Evaluation of pediatric liver transplant recipients using quantitative hepatobiliary scintigraphy

Use of imaging to assess the activity of hepatic transporters

Introduction: Membrane transporters of the SLC and ABC families are abundantly expressed in the liver, where they control the transfer of drugs/drug metabolites across the sinusoidal and canalicular hepatocyte membranes and play a pivotal role in hepatic drug clearance. Noninvasive imaging methods, such as PET, SPECT or MRI, allow for measuring the activity of hepatic transporters in vivo, provided that suitable transporter imaging probes are available.Areas covered: We give an overview of the working principles of imaging-based assessment of hepatic transporter activity. We discuss different currently available PET/SPECT radiotracers and MRI contrast agents and their applications to measure hepatic transporter activity in health and disease. We cover mathematical modeling approaches to obtain quantitative parameters of transporter activity and provide a critical assessment of methodological limitations and challenges associated with this approach.Expert opinion: PET in combination with pharmacokinetic modeling can be potentially applied in drug development to study the distribution of new drug candidates to the liver and their clearance mechanisms. This approach bears potential to mechanistically assess transporter-mediated drug-drug interactions, to assess the influence of disease on hepatic drug disposition and to validate and refine currently available in vitro-in vivo extrapolation methods to predict hepatic clearance of drugs.

Monitoring Hepatocyte Dysfunction and Biliary Complication After Liver Transplantation Using Quantitative Hepatobiliary Scintigraphy

The significance of hepatobiliary scintigraphy (HBS) for hepatic graft function assessment was established mostly on retrospective studies and was not widely recognized due to the lack of quantitative data and variation in accuracy. This prospective study was performed to investigate the effectiveness of quantitative HBS for assessing hepatocyte dysfunction and biliary complication in liver transplant recipients.In 57 recipients who had undergone orthotopic liver transplantation, a total of 67 dynamic Tc-EHIDA scans were performed and quantitative parameters including the hepatocyte extraction fraction (HEF), time to maximum hepatic radioactivity (Tmax), and time for peak activity to decrease by 50% (T1/2) were calculated. The scintigraphic results based on the 3 parameters were compared against the final diagnosis. A ROC curve analysis was carried out to identify the cutoff value of Tmax for diagnosis of biliary stricture. Correlation between the parameters of postoperative HBS and conventional biochemical liver function indices were also analyzed.Quantitative Tc-EHIDA HBS had an overall sensitivity of 94.12% (16/17), specificity of 93.33% (42/45), and diagnostic accuracy of 93.55% (58/62) for detecting hepatocyte dysfunction and biliary complication in liver transplant recipients. The recommended cutoff value of Tmax for diagnosis of post-transplant biliary stricture was set at 15.75 min with a sensitivity of 100.0% and a specificity of 94.0%. The scintigraphic parameters (HEF, Tmax) were statistically significantly associated with the conventional liver function parameters.Quantitative Tc-EHIDA HBS offers a noninvasive imaging modality with high sensitivity and specificity to diagnose hepatocyte dysfunction as well as distinguish between patients with or without biliary stricture following liver transplantation. Furthermore, HEF and Tmax values obtained from dynamic HBS show good correlation with conventional liver function parameters.

Liver function testing with nuclear medicine techniques is coming of age

Liver function is a broad term, as the organ participates in a multitude of different physiological and biochemical processes, including metabolic, synthetic, and detoxifying functions. However, it is the function of the hepatocyte that is central to sustaining normal life and dealing with disease states. When the liver begins to fail in severely ill patients, it forecasts a terminal outcome. However, unlike the glomerular filtration rate which clearly quantifies the key renal function, at most practice sites, there is no clinically available quantitative test for liver function. Although it is commonplace to assess indirect evidence of that function (by measuring blood levels of its end products and by-products) and to detect an acute injury (by following rising transaminases), a widely available test that would directly measure hepatocellular function is lacking. This article reviews current knowledge on liver function studies and focuses on those nuclear medicine tests available to study the whole liver and regional liver function. The clinical application driving these tests, prediction of remnant liver function after partial hepatectomy for primary liver malignancy or metastatic disease, is addressed here in detail. The test was recently validated for this specific application and was shown to be better than the current standard of practice (computed tomography volumetry), particularly in patients with hepatic comorbidities like cirrhosis, steatosis, or cholestasis. Furthermore, early assessment of regional liver function increase after preoperative portal vein embolization becomes possible with this technology. The limiting factor to a wider acceptance of this test is based on the lack of clinical software that would allow calculation of liver function parameters. This article provides information that enables a clinical nuclear medicine facility to provide this test using readily available equipment. Furthermore, it addresses emerging clinical applications that are under investigation.

