Radionuclide evaluation of liver transplants

Effect of Ritonavir on (99m)Technetium-Mebrofenin Disposition in Humans: A Semi-PBPK Modeling and In Vitro Approach to Predict Transporter-Mediated DDIs

A semiphysiologically based pharmacokinetic (semi-PBPK) model was developed to describe a unique blood, liver, and bile clinical data set for the hepatobiliary imaging agent ^99mTechnetium–mebrofenin (^99mTc–mebrofenin), and to simulate sites/mechanisms of a ^99mTc–mebrofenin–ritonavir drug–drug interaction (DDI). The transport inhibitor ritonavir (multiple-dose: 2 × 300 mg) significantly increased systemic ^99mTc–mebrofenin exposure as compared with control (4,464 ± 1,861 vs. 1,970 ± 311 nCi min/ml; mean ± SD), without affecting overall hepatic exposure or biliary recovery. A novel extrahepatic distribution compartment was required to characterize ^99mTc–mebrofenin disposition. Ritonavir inhibited ^99mTc–mebrofenin accumulation in human sandwich-cultured hepatocytes (SCH) (half maximal inhibitory concentration (IC₅₀) = 3.46 ± 1.53 µmol/l). Despite ritonavir accumulation in hepatocytes, intracellular binding was extensive (97. 6%), which limited interactions with multidrug resistance protein 2 (MRP2)-mediated biliary excretion. These in vitro data supported conclusions from modeling/simulation that ritonavir inhibited ^99mTc–mebrofenin hepatic uptake, but not biliary excretion, at clinically relevant concentrations. This integrated approach, utilizing modeling, clinical, and in vitro data, emphasizes the importance of hepatic and extrahepatic distribution, assessment of inhibitory potential in relevant in vitro systems, and intracellular unbound concentrations to assess transporter-mediated hepatic DDIs.

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.

Undetectable late hepatic sequelae after hypofractionated stereotactic radiotherapy for liver tumors

Hypofractionated liver stereotactic radiotherapy has produced long-term survival, but the hepatobiliary system is radiosensitive and may be severely damaged by the treatment. We have evaluated long-term radiation effects on hepatobiliary functions in the first long-term survivors reported after radiotherapy to the hepatobiliary system for liver tumors. Eleven patients were followed for up to 13 years after treatment of tumors≤9 cm in size. Conventional blood chemistry, clearance of indocyanine green and segmental uptake and excretion of radiolabeled mebrofenin were assayed. Slightly abnormal routine blood chemistry was found during the first 2 years in some patients with pre-existing liver damage. Other parameters were seemingly unaffected, and liver segments which received differing mean doses did not differ measurably with regard to parenchymal or ductal function. Late liver functions were therefore not demonstrably affected by the radiotherapy in most patients even in the presence of mild cirrhosis, after previous exposure to liver toxic agents, or after resection. However, slight to moderate late dysfunction occurred in one patient after three courses of irradiation, and in a cirrhotic patient after two major liver resections following radiotherapy. Our previous doses for irradiation of liver tumors gave no measurable chronic side effects and may be increased in order to control tumors more effectively. In selected patients, irradiation is possible even in the presence of liver dysfunction, and previous irradiation or resection does not absolutely contraindicate salvage treatment by re-irradiation or resection.

Hepatobiliary scintigraphy for the assessment of biliary strictures after pediatric liver transplantation

HBS is used in the management of liver transplantation, a significant complication of which is biliary stricture. Strictures may be intraparenchymal within segments and main duct (non-anastomotic) or at the biliary-enteric anastomosis (anastomotic). Strictures are definitively diagnosed, and often managed, by PTC. This is invasive, technically challenging, and requires general anesthesia in young children. HBS may allow early detection of these complications and is non-invasive. The aim of this study was to review the scintigraphic pattern of biliary strictures using (99m)TcDISIDA HBS following pediatric orthotopic liver transplantation, and to assess its role in the diagnostic algorithm of suspected biliary strictures. All available hepatobiliary studies performed post-transplant in 101 episodes of liver transplantation in 92 pediatric patients were reviewed. Twenty-three (23%) patients had known biliary strictures. Twenty-two patients had adequate studies available for review; five had intrahepatic (non-anastomotic) strictures alone, nine had a stricture of the anastomosis alone, and eight had both intrahepatic and anastomotic strictures. HBS patterns (either segmental or global changes) correlated very highly with clinically significant biliary strictures. All patients with known strictures had abnormal HBS; hence, in patients with abnormal liver function tests post-liver transplant, a normal HBS makes strictures very unlikely. We propose that HBS can thus be used to determine if further investigation is required.

