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We read with interest the review article by Oh-Ici et al.1 on the subject of T1 mapping in ischaemic heart disease. We agree that T1 mapping has the potential to provide incremental information over late gadolinium enhancement imaging. We would like to add to the authors' comments regarding technical factors affecting T1. In our experience, the most important component of image post-processing to measure myocardial T1 values is the selection of the region of interest (ROI). ROIs can either be drawn on each ‘raw’ image obtained from the T1 sequence (11, 11, 8, or 7 images for MOLLI, SASHA, 3′5 MOLLI or shMOLLI, respectively) or on the aggregated pixel-by-pixel map. It is important to recognize that maps are subject to co-registration errors from cardiac and respiratory motion, although motion-correction post-processing tools do exist.2 To minimize error, we recommend drawing the ROI conservatively within the left ventricular myocardial wall, rather than using endocardial and epicardial contours as margins. This conservative approach ensures that the ROI is not contaminated by voxels spanning the myocardium and blood pool or lung. In our centre, using this conservative approach we demonstrated greater differences in T1 values between septal and lateral myocardium (3.4 and 5.1% at 1.5 T and 3 T, respectively3) than those referenced in the review article.4 We also found that lateral wall ROIs were subject to greater intra-observer, inter-observer, and inter-study variability than septal ROIs at both field strengths. It is unlikely that these differences represent a true regional disparity in longitudinal relaxation. Rather, they are likely related to a number of confounding factors, including magnetic susceptibility artefacts, issues pertaining to receiver coil sensitivity, and signal gradient between septal and lateral myocardium due to greater distance from the receiver coil elements. Therefore, we advise caution when interpreting regional differences in T1 values in patients with ischaemic heart disease until cut-off values for infarct and area at risk within each coronary territory have been delineated.

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Letters to the Editor
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