Validation of in vivo myocardial strain measurement by magnetic resonance tagging with sonomicrometry

OBJECTIVES This study was designed to validate strain measurements obtained using magnetic resonance tagging with spatial modulation of magnetization (SPAMM). We compared circumferential segment shortening measurements (%S) obtained using SPAMM to sonomicrometry %S in a canine model with (n = 28) and without (n = 3) coronary artery ligation . BACKGROUND Magnetic resonance tagging enables noninvasive measurement of myocardial strain, but such strain measurements have not yet been validated in vivo. METHODS Circumferential sonomicrometry crystal pairs were placed in apical myocardium at ischemic risk in ligation studies and in adjacent and remote myocardium. The %S was obtained from closely juxtaposed sonomicrometry and SPAMM sites. RESULTS Paired data were available from 19 of 31 studies. Both methods distinguished remote from ischemic function effectively (p = 0.014 for SPAMM and p = 0.002 for sonomicrometry). SPAMM %S was similar to sonomicrometry %S in ischemic myocardium (2 ± 3 vs. 0 ± 3, p = 0.067) but was slightly higher than sonomicrometry %S in remote myocardium (11 ± 10 vs. 7 ± 5, p = 0.033). End-systolic (n = 30) and late systolic (n = 34) SPAMM %S correlated well with sonomicrometry %S (r = 0.84, p < 0.0001 and r = 0.88, p < 0.0001). CONCLUSIONS Magnetic resonance tagging using SPAMM can quantitate myocardial strain in ischemic and remote myocardium. This study validates its application in scientific investigation and clinical assessment of patients with myocardial ischemia.