Determining the calibration gain for calibrated perfusion maps with oxford_asl

Hi all,

Does anyone have experience with setting the calibration gain with the oxford_asl tools? I cannot find good documentation about how to choose the parameter value.

My raw ASL signal is much smaller than my calibration image because it has background suppression, and I get perfusion values that are too low. My ASL images are ~10% intensity of the calibration image, but if I reduce the calibration gain to 0.10, I get perfusion values that are too high. In both cases, the perfusion maps look good, so I believe that it is just a scaling issue.