Ultrasounds are only 80% accurate in diagnosing liver shunts according to studies done at the University of Tennessee (Dr. Tobias). Dr. Center estimates their accuracy to be as low as 60%.
Your next step after a BAT would be a Protein C test and depending on the results, a scintigraphy, not an ultrasound.
A liver biopsy would be your last resort, only after the Protein C test and scintigraphy. Since it is an invasive surgical procedure, hopefully it can be avoided.
If you vet has questions, why don't you have him contact Dr. Center? She is very accessible for consults.
http://www.vin.com/proceedings/Proce...2675&O=Generic