Diffusion MRI is a specific Magnetic Resonace Imaging (MRI) modality that produces in vivo images of biological tissues weighted with the local microstructural characteristics of water diffusion. The mri are a fictional alien species in the Faded Sun Trilogy of C.J. Cherryh. ... Schematic drawing of the effects of diffusion through a semipermeable membrane. ...

More precisely, the image-intensities at each position are attenuated, depending on the strength (b-value) and direction of the so-called magnetic diffusion gradient, as well as on the local microstructure in which the water molecules diffuse. The more attenuated the image is at a given position, the more diffusion there is in the direction of the diffusion gradient. In order to measure the tissues complete diffusion profile, one needs to repeat the MR scans, applying different directions (and possibly strengths) of the diffusion gradient for each scan.

Traditionally, in Diffusion-weighted imaging (DWI), usually three gradient-directions are applied, sufficient to estimate the trace of the diffusion tensor or 'average diffusivity', a putative measure of oedema. Clinically, trace-weighted images have proven to be very useful to diagnose vascular strokes in the brain, by early detection (within a couple of minutes) of the hypoxic oedema. Diffusion-weighted imaging is a specific MRI modality that produces in vivo magnetic resonances images of biological tissues weighted with the local caracteristics of water diffusion. ... Edema (BE: oedema, formerly known as dropsy) is swelling of any organ or tissue due to accumulation of excess fluid. ...

More extended diffusion tensor imaging (DTI) scans comprise at least six gradient directions, sufficient to compute the diffusion tensor. The diffusion model is a rather simple model of the diffusion process, assuming homogeneity and linearity of the diffusion within each image-voxel. From the diffusion tensor diffusion anisotropy measures, such as the Fractional Anisotropy (FA), can be computed. Moreover, the principal direction of the diffusion tensor can be used try infer the white-matter connectivity of the brain (i.e. tractography; try to see which part of the brain is connected to which other part). Diffusion tensor imaging (DTI) is a new magnetic resonance imaging (MRI)-based technique that allows us to visualize the location, the orientation, and the anisotropy of the brains white matter tracts. ... In mathematics, a tensor is (in an informal sense) a generalized linear quantity or geometrical entity that can be expressed as a multi-dimensional array relative to a choice of basis; however, as an object in and of itself, a tensor is independent of any chosen frame of reference. ... Tractography Tractography is a procedure to demonstrate the neural tracts. ...

Recently, more advanced models of the diffusion process have been proposed that aim to overcome the weaknesses of the diffusion tensor model. Amongst others, these include q-space imaging and generalized diffusion tensor imaging.