Premium
The effects of microscopic tissue parameters on the diffusion weighted magnetic resonance imaging experiment
Author(s) -
Norris David G.
Publication year - 2001
Publication title -
nmr in biomedicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.278
H-Index - 114
eISSN - 1099-1492
pISSN - 0952-3480
DOI - 10.1002/nbm.682
Subject(s) - nuclear magnetic resonance , diffusion , tortuosity , magnetic resonance imaging , chemistry , molecular diffusion , intravoxel incoherent motion , capillary action , diffusion mri , materials science , physics , thermodynamics , porosity , medicine , metric (unit) , operations management , organic chemistry , radiology , economics , composite material
This review examines the way in which microscopic tissue parameters can affect MR experiments which are sensitive to diffusion. The interaction between the intra‐ and extravascular as well as that between the intra‐ and extracellular spaces is examined. Susceptibility gradients due to the presence of deoxyhemoglobin can cause diffusion‐induced signal losses which are significant in functional magnetic resonance experiments, particularly at higher main magnetic field strengths. This is also true of the fast response that manifests itself as an early negative signal change in functional magnetic resonance experiments. The fields surrounding paramagnetic vessels are described and the way in which diffusion in these fields contributes to functional signal changes is examined. Flow in the capillary bed can be a confounding factor in experiments which aim to examine the diffusion characteristics of extravascular water. It is potentially also a method for assessing capillary perfusion. The intravoxel incoherent motion experiment is described in terms of how significantly this effect can influence diffusion attenuation curves from water. The major models for describing water diffusion in tissue are presented, as are the main experimental results that have contributed to an understanding of the mechanisms of diffusion contrast. The widely accepted view that changes in the diffusion characteristics are caused by a shift of water to the intracellular space and a concomitant change in extracellular tortuosity is examined critically. More recent experiments that indicate that a reduction in the intracellular diffusion may occur simultaneously with the cell swelling are described and their compatibility with existing models discussed. Copyright © 2001 John Wiley & Sons, Ltd. Abbreviations used: 2FDG‐6P fluor‐2‐deoxyglucose‐6‐phosphateADC apparent diffusion coefficientBOLD blood oxygen level dependentCNS central nervous systemCSF cerebro spinal fluidDTI diffusion tensor imagingDWI diffusion weighted imagingfMR functional magnetic resonanceFR fast responseIVCM intravoxel coherent motionIVIM intravoxel incoherent motionMCAO middle cerebral artery occlusionMRI magnetic resonance imagingNMDA N ‐methyl‐ D ‐aspartateNMR nuclear magnetic resonancePFG pulsed field gradientrBF regional blood flowSGP short gradient pulseTE echo time.