Diagnostic Approach for Elevated Liver Function Tests and Right Upper Quadrant Pain

Primary Recommendation: MRCP as First-Line Advanced Imaging

• The American College of Radiology recommends MRCP as the preferred imaging modality over HIDA scan for detecting choledocholithiasis and biliary obstruction, with sensitivity of 85-100% and specificity of 90% 1, 2, 3, 4
• MRCP excels at detecting choledocholithiasis with reported sensitivity of 85-100%, specificity of 90%, and accuracy of 89-90% 1, 2, 3, 4
• MRCP is superior to CT for assessing suspected biliary sources of RUQ pain and provides comprehensive evaluation of the entire hepatobiliary system 1, 2, 3
• MRCP visualizes the common bile duct and cystic duct better than ultrasound, which is a significant advantage when evaluating for bile duct stones or obstruction causing elevated LFTs 1, 2, 3
• MRCP can identify the level and cause of biliary obstruction with accuracy of 91-100%, including stones, strictures, masses, and lymph nodes 2, 4

When to Consider HIDA Scan Instead

• HIDA scan is appropriate for suspected acute cholecystitis when ultrasound is equivocal, particularly in the setting of fever and elevated WBC count 2, 4, 5, 6
• HIDA scan is the imaging examination of choice for suspected acalculous cholecystitis 7, 6
• HIDA scan can be used to evaluate chronic gallbladder disease or biliary dyskinesia with calculation of gallbladder ejection fraction after cholecystokinin infusion 2, 4
• HIDA scan can be used to evaluate low-grade, partial, or intermittent biliary obstruction presenting with recurrent RUQ pain, mimicking chronic cholecystitis 2, 4

Clinical Algorithm for Elevated LFTs + RUQ Pain

• The American College of Radiology recommends performing right upper quadrant ultrasound first as the initial imaging modality 1, 2, 3
• If ultrasound is negative or equivocal, order MRCP to comprehensively evaluate the biliary tree for stones, strictures, or obstruction 1, 2, 3, 4, 8

Important Clinical Caveats

• Elevated LFTs indicate biliary obstruction or cholestasis, which requires anatomic visualization of the bile ducts—something MRCP provides but HIDA scan does not 8
• Do not order HIDA scan as the primary test for elevated LFTs and RUQ pain unless acute cholecystitis is the primary clinical concern 2, 4, 5, 6
• MRCP also helps identify non-biliary causes of RUQ pain including hepatic masses, pancreatic inflammation, and other abdominal pathology 1, 2, 8

Diagnostic Approach for Jaundice and Suspected Biliary Obstruction

Initial Evaluation

• The American College of Radiology recommends ultrasound as the initial evaluation for jaundice with suspected biliary obstruction, with specificities ranging between 71% to 97% for confirming or excluding mechanical obstruction 9, 10, 11
• Ultrasound can detect biliary dilatation, which is the critical first step in determining whether obstruction is present and guides subsequent management 9, 12
• Ultrasound has high sensitivity (65-95%) and positive predictive value (98%) for detecting cirrhosis, which may be an alternative cause of jaundice 9, 10, 11

Comparison with Other Imaging Modalities

• CT is less sensitive than ultrasound for initial biliary evaluation and exposes patients to radiation without clear advantage as a first-line test 12, 13
• The American College of Radiology Appropriateness Criteria explicitly recommend ultrasound first, followed by advanced imaging based on ultrasound findings 9, 10

CT Abdomen/Pelvis in Biliary Obstruction Diagnosis

Introduction to Biliary Obstruction Diagnosis

• In patients with right upper quadrant pain, where ultrasound demonstrates gallstones and a dilated common bile duct, the American College of Radiology recommends proceeding to MRCP to evaluate the cause of biliary obstruction or directly to therapeutic intervention based on clinical context 14

Clinical Scenarios Where CT Adds Value

• If the patient is critically ill, has atypical presentation, or there is suspicion of complications beyond simple biliary obstruction, CT with IV contrast may be appropriate, as recommended by the American Family Physician and the American College of Radiology 14, 15

Recommended Clinical Algorithm

• If a patient has elevated liver function tests suggesting biliary obstruction, the American College of Radiology suggests proceeding directly to MRCP 14
• If the patient is critically ill or has peritoneal signs, CT with IV contrast may be warranted to evaluate for complications, according to the American Family Physician and the American College of Radiology 14, 15

