Effects of CBV, CBF, and blood-brain barrier permeability on accuracy of PASL and VASO measurement

Abstract

Cerebral blood flow, cerebral blood volume (CBV), and water permeability through blood-brain barrier are important hemodynamic parameters in brain physiology. Pulsed arterial spin labeling and vascular-space occupancy techniques have been used to measure regional cerebral blood flow and CBV, respectively. However, these techniques generally ignore the effects of one hemodynamic parameter on the measurement of others. For instance, the influences of CBV changes on arterial spin labeling or the permeability effects on vascular-space occupancy typically were not accounted for in the quantification of blood flow or volume. In the current work, the biophysical effects of CBV on pulsed arterial spin labeling and permeability on vascular-space occupancy signals are evaluated using a general two-compartment model. The dependence of these effects on the T(1) at various field strengths is also assessed by simulations. Results indicate that CBV has negligible to small influences on pulsed arterial spin labeling signal (<6.6% at 3 T) and permeability effects are negligible on vascular-space occupancy signal (<0.1% at 3 T) under normal physiologic conditions. In addition, CBV effect on pulsed arterial spin labeling is further diminished at high field strengths, but residual blood contamination in vascular-space occupancy signal may be enhanced at high fields due to the reduced difference between extra- and intravascular T(1) values.

Figure 1

An illustration of two-compartment model with blood flow and permeability effects. Each compartment has its own magnetization (M) and longitudinal relaxation time (T₁).

Figure 2

Estimations of percent CBV contribution (a) at different absolute CBV values at 3T, and (b) at different magnetic fields with absolute CBV = 5 ml/100g, under two types of perfusion scenarios.

Figure 3

(a) Decomposition of CBF and CBV effects from VASO signal changes at different magnetic fields (b) Optimal CNR of VASO over multiple repetition times and field strengths.

Figure 4

Percent blood contribution in VASO signal to evaluate the permeability effects. (a) under 3 baseline CBF conditions at 3T, (c) under multiple field strengths with CBF = 60 ml/100g/min.