**7. Dynamic MR**

Quantification of tumor vascularity by dynamic MR (DCE MR) is technically more challeng‐ ing than perfusion CT because there is a lack of a direct relationship between MR signal in‐ tensity and contrast agent concentration. This is due to the fact that tissue signal intensity on MR is related to the effect of CM on water in the microenvironment, which changes tissue relaxivity in complex and unpredictable ways [66].

While perfusion CT yield information is based predominantly on the first pass of CM (BV, BF), the MR imaging technique may sample a volume of interest over a longer time and yields parameters that reflect microvessel perfusion, permeability and extracellular leakage of space. In addition, by applying pharmacokinetic models to the MR imaging acquisitions, it is possible to calculate quantitative parameters, such as the transfer constant (Ktrans) that describes the transendothelial transport of the CM.

A central flaw of dynamic MR is that acquisition and pharmacokinetic models vary widely. Thus, comparing studies from different institutions is difficult. This technique, on the other hand, is of limited value in organs with physiological movement such as the lungs.

Few studies have applied dynamic MR in the assessment of lung cancer. Ohno et al [67] evaluated the role of DCE MR as a prognostic indicator in NSCLC patients treated with che‐ motherapy using cisplatin and vincristine. In their study, the mean survival period of pa‐ tients with lower slope of enhancement was significantly longer than that seen in the group with higher slope of enhancement. This study provides promising data for the application of dynamic MR in response assessment to chemotherapy and targeted therapy.
