A compact solution for estimation of physiological parameters from ultrafast prostate dynamic contrast enhanced MRI

Abstract

The Tofts pharmacokinetic model requires multiple calculations for analysis of dynamic contrast enhanced (DCE) MRI. In addition, the Tofts model may not be appropriate for the prostate. This can result in error propagation that reduces the accuracy of pharmacokinetic measurements. In this study, we present a compact solution allowing estimation of physiological parameters Ktrans and ve from ultrafast DCE acquisitions, without fitting DCE-MRI data to the standard Tofts pharmacokinetic model. Since the standard Tofts model can be simplified to the Patlak model at early times when contrast efflux from the extravascular extracellular space back to plasma is negligible, Ktrans can be solved explicitly for a specific time. Further, ve can be estimated directly from the late steady-state signal using the derivative form of Tofts model. Ultrafast DCE-MRI data were acquired from 18 prostate cancer patients on a Philips Achieva 3T-TX scanner. Regions-of-interest (ROIs) for prostate cancer, normal tissue, gluteal muscle, and iliac artery were manually traced. The contrast media concentration as function of time was calculated over each ROI using gradient echo signal equation with pre-contrast tissue T1 values, and using the ‘reference tissue’ model with a linear approximation. There was strong correlation (r = 0.88–0.91, p < 0.0001) between Ktrans extracted from the Tofts model and Ktrans estimated from the compact solution for prostate cancer and normal tissue. Additionally, there was moderate correlation (r = 0.65–0.73, p < 0.0001) between extracted versus estimated ve. Bland–Altman analysis showed moderate to good agreement between physiological parameters extracted from the Tofts model and those estimated from the compact solution with absolute bias less than 0.20 min−1 and 0.10 for Ktrans and ve, respectively. The compact solution may decrease systematic errors and error propagation, and could increase the efficiency of clinical workflow. The compact solution requires high temporal resolution DCE-MRI due to the need to adequately sample the early phase of contrast media uptake.