To finally get perfusion in absolute units we also need to calculate the equilibrium magnetization of arterial blood and include that in the calculations. Now we need to know some more information about our data.
Background suppression was ON.
This should have improved our perfusion contrast by removing as much static tissue signal as possible. However, we with this cannot use the control images to estimate equilibrium magnetization values. Instead there is a separate dataset, called calib, which is a series of control images with BGS OFF.
I didn't realize that we couldn't use the control volumes when background suppression was enabled.
Summary
From https://asl-docs.readthedocs.io/en/latest/cli_tutorial.html#single-delay-asl:
I didn't realize that we couldn't use the control volumes when background suppression was enabled.
Additional details
What were you trying to do?
What did you expect to happen?
What actually happened?
Reproducing the bug