ 3 matrix, and its eigenvalues and eigenvectors correspond to the diffusivities and orientations of the principal axes of diffusion, respectively. By quantifying diffusion along at least six noncoplanar directions, as specified by the relative amplitudes of the diffusion-encoding gradient pulses in the laboratory reference frame, a unique set of solutions to the six independent variables of the diffusion tensor can be determined. Compared to conventional histology, the noninvasive nature and relative speed of DTI makes it an attractive alternative for assessing the structure of ordered tissues. DTI has so far been utilized to characterize the fiber architectures of the brain white matter (3), spinal cord (4,5), cartilage (6), myocardium (7-10), and other musculature (11,12).While qualitative agreements with the known tissue structure were found in most cases, conventional DTI studies implicitly assume that 1) the eigenvector corresponding to the largest ranked diffusion tensor eigenvalue (i.e., the direction in which diffusion is fastest) coincides with the local tissue fiber orientation, and 2) diffusion in these tissues exhibits a monoexpone...

The clinical phenotype of leucine-rich glioma-inactivated protein 1 (LGI1) and contactin-associated proteinlike 2 (CASPR2) autoimmunity is well defined in adults. Data for children are limited (<10 cases). Among 13,319 pediatric patients serologically tested for autoimmune neurological disorders (2010-2017), 264 were seropositive for voltage-gated potassium channel-complex-IgG (radioimmunoprecipitation). Only 13 (4.9%) were positive by transfected cell-binding assay for LGI1-IgG (n = 7), CASPR2-IgG (n = 3), or both (n = 3). This is significantly less than in adults. Encephalopathy, seizures, and peripheral nerve hyperexcitability were common, as was coexisting autoimmunity. No faciobrachial dystonic seizures or cancers were identified. Functional neurologic disorders were frequently the initial diagnosis, and immunotherapy appeared beneficial. Ann Neurol 2018;84:473-480.

Magnetic resonance imaging (MRI) is now a leading diagnostic technique. As technology has improved, so has the spatial resolution achievable. In 1986 MR microscopy (MRM) was demonstrated with resolutions in the tens of microns, and is now an established subset of MRI with broad utility in biological and non-biological applications. To date, only large cells from plants or aquatic animals have been imaged with MRM limiting its applicability. Using newly developed microsurface coils and an improved slice preparation technique for correlative histology, we report here for the first time direct visualization of single neurons in the mammalian central nervous system (CNS) using native MR signal at a resolution of 4–8µm. Thus MRM has matured into a viable complementary cellular imaging technique in mammalian tissues.