Controversies in cardiovascular MR imaging: T2-weighted imaging should not be used to delineate the area at risk in ischemic myocardial injury.
The use of T2-weighted MR imaging to delineate the area at risk and subsequently quantify myocardial salvage is problematic on many levels. The validation studies available thus far are inadequate. Unlike the data validating DE MR imaging, in which pathologic analysis has shown the precise shape and contour of the bright region exactly match the infarcted area, this level of validation does not exist for T2-weighted MR imaging. Technical advances have occurred, but image contrast between abnormal and normal regions remains limited, and in this situation, measured size differences between MR imaging data sets should not be overinterpreted. Moreover, with any T2 technique, there remains the key issue that there is no physiologic basis for the apparent T2 findings. Indeed, a homogeneously bright area at risk on T2-weighted MR images is incompatible with the known levels of edema that occur in infarcted and salvaged myocardium, and the finding that the lateral borders of T2 hyperintense regions frequently extend far beyond that of infarction is contrary to the wavefront phenomenon. Even if T2-weighted MR imaging provided an accurate measure of myocardial edema, the level of edema within the area at risk is dependent on multiple variables, including infarct size, age, reperfusion status, reperfusion injury, and therapies that could have an antiedema effect. The area at risk is a coronary perfusion territory. There is a fundamental limitation with defining the area at risk by using a nonperfusion-based indicator that can vary with different postreperfusion therapies. There are several applications for T2 myocardial imaging, including differentiation of acute from chronic MI and identification of acute myocarditis. On the basis of the currently available data; however, we conclude that T2-weighted MR imaging should not be used to delineate the area at risk in patients with ischemic myocardial injury.
Croisille, P; Kim, HW; Kim, RJ
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