MRI relaxation fluctuations in acute reperfused hemorrhagic infarction

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Abstract
MRI evaluations of intramyocardial hemorrhage in acute infarction have relied on T2 and T shortening only. We propose a more comprehensive evaluation of hemorrhagic infarction based on the concept that fluctuations in T2 and T1 relaxation in acute reperfused infarction will reflect transient edema and hemoglobin oxidative denaturation to uncompartmentalized methemoglobin. Anteroapical infarction was created via percutaneous balloon in young swine (22–25 kg, N = 12). T2, T1, diastolic wall thickness (DWT), and the Gd‐DTPA partition coefficient (λ) were measured on days 0, 2, and 7. DWT was elevated at 1 hr postreperfusion (128% ± 53%, P = 0.0001), and alleviated on days 2 and 7 (48% ± 10%, P = 0.008; 53% ± 24%, P = 0.003). T2 and T1 elevations were coincident with early edema (ΔT2 = 55% ± 24%, P < 0.0001; ΔT1 = 27% ± 18%, P < 0.04). T2 and T1 were nearly normal on day 2 (ΔT2 = 8% ± 8%, P = 0.27; ΔT1 = 0% ± 1%, P = 0.65). On day 7, T2 increased while T1 decreased (ΔT2 = 27% ± 16%, P = 0.005; ΔT1 = −14% ± 10%, P = 0.02). λ was elevated by >150% at all time points (P ≤ 0.002). Histology verified hemorrhagic injury. T1 and T2 fluctuations are consistent with transient edema, as well as hemoglobin oxidative denaturation to decompartmentalized methemoglobin. This methodological development may broaden our understanding of hemorrhagic microvascular injury and improve its detection in clinical populations. Magn Reson Med, 2006.