Dose correction for post-contrast T1 mapping of the heart: the MESA study

Post-contrast myocardial T1 (T1_myo,c) values have been shown to be sensitive to myocardial fibrosis. Recent studies have shown differences in results obtained from T1_myo,c and extracellular volume fraction (ECV) with respect to percentage fibrosis. By exploring the relationship between blood plasma volume and T1_myo,c, the underlying basis for the divergence can be explained. Furthermore, dose administration based on body mass index (BMI), age and gender can mitigate the divergence in results. Inter-subject comparison of T1_myo,c required adjustment for dose (in mmol/kg), time and glomerular filtration rate. Further adjustment for effective dose based on lean muscle mass reflected by blood/plasma volume was performed. A test case of 605 subjects from the MESA study who had undergone pre- and post-contrast T1 mapping was studied. T1_myo,c values were compared between subjects with and without metabolic syndrome (MetS), between smoking and non-smoking subjects, and subjects with and without impaired glucose tolerance, before and after dose adjustment based on plasma volume. Comparison with ECV (which is dose independent), pre-contrast myocardial T1 and blood normalized myocardial T1 values was also performed to validate the correction. There were significant differences in T1_myo,c (post plasma volume correction) and ECV between current and former smokers (p value 0.017 and 0.01, respectively) but not T1_myo,c prior to correction (p = 0.12). Prior to dose adjustment for plasma volume, p value was <0.001 for T1_myo,c between MetS and non-MetS groups and was 0.13 between subjects with and without glucose intolerance; after adjustment for PV, p value was 0.63 and 0.99. Corresponding ECV p values were 0.44 and 0.99, respectively. Overall, ECV results showed the best agreement with PV corrected T1_myo,c (mean absolute difference in p values = 0.073) and pre-contrast myocardial T1 in comparison with other measures (T1_myo,c prior to correction, blood/plasma T1 value normalized myocardium). Weight-based contrast dosing administered in mmol/kg results in a bias in T1 values which can lead to erroneous conclusions. After adjustment for lean muscle mass based on plasma volume, results from T1_myo,c were in line with ECV derived results. Furthermore, the use of a modified equivalent dose adjusted for BMI, age, sex and hematocrit can be adopted for quantitative imaging.