In-vivo multi-exponential T 2, magnetization transfer and quantitative histology in a rat model of intramyelinic edema

摘要

Two MRI methods, multi-exponential analysis of transverse relaxation (MET 2 ) and quantitative magnetization transfer (qMT), were used along with quantitative evaluation of histology in a study of intra-myelinic edema in rat spinal white matter. The results showed a strong linear correlation between a distinct long-T 2 signal from MET 2 analysis and the edema water volume fraction as measured by histology, although this analysis overestimated the edema water content by ≈100% relative to quantitative histological measurements. This overestimation was reasoned to result from the effects of inter-compartmental water exchange on observed transverse relaxation. Commonly studied MRI markers for myelin, the myelin water fraction (from MET 2 analysis) and the macromolecular pool size ratio (from qMT analysis) produced results that could not be explained purely by changes in myelin content. The results demonstrate the potential for MET 2 analysis as well as the limits of putative myelin markers for characterizing white matter abnormalities involving intra-myelinic edema. Highlights ? We studied a rat model of intra-myelinic edema induced by hexachlorophene ingestion. ? We used multi-exponential T 2 (MET 2 ) and quantitative magnetization transfer MRI. ? Histology was quantitatively evaluated to measure edema volume and myelin content. ? MET 2 provides a measure that correlates but overestimates with edema volume fraction. ? MET 2 measure of edema is affected by microscopic water dynamics.