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 greater than 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 x 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 (less than 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 greater than 150 ml/100 g/min, a more reliable parameter would be the time constant of the MR signal attenuation during the infusion.

A novel fast T1‐mapping method

“…Accurate T1 maps can then be calculated from the T1* maps by using Equation (5). The novelty of the technique lies in the realization that given two sets of data, one T1 weighted and one not, it is always possible, in prin- ciple, to extract not only the magnitude and phase distributions of the magnetizations but also the T1 distribution.…”

Use of 19F magnetic resonance imaging to measure local cerebral blood volume

“…, and utilized by Rudin and Sauter (12) for blood flow imaging in the rat brain, depends on an extravascular effect of an intravascular agent whose magnitude and accuracy are difficult to predict. In our technique, on the other hand, the obtained fluorine signal is directly proportional to the quantity of fluorine in the vascular system without the need for any further physiologic assumptions.…”

Magnetic Resonance Methods and Applications in Pharmaceutical Research

“…Dynamic imaging of the brain provides information on changes in cerebral blood flow (CBF), 179,180 whereas methods exploiting blood-oxygenationlevel-dependent (BOLD) contrast assess relative tissue oxygenation. MR angiography finally allows the identification of the site of the vascular occlusion.…”

“…180,184 This property has been exploited in several experimental animal models of inflammation to follow, in vivo, the infiltration of macrophages into inflamed areas by MRI. For instance, 24 h after intravenous administration of USPIO, signal attenuations have been observed within or near ischemic brain lesions induced by MCAO in the rat.…”