Diagnostic Approach to Suspected Biliary Obstruction

Rationale for Ultrasound as First-Line Imaging

• The American College of Radiology recommends ultrasound as the initial evaluation for patients presenting with jaundice and suspected biliary obstruction, with specificities ranging between 71% to 97% for confirming or excluding mechanical obstruction 16
• Ultrasound can detect biliary dilatation, identify gallstones with 96% accuracy, assess gallbladder wall thickening and pericholecystic fluid, evaluate intrahepatic and extrahepatic bile ducts, and detect alternative diagnoses such as cirrhosis (sensitivity 65-95%, positive predictive value 98%) 16, 17, 18

Clinical Algorithm for This Patient

• The American College of Radiology guidelines suggest performing abdominal ultrasound immediately to assess for biliary dilatation, gallstones, gallbladder wall thickening, and signs of cirrhosis or other hepatic parenchymal disease 16, 17, 18
• Ultrasound has shorter study time, is portable, lacks radiation exposure, and costs less than CT or MRI, making it ideal for initial evaluation 17

Important Clinical Caveats

• The sonographic Murphy sign has relatively low specificity for acute cholecystitis and is unreliable if the patient has received pain medication prior to imaging 17
• In critically ill patients, gallbladder abnormalities are common even in the absence of acute cholecystitis, which may limit ultrasound's diagnostic utility in this specific population 17

MRI Protocol for Cholecystitis

Introduction to Cholecystitis Imaging

• The American College of Radiology recommends MRI abdomen with MRCP and IV gadolinium-based contrast for a patient with cholecystitis when advanced imaging is needed 19, 20

When to Order MRI for Cholecystitis

• MRI is not a first-line imaging modality for acute cholecystitis—ultrasound remains the initial test of choice, but MRI with MRCP becomes the preferred advanced imaging when ultrasound findings are equivocal or when you need to evaluate for complications and biliary tree abnormalities 19, 20, 21
• The American College of Radiology suggests that MRI with MRCP is useful in specific clinical scenarios, such as equivocal ultrasound findings in a patient who is difficult to examine with US 19, 20
• MRI performs superiorly to ultrasound in evaluating the gallbladder neck, cystic duct, or common bile duct stones 19, 20, 21

Recommended MRI Protocol Components

• The American College of Radiology recommends MRI abdomen with MRCP that includes IV gadolinium-based contrast agent for comprehensive evaluation of cholecystitis 19, 20, 21
• This protocol provides T2-weighted sequences to demonstrate gallbladder wall edema and pericholecystic fluid better than CT 19, 20, 21
• MRCP sequences are used for excellent visualization of the biliary tree, with superior accuracy for detecting bile duct stones compared to noncontrast CT 19, 20
• Contrast-enhanced T1-weighted sequences are used to assess gallbladder wall enhancement, adjacent liver parenchymal hyperemia, and to detect wall necrosis or perforation 19

Diagnostic Performance

• MRI for acute cholecystitis demonstrates a sensitivity of 85% (95% CI: 66%-95%) 19, 20, 21
• MRI for acute cholecystitis demonstrates a specificity of 81% (95% CI: 69%-90%) 19, 20, 21

Important Clinical Caveats

• Without IV gadolinium contrast, you will miss critical findings including abnormal gallbladder wall enhancement, adjacent liver parenchymal hyperemia, and the ability to distinguish gangrenous from uncomplicated cholecystitis 19, 20
• The American College of Radiology suggests that longer acquisition times limit MRI use in unstable patients 19, 20
• The American College of Radiology recommends that MRI should not be used as the primary imaging test for acute right upper quadrant pain—start with ultrasound 19, 20
• If acalculous cholecystitis is suspected, cholescintigraphy (HIDA scan) remains the imaging examination of choice, not MRI 19, 20, 21

Diagnostic Approach for Suspected Biliary Obstruction

Clinical Context and Diagnostic Pathway

• The Infectious Diseases Society of America (IDSA) guidelines suggest that clinical signs, laboratory findings, and imaging findings are key diagnostic components for acute cholangitis, which can be diagnosed with MRCP 22, 23
• The IDSA 2024 guidelines recommend initial imaging with abdominal ultrasound, and if ultrasound is negative or equivocal, proceeding directly to MRCP for comprehensive evaluation of the biliary tree 22, 23

Imaging Modalities

• The IDSA guidelines suggest that CT should be reserved for critically ill patients with peritoneal signs or suspected complications beyond simple biliary obstruction, and is primarily used to rule out complications, not to definitively diagnose biliary obstruction 22, 23

