T 2 ‐weighted STIR imaging of myocardial edema associated with ischemia‐reperfusion injury: The influence of proton density effect on image contrast

Purpose To investigate the contribution of proton density (PD) in T 2 ‐STIR based edema imaging in the setting of acute myocardial infarction (AMI). Materials and Methods Canines ( n = 5), subjected to full occlusion of the left anterior descending artery for 3 hours, underwent serial magnetic resonance imaging (MRI) studies 2 hours postreperfusion (day 0) and on day 2. During each study, T 1 and T 2 maps, STIR (TE = 7.1 msec and 64 msec) and late gadolinium enhancement (LGE) images were acquired. Using T 1 and T 2 maps, relaxation and PD contributions to myocardial edema contrast (EC) in STIR images at both TEs were calculated. Results Edematous territories showed significant increase in PD (20.3 ± 14.3%, P < 0.05) relative to healthy territories. The contributions of T 1 changes and T 2 or PD changes toward EC were in opposite directions. One‐tailed t ‐test confirmed that the mean T 2 and PD‐based EC at both TEs were greater than zero. EC from STIR images at TE = 7.1 msec was dominated by PD than T 2 effects (94.3 ± 11.3% vs. 17.6 ± 2.5%, P < 0.05), while at TE = 64 msec, T 2 effects were significantly greater than PD effects (90.8 ± 20.3% vs. 12.5 ± 11.9%, P < 0.05). The contribution from PD in standard STIR acquisitions (TE = 64 msec) was significantly higher than 0 ( P < 0.05). Conclusion In addition to T 2 ‐weighting, edema detection in the setting of AMI with T 2 ‐weighted STIR imaging has a substantial contribution from PD changes, likely stemming from increased free‐water content within the affected tissue. This suggests that imaging approaches that take advantage of both PD as well as T 2 effects may provide the optimal sensitivity for detecting myocardial edema. J. Magn. Reson. Imaging 2011;33:962–967. © 2011 Wiley‐Liss, Inc.