  Intravoxel incoherent motion (IVIM) is a method that can provide quantitative
information about perfusion in the human body, in vivo, and without contrast
agent. Unfortunately, the IVIM perfusion parameter maps are known to be
relatively noisy in the brain, in particular for the pseudo-diffusion
coefficient, which might hinder its potential broader use in clinical
applications. Therefore, we studied the conditions to produce optimal IVIM
perfusion images in the brain. IVIM imaging was performed on a 3-Tesla clinical
system in four healthy volunteers, with 16 b values 0, 10, 20, 40, 80, 110,
140, 170, 200, 300, 400, 500, 600, 700, 800, 900 s/mm2, repeated 20 times. We
analyzed the noise characteristics of the trace images as a function of
b-value, and the homogeneity of the IVIM parameter maps across number of
averages and sub-sets of the acquired b values. We found two peaks of noise of
the trace images as function of b value, one due to thermal noise at high
b-value, and one due to physiological noise at low b-value. The selection of b
value distribution was found to have higher impact on the homogeneity of the
IVIM parameter maps than the number of averages. Based on evaluations, we
suggest an optimal b value acquisition scheme for a 12 min scan as 0 (7), 20
(4), 140 (19), 300 (9), 500 (19), 700 (1), 800 (4), 900 (1) s/mm2.
