Measurement of perfusion rate in human melanoma xenografts by contrast-enhanced magnetic resonance imaging.

Reliable methods based on MRI for measurement of the perfusion rate in human tumors are highly warranted. Tumors of two amelanotic human melanoma xenograft lines were subjected to dynamic 1H MRI after i.v. administration of gadopentetate dimeglumine (Gd-DTPA). The aim was to investigate to what extent different perfusion parameters determined from the Gd-DTPA kinetics, i.e., the initial uptake rate, the maximal uptake, the decay rate, and the perfusion rate calculated by use of the Kety equation, can be used as a reliable estimate of tumor perfusion rate. Each parameter was calculated in dual; one calculation was based on relative signal intensity increase (RSII) in T1-weighted MR images and the other on Gd-DTPA concentration determined from the images. The perfusion parameters were compared with the perfusion rates determined from measurement of tumor uptake of 86Rb or [14C]iodoantipyrine. The results showed that reliable estimates of tumor perfusion rate can be achieved from analysis of Gd-DTPA kinetics by use of the Kety equation. Gd-DTPA kinetics based on concentration might be used to achieve reliable estimates of absolute tumor perfusion rate, whereas reliable estimates of the relative perfusion rate might also be achieved from Gd-DTPA kinetics based on RSII. The initial uptake rate, the maximal uptake, and the decay rate of Gd-DTPA, however, are not reliable estimates of tumor perfusion rate, mainly because these parameters are highly influenced by the tumor extracellular volume fraction in addition to the perfusion rate.