Measurement of parenchymal function and bile duct flow in primary sclerosing cholangitis using dynamic 99mTc-HIDA SPECT

BACKGROUND AND AIM

Primary sclerosing cholangitis is a chronic cholestatic disease characterized by obliterative fibrosis of intrahepatic and/or extrahepatic bile ducts. The unpredictable clinical course of the disease can be relentless, leading to premature death in a large percentage of patients. Prognostic index formulas, the revised Mayo model being the most frequently used, have been developed to predict clinical course and prognosis. The aim of this study was to investigate the potential value of dynamic (99m)Tc-HIDA SPECT in patients with primary sclerosing cholangitis by correlating scintigraphic results with cholangiographic and biochemical findings and prognostic scoring systems used in clinical practice.

METHODS

In 18 patients with primary sclerosing cholangitis, segmental parenchymal and bile duct functions were measured using dynamic (99m)Tc-HIDA SPECT. Quantitative scintigraphic results were compared to cholangiographic findings, as graded by a biliary classification system, the Child-Pugh score and revised Mayo prognostic score, as well as the individual biochemical parameters included in the scoring systems.

RESULTS

In individual segments, scintigraphic quantitative parameters indicative of bile flow showed a statistically significant correlation with the state of the bile-flow path for the respective segments as assessed by the biliary classification system. The revised Mayo score correlated with the scintigraphic quantitative parameters indicative of parenchymal function and bile flow as calculated for the whole liver.

CONCLUSIONS

Dynamic (99m)Tc-HIDA SPECT, capable of assessing different aspects of liver function for the total liver, as well as for individual segments, has potential value in the management of patients with primary sclerosing cholangitis.

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.

Hepatobiliary scintigraphy in liver transplant patients: the "blind end sign" and its differentiation from bile leak

PURPOSE

Hepatobiliary scintigraphy is commonly performed on liver transplant patients to exclude biliary complications such as obstruction or leak. Biliary reconstruction in these patients is performed using either a direct duct-to-duct anastomosis (choledochocholedochostomy) or a biliary-enteric anastomosis (Roux-en-Y hepaticojejunostomy). The authors have observed a finding in scans performed on the latter group of patients that often simulates a bile leak. They postulate this finding to represent retention of activity in the blind end of the Roux limb (the "blind end sign"). The purpose of this study was to determine characteristics of this blind end activity, which may help differentiate it from true bile leaks.

METHODS

Two nuclear medicine physicians reviewed 36 Tc-99m mebrofenin hepatobiliary scans (31 patients). Biliary reconstruction was performed in 25 patients with a Roux-en-Y hepaticojejunostomy, and in 6 patients with a choledochocholedochostomy. Each scan was evaluated regarding whether there was focal, persistent retention of activity in the anastomotic region, and, if so, various features of the activity were noted. Activity was concluded to represent a true bile leak based on subsequent surgical confirmation, and if there was no such confirmation, the activity was concluded to represent blind end retention in patients with Roux-en-Y hepaticojejunostomies.

RESULTS

There were 8 total examples of blind end activity and 3 examples of bile leak activity. Useful discriminators between the 2 types of activity included the following: fluctuation in size and/or intensity with time (8 of 8 blind end cases vs. 0 of 3 bile leak cases); size comparable with bowel (8 of 8 vs. 1 of 3); tubular (4 of 8 vs. 0 of 3), round (4 of 8 vs. 1 of 3), or irregular (0 of 8 vs. 2 of 3) shape; and movement into bowel (3 of 8 vs. 0 of 3). Delayed imaging was performed in 3 cases at 1.5 hours, but was only conclusive in 1 case in which diffuse extravasation was seen consistent with bile leak.