Differentiation of liver transplantation complications by quantitative analysis of dynamic hepatobiliary scintigraphy

OBJECTIVE

We retrospectively investigated the value of dynamic Tc-diisopropyl-iminodiacetic acid hepatobiliary scintigraphy (HBS) in discriminating postsurgical complications following liver transplantation (LT).

METHODS

Dynamic HBS was performed for suspected post-LT complications in 201 cases. Hepatic uptake and excretion was visually graded. The portal perfusion index (PPI) and kinetic parameters were quantitatively analyzed.

RESULTS

HBS findings were normal in all 119 (59%) cases without complications. Complications were confirmed in 82 cases: 24 had graft rejection, 48 had biliary obstruction, and 10 had hepatitis. Visual grades of uptake and excretion were abnormal for all three types of complications and showed no discriminative value. The PPI level was significantly higher for grafts with rejection (0.83 ± 0.07) compared with no complication (0.57 ± 0.08), biliary obstruction (0.69 ± 0.06), and hepatitis (0.65 ± 0.07; all P<0.0001). Receiver operating characteristic curve analysis confirmed PPI to be highly accurate for discerning rejection from no rejection (area under the curve, 0.97; sensitivity, 95.8%; specificity, 91.7%) or biliary obstruction (area under the curve, 0.93; sensitivity, 95.8%; specificity, 79.2%).

CONCLUSION

PPI measured from dynamic HBS offers a highly accurate method for identifying post-LT rejection and distinguishing it from biliary obstruction or hepatitis.

Nuclear imaging techniques for the assessment of hepatic function in liver surgery and transplantation

This review describes the application of 2 nuclear imaging techniques for assessment of hepatic function in the setting of liver surgery and transplantation. The biochemical and technical background, as well as the clinical applications, of (99m)Tc-labeled diethylenetriaminepentaacetic acid galactosyl human serum albumin (GSA) scintigraphy and hepatobiliary scintigraphy (HBS) with (99m)Tc-labeled iminodiacetic acid derivates is discussed. (99m)Tc-mebrofenin is considered the most suitable iminodiacetic acid agent for (99m)Tc-HBS. (99m)Tc-GSA scintigraphy and (99m)Tc-mebrofenin HBS are based on 2 different principles. (99m)Tc-GSA scintigraphy is a receptor-mediated technique whereas HBS represents hepatic uptake and excretion function. Both techniques are noninvasive and provide visual and quantitative information on both total and regional liver function. They can be used for preoperative assessment of future remnant liver function, follow-up after preoperative portal vein embolization, and evaluation of postoperative liver regeneration. In liver transplantation, these methods are used to assess graft function and biliary complications.

Use of tc-99m mebrofenin as a clinical probe to assess altered hepatobiliary transport: integration of in vitro, pharmacokinetic modeling, and simulation studies

PURPOSE

Transport of the hepatobiliary scintigraphy agent Tc-99m mebrofenin (MEB) was characterized and simulation studies were conducted to examine the effects of altered hepatic transport on MEB pharmacokinetics in humans.

METHODS

MEB transport was investigated in Xenopus laevis oocytes expressing OATP1B1 or OATP1B3, and in membrane vesicles prepared from HEK293 cells transfected with MRP2 or MRP3. A pharmacokinetic model was developed based on blood, urine and bile concentration-time profiles obtained in healthy humans, and the effect of changes in hepatic uptake and/or excretion associated with disease states (hyperbilirubinemia and cholestasis) on MEB disposition was simulated.

