T1 Mapping in cardiomyopathy at cardiac MR: comparison with endomyocardial biopsy

Abstract

Purpose: To determine the utility of cardiac magnetic resonance (MR) T1 mapping for quantification of diffuse myocardial fibrosis compared with the standard of endomyocardial biopsy.

Materials and methods: This HIPAA-compliant study was approved by the institutional review board. Cardiomyopathy patients were retrospectively identified who had undergone endomyocardial biopsy and cardiac MR at one institution during a 5-year period. Forty-seven patients (53% male; mean age, 46.8 years) had undergone diagnostic cardiac MR and endomyocardial biopsy. Thirteen healthy volunteers (54% male; mean age, 38.1 years) underwent cardiac MR as a reference. Myocardial T1 mapping was performed 10.7 minutes ± 2.7 (standard deviation) after bolus injection of 0.2 mmol/kg gadolinium chelate by using an inversion-recovery Look-Locker sequence on a 1.5-T MR imager. Late gadolinium enhancement was assessed by using gradient-echo inversion-recovery sequences. Cardiac MR results were the consensus of two radiologists who were blinded to histopathologic findings. Endomyocardial biopsy fibrosis was quantitatively measured by using automated image analysis software with digital images of specimens stained with Masson trichrome. Histopathologic findings were reported by two pathologists blinded to cardiac MR findings. Statistical analyses included Mann-Whitney U test, analysis of variance, and linear regression.

Results: Median myocardial fibrosis was 8.5% (interquartile range, 5.7-14.4). T1 times were greater in control subjects than in patients without and in patients with evident late gadolinium enhancement (466 msec ± 14, 406 msec ± 59, and 303 msec ± 53, respectively; P < .001). T1 time and histologic fibrosis were inversely correlated (r = -0.57; 95% confidence interval: -0.74, -0.34; P < .0001). The area under the curve for myocardial T1 time to detect fibrosis of greater than 5% was 0.84 at a cutoff of 383 msec.

Conclusion: Cardiac MR with T1 mapping can provide noninvasive evidence of diffuse myocardial fibrosis in patients referred for evaluation of cardiomyopathy.

© RSNA, 2012.

Figures

Figure 1:

Representative paired T1 maps and endomyocardial biopsy samples demonstrate a heart with normal myocardium (top row) and one with significant fibrosis (bottom row). The patient with histologically normal myocardium had, A, a mean T1 time of 416 msec and, B, 1.5% fibrosis at biopsy. The second had, C, short T1 time (296 msec) and, D, 19.1% fibrosis at biopsy. Images in both patients were without LGE. T1 maps were derived from a postcontrast steady-state free procession Look-Locker inversion-recovery sequence in the four-chamber view. Pixels in color were included in the mean myocardial T1 time reported. Blue end of the color scale = shortest T1 time. Tissue is stained with Masson trichrome, rendering myocardium red and fibrotic tissue blue. Photomicrographs are ×4 magnification. Scale bar = 500 µm.

Figure 2:

Univariate correlation between mean myocardial T1 time and myocardial fibrosis (log transformed). Myocardial fibrosis was calculated as a percentage of total tissue in endomyocardial biopsy samples.

Figure 3:

Myocardial T1 time according to disease category. Boxes = interquartile range (25th–75th percentile), whiskers = maximum and minimum for each group. CM, no LGE = cardiomyopathy without visually evident LGE, CM, +LGE = cardiomyopathy with visually evident LGE.

Figure 4:

Diagnostic performance of myocardial T1 time to detect fibrosis. Receiver operating characteristic curve demonstrates the diagnostic performance of postcontrast myocardial T1 time to identify histologic fibrosis greater than 5% of myocardial volume. The AUC is 0.84 (95% CI: 0.70, 0.93; P < .0001).