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

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 T, 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-' (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'-minin) = [19F]trifluoromethane (7-9), and chelated gadolinium contrast agents (10), have led to measurements of tissue perfusion.Here we describe an alternative technique for proton magnetic resonance imaging (MRI) of perfusion rates in the brain by using endogenous water as a diffusable tracer. The method involves labeling the water proton nuclear spins in the arterial blood by continuously inverting them in the neck region before they enter the brain. Continuous inversion is accomplished adiabatically, taking advantage of the linear bulk motion of the blood (11). Proton MRI is used to monitor the effects of perfusion delivering the spin-labeled water to the brain. Solutions to the Bloch equations, which describe the time dependence of magnetization, modified to include the effects of flow, allow regional perfusion rates to be calculated from a set of three images. These are an image with spin inversion, a control image, and a T1 image. We apply this technique to the measurement ofrat brain cerebral blood flow (CBF). To assess the technique's sensitivity to changes in perfusion, we have determined CBF under graded hypercarbia, a condition that is known to increase CBF (12). Finally, by generating perfusion images of a freeze-injured rat brain, we demonstrate that the technique can detect abnormalities in regional CBF. MATERIALS AND METHODSAnimal Preparation. Male Sprague-Dawley rats (200-300 g; Taconic Farms) were anesthetized with 5% halothane, orally intubated, and ventilated on 1% halothane and a 1:1 N20/02 mixture. A femoral arterial line was used for monitoring blood pressure and to sample blood for blood gas determinations. The core temperature of the rats was maintained at 37 ± 1PC by using a circulating water pad. Arterial pCO2 was altered by adding various amounts of CO2 to the ventilator gas mixture up to a...

Blood-flow magnetic resonance imaging of the retina

“…A small circular surface coil (inner diameter ~7 mm) was placed on the left eye. A butterfly neck coil, built into the animal holder, was placed at the neck position for continuous arterial spin labeling (Williams et al, 1992;Shen et al, 2005). The two coils were actively decoupled.…”

“…Blood-flow MRI was acquired using the continuous ASL technique (Williams et al, 1992;Shen et al, 2005) with four-segment, gradient-echo echo-planar imaging (EPI). Paired images were acquired in an interleaved fashion-one with arterial spin labeling and the other without spin labeling.…”

Chronic Hyperperfusion and Angiogenesis Follow Subacute Hypoperfusion in the Thalamus of Rats with Focal Cerebral Ischemia

“…Absolute CBF was quantified using continuous ASL (Williams et al, 1992), with a fast spin-echo read out with a field of view = 4 Â 4 cm 2 , 128 Â 128 points, slice Figure 1 T 2 -weighted coronal slices (A-E) and corresponding cerebral blood flow (CBF) maps (F-J) from a representative rat acquired at baseline (A, F), 2 days (B, G), 7 days (C, H), 30 days (D, I), and 3 months (E, J) after focal cerebral ischemia. Abbreviations for ipsilateral regions of interest: C, cortex; T, thalamus.…”

Visualization of Altered Neurovascular Coupling in Chronic Stroke Patients using Multimodal Functional MRI

“…It has been hypothesized that less widely utilized noninvasive fMRI techniques, for example, arterial spin labeling (ASL) (Williams et al, 1992), which is sensitive to changes in CBF, and vascularspace-occupancy (VASO) (Lu et al, 2003), which is sensitive to changes in CBV, might more accurately quantify details of cortical hemodynamics in chronic stroke (Donahue et al, 2012). Clinically, ASL has been used to show perfusion deficits in acute (MacIntosh et al, 2010b) and chronic (Brumm et al, 2010) stroke and VASO has been successfully applied in studies of ischemic steno-occlusive disease (Donahue et al, 2009c(Donahue et al, , 2010.…”