Abdominal Ultrasound in Diagnosing Biliary Obstruction

Rationale for Ultrasound First

• The American College of Radiology recommends ultrasound as the initial evaluation for jaundice with suspected biliary obstruction, with specificities ranging between 71% to 97% for confirming or excluding mechanical obstruction 24, 25
• The American College of Gastroenterology designates ultrasound as the initial diagnostic test of choice in patients with suspected common duct obstruction 24

Diagnostic Capabilities of Ultrasound

• Ultrasound detects biliary dilatation with high accuracy, guiding subsequent management decisions 25
• Ultrasound evaluates for cirrhosis as an alternative cause of jaundice, with sensitivity of 65-95% and positive predictive value of 98% 24, 25
• Ultrasound has limitations for visualizing the distal common bile duct due to overlying bowel gas, with reported sensitivities for CBD stone detection ranging from only 22.5% to 75% 24

Clinical Algorithm

• A normal CBD caliber on ultrasound has a 95-96% negative predictive value for choledocholithiasis in patients with symptomatic cholelithiasis 24
• Older comparative studies demonstrate CT has sensitivity between only 39% to 75% for detection of gallstones compared with ultrasound 24
• Many gallstones are not radiopaque (up to 80% are noncalcified), limiting CT's utility for detecting the most common cause of biliary obstruction 24

Diagnostic Approach for Suspected Biliary Obstruction

Initial Evaluation

• The American College of Radiology recommends ultrasound as the initial evaluation for patients presenting with jaundice and suspected biliary obstruction, with specificities ranging between 71% to 97% for confirming or excluding mechanical obstruction, in patients with clinical presentation of right upper quadrant pain, fever, jaundice, and elevated liver enzymes 26
• Ultrasound provides comprehensive initial evaluation by identifying gallstones with 96% accuracy, assessing gallbladder wall thickening and pericholecystic fluid, evaluating intrahepatic and extrahepatic bile ducts, and detecting alternative diagnoses, in patients presenting with right upper quadrant pain, fever, and jaundice 27

Diagnostic Algorithm

• If ultrasound demonstrates biliary dilatation or choledocholithiasis with elevated liver function tests, the American College of Radiology recommends proceeding directly to MRCP for comprehensive evaluation of the biliary tree, which has sensitivity of 85-100% and specificity of 90% for detecting bile duct stones and obstruction, although the exact citation for this sensitivity and specificity is not provided, the recommendation is based on 26
• The American College of Radiology reserves CT for critically ill patients with suspected complications, such as emphysematous cholecystitis, gallbladder perforation, or abscess formation, and not for initial diagnostic evaluation, due to its lower sensitivity for detecting gallstones and exposure to unnecessary radiation 27

Therapeutic Interventions

• ERCP is a therapeutic intervention, not a diagnostic test, and should only be performed after non-invasive imaging (ultrasound ± MRCP) has confirmed biliary obstruction requiring intervention, due to its risks of pancreatitis and perforation 26, 27

MRCP Diagnostic Accuracy for Choledocholithiasis

Diagnostic Performance

• The American College of Radiology recommends that MRCP sequences themselves, using heavily T2-weighted imaging, provide the diagnostic information for detecting bile duct stones, with no need for IV contrast 28, 29
• Non-contrast MRCP achieves sensitivity of 85-100% and specificity of 90% for detecting choledocholithiasis, according to the World Journal of Emergency Surgery 30, 31
• MRCP uses heavily T2-weighted sequences that make stationary fluid (bile) appear bright, while stones appear as dark filling defects within the bright bile column, allowing for accurate diagnosis 28, 29

Clinical Guidelines

• The American College of Radiology guidelines clarify that IV contrast improves detection of complications and alternative diagnoses, such as acute cholangitis, hepatic metastases, primary sclerosing cholangitis, and distinguishing the etiology of biliary obstruction, but not the stones themselves 28, 29
• For suspected choledocholithiasis, the recommended clinical algorithm is to order "MRI abdomen with MRCP" or "MRCP without contrast", and add IV gadolinium contrast only if necessary to evaluate for other conditions 28, 29

Contrast Agents in MRCP

Introduction to MRCP Contrast Agents

• The American College of Radiology states that a history of iodinated contrast allergy does not require premedication or special precautions when performing MRCP, even if gadolinium is administered, because these are completely different agents with different reaction profiles 32, 33
• The contrast allergy to iodinated contrast media, used in CT scans, is distinct from gadolinium-based contrast agents used in MRI, and does not necessitate precautions when performing MRCP 32, 33
• The American College of Radiology explicitly states that premedication is not recommended for patients with isolated history of hypersensitivity reactions to iodinated contrast media when they are to receive gadolinium-based contrast agents 32, 33

