MR perfusion measurement of contrast uptaking lesions consideration of T2* shortening due to interstitial contrast agent

Aim: In MR perfusion measurements of contrast uptaking lesions, time intensity curves are hampered by T(1) shortening as well as by the change of T(2)* due to interstital contrast material (CM). Using double echo sequences, the influence of T(1) can be mathematically eliminated. For correction of the T2* influence an empirical algorithm using time-intensity-curves exclusively measured in the suspected lesion is proposed. Methods: The interstitial CM concentration is assumed to be proportional to the change of the intensity for T(E) = 0 or to the change of the relaxation rate DeltaR(1), respectively. The intravascular CM concentration is estimated from DeltaR(2)*. It is adjusted to zero for a time point sufficiently late after the bolus injection by subtraction of the interstitial concentration. This method was applied to double echo FLASH measurements on 15 pharyngeal tumors. Results: The proposed correction transforms the time dependence of the estimated intravascular CM concentration into a plausible course. Conclusion: Double echo perfusion measurements can be corrected for the interstitial CM induced T2* shortening without additional measurements with proneness to errors. This does not necessarily improve the diagnostic value, since possibly "implied multivariate aspects" of uncorrected parameters (here: contrast uptake of the lesion is related to tumor neoangiogenesis as well) are eliminated.