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Why do we see myocardial edema in acute myocardial infarcts with balanced SSFP imaging?
© Zhou et al; licensee BioMed Central Ltd. 2010
Published: 21 January 2010
Recent studies have demonstrated that conventional balanced steady-state free precession (b-SSFP) cine imaging can identify regions of myocardial edema in-and-around acute myocardial infarctions (AMI). However, the underlying mechanisms of b-SSFP edema contrast are not well understood. A more detailed understanding of the contrast mechanisms at play may enable opportunities for optimization of SSFP-based edema contrast.
To investigate the mechanisms contributing to the b-SSFP-based edema contrast surrounding AMI in conventional cine b-SSFP images
Dogs (n = 3) subjected to ischemia-reperfusion injury (LAD occlusion for 3 hours followed by reperfusion) were studied at baseline (pre-injury), 2-hours post-reperfusion (day 0), and on days 2, 5, and 7. Multiple breath-held short-axis cine b-SSFP images, and T2- and T1-maps were acquired at late diastole using a Siemens Espree (1.5 T) system. All studies were terminated with PSIR late-gadolinium-enhancement (LGE) acquisitions to confirm LAD infarction. Cine SSFP imaging was performed with TR/TE = 3.5/1.75 ms; flip angle = 70°; 20-25 phases. The cardiac phase corresponding to the T1 and T2 maps were identified from the cine b-SSFP images. On these SSFP images, and the relaxation maps, a semi-automated approach was used to identify the edematous territory. Using the Freeman-Hill equation for b-SSFP and the measured signal, T1 and T2 values for edematous and healthy territories, the relative contributions from relaxation and thermal magnetization (M0) effects were estimated.
Relaxation effects alone cannot explain the observed myocardial edema contrast in b-SSFP images. Results show that M0 effects, likely from proton density and/or magnetization transfer changes between healthy and edematous territories, have a substantial contribution to the b-SSFP image contrast. Optimization strategies that wish to maximize myocardial edema contrast in b-SSFP imaging should take relaxation and M0 effects into account.
This article is published under license to BioMed Central Ltd.