CONCLUSION

Retention of activity in the blind end of the Roux limb in patients with Roux-en-Y hepaticojejunostomies may simulate bile leak, but certain typical features, as well as delayed imaging, may aid in distinguishing the two.

Dynamic 99Tcm-HIDA SPET: non-invasive measuring of intrahepatic bile flow. Description of the method and a study in primary sclerosing cholangitis

In this study dynamic 99Tcm-HIDA single photon emission tomography (SPET) was performed in patients with primary sclerosing cholangitis and normal test subjects. The method offers the possibility of functional analysis of individual liver segments. After injection of 120 MBq of 99Tcm-HIDA, 12 consecutive SPET examinations were performed at 6-min intervals. The segmental borders of liver segments as seen on computed tomography or magnetic resonance examinations were superimposed on the scintigraphic images allowing placement of regions of interest (ROIs) in specific liver segments. Sampling from the same ROIs in consecutive SPET images enabled creation of time-activity curves for individual liver segments. A range of normal values was created by quantitative analysis of normal volunteer studies. Results of the studies in patients correlated well with cholangiographic extent of disease, liver function tests and histological stage. The technique may have particular value in diseases that affect the liver in a nonhomogenous or segmental fashion. Giving an indication of bile clearance from individual liver segments, it can quantify the functional importance of radiologically detected strictures. Percutaneous liver biopsy can be directed to the worst affected parts of the liver, making biopsy more representative. Sequential studies may allow monitoring of disease progression, aiding in selection and timing of therapeutic procedures.

The role of hepatobiliary scintigraphy in the evaluation of the protective effects of dimethylsulphoxide in ischaemic/reperfusion injury of liver

Liver ischaemia may lead to parenchymal damage depending on the duration of the ischaemia. Dimethylsulphoxide (DMSO), a well-known radical oxygen scavenger, is a protective agent against ischaemia/reperfusion injury. In this study we aimed to investigate the role of hepatobiliary scintigraphy (HBSc) in detecting the protective effect of DMSO. Eighteen rabbits, in three groups of six, were injected with 37 MBq technetium-99m-mebrofenin via the ear veins. Dynamic scintigrams were taken for 60 min (1 frame/min). In group A, HBSc was performed without any surgery. In groups B and C the Pringle manoeuvre (PM) was applied for 30 min, and tissue specimens for electron microscopy were taken from the liver parenchyma 5 min after the end of the PM. In addition, in group C 1 g/kg DMSO was injected into each rabbit 5 min before application of the PM. HBSc was then performed in groups B and C. From the dynamic images time-activity curves (TACs) were obtained for each group, and the time of peak uptake (TPU) and time for half of the activity to clear from the liver (T1/2) were calculated. The TPU and T1/2 of group B were significantly longer than those of groups A and C (P<0.0005 and P<0.005 for TPU, and P<0.0005 and P<0.02 for T1/2, respectively). The TPU and T1/2 of group C were significantly longer than those of group A (P < 0.005 and P < 0.02, respectively). While the electron microscopic images in group C showed reversible changes, those in group B showed both irreversible and reversible changes. The electron microscopic findings of groups B and C confirmed the scintigraphic findings. In conclusion, HBSc might be used as a practical quantitative method for detecting the protective effects of DMSO. However, its clinical value should be evaluated by further studies with human subjects.

Radiolabeled annexin V imaging: diagnosis of allograft rejection in an experimental rodent model of liver transplantation

PURPOSE

To assess the value of imaging rejection-induced apoptosis with technetium 99m and annexin V, a human protein-based radiopharmaceutical used in the diagnosis of acute rejection of a liver transplant, in a well-characterized rodent model of orthotopic liver transplantation.

MATERIALS AND METHODS

99mTc-radiolabeled annexin V was intravenously administered to six allografted (immunologically mismatched) and five isografted (immunologically matched) recipient rats on days 2, 4, and 7 after orthotopic liver transplantation. Animals were imaged 1 hour after injection of 0.2-2.0 mCi (8.0-74.0 MBq) of radiolabeled annexin V by use of clinical nuclear scintigraphic equipment.

