On the mechanical behavior of the human biliary system

Classification of anatomical morphology of cystic duct and its association with gallstone

BACKGROUND

Gallstones are common lesions that often require surgical intervention. Laparoscopic cholecystectomy is the treatment of choice for symptomatic gallstones. Preoperatively, the anatomical morphology of the cystic duct (CD), needs to be accurately recognized, especially when anatomical variations occur in the CD, which is otherwise prone to bile duct injury. However, at present, there is no optimal classification system for CD morphology applicable in clinical practice, and the relationship between anatomical variations in CDs and gallstones remains to be explored.

AIM

To create a more comprehensive clinically applicable classification of the morphology of CD and to explore the correlations between anatomic variants of CD and gallstones.

METHODS

A total of 300 patients were retrospectively enrolled from October 2021 to January 2022. The patients were divided into two groups: The gallstone group and the nongallstone group. Relevant clinical data and anatomical data of the CD based on magnetic resonance cholangiopancreatography (MRCP) were collected and analyzed to propose a morphological classification system of the CD and to explore its relationship with gallstones. Multivariate analysis was performed using logistic regression analyses to identify the independent risk factors using variables that were significant in the univariate analysis.

RESULTS

Of the 300 patients enrolled in this study, 200 (66.7%) had gallstones. The mean age was 48.10 ± 13.30 years, 142 (47.3%) were male, and 158 (52.7%) were female. A total of 55.7% of the patients had a body mass index (BMI) ≥ 24 kg/m2. Based on the MRCP, the CD anatomical typology is divided into four types: Type I: Linear, type II: n-shaped, type III: S-shaped, and type IV: W-shaped. Univariate analysis revealed differences between the gallstone and nongallstone groups in relation to sex, BMI, cholesterol, triglycerides, morphology of CD, site of CD insertion into the extrahepatic bile duct, length of CD, and angle between the common hepatic duct and CD. According to the multivariate analysis, female, BMI (≥ 24 kg/m2), and CD morphology [n-shaped: Odds ratio (OR) = 10.97, 95% confidence interval (95%CI): 5.22-23.07, P < 0.001; S-shaped: OR = 4.43, 95%CI: 1.64-11.95, P = 0.003; W-shaped: OR = 7.74, 95%CI: 1.88-31.78, P = 0.005] were significantly associated with gallstones.

CONCLUSION

The present study details the morphological variation in the CD and confirms that CD tortuosity is an independent risk factor for gallstones.

Analysis and numerical investigation of bile flow dynamics within the strictured biliary duct

The mechanics of bile flow in the biliary system plays an important role in studying bile stasis and gallstone formation. Bile duct stricture is an abnormal phenomenon that refers to the bile duct getting smaller or narrower. The main objective of this study is to study the influence of stricture on bile flow dynamics using numerical methods. We employed a numerical Computational Fluid Dynamics model of the bile flow within a strictured hepatic duct. We studied and compared the influence of stricture severity, stricture length, eccentricity, and bile flow property on the bile flow dynamics. The bile flow velocity, pressure distribution, pressure drop, and wall shear stress are provided in detail. The stricture alters the normal bile flow pattern and increases flow resistance. At the location upstream and downstream of the stricture, bile flow slows down. In the area of the stricture throat, bile flow is accelerated, and recirculation forms behind the stricture. The maximum pressure drop of the biliary system increases with the stricture length. The eccentricity makes the flow deflect away from the duct's centerline. The behavior of the deflected flow is significantly altered downstream of the stricture. Such bile flow behavior as deceleration and recirculation may lead to cholestasis. Stricture alters bile flow in the biliary tract, causing changes in biliary hydrodynamic indexes, which could potentially serve as an omen for gallstone formation and other related diseases. The consideration of the bile duct stricture could lead to better patient stratification.

Review on bile dynamics and microfluidic-based component detection: Advancing the understanding of bilestone pathogenesis in the biliary tract

Bilestones are solid masses found in the gallbladder or biliary tract, which block the normal bile flow and eventually result in severe life-threatening complications. Studies have shown that bilestone formation may be related to bile flow dynamics and the concentration level of bile components. The bile flow dynamics in the biliary tract play a critical role in disclosing the mechanism of bile stasis and transportation. The concentration of bile composition is closely associated with processes such as nucleation and crystallization. Recently, microfluidic-based biosensors have been favored for multiple advantages over traditional benchtop detection assays for their less sample consumption, portability, low cost, and high sensitivity for real-time detection. Here, we reviewed the developments in bile dynamics study and microfluidics-based bile component detection methods. These studies may provide valuable insights into the bilestone formation mechanisms and better treatment, alongside our opinions on the future development of in vitro lithotriptic drug screening of bilestones and bile characterization tests.

