[Testing of model assumptions of MR oxygen extraction fraction mapping using a phantom study]

Oxygen supply is an important parameter for the evaluation of tissue viability and therefore of high interest in cancer diagnosis and therapy. One promising approach to extract relevant information from imaging data is the determination of oxygen saturation by means of the BOLD-effect. Using a simple model of tissue structure allows to evaluate the susceptibility difference between tissue and venous blood, from which the blood oxygen extraction fraction can be derived indirectly. The present study tested the validity of two model assumptions needed for exact quantification: the independence of the results of both capillary diameter d and the relative blood volume lambda. For this purpose a phantom was built, which allows the evaluation of susceptibility differences depending on d (27 microm-238 microm) and lambda (3%-12%). In agreement with model assumptions, delta chi(lambda) was widely constant and independent of ) lambda. In contradiction to the model, delta chi (d) showed a positive slope (delta chi range: 0.35-0.57 ppm). The present study suggests that the simple model investigated here has shortcomings in the quantification of oxygen extraction due to insufficient model assumptions.