Quantification of myocardial blood flow and flow reserve in rats using arterial spin labeling MRI: comparison with a fluorescent microsphere technique.

To quantify noninvasively myocardial blood flow (MBF) and MBF reserve in isoflurane-anesthetized rats using the Look-Locker flow-alternating inversion recovery gradient-echo arterial spin labeling technique (LLFAIRGE-ASL), and to compare the results with the fluorescent microsphere (FM) technique. Male Wistar rats (weight = 200-240 g, n = 21) were anesthetized with 2.0% isoflurane. Hemodynamic parameters were recorded. In seven rats, MBF was assessed on a Bruker Biospec 4.7T MR system using an ECG- and respiration-gated LLFAIRGE-ASL (pixel size = 234 × 468µm(2) , TE = 1.52ms) at rest and during adenosine infusion (140 µg/kg/min). A mixture of 200 000 FM was injected into a second group of rats at rest and during adenosine infusion (n = 7 each), under similar physiologic conditions. Hearts and skeletal muscle samples were processed for fluorescence spectroscopy. Two-tailed unpaired, paired Student's t-test and ANOVA were used to compare groups. MBF measured with LLFAIRGE-ASL was 5.2 ± 1.0 mL/g/min at rest and 13.3 ± 3.0 mL/g/min during adenosine infusion. Results obtained with fluorescent microspheres yielded 5.9 ± 2.3 mL/g/min (nonsignificant vs. LLFAIRGE-ASL, p = 0.9) at rest and 13.1 ± 2.1 mL/g/min (nonsignificant vs. LLFAIRGE-ASL, p = 0.4) during adenosine infusion. Myocardial blood flow reserve measured using LLFAIRGE-ASL and FM were not significantly different (2.5 ± 0.6 vs. 2.4 ± 0.9, respectively; p = 0.8). Hemodynamic parameters during the experiments were not different between the groups. The myocardial blood flow reserve determined under isoflurane anesthesia was 2.5 ± 0.6, which was not different from the value obtained with FM. LLFAIRGE-ASL provided MBF maps with high spatial resolution in rats under isoflurane anesthesia. LLFAIRGE-ASL is a noninvasive measure to assess myocardial blood flow reserve and provides an interesting tool for cardiovascular research.