Understanding bacterial infiltration of the pancreas through a deformable pancreatic duct

Tiny amount of bacteria are found in the pancreas in pancreatitis and cancer, which seemed involved in inflammation and carcinogenesis. However, bacterial infiltration from the duodenum is inhibited by the physical defense mechanisms such as bile flow and the sphincter of Oddi. To understand how the bacteria possibly infiltrate the pancreas through a deformable pancreatic duct, influenced by the periodic contractions of the sphincter of Oddi, a mathematical model of bacterial infiltration is developed that considered large deformation, fluid flow, and bacterial transport in a deformable pancreatic duct. In addition, the sphincter's contraction wave is modeled by including its propagation from the pancreas toward the duodenum. Simulated structure of the deformed duct with the relaxed sphincter and simulated bile distribution agreed reasonably well with the literature, validating the model. Bacterial infiltration from the duodenum in a deformable pancreatic duct, following the sphincter's contraction, is counteracted by a gradual peristalsis-like deformation of the pancreatic duct, due to an antegrade contraction wave propagation from the pancreas to the duodenum, Parametric sensitivity analysis demonstrated that bacterial infiltration is increased with lower bile and pancreatic juice flow rate, greater contraction amplitude and frequency, thinner wall thickness, and retrograde contraction wave propagation. Since contraction waves following retrograde propagation are increased in patients with common bile duct stones and pancreatitis, they may possibly be factors for continuum inflammation of pancreas. (224 words).

A composite scaffold fabricated with an acellular matrix and biodegradable polyurethane for the in vivo regeneration of pig bile duct defects

Bile duct regeneration is urgently needed to restore the normal function of the damaged biliary system. In this study, an artificial bile duct (ABD) was fabricated for extrahepatic bile duct regeneration based on biodegradable polyurethane (BPU) and ureter acellular matrix (UAM) to endow it with favorable biocompatibility and eliminate bile leakage during in vivo bile duct regeneration. The mechanical properties, in vitro simulation of bile flow and cytocompatibility of BPU-UAM ABD were evaluated in vitro, and surgical implantation in the biliary defect site in minipigs was implemented to reveal the in vivo degradation of BPU-UAM and regeneration of the new bile duct. The results indicated that BPU-UAM ABD with a mechanical strength of 11.9 MPa has excellent cytocompatibility to support 3T3 fibroblast survival and proliferation in extraction medium and on the scaffolds. The in vivo implantation of BPU-UAM ABD revealed the change of collagen content throughout the new bile duct regeneration. Biliary epithelial cells were observed at day 70, and continuous biliary epithelial layer formation was observed after 100 days of implantation. Altogether, the BPU-UAM ABD fabricated in this study possesses excellent properties for application study in the regeneration of bile duct. STATEMENT OF SIGNIFICANCE: Extrahepatic bile duct defects carry considerable morbidity and mortality because they are the only pathway for bile to go down into the intestinal tract. At present, no artificial bile duct can promote biliary regeneration. In this study, BPU-UAM ABD was built based on biodegradable polyurethane and ureter acellular matrix to form a continuous compact layer of polyurethane in the internal wall of UAM and avoid bile leakage and experimental failure during in vivo implantation. Our work verified the effectiveness of the synthesized biodegradable polyurethane emulsion-modified urethral acellular matrix in bile regeneration and continuous biliary epithelial layer formation. This study provided a new approach for the curing of bile duct defects and inducing new bile tissue formation.

Acute Cholecystitis Presenting With Septic Shock as the First Presentation in an Elderly Patient

Gangrenous cholecystitis (GC), a severe complication of acute cholecystitis, is associated with higher morbidity and mortality rates than uncomplicated cholecystitis. In this report, we present the case of an 81-year-old female with diabetes mellitus and hypertension who presented in the emergency department complaining of severe generalized abdominal pain for 10 days. The pain was associated with nausea and vomiting. She had septic shock, prompting admission, and was eventually diagnosed with perforated GC. Interventional radiology was conducted, and a cholecystostomy tube was placed under radiology guidance with continuous daily irrigation and intravenous antibiotic coverage for four weeks. Subsequently, the patient’s condition improved, and she was finally discharged.

