Towards intrinsic R2* imaging in the prostate at 3 and 7tesla

Hypoxia is an important marker for resistance to therapy. In this study, we quantify the macroscopic effects of R2* mapping in prostate cancer patients incorporating susceptibility matching and field strengths effects.

91 patients were scanned without endorectal coil (ERC) at 3T. Only when rectal gas was absent, data was included for analysis. Another group of 10 patients was scanned using a susceptibility matched ERC. To assess the residual contamination of R2 and macroscopic field non-uniformities, a group of 10 patients underwent ultra-high resolution 7T MRI.

Of the patients scanned at 3T 60% presented rectal gas and were excluded, due to susceptibility artifacts. At 3T the tumor was significantly different (P<0.01) from the healthy surrounding tissue in R2* values at intrapatient level. Using the measured median R2* value of 24.9s^-1 at 3T and 43.2s^-1 at 7T of the peripheral zone, the minimum contribution of macroscopic susceptibility effects is 15% at 3T.

R2* imaging might be a promising tool for hypoxia imaging, particularly when minimizing macroscopic susceptibility effects contaminating intrinsic R2* of tissue, such as rectal gas. At 3T macroscopic effects still contribute 15% in the R2* value, compared to ultra-high resolution R2* mapping at 7T.