RESULTS

All animals in the allografted group demonstrated marked increases of 55% and 97% above the activity in the isografted group in hepatic uptake of annexin V on days 4 and 7, respectively. Severe acute rejection was histologically detected in all allografted livers on day 7. There was no histologic evidence of acute rejection in isografted animals. Dynamic hepatobiliary imaging with 99mTc and mebrofenin, an iminodiacetic acid derivative, demonstrated no correlation with the presence or absence of acute rejection or with annexin V uptake.

CONCLUSION

Noninvasive imaging with radiolabeled annexin V is more sensitive and specific than imaging with 99mTc-mebrofenin in the diagnosis of acute rejection of a liver transplant.

In liver transplantation, T tube bile represents total bile flow: physiological and scintigraphic studies on biliary secretion of organic anions

The present study was performed to clarify the recovery of hepatocellular uptake and the biliary secretion of bile acids during the first 14 days after orthotopic liver transplantation (OLT) and to determine the fraction of bile flow appearing outside through the T tube and entering the duodenum. Therefore, we determined primary and secondary bile acids in bile samples obtained from the T tube at day 5 after OLT, while the T tube was permanently open, and at days 10 and 14 after OLT, i.e., 4 and 9 days after closure of the T tube, respectively, thus restoring enterohepatic bile acid circulation. In addition, we performed hepatobiliary scintigraphy using technetium 99m-labeled [2,4,6 trimethyl-3-bromo]imino-diacetic acid (technetium 99m-BRIDA) in 12 patients between days 4 and 17 after OLT. Chromatographic analyses of biliary bile acids showed no secondary bile acids during the first 5 days after OLT, as opposed to 10 and 14 days after OLT when enterohepatic circulation was restored. Eleven patients with an uncomplicated postoperative course after OLT showed a significantly reduced hepatic uptake and biliary secretion of 99mTc-BRIDA during the first days after OLT with progressive recovery. One patient with an acute allograft rejection episode showed almost no uptake and only minimal secretion. The bile fraction appearing outside through the inserted T tube represented 94.6% +/- 6.2% of the injected 99mTc-BRIDA. We conclude that OLT results in markedly impaired hepatocellular uptake and biliary secretion of organic anions. Simultaneously, bile acid synthesis is significantly reduced, which, in addition, diminishes bile secretion of the graft. We show that T tube bile is a valid tool for bile physiological studies in patients in whom transplantation was successfully performed.

Role of nuclear medicine in liver transplantation

Orthotopic liver transplantation is now a very well-established technique for treating patients with end-stage liver disease. Since 1967, more than 26,000 liver transplants have been performed, including 15,000 in the United States. The overall 1-year survival rate is approximately 80% and 5-year survival is 70%. Nuclear imaging plays an important role in the management of liver transplant recipients before and after liver transplantation. The evaluation of candidates potentially includes liver-spleen scan for liver volume, multiple gated acquisition scan, adenosine or stress thallium study, bone scan, and quantitative ventilation perfusion scan for hepatopulmonary syndrome. In the post-transplant phase, the deconvolution analysis (which corrects for the problem of recirculation) is a promising tool for diagnosing rejection, although its role in the transplant population has to be established. A variety of nuclear medicine techniques are helpful in the postoperative diagnosis of biliary complications. By performing a semiquantitative analysis to discriminate hepatocyte dysfunction from biliary disease and measuring hepatocyte extraction fraction by deconvolution analysis and excretion, (T1/2 values measured by the nonlinear list squares technique) have been very promising.

Liver transplant rejection and cholestasis: comparison of technetium 99m-diisopropyl iminodiacetic acid hepatobiliary imaging with liver biopsy

To determine whether the scintigraphic evaluation of technetium-99m diisopropyl iminodiacetic acid (DISIDA) uptake and excretion can distinguish among liver transplant patients with biopsy evidence for rejection, cholestasis or neither condition, we reviewed scintigrams and biopsies in 36 patients. There were 76 scintigrams with corresponding biopsies. Uptake and excretion were graded from image data on scales reflecting normal through severely abnormal values. Biopsies were evaluated for findings of cholestasis and rejection. The majority of scintigrams demonstrated normal uptake (60/75, 80%) and delayed excretion (65/76, 85%), which was most marked immediately after transplantation. One-way analysis of variance showed that the mean excretion values significantly differed between patients with normal biopsies and those with cholestasis and/or rejection (P = 0.0003). However, mean uptake scores demonstrated no statistically significant difference between these two groups of patients (P = 0.1). These findings suggest that 99mTc-DISIDA scintigraphy can differentiate between transplants with and without rejection/cholestasis but not between rejection and cholestasis. If 99mTc-DISIDA excretion is normal, rejection and cholestasis are unlikely.

