Image-based dynamic liver testing : Studies of segmental hepatic parenchymal function and biliary flow using dynamic 99Tcm-HIDA SPECT

Abstract: The aim of the study was to create a dynamic liver function test using a tomographic imaging procedure as sampling method. The liver has multiple and complex functions. It is obvious that no single test can give a comprehensive measurement of total liver function. Currently available tests, including analyte measurements and clearance tests, give limited information. Furthermore, no test is able to measure function on a segmental level. The ultimate liver function test is probably multi-compartment quantitative analysis (QA) of a dynamic test. This requires a safe, well tolerated test substance, not influenced by diet, drugs or genetic factors. As a dynamic test requires repetitive sampling, the sampling method should be noninvasive and able to detect the test substance in all compartments involved in the kinetics of the test substance. We have developed a technique of dynamic 99Tcm-HIDA SPECT (single photon emission computed tomography) allowing creation of time-activity curves for the isotope in individual liver segments. QA of these curves can measure uptake and excretion of the isotope as an indication of function on a segmental level. In principle, the test is a dynamic liver function test using an imaging modality (SPECT) as sampling device. The concept was simulated in a 3-D virtual reality liver model. Advancing the dynamic SPECT technique according to the model, we separated activity for parenchyma and bile ducts and created separate dynamic studies for these structures. This refinement, being a step in the direction of a true multi-compartmental dynamic test, using image sampling, was tested in a normal volunteer population and in patients with primary sclerosing cholangitis (PSC). The complicated management of PSC stresses the limitations of currently used liver function tests. In patients with PSC, QA of the dynamic SPECT data correlated statistically significantly with biochemical parameters and the revised Mayo prognostic score. On a segmental level, the scintigraphic data reflecting biliary flow correlated with cholangiographic findings. A method capable of evaluating liver function and quantifying bile flow on a segmental level has several possible applications, particularly in segmental liver diseases. It may aid in predicting prognosis and selecting and timing of various treatment options. Specifically, the importance of radiologically detected strictures in terms of flow obstruction can be quantified and the outcome of intervention measured. Our data suggest differences in liver function between different segments in normal livers. Expressing total liver function as the total of the product of volume and segmental function in individual segments, may give a more accurate estimate of total liver function. Physiological differences between the left and right hemi-livers, as indicated by our results, may play a role in the non-homogeneity and hemi-liver preferences of some liver diseases.