Blood oxygen level-dependent (BOLD) MRI: A novel technique for the assessment of myocardial ischemia as identified by nuclear imaging SPECT.

Background: The different levels of deoxyhemoglobin in the ischemic myocardium, induced by stressors such as dipyridamole, can be detected by blood oxygen level-dependent (BOLD) MRI and may be used to diagnose myocardial ischemia. The aim of this study was to assess the signal change in the myocardium on BOLD MRI as well as wall thickening between rest and dipyridamole stress images in ischemic and non-ischemic myocardium as identified on SPECT imaging.

Methods: Twelve patients with stress-induced myocardial ischemia on SPECT underwent rest and dipyridamole stress MRI using a double breath-hold, T2()-weighted, ECG-gated sequence to produce BOLD contrast images as well as cine-MRI for wall thickening assessment in 10 of the 12 patients. Signal change on BOLD MRI and wall thickening were compared between rest and stress images in ischemic and non-ischemic myocardial segments as identified on SPECT. In each patient, two MRI slices containing 16 segments per slice were analysed.

Results: In total, there were 384 segments for BOLD analysis and 320 for wall thickening. For BOLD signal 137 segments correlated to segments with reversible ischemia on SPECT and 247 to normal segments, while for wall thickening 112 segments correlated to segments with reversible ischemia and 208 to normal segments. The average BOLD MRI signal intensity change was -13.8 (+/-16.3)% in the ischemic segments compared to -10.3 (+/-14.7)% in the non-ischemic segments (p=0.05). The average wall thickening was 6.4 (+/-3.4) mm in the ischemic segments compared to 8.7 (+/-3.8) mm in the non-ischemic segments (p<0.0001).

Conclusion: Stress-induced ischemic myocardium has a different signal change and wall thickening than non-ischemic myocardium and may be differentiated on BOLD MRI. Larger studies are needed to define a threshold for detection and to determine the sensitivity and specificity of this technique.