The resistive index (RI) is the most common Doppler parameter used for hepatic arterial evaluation. The usual range in normal, as well as post-transplant individuals, is between 0.55 and 0.8.
It is measured by:
Resistive index (RI) = (peak systolic velocity - end-diastolic velocity)/peak systolic velocity
Hepatic arterial resistive index is most often assessed during the evaluation of a liver transplant. In this setting, a low RI is usually more specific for disease than a high RI (the opposite situation from a renal transplant) 5.
Low RI: more specific for disease in a liver transplant, a low RI may result from:
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proximal partial arterial occlusion 5
steno-occlusive disease of the transplant hepatic artery 7
celiac artery stenosis
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distal peripheral vascular shunts (arteriovenous or arterioportal) 5
hepatic arteriovenous malformations in the hereditary hemorrhagic telangiectasia syndrome 5
portal hypertension as in severe liver cirrhosis 5
trauma 5
High RI: less specific for disease in a liver transplant, a high RI may result from:
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microvascular compression or disease 5
chronic hepatocellular disease 5
transplant rejection
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hepatic venous congestion
chronic congestive hepatopathy
nonocclusive hepatic artery hypoperfusion syndrome 8
-
physiologic
postprandial state 5
advanced patient age 5
may transiently elevate within 72 hours after transplant
A high RI can be classified into four types 4:
type I: RI >0.80 with continuous blood flow in the diastolic phase
type II: RI = 1, complete absence of the diastolic signal and preserved systolic velocity
type III: absence of diastolic signal and diminished systolic velocity
type IV: undetectable Doppler flow
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