Myocardial perfusion and intracapillary blood volume in rats at rest and with coronary dilatation: MR imaging in vivo with use of a spin-labeling technique

PURPOSE: To validate a magnetic resonance (MR) imaging technique that is no t first pass and that reveals perfusion and regional blood volume (RBV) in the intact rat. MATERIALS AND METHODS: Measurement of perfusion was based on the perfusion- sensitive T1 relaxation after magnetic spin labeling of water protons. REV was determined from steady-state measurements of T1 before and after admini stration of an intravascular contrast agent. The colored microsphere techni que was used as a reference method for perfusion measurement. REV and perfu sion maps were obtained with the rats at rest and during administration of 3 mg of adenosine phosphate per kilogram of body weight per min ute. RESULTS: At MR imaging, perfusion during resting conditions was 3.5 mL/g/mi n +/- 0.1 (SEM), and REV was 11.6% +/- 0.6 (SEM). Adenosine phosphate signi ficantly increased perfusion to 4.5 mL/g/min +/- 0.3 (SEM) and decreased me an arterial pressure from 120 mm Hg to 65 mm Hg, which implies a reduction of coronary resistance to 40% of baseline. REV increased consistently to 23 .8% +/- 0.6 (SEM). CONCLUSION: The study results show that quantitative mapping of perfusion a nd REV may be performed noninvasively by means of MR imaging in the intact animal. The presented method allows determination of vasodilative and perfu sion reserve, which reflects the in vivo regulation of coronary microcircul ation for a given stimulus.