Measurement of cerebral mean transit time by dynamic susceptibility contrast magnetic resonance imaging

Objective: To determine whether direct measurement of mean transit time from pixels over in-plane vessels on high spatial resolution echo planar imaging is a reliable method for quantitative assessment of cerebral circulation. Methods and materials: Dynamic susceptibility contrast studies were performed using high spatial resolution echo planar imaging (echo time, 60 ms; field of view, 256x192-270x203 mm; matrix size, 256x192; slice thickness, 4 mm) in ten healthy subjects. Forty sequential measurements of five images between the level of the middle cerebral arteries and that of the centrum semiovale were acquired every 1.5 s before, during, and after intravenous injection of 0.12 mmol/kg of gadopentetate dimeglumine. Mean transit times were calculated from the results of gamma variate fitting to the measured ΔR2* data of the middle cerebral arteries, cerebral cortex and white matter. Results: The calculated true mean transit times for cerebral cortex and white matter varied greatly among individuals and from side to side even in a given individual. The fitness of regression models for the ΔR2* curves of the middle cerebral arteries was significantly lower than those for cerebral cortex and white matter. Conclusion: Direct measurement of mean transit time from pixels over in-plane vessels was not sufficiently accurate for quantitative assessment of cerebral circulation, probably because the echo planar imaging we used had spatial resolution and dynamic range insufficient for determination of mean transit time for in-plane vessels