Abstract 20415: Spin Labeling MRI Detects Improvements of Regional Myocardial Perfusion in the Ischemic Heart after Stem Cell Engraftment
MRI-based quantification of myocardial blood flow (perfusion) is especially challenging in rodent models, particularly in the setting of their high heart rates. We assessed the hypotheses that 1) the spin labeling (SL) technique could be validated against the gold standard microsphere method for estimation of myocardial perfusion; 2) the improvement of myocardial perfusion after engraftment of endothelial progenitor cells in a rodent model of myocardial ischemia could be detected by SL-MRI. For validation, five rats were cannulated and subjected to SL- MRI, in which the blood flow was calculated from T1 relaxation times obtained under the global or slice-selective inversion of spins respectively. Immediately after MR, 0.2 million fluorescence microspheres (FMs) were injected into the left ventricle and blood sample was withdrawn. To examine the utility of the spin labeling technique, myocardial ischemia was induced by surgery in athymic rats. Five millions of human umbilical vessel endothelial cells (HUVEC) or culture media were injected into the infarct border zone. Initial infarction size was estimated at day 1 post surgery by MRI and animals with infarction size 10–30% of left ventricle mass were included. Myocardial perfusion and cardiac function were measured over time by MRI. A strong correlation (R2=0.94) was obtained for the absolute value of blood flow measured by spin labeling MRI and FM techniques with a slope close to 1. At 2 weeks post HUVEC injection, the absolute perfusion (HUVEC vs control) in the infarcted region (2.92 ± 1.07 vs 1.60 ± 0.16 ml/min•gram) and anterior region (2.65 ± 0.35 vs 1.87 ± 0.26 ml/min•gram) was significantly higher in HUVEC treated than control group (p<0.05, n=5 for each group). In conclusion, SL-MRI allows high resolution mapping of myocardial perfusion in rodents which have rapid heart rates (400–600 bpm) and are not suitable for other techniques such as dynamic contrast enhanced MRI. The absolute perfusion values by SL-MRI are in excellent agreement with those obtained by standard but invasive FM method. This noninvasive method enabled serial monitoring of myocardial perfusion improvement in response to stem cell engraftment. Such capability is crucial in the development of cell therapy for myocardial infarction.
- © 2010 by American Heart Association, Inc.