Patient-specific fluid-structure interaction model of bile flow: comparison between 1-way and 2-way algorithms

Gallbladder disease is one of the most spread pathologies in the world. Despite the number of operations dealing with biliary surgery increases, the number of postoperative complications is also high. The aim of this study is to show the influence of the biliary system pathology on bile flow character and to numerically assess the effect of surgical operation (cholecystectomy) on the fluid dynamics in the extrahepatic biliary tree, and also to reveal the difference between 1-way and 2-way FSI algorithms on the results. Moreover, the bile viscosity and biliary tree geometry influence on the choledynamics were evaluated. Bile velocity, pressure, wall shear stress (WSS), displacements and von Mises stress distributions in the extrahepatic biliary tree are presented, and comparison is made between a healthy and a lithogenic bile. The patient-specific biliary tree model is created using magnetic resonance imaging (MRI) and imported in a commercial finite element analysis software. It is found that in the case of lithogenic bile, velocities have lower magnitude while pressures are higher. Furthermore, stress analysis of the bile ducts shows that the WSS distribution is found mostly prevailing in the common hepatic duct and common bile duct areas. It is shown that when it is necessary to evaluate the bile flow dynamics in urgent medical situations, 1-way analysis is acceptable. Nevertheless, 2-way FSI provides more accurate data, if necessary to evaluate the stress-strain state of bile ducts. The proposed model can be applied to medical practice to reduce the number of post-operative complications.

Intraductal Tissue Sampling Device Designed for the Biliary Tract

Clinical sampling of tissue that is read by a pathologist is currently the gold standard for making a disease diagnosis, but the few minimally invasive techniques available for small duct biopsies have low sensitivity, increasing the likelihood of false negative diagnoses. We propose a novel biopsy device designed to accurately sample tissue in a biliary stricture under fluoroscopy or endoscopic guidance. The device consists of thin blades organized around the circumference of a cylinder that are deployed into a cutting annulus capable of comprehensively sampling tissue from a stricture. A parametric study of the device performance was done using finite element analysis; this includes the blade deployment under combined axial compression and torsion followed by an axial 'cutting' step. The clinical feasibility of the device is determined by considering maximum deployment forces, the radial expansion achieved and the cutting stiffness. We find practical parameters for the device operation to be an overall length of 10 mm and a diameter of 3.5 mm for a [Formula: see text] blade thickness, which allow the device to be safely deployed with a force of 10N and achieve an expansion over 3x its original diameter. A model device was fabricated with these parameters and a [Formula: see text] thickness out of a NiTi superalloy and tested to validate the performance. The device showed strong agreement with an equivalent numerical model, reaching a peak force within 2% of that predicted numerically and fully recovering after compression to 20% of its length. Clinical and Translational Impact Statement -This pre-clinical research conceptually demonstrates a novel expandable device to biopsy tissue in narrow strictures during an ERCP procedure. It can greatly improve diagnostic tissue yield compared to existing methods.

3D Printed Model of Extrahepatic Biliary Ducts for Biliary Stent Testing

Several inflammatory conditions of the bile ducts cause strictures that prevent the drainage of bile into the gastrointestinal tract. Non-pharmacological treatments to re-establish bile flow include plastic or self-expanding metal stents (SEMs) that are inserted in the bile ducts during endoscopic retrograde cholangiopancreatography (ERCP) procedures. The focus of this study was to 3D print an anatomically accurate model of the extrahepatic bile ducts (EHBDs) with tissue-like mechanical properties to improve in vitro testing of stent prototypes. Following generation of an EHBD model via computer aided design (CAD), we tested the ability of Formlabs SLA 3D printers to precisely print the model with polymers selected based on the desired mechanical properties. We found the printers were reliable in printing the dimensionally accurate EHBD model with candidate polymers. Next, we evaluated the mechanical properties of Formlabs Elastic (FE), Flexible (FF), and Durable (FD) resins pre- and post-exposure to water, saline, or bile acid solution at 37 °C for up to one week. FE possessed the most bile duct-like mechanical properties based on its elastic moduli, percent elongations at break, and changes in mass under all liquid exposure conditions. EHBD models printed in FE sustained no functional damage during biliary stent deployment or when tube connectors were inserted, and provided a high level of visualization of deployed stents. These results demonstrate that our 3D printed EHBD model facilitates more realistic pre-clinical in vitro testing of biliary stent prototypes.

