Magnetic resonance imaging of perfusion using spin inversion of arterial water.

TLDR

The authors developed a proton MRI technique that uses freely diffusing water as a tracer to measure cerebral blood flow in rats. The method labels arterial water spins by continuous inversion at the neck using adiabatic fast passage, solves modified Bloch equations with flow, and derives regional perfusion rates from inversion, control, and T1 images. The technique yielded an average whole‑brain CBF of 1.39 ± 0.19 ml g⁻¹ min⁻¹, a linear CBF–pCO₂ relationship (CBF = 0.052 pCO₂ – 0.173), and successfully visualized perfusion deficits in a freeze‑injured rat brain.

Abstract

A technique has been developed for proton magnetic resonance imaging (MRI) of perfusion, using water as a freely diffusable tracer, and its application to the measurement of cerebral blood flow (CBF) in the rat is demonstrated. The method involves labeling the inflowing water proton spins in the arterial blood by inverting them continuously at the neck region and observing the effects of inversion on the intensity of brain MRI. Solution to the Bloch equations, modified to include the effects of flow, allows regional perfusion rates to be measured from an image with spin inversion, a control image, and a T1 image. Continuous spin inversion labeling the arterial blood water was accomplished, using principles of adiabatic fast passage by applying continuous-wave radiofrequency power in the presence of a magnetic field gradient in the direction of arterial flow. In the detection slice used to measure perfusion, whole brain CBF averaged 1.39 +/- 0.19 ml.g-1.min-1 (mean +/- SEM, n = 5). The technique's sensitivity to changes in CBF was measured by using graded hypercarbia, a condition that is known to increase brain perfusion. CBF vs. pCO2 data yield a best-fit straight line described by CBF (ml.g-1.min-1) = 0.052pCO2 (mm Hg) - 0.173, in excellent agreement with values in the literature. Finally, perfusion images of a freeze-injured rat brain have been obtained, demonstrating the technique's ability to detect regional abnormalities in perfusion.