Purpose: To investigate the mechanism of late gadolinium enhancement in irreversibly damaged myocardium in patients with acute myocardial infarct by determining kinetics of Gd-DTPA over time.
Methods: Twenty-nine patients (24 men; 64 +/- 9 years) with acute myocardial infarction were imaged with functional and gadolinium enhanced cardiovascular magnetic resonance (CMR) 18 minutes post 0.2 mmol/kg Gd-DTPA. T1 of blood, remote and enhanced myocardium, as well as microvascular obstruction (MVO) was determined before and 5-40 minutes post contrast injection (Look-Locker), and the partition coefficient (lambda) was calculated.
Results: T1 and lambda were significantly different from 5-40 minutes post contrast in enhanced (lambda = 0.90 +/- 0.09, p < 0.001) compared to remote myocardium (lambda = 0.40 +/- 0.07). lambda achieved a steady state in remote but increased continuously in infarcted myocardium and to an even greater extent in MVO. T1 of enhanced myocardium was higher from 5-15 minutes, equal at 20 minutes and lower 25-40 minutes post contrast compared to blood, indicating a changing contrast between blood and late gadolinium enhancement over time.
Conclusion: Enhancement in patients with acute infarction is mainly due to an increased lambda, although reduced wash-in-wash-out adds to the effect. Differentiation between blood and enhanced myocardium may be difficult to achieve, if only little differences of T1 are available. Imaging at a later point will restore the contrast.