Kupffer cell and hepatocyte function in rat transplanted liver

The liver consists essentially of two compartments, parenchymal cells (PC) and non parenchymal cells (NPC) i. e. Kupffer cells, endothelial cells, fat storing cells and pit cells. PC remain after transplantation but NPC are eventually exchanged with host cells. Dynamic liver scintigraphy with albumin colloid, extracted by NPC, and IODIDA, extracted by PC, were tested to evaluate function as determined by clearance rates in these two cellular compartments. Experimental liver transplantation was performed in 15 syngeneic rats. Following transplantation, we performed dynamic liver scintigraphy with 0.5 ml 5 MBq 99mTc-Nanocoll and 0.5 ml 20 MBq 99mTc-IODIDA, 10 s per frame, 30 min for each examination. Percentage clearance rate, per minute was calculated from uptake curves over the liver. Uptake curves were nearly exponential and clearance rates could be estimated from a logarithmic plot of uptake versus time. The clearance rate was 25 +/- 4% per min (mean +/- SD) for NPC and 32 +/- 15% per min for PC in controls. After liver transplantation it was 31 +/- 7% per min for NPC and 30 +/- 15% per min for PC. Dynamic liver scintigraphy with 99mTc-Nanocoll and 99mTc-IODIDA alloweds a separate assessment of the function of PC and NPC after experimental liver transplantation in rats.

Sequential changes in relative liver function assessed by 99mTc-HIDA scintigraphy after auxiliary heterotopic liver transplantation in dogs

Auxiliary heterotopic liver transplantation (HLT) was used to achieve functional repair in a dog model with an inborn error of metabolism. For the interpretation of the results, information on separate liver function is essential when a normal host liver is also present. We developed a radionuclear method to quantitate the relative contribution of each liver to the total uptake of intravenously (IV) injected 99mTc-HIDA. The HLT was performed between 20 mismatched pairs of dogs from two different strains. Four surgical procedures were used. After autopsy the outcome of the premortem HIDA-scan was compared with the wet weight of the graft and the host liver. A good linear correlation was noted between the relative contribution of the uptake and weight of the graft to the total HIDA uptake and total liver weight. Therefore, the relative contribution of an auxiliary heterotopic liver graft to the total liver function can be quantitated with a 99mTc-HIDA scan. With this technique, changes in relative function after an HLT under various flow conditions can be sequentially followed.

Detection of complications after liver transplantation by technetium-99m mebrofenin hepatobiliary scintigraphy

Fifty-five hepatobiliary scintigraphic studies using 99mTc-Mebrofenin were performed in 52 orthotopic liver transplant patients to evaluate suspected biliary complications, namely biliary extravasation and extrahepatic obstruction. Final diagnosis was made by analysis of the clinical course and other procedures. Three out of three studies of biliary leak and four out of five studies of biliary obstruction were detected. There were no false positives in either complication. The sensitivity, specificity and accuracy were 100, 100, 100% for ectravasation and 80, 100, 98% for obstruction, respectively. Hepatobiliary scintigraphy appears to be an accurate means of detecting biliary leak and obstruction associated with the transplanted liver.

The role of radiology in the diagnosis and treatment of biliary complications after liver transplantation

Hepatic transplantation is now an accepted therapeutic option for selected patients with terminal liver disease. Biliary complications are, however, relatively common after transplantation. We reviewed our experience with diagnostic and therapeutic biliary radiologic procedures in 151 hepatic recipients. Biliary complications were seen in 25% of patients. Interventional radiologic procedures were an integral part of the diagnostic and therapeutic management of these patients; reoperation was, nonetheless, occasionally required.