Risk of Gallstone Formation in Aberrant Extrahepatic Biliary Tract Anatomy: A Review of Literature

The age-long mnemonic of '5Fs' (fat, female, fertile, forty, and fair) has traditionally been used in medical school instructions to describe the risk factors for gallstone disease. However, evidence suggests that aberrant extrahepatic biliary tract (EHBT) anatomy may contribute significantly to the risk of gallstone disease. This review explores the anatomy and embryological bases of EHBT variations as well as the prevalence of these variations. Also, we discuss the risk factors for gallstone formation in the relationship between gallstone disease and aberrant EHBT anatomy.

Three-dimensional spatially resolved geometrical and functional models of human liver tissue reveal new aspects of NAFLD progression

Early disease diagnosis is key to the effective treatment of diseases. Histopathological analysis of human biopsies is the gold standard to diagnose tissue alterations. However, this approach has low resolution and overlooks 3D (three-dimensional) structural changes resulting from functional alterations. Here, we applied multiphoton imaging, 3D digital reconstructions and computational simulations to generate spatially resolved geometrical and functional models of human liver tissue at different stages of non-alcoholic fatty liver disease (NAFLD). We identified a set of morphometric cellular and tissue parameters correlated with disease progression, and discover profound topological defects in the 3D bile canalicular (BC) network. Personalized biliary fluid dynamic simulations predicted an increased pericentral biliary pressure and micro-cholestasis, consistent with elevated cholestatic biomarkers in patients' sera. Our spatially resolved models of human liver tissue can contribute to high-definition medicine by identifying quantitative multiparametric cellular and tissue signatures to define disease progression and provide new insights into NAFLD pathophysiology.

Biomechanical behaviour of human bile duct wall and impact of cadaveric preservation processes

Biliary diseases are the third most common cause of surgical digestive disease. There is a close relationship between the mechanical performance of the bile duct and its physiological function. Data of biomechanical properties of human main bile duct are scarce in literature. Furthermore, mechanical properties of soft tissues are affected by these preservation procedures. The aim of the present work was, on the one hand, to observe the microstructure of the human bile duct by means of histological analysis, on the other hand, to characterize the mechanical behavior and describe the impact of different preservation processes. A mechanical study in a controlled environment consisting of cyclic tests was made. The results of the mechanical tests are discussed and explained using the micro-structural observations. The results show an influence of the loading direction, which is representative of an anisotropic behavior. A strong hysteresis due to the viscoelastic properties of soft tissues was also observed. Embalming and freezing preservation methods had an impact on the biomechanical properties of human main bile duct, with fiber network deterioration. That may further provide a useful quantitative baseline for anatomical and surgical training using embalming and freezing.

A fully coupled porous media and channels flow approach for simulation of blood and bile flow through the liver lobules

Two dimensional, steady state, and incompressible blood and bile flows through the liver lobules are numerically simulated. Two different geometric models A and B are proposed to study the effects of lobule structure on the fluid flow behaviour. In Model A, the lobule tissue is represented as a hexagonal shape porous medium with a set of flow channels at its vertices accounting for the hepatic artery, portal and central veins along with bile ductules. Model B is a channelized porous medium constructed by adding a set of flow channels, representing the bile canaliculies and lobule sinusoids, to Model A. The bile and blood flow through the lobule is simulated by the finite element approach, based on the Darcy/Brinkman equations in the lobule tissue and the Navier-Stokes (or Stokes) equations in the flow channels. In Model B, a transmission factor on the boundaries of the bile canaliculies is introduced to connect the bile and blood flows. First, a single regular lobule is utilized to exhibit the fluid flow pattern through the liver lobule represented by proposed geometric models. Then, the model is extended to a group of liver lobules to demonstrate the flow through a liver slice represented by irregular lobules. Numerical results indicate that the Darcy and Brinkman equations provide nearly the same solutions for Model A and similar solutions with a little difference for Model B. It is shown that the existence of sinusoids and bile canaliculies inside the liver lobules has noticeable effects on its fluid flow pattern, in terms of pressure and velocity fields.

