Noninvasive determination of regional cerebral blood flow in rats using dynamic imaging with Gd(DTPA)

Abstract

A method for the noninvasive, quantitative determination of regional cerebral blood flow (rCBF) in small laboratory animals, such as the rat, is described. The change in magnetic susceptibility in the vicinity of brain capillaries evoked by iv infusion of Gd(DTPA), a paramagnetic agent not crossing the blood-brain barrier, is detected as an attenuation of the ¹H signal in T₂-weighted MRI sequences. The reduction of the MR signal intensity after 1 or 2 min of Gd(DTPA) infusion correlates well (r > 0.95) with the rCBF values obtained using the well-established [¹⁴C] iodoantipyrine method. At a slice thickness of 3 mm, the pixel size typically is 0.15 × 0.5 mm². The clearance rate of Gd(DTPA) from blood allows repeated measurements of CBF to be made using this technique approximately every 30 min. The experimental results obtained in normal and ischemic rat brain have been rationalized within the frame of a two-compartment model, allowing the definition of optimal experimental conditions for a given CBF: for normal and reduced CBF values (<150 ml/100 g/min) the reduction in MR signal intensity, measured after 1 or 2 min of Gd(DTPA) infusion, correlates closely with the CBF. However, for CBF values<150 ml/100g/min, a more reliable parameter would be the time constant of the MR signal attenuation during the infusion. © 1991 Academic Press, Inc.