Characterization of myocardial T1 and partition coefficient as a function of time after gadolinium delivery in healthy subjects

Abstract

Background: Diffuse myocardial fibrosis is associated with myocardial infarction [1], heart failure [2] and dilated cardiomyopathy [3]. Conventional T1-weighted late gadolinium enhancement (LGE) imaging highlights focal scaring in contrast to remote reference tissue, but it cannot detect global changes in T1 associated with diffuse fibrosis. Quantitative T1 imaging permits assessment of diffuse fibrosis by eliminating the use of reference tissue, but the dependence of the derived partition coefficient (lambda) on the time post-contrast injection (tpost) is not well established. Purpose: Determine blood and myocardial T1 values as a function of tpost and the resulting dependence of the blood-tissue partition coefficient. Methods: Nine healthy subjects (22.0±5.5 yrs, 6 male) were imaged using a Siemens Avanto 1.5T MRI. T1 mapping was performed on a mid-ventricular short-axis slice using a custom saturation recovery single-shot TrueFISP sequence at baseline and one-minute intervals for 15 minutes following a bolus injection of gadopentetate dimeglumine (0.1 mmol/kg). At each time point, one “no-saturation” image and nine images with varying saturation recovery times spanning the cardiac cycle were acquired during a single breath-hold. The myocardium was divided into 18 segments and mean values were fitted to a 3 parameter saturation recovery curve to determine T1 values for each segment at every time point. Blood T1 values were computed using a region of interest within the left ventricular cavity. Lambda was computed using {lambda=[R1(myocardiumpost) - R1(myocardiumpre)]/[R1(bloodpost) - R1 (bloodpre)]}, where R1=1/T1. Results: Figure 1 shows myocardial T1, blood T1, and lambda values averaged over all segments and subjects as a function of tpost. Average within-subject standard deviations of T1 and lambda for tpost from 3-15 min were 34.1 ms and 0.046 respectively. Linear regression for lambda and tpost (3-15 min) shows an increase in lambda of 0.001 min-1 (R2=0.75). Quantitative T1 imaging is likely to be added to a clinical protocol following LGE imaging (tpost 10-15 min), where T1 values increase by 5.9±1.6% and lambda increase by 1.1±2.7%(Figure Presented). Conclusion Saturation recovery SSFP T1 mapping can be performed in a single breath-hold with derived blood-tissue partition coefficient (lambda) values in good agreement with previous measurements3. In the post-LGE window of 10-15 min after contrast bolus, derived lambda values show less time dependence than myocardial T1.