Wet-tip versus dry-tip regimes of osmotically driven fluid flow

The secretion of osmolytes into a lumen and thereby caused osmotic water inflow can drive fluid flows in organs without a mechanical pump. Such fluids include saliva, sweat, pancreatic juice and bile. The effects of elevated fluid pressure and the associated mechanical limitations of organ function remain largely unknown since fluid pressure is difficult to measure inside tiny secretory channels in vivo. We consider the pressure profile of the coupled osmolyte-flow problem in a secretory channel with a closed tip and an open outlet. Importantly, the entire lateral boundary acts as a dynamic fluid source, the strength of which self-organizes through feedback from the emergent pressure solution itself. We derive analytical solutions and compare them to numerical simulations of the problem in three-dimensional space. The theoretical results reveal a phase boundary in a four-dimensional parameter space separating the commonly considered regime with steady flow all along the channel, here termed “wet-tip” regime, from a “dry-tip” regime suffering ceased flow downstream from the closed tip. We propose a relation between the predicted phase boundary and the onset of cholestasis, a pathological liver condition with reduced bile outflow. The phase boundary also sets an intrinsic length scale for the channel which could act as a length sensor during organ growth.

A Predictive 3D Multi-Scale Model of Biliary Fluid Dynamics in the Liver Lobule

Bile, the central metabolic product of the liver, is transported by the bile canaliculi network. The impairment of bile flow in cholestatic liver diseases has urged a demand for insights into its regulation. Here, we developed a predictive 3D multi-scale model that simulates fluid dynamic properties successively from the subcellular to the tissue level. The model integrates the structure of the bile canalicular network in the mouse liver lobule, as determined by high-resolution confocal and serial block-face scanning electron microscopy, with measurements of bile transport by intravital microscopy. The combined experiment-theory approach revealed spatial heterogeneities of biliary geometry and hepatocyte transport activity. Based on this, our model predicts gradients of bile velocity and pressure in the liver lobule. Validation of the model predictions by pharmacological inhibition of Rho kinase demonstrated a requirement of canaliculi contractility for bile flow in vivo. Our model can be applied to functionally characterize liver diseases and quantitatively estimate biliary transport upon drug-induced liver injury.

Biliary tract pressure before and after endoscopic papillary balloon dilation treatment for common bile duct stones

AIM: To determine the biliary tract pressure before and after endoscopic papillary balloon dilation (EPBD) treatment for common bile duct stones.

METHODS: Clinical data for 96 patients with common bile duct stones who successfully underwent EPBD and biliary manometry from September 2011 to January 2014 were retrospectively analyzed.

RESULTS: Biliary tract pressure was significantly higher in patients with common bile duct stones than in healthy controls, which could be relieved by EPBD. Biliary tract pressure in patients who underwent cholecystectomy was higher than in patients with gallbladder stones. After operation, there were 2 cases of hyperamylasemia, 2 cases of acute pancreatitis and 2 cases of mild cholangitis, all of which resolved after non-operative treatment. The incidence of complications was 6.3% (6/96). No serious complications occurred.

CONCLUSION: EPBD treatment can effectively solve biliary obstruction and reduce biliary pressure.

Assessment of physiologic bile flow in the extrahepatic bile duct with cine-dynamic MR cholangiopancreatography and a spatially selective inversion-recovery pulse

PURPOSE

To determine the feasibility of directly and noninvasively visualizing physiologic bile flow in the extrahepatic bile duct by means of nonpharmacologic cine-dynamic magnetic resonance (MR) cholangiopancreatography with a spatially selective inversion-recovery (IR) pulse and assess the flow dynamic pattern of bile in the extrahepatic bile duct.

MATERIALS AND METHODS

The institutional review board approved this retrospective study and waived the need for informed consent. Thirty-five patients without known pancreatobiliary diseases and 11 patients with dilatation of the extrahepatic bile duct were included. Cine-dynamic MR cholangiopancreatography with a spatially selective IR pulse was performed by imaging every 15 seconds over a 5-minute interval (20 images acquired total). The images were evaluated for the visualization of bile flow, the frequency that bile flow was observed in the extrahepatic bile duct, and the distance the bile moved within the area of the IR pulse. Statistical analysis was performed by using Spearman rank correlation coefficient and Mann-Whitney U tests.

