T₂STIR preparation for single-shot cardiovascular magnetic resonance myocardial edema imaging

Myocardial edema in acute myocardial infarction (AMI) is commonly imaged using dark-blood short tau inversion recovery turbo spin echo (STIR-TSE) cardiovascular magnetic resonance (CMR). The technique is sensitive to cardiac motion and coil sensitivity variation, leading to myocardial signal nonuniformity and impeding reliable depiction of edematous tissues. T₂-prepared balanced steady state free precession (T₂p-bSSFP) imaging has been proposed, but its contrast is low, and averaging is commonly needed. T₂ mapping is useful but requires a long scan time and breathholding. We propose here a single-shot magnetization prepared sequence that increases the contrast between edema and normal myocardium and apply it to myocardial edema imaging.

A magnetization preparation module (T₂STIR) is designed to exploit the simultaneous elevation of T₁ and T₂ in edema to improve the depiction of edematous myocardium. The module tips magnetization down to the -z axis after T₂ preparation. Transverse magnetization is sampled at the fat null point using bSSFP readout and allows for single-shot myocardial edema imaging. The sequence (T₂STIR-bSSFP) was studied for its contrast behavior using simulation and phantoms. It was then evaluated on 7 healthy subjects and 7 AMI patients by comparing it to T₂p-bSSFP and T₂ mapping using the contrast-to-noise ratio (CNR) and the contrast ratio as performance indices.

In simulation and phantom studies, T₂STIR-bSSFP had improved contrast between edema and normal myocardium compared with the other two edema imaging techniques. In patients, the CNR of T₂STIR-bSSFP was higher than T₂p-bSSFP (5.9 ± 2.6 vs. 2.8 ± 2.0, P < 0.05) but had no significant difference compared with that of the T₂ map (T₂ map: 6.6 ± 3.3 vs. 5.9 ± 2.6, P = 0.62). The contrast ratio of T₂STIR-bSSFP (2.4 ± 0.8) was higher than that of the T₂ map (1.3 ± 0.1, P < 0.01) and T₂p-bSSFP (1.4 ± 0.5, P < 0.05).

T₂STIR-bSSFP has improved contrast between edematous and normal myocardium compared with commonly used bSSFP-based edema imaging techniques. T₂STIR-bSSFP also differentiates between fat that was robustly suppressed and fluids around the heart. The technique is useful for single-shot edema imaging in AMI patients.