Thanks for the great questions, @staystrong.
There have been studies showing that MRI is more sensitive (i.e., can rule out HCC if a test is negative) compared to ultrasound, but the difference in detection rate isn’t enough to offset the much greater costs of MRI compared to ultrasound. Also MRI isn’t as widely accessible as ultrasound.
Regarding contrast agent hazards, this has been discussed in a previous thread:
Regarding Fib4 scoring, there is an additional caveat in that calculator:
Lastly, the cut offs for HCV are different than those with NASH or HBV.
Sometimes it is difficult to extend the results from one group to another. My understanding is that Fib-4 was a way to very quickly and easily find people with advanced liver disease from standard liver function tests (which are cheaper and more widely prescribed) rather than using a fibroscan (which are less accessible and more expensive). The fibroscan would still be the best non-invasive way to confirm the level of liver fibrosis.
Hope this helps,
Thomas