MRI relaxation fluctuations in acute reperfused hemorrhagic infarction

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.