The implication of doing that kind of calculation is that when the ventricle is in one state, the density of the muscle blocks the radiation source more than when ventricle is in the other state when the ventricle is open with blood.
And that in turn implies that different patients might have different densities or different amounts of (whatever) to go through, and that therefore the numbers being seen are not absolute numbers but rather relative numbers. Or perhaps the numbers are absolute numbers (e.g., a particular brightness might represent a particular absolute radiation count), but that the significance of the numbers are relative.
When you have relative numbers or numbers of relative significance, then you should normalize.
When you have numbers of absolute significance you probably should not normalize.