RESULTS

Antegrade bile flow was observed in 29 of 35 patients (83%) in the nondilated group. Bile flow was observed much more frequently in the nondilated group than in the dilated group (4.4 times vs 1.8 times, P = .029). The distance that bile moved forward within the area of the IR pulse was significantly greater in the nondilated group than in the dilated group (mean grade, 0.44 vs 0.14; P = .033), suggesting stagnation or slowdown of antegrade bile flow in patients with biliary dilatation. Reversed bile flow was also observed in 26 of 35 patients (74%) in the nondilated group without biliary diseases.

CONCLUSION

Nonpharmacologic cine-dynamic MR cholangiopancreatography with a spatially selective IR pulse allows direct and noninvasive visualization of bile flow in the extrahepatic bile duct, demonstrating that reversed bile flow is a physiologic phenomenon.

Human hepatic stem cell and maturational liver lineage biology

Livers are comprised of maturational lineages of cells beginning extrahepatically in the hepato-pancreatic common duct near the duodenum and intrahepatically in zone 1 by the portal triads. The extrahepatic stem cell niches are the peribiliary glands deep within the walls of the bile ducts; those intrahepatically are the canals of Hering in postnatal livers and that derive from ductal plates in fetal livers. Intrahepatically, there are at least eight maturational lineage stages from the stem cells in zone 1 (periportal), through the midacinar region (zone 2), to the most mature cells and apoptotic cells found pericentrally in zone 3. Those found in the biliary tree are still being defined. Parenchymal cells are closely associated with lineages of mesenchymal cells, and their maturation is coordinated. Each lineage stage consists of parenchymal and mesenchymal cell partners distinguishable by their morphology, ploidy, antigens, biochemical traits, gene expression, and ability to divide. They are governed by changes in chromatin (e.g., methylation), gradients of paracrine signals (soluble factors and insoluble extracellular matrix components), mechanical forces, and feedback loop signals derived from late lineage cells. Feedback loop signals, secreted by late lineage stage cells into bile, flow back to the periportal area and regulate the stem cells and other early lineage stage cells in mechanisms dictating the size of the liver mass. Recognition of maturational lineage biology and its regulation by these multiple mechanisms offers new understandings of liver biology, pathologies, and strategies for regenerative medicine and treatment of liver cancers.

Experimental Investigation of the Flow of Bile in Patient Specific Cystic Duct Models

Three-dimensional scaled-up transparent models of three human cystic ducts were prepared on the basis of anatomical specimens. The measurement of pressure drop across the cystic duct models and visualization of the flow structures within these ducts were performed at conditions replicating the physiological state. The flow visualization study confirmed the laminar nature of the flow of bile inside the cystic duct and values of pressure drop coefficient (Cp) decreased as the Reynolds number (Re) increased. The three tested models showed comparable behavior for the curve of Reynolds number versus the pressure drop coefficient. The results show that the tested cystic ducts have both increased pressure drop and complicated flow structures when compared with straight conduits. High resistance in a cystic duct may indicate that the gallbladder has to exert large force in expelling bile to the cystic duct. For patients with diseased gallbladder, and even in healthy persons, gallbladder is known to stiffen with age and it may lose its compliance or flexibility. A high resistance cystic duct coupled with a stiffened gallbladder may result in prolonged stasis of bile in the gallbladder, which is assumed to encourage the formation of gallstones.

Mandatory and optional function tests for biliary disorders

Function tests in gastroenterology and hepatology aim to provide criteria for diagnosis of specific disorders and for prediction of patient responses to therapy. This review focuses on the utility of function tests in the management of gallstone disease and functional biliary disorders. In gallstone disease, function tests may be considered in the selection of candidates for nonsurgical therapy of gallbladder stones only. In cases of suspected functional biliary disorders, experts have advocated the use of classical noninvasive tests such as hepatobiliary scintigraphy. However, unequivocal evidence for their utility in diagnosis or patient selection for invasive treatment is yet to be provided. Recently, more advanced noninvasive tests such as real-time ultrasonography or secretin-stimulated magnetic resonance cholangiopancreaticography have been described. Controlled trials using these novel techniques may provide a rationale for the use of function tests in clinical management of calculous and acalculous biliary diseases, but are currently not available.