Native T1 Mapping by 3-T CMR Imaging for Characterization of Chronic Myocardial Infarctions

OBJECTIVES:  The purpose of this study was to investigate whether native T1 maps at 3-T can reliably characterize chronic myocardial infarctions (MIs) in patients with prior ST-segment elevation myocardial infarction (STEMI) or non-ST-segment elevation myocardial infarction (NSTEMI). Late gadolinium enhancement (LGE) cardiac magnetic resonance is the gold standard for characterizing chronic MIs, but it is contraindicated in patients with end-stage chronic kidney disease.

METHODS:  Native T1 and LGE images were acquired at 3-T in patients with prior STEMI (n = 13) and NSTEMI (n = 12) at a median of 13.6 years post-MI. Infarct location, size, and transmurality were measured using mean ± 5 SDs thresholding criterion from LGE images and T1 maps and compared against one another. Independent reviewers assessed visual conspicuity of MIs on LGE images and T1 maps.

RESULTS: Native T1 maps and LGE images were not different for measuring infarct size (STEMI: p = 0.46; NSTEMI: p = 0.27) and transmurality (STEMI: p = 0.13; NSTEMI: p = 0.21) using thresholding criterion. Using thresholding criterion, good agreement was observed between LGE images and T1 maps for measuring infarct size (STEMI: bias = 0.6 ± 3.1%; R2 = 0.93; NSTEMI: bias = −0.4 ± 4.4%; R2 = 0.85) and transmurality (STEMI: bias = 2.0 ± 4.2%; R2 = 0.89; NSTEMI: bias = −2.7 ± 7.9%; R2 = 0.68). Sensitivity and specificity of T1 maps for detecting chronic MIs based on thresholding criterion were 89% and 98%, respectively (STEMI), and 87% and 95%, respectively (NSTEMI). Relative to LGE images, the mean visual conspicuity score for detecting chronic MIs was significantly lower for T1 maps (p < 0.001 for both cases). Median infarct-to-remote myocardium contrast-to-noise ratio was 2.5-fold higher for LGE images relative to T1 maps (p < 0.001). Sensitivity and specificity of T1 maps for visual detection were 60% and 86%, respectively (STEMI), and 64% and 91% (NSTEMI), respectively.

CONCLUSIONS:  Chronic MIs in STEMI and NSTEMI patients can be reliably characterized using threshold-based detection on native T1 maps at 3-T. Visual detection of chronic MIs on native T1 maps in both patient populations has high specificity, but modest sensitivity.
COMPETENCY IN MEDICAL KNOWLEDGE: In relation to LGE CMR, native T1 mapping at 3-T can characterize chronic STEMIs and NSTEMIs with high diagnostic accuracy when semiautomated (threshold-based) detection is used. Native T1 mapping at 3-T can be a potential alternative to LGE CMR for characterizing chronic MIs in patients who are contraindicated for gadolinium administration.

TRANSLATIONAL OUTLOOK: Additional studies, preferably in a larger patient cohort, are also needed to assess the intraobserver and interobserver differences of native T1 mapping at 3-T for detecting and characterizing chronic MI. The ability of this technique to detect pathologies beyond those detected by LGE imaging also needs to be investigated. The modest sensitivity of native T1 mapping for visually detecting chronic MIs relative to LGE CMR at 3-T is a limitation, and future efforts should focus on improving image contrast.

PMID: 26298071

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