  Intravoxel Incoherent Motion (IVIM) is a non-contrast magnetic resonance
imaging diffusion-based scan that uses a multitude of b-values to measure
various speeds of molecular perfusion and diffusion, sidestepping inaccuracy of
arterial input functions or bolus kinetics in quantitative imaging. We test a
new method of IVIM quantification and compare our values to reference standard
neutron capture microspheres across normocapnia, CO2 induced hypercapnia, and
middle cerebral artery occlusion in a controlled animal model. Perfusion
quantification in ml/100g/min compared to microsphere perfusion uses the 3D
gaussian probability distribution and defined water transport time as when 50%
of the molecules remain in the tissue of interest. Perfusion, water transport
time, and infarct volume was compared to reference standards. Simulations were
studied to suppress non-specific cerebrospinal fluid (CSF). Linear regression
analysis of quantitative perfusion returned correlation (slope = .55, intercept
= 52.5, $R^2$= .64). Linear regression for water transport time asymmetry in
infarcted tissue was excellent (slope = .59, intercept = .3, $R^2$ = .93).
Strong linear agreement also was found for infarct volume (slope = 1.01, $R^2$=
.79). Simulation of CSF suppression via inversion recovery returned blood
signal reduced by 82% from combined T1 and T2 effects. Intra-physiologic state
comparison of perfusion shows potential partial volume effects which require
further study especially in disease states. The accuracy and sensitivity of
IVIM provides evidence that observed signal changes reflect cytotoxic edema and
tissue perfusion. Partial volume contamination of CSF may be better removed
during post-processing rather than with inversion recovery to avoid artificial
loss of blood signal.
