LAUSR

Native T1 mapping of the myocardium has emerged as an objective quantitative method to assess myocardial pathology. Considerable improvements in technical methodology and promising clinical applications have advanced native T1 mapping to the clinical arena. Currently, the most robust clinical applications are seen with suspected diseases that show large changes in native T1 values, such as myocardial infarction, myocarditis, and amyloidosis. Myocardial T1 mapping also has the potential to identify diseases with smaller changes in native T1 values such as those leading to diffuse interstitial fibrosis. However, the variability in native T1 measurements at present precludes valuable clinical utility in this scenario. Sources of native T1 variability can be broadly classified into those arising from 1) technical factors such as variability in T1 mapping magnetic resonance (MR) pulse sequences or their implementations on different scanners and 2) physiological variability. Technical sources of variability have received considerable attention and consensus papers were published to promote standardization. Acknowledging the different sources of variability, imaging sites are encouraged to measure their site-specific native T1 reference values using the sequence, scanner platform, postprocessing tools, and population for their intended clinical use. In this JMRI issue, the work by Meloni et al contributes to this body of knowledge by providing native T1 myocardium values for the GE 1.5 T scanner platform. A more important contribution of Meloni et al’s work is the assessment of physiological variation of native T1 values. They comprehensively investigated the segmental variation, gender-based variation, and cardiac phase-based variation in native myocardial T1 values. In this regard, this study is significant in that a large number of subjects were included with a careful study design to ensure representation across gender and age groups. Their findings of increased T1 values in septal myocardium and during systole corroborate those of prior studies done with other MR pulse sequences or scanner platforms. The authors also confirmed previous data that show women have higher native T1 values than men, providing sex-specific normal ranges for their scanner platform. Accruing evidence of physiological variation in T1 further highlights the need to understand differences by age, gender, and ethnicity and to establish reference values for specific patient populations. A limitation of the current study is that it did not assess T1 variability related to ethnicity, a rarely addressed area of research. As other known cardiovascular biomarkers are known to vary between different ethnical backgrounds, this remains an important but unexplored area. The variability of native T1 values on both technical factors and physiological factors simultaneously affects our ability to discern health and disease. As there are many technical and physiological parameters determining native T1 variability, it is unlikely that a single study can address this concern. Hence, this is an area where meta-analysis approach can be quite useful. One such meta-analysis shows that while modified look-locker inversion recovery (MOLLI) based native T1 reference values for Siemens/ Philips 1.5 T platforms are available, there is a dearth of such studies on other scanner platforms. In this regard, the current study using MOLLI on GE 1.5 T is a valuable addition to future meta-analysis efforts. Targeted studies such as these might fill the gaps in knowledge required to advance native T1 myocardial mapping to full clinical utilization to identify early myocardial abnormalities in multiple disease states and aid on diagnoses and management of a broader range of cardiac diseases.