When comparing CRF with RRF, no significant difference was found in RMSE and R 2 -values, except for the liver. It was the only tissue with RMSE difference over 0.05 [The R 2 -value of liver in RRF (0.49) was higher than CRF (0.38)]. Similar results for CRF and RRF in most tissues indicates that using all the predicted Kp values is not always effective as this might lead to the concept of each tissue being similar to a specific tissue and not all tissues.