Quantitative measurements of cerebral blood flow in rats using the FAIR technique: Correlation with previous lodoantipyrine autoradiographic studies

Abstract

Flow-sensitive alternating inversion recovery (FAIR) is a recently introduced MRI technique for assessment of perfusion that uses blood water as an endogenous contrast agent. To characterize the FAIR signal dependency on spin tagging time (inversion time (TI)) and to validate FAIR for cerebral blood flow (CBF) quantification, studies were conducted on the rat brain at 9.4 T using a conventional gradient-recalled echo sequence. The T1 of cerebral cortex and blood was found to be 1.9 and 2.2 s, respectively, and was used for CBF calculations. At short TIs (<0.8 s), the FAIR signal originates largely from vascular components with fast flows, resulting in an overestimation of CBF. For TI > 1.5 s, the CBF calculated from FAIR is independent of the spin tagging time, suggesting that the observed FAIR signal originates predominantly from tissue/capillary components. CBF values measured by FAIR with TI of 2.0 s were found to be in good agreement with those measured by the iodoantipyrine technique with autoradiography in rats under the same conditions of anesthesia and arterial pCO2. The measured pCO2 index on the parietal cortex using the FAIR technique was 6.07 ml/100 g/min per mmHg, which compares well with the pCO2 index measured by other techniques. The FAIR technique was also able to detect the regional reduction in CBF produced by middle cerebral artery occlusion in rats.

FAIR true‐FISP perfusion imaging of the kidneys

“…For example, HASTE and UFLARE sequences were reported to allow imaging without susceptibility artifacts, but long acquisition times and blurring must be accepted (7,8). FLASH data acquisition with repeated RF small angle excitation was reported to result in undesired saturation effects on the magnetization in perfusion imaging (9,10) and SNR per measuring time is limited as well. In contrast to the spoiled gradient echo acquisition in FLASH sequences, True-FISP sequences with fully refocused transverse magnetization result in a clearly better signal yield and in fewer saturation effects (11,14).…”

Alpha-chloralose is a suitable anesthetic for chronic focal cerebral ischemia studies in the rat: A comparative study

“…Unfortunately the cerebrovascular effects of α-chloralose have not been extensively studied. The cerebral blood flow under α-chloralose anesthesia in the rat is between 0.69−0.85 ml/g/ min (Duong et al, 2000;Tsekos et al, 1998;Ueki et al, 1988), so the calculated ISO/AC ratio is 1.7−1.9. In the present study the mean initial drop in flow after MCAO was slightly larger in the α-chloralose group (p=0.053), and hyperemia during reperfusion was greater, due in part to the vasodilative features of isoflurane (Lorenz et al, 2001).…”

How accurate is magnetic resonance imaging of brain function?

“…Because the arterial side is permeated with fresh blood significantly faster than the tissue, tagging times that are sufficiently long to allow the equilibrium state to be reached in the large arteries differ from those that allow equilibrium to be reached in the tissue. Thus, long tagging times (,2 s [29]) eliminate the arterial component from perfusion images. Long tagging times, however, can lead to the tagged spins appearing in the venous side, thereby leading to false activation in the veins.…”