Endogenous assessment of chronic myocardial infarction with T1ρ-mapping in patients

Abstract

Background: Detection of cardiac fibrosis based on endogenous magnetic resonance (MR) characteristics of the myocardium would yield a measurement that can provide quantitative information, is independent of contrast agent concentration, renal function and timing. In ex vivo myocardial infarction (MI) tissue, it has been shown that a significantly higher T1ρ is found in the MI region, and studies in animal models of chronic MI showed the first in vivo evidence for the ability to detect myocardial fibrosis with native T1ρ-mapping. In this study we aimed to translate and validate T1ρ-mapping for endogenous detection of chronic MI in patients. Methods: We first performed a study in a porcine animal model of chronic MI to validate the implementation of T1ρ-mapping on a clinical cardiovascular MR scanner and studied the correlation with histology. Subsequently a clinical protocol was developed, to assess the feasibility of scar tissue detection with native T1ρ-mapping in patients (n = 21) with chronic MI, and correlated with gold standard late gadolinium enhancement (LGE) CMR. Four T1ρ-weighted images were acquired using a spin-lock preparation pulse with varying duration (0, 13, 27, 45 ms) and an amplitude of 750 Hz, and a T1ρ-map was calculated. The resulting T1ρ-maps and LGE images were scored qualitatively for the presence and extent of myocardial scarring using the 17-segment AHA model. Results: In the animal model (n = 9) a significantly higher T1ρ relaxation time was found in the infarct region (61 ± 11 ms), compared to healthy remote myocardium (36 ± 4 ms). In patients a higher T1ρ relaxation time (79 ± 11 ms) was found in the infarct region than in remote myocardium (54 ± 6 ms). Overlap in the scoring of scar tissue on LGE images and T1ρ-maps was 74%. Conclusion: We have shown the feasibility of native T1ρ-mapping for detection of infarct area in patients with a chronic myocardial infarction. In the near future, improvements on the T1ρ -mapping sequence could provide a higher sensitivity and specificity. This endogenous method could be an alternative for LGE imaging, and provide additional quantitative information on myocardial tissue characteristics.