The Impact of Water Exchange on Estimates of Myocardial Blood Flow and Extracellular Volume Fraction Using Dynamic Contrast-Enhanced MRI in Patients Treated for Severe Aortic Stenosis.

PURPOSE: To investigate the impact of intra/extracellular water exchange (WX) on quantitative dynamic contrast-enhanced (DCE) MRI in patients with severe aortic stenosis (AS). The aims were to compare low-dose (WX insensitive) and high-dose (WX sensitive) DCE-MRI measurements, and to compare data acquired before and after aortic valve replacement (AVR) to test whether DCE-MRI was able to detect changes in myocardial extracellular volume fraction (ECV).

METHODS

Twenty-five patients with severe AS were studied at 3 T before and 6 months after AVR. DCE-MRI was performed at rest twice using a low contrast agent dose (0.05 mmol/kg gadobutrol) followed by a high-dose (0.1 mmol/kg gadobutrol). Estimates of myocardial blood flow (MBF) and ECV were obtained using models which assume instantaneous WX (fast exchange [FX]) and which incorporate WX (a two-site exchange [2SX] model). ECV estimates were also made using T1 maps acquired before and after contrast administration, both assuming FX and incorporating WX.

RESULTS

FX model estimates of MBF and ECV obtained before AVR decreased from low- to high-dose contrast consistent with the effect of limited WX. This decrease was partially corrected using a 2SX model. However, 2SX model fits were preferred over FX fits in only 2 of 24 high-dose data sets (F-test). ECV estimates made using DCE-MRI increased after AVR consistent with changes seen using T1 maps, but the ECV estimates were lower.

CONCLUSION

Estimates of MBF using DCE-MRI showed negligible sensitivity to WX. DCE-MRI-based ECV estimates changed post-AVR but were systematically lower than those made using T1 maps.