RESULTS

MEB (80 pM) transport by OATP1B1 and OATP1B3 was inhibited by rifampicin (50 microM) to 10% and 4% of control, respectively. MEB (0.4 nM) transport by MRP2 was inhibited to 12% of control by MK571 (50 microM); MRP3-mediated transport was inhibited to 5% of control by estradiol-17-beta-glucuronide (100 microM). A two-compartment model described MEB (2.5 mCi) systemic disposition in humans (systemic clearance = 16.2 +/- 2.7 ml min(-1) kg(-1)); biliary excretion was the predominant route of hepatic elimination (efflux rate constants ratio canalicular/sinusoidal = 3.4 +/- 0.8). Based on simulations, altered hepatic transport markedly influenced MEB systemic and hepatic exposure.

CONCLUSIONS

MEB may be a useful probe to assess how altered hepatic function at the transport level modulates hepatobiliary drug disposition.

Usefulness of hepatobiliary scintigraphy for the evaluation of living related liver transplant recipients in the early postoperative period

AIM

The aim of this study was to investigate the usefulness of hepatobiliary scintigraphy for the evaluation of liver grafts in the early postoperative period in patients receiving liver transplants from living related donors.

MATERIALS AND METHODS

Fifty-six liver transplant recipients who received grafts from living related donors were included in the study. We examined the hepatobiliary scintigraphies of all patients, which were performed 7 to 10 days after the transplantation. The scintigraphic images were evaluated visually in terms of hepatic parenchymal function and biliary and vascular complications.

RESULTS

In 44/56 recipients, hepatobiliary scintigraphy was completely normal in the early postoperative period. However, in 6/56 cases, scintigraphy was interpreted to show parenchymal dysfunction. In these patients, histopathologic confirmation by biopsies revealed four cases of hepatocellular damage/cholestasis, one acute rejection, and one cholangitis. In 3/56 patients, hepatobiliary scintigraphy demonstrated a hypoactive area in the liver graft; however, the other areas showed normal function. When the abdominal computed tomography (CT) and CT angiography were evaluated, these hypoactive areas were discovered to be related to minor vascular problems. In 3/56 liver graft recipients whose grafts showed normal parenchymal function scintigraphically, images were interpreted to indicate bile leak because accumulation of tracer was seen at an abnormal physiological site.

CONCLUSION

Hepatobiliary scintigraphy, which is a noninvasive and objective method, is useful to assess grafts in the early postoperative period among patients who received liver transplants from living related donors.

Hepatobilijarna scintigrafija u proceni funkcije transplantirane jetre

The aim of the study is evaluation of hepatocellular function, as well as morphology and patency of the biliary three of the liver transplants by dynamic hepatobiliary scintigraphy. The study was performed in 10 controls and 10 patients after orthotopic transplantation (up to two years). Sixty minutes dynamic acquisition (1 frame/min) was performed with scintillation camera after injection of 360 MBq 99mTc-diethyl-IDA. Hepatobiliary scintigrams were analysed for morphology, and parenchymal and hepatobiliary TA curves were generated and analysed as regard to the time to maximal acitivity (Tmax) and the time to half of maximum acitivity (T1/2). Uptake of the radiopharmaceutical was slightly but not significantly delayed (Tmax=18.5+2.9 min) in comparison to the controls (Tmax=14.2+ 3.4min), while excretion was significantly prolonged (T1/2=59.5+ 12.1 min) than physiological (Tmax=34.2+4.1min). Intrahepatic bile flow was nonsignificantly prolonged (Tmax=31.3+3.7 min) in comparison to the controls (Tmax=25.7+ 3.5 min) while extrahepatic one is high significantly prolonged (T1/2=89.0+14.3 min) than physiological (T1/2 =45.0+ 7.2 min). Biliary phase of hepatobiliary scintigraphy showed increased accumulation of radiopharmaceutical in the left (n=1) or right (n=2) hepatic duct. Radionuclide methods are noninvasive, and apear to be sensitive and valuable for the monitoring of liver transplants.