Early detection of regional myocardial ischemia in ex vivo piglet hearts: MR imaging with magnetization transfer

Abstract

The effects of regional myocardial ischemia and reperfusion on magnetization transfer (MT) contrast were investigated in an ex vivo perfused piglet heart model. The extent of the ischemic area was defined with perfusion magnetic resonance (MR) studies performed with use of extracellular contrast agents. Relative MT contrast was calculated for a total of 106 regions of interest in nine hearts. In the areas defined as being severely ischemic in the perfusion studies, a small but significant increase in the MT contrast of 18% +/- 9 (standard deviation) (n = 35) was found as early as 10 minutes after the start of ischemia. This contrast difference was reduced to 11% +/- 10 after 2 hours of total occlusion. The contrast between normal and ischemic tissue can be explained in part by the effect of inflowing blood, which leads to changes in both equilibrium magnetization and the apparent T1 of the perfused tissue. However, theoretical estimation suggests that these flow-related changes would produce a maximal relative change in MT contrast of approximately 4%. The most likely explanation for the rest of the observed changes is alteration in the distribution of cellular water related to the so-called intracellular edema that is known to be associated with the acute phase of myocardial ischemia.

CMR Imaging of Edema in Myocardial Infarction Using Cine Balanced Steady-State Free Precession

“…It is known that bSSFP signals are influenced by T1, T2 (6), and magnetization transfer effects (7). With increased free water resulting from edema, T1 and T2 are both increased (8) and magnetization transfer is reduced (9). Although T2 and T1 effects are antagonistic in the setting of bSSFP imaging and will work to reduce the overall effect from relaxation changes, the residual relaxational contribution combined with alterations in magnetization transfer (10), it may be possible to visualize reperfused acute myocardial infarct territories as hyperintense zones relative to healthy/remote myocardium.…”

Assessment of magnetization transfer effects in myocardial tissue using balanced steady‐state free precession (bSSFP) cine MRI

“…A small number of other reports addressed tissue characterization, mostly in experimental models. It has been shown that MT affects the signal intensity of myocardium in both acute and chronic infarct (23, 24), as well as in ischemia (25, 26). Furthermore, changes in MT‐weighted images of myocardial tissue were found after heat treatment (27) and in patients with thalassemia (28).…”