Jos
Rufino Solera Urea1, Salvador Olmos Gass1, Valerij G.
Kiselev2
1Aragon Institute of Engineering
Research, Universidad de Zaragoza, Zaragoza, Spain; 2Dept. of
Diagnostic Radiology, Medical Physics, University Hospital Freiburg,
Freiburg, Germany
The
signal attenuation observed in DSCMRI measurements is considered largely to
obey to susceptibility-induced magnetic inhomogeneities at the mesoscopic
scale. Another mesoscopic process contributing to increased spin dephasing is
the diffusion of tissue water carrying a transverse magnetisation M into the
blood pool, where it then experiences faster relaxation due to the presence
of paramagnetic contrast agent. To quantify this effect, an effective
extravascular dephased volume is defined. Analytical expressions are given
for various exchange regimes and numerical estimates are compared with the
vascular volume. Results indicate that in the brain the exchange of tissue
magnetisation across the bloodbrain barrier is permeability limited and does
not contribute significantly to the signal dephasing. However, the
contribution of magnetisation exchange may be important in organs with
increased capillary permeability and/or blood volume. The method is applicable to other problems in
quantitative perfusion MRI.