Guidance on Ordering MRCP

• For patients with iodinated contrast allergy, ordering "MRCP without IV contrast" provides complete diagnostic information for choledocholithiasis, biliary obstruction, and pancreatic duct abnormalities, and IV gadolinium can be added if necessary to evaluate other conditions beyond simple biliary tree visualization 32, 33

Diagnostic Findings and Recommendations

Introduction to Diagnostic Results

• The American College of Radiology suggests that elevated bilirubin levels typically indicate either a blockage in the bile ducts or a problem with liver processing bile 34

CT Scan Findings

• A normal pancreas on the CT scan, with no signs of inflammation or other problems, is a good indicator of no serious pancreatic disease, as suggested by the World Journal of Emergency Surgery 35, 36
• A contracted gallbladder with no visible gallstones on CT and no blockage in the bile ducts is a significant finding, according to the Journal of the American College of Radiology 34

Specialist Recommendations

• The presence of a small hiatal hernia with possible swelling around the lower esophagus warrants evaluation by a gastroenterologist, as recommended by the World Journal of Emergency Surgery 37
• The American College of Radiology recommends an MRI/MRCP to comprehensively evaluate elevated bilirubin levels despite normal-appearing bile ducts on CT, due to the high accuracy of MRCP in detecting bile duct stones 34

Management of Upper Quadrant Abdominal Pain with Heterogeneous Liver on Ultrasound

Initial Evaluation and Imaging

• The American College of Radiology recommends obtaining a complete metabolic panel with liver function tests to assess for hepatobiliary pathology, specifically checking transaminases, alkaline phosphatase, GGT, and total/direct bilirubin 38
• MRI abdomen with MRCP is superior to CT for comprehensive hepatobiliary evaluation, providing excellent visualization of liver parenchyma, biliary tree anatomy, and detection of masses or infiltrative processes 38
• MRCP achieves 85-100% sensitivity and 90% specificity for detecting biliary pathology, including choledocholithiasis, strictures, and obstruction that may be causing pain despite normal ultrasound findings 38

Differential Diagnosis and Advanced Imaging

• The American College of Radiology and Hepatology society suggest considering chronic liver disease, including cirrhosis, fatty liver disease, or metabolic syndrome-associated hepatic steatosis, as a potential cause of heterogeneous liver on ultrasound with upper quadrant pain 38, 39
• Biliary pathology, including chronic cholecystitis, choledocholithiasis, biliary strictures, or intrahepatic biliary lithiasis, should be considered as a potential cause of symptoms, even if not apparent on initial ultrasound 38, 39
• Other causes of chronic liver disease, including chronic viral hepatitis, autoimmune liver disease, alpha-1 antitrypsin deficiency, Wilson disease, and alcohol-associated liver disease, should be evaluated 39

Critical Clinical Algorithm and Pitfalls

• The American College of Radiology recommends ordering MRI abdomen with MRCP with IV gadolinium contrast as the next imaging study to comprehensively evaluate the heterogeneous liver and biliary tree 38
• If cholestatic liver tests are elevated with inconclusive imaging, MRCP is superior to additional ultrasound or CT for detecting hepatolithiasis, choledocholithiasis, and biliary strictures 39
• The Hepatology society advises against dismissing a heterogeneous liver as "normal variant" and recommends investigation, especially in the context of upper quadrant pain 38

Management of Persistent Right Upper Quadrant Pain After Negative Biliary Imaging

Advanced Imaging Recommendations

• The American College of Radiology recommends that, in patients with ongoing right‑upper‑quadrant (RUQ) pain after normal ultrasound, HIDA scan, and CT, magnetic resonance cholangiopancreatography (MRCP) should be performed as the next imaging study because it provides superior visualization of the biliary tree compared with repeat CT. 40

Empiric Medical Therapy

• In the same patient population, an empiric trial of a proton‑pump inhibitor (e.g., omeprazole 20–40 mg daily for 4–8 weeks) is advised to address possible gastro‑esophageal reflux disease, peptic ulcer disease, or other gastroduodenal sources of RUQ pain that are not detectable on abdominal imaging. 40

Diagnostic Algorithm

• If MRCP and the PPI trial both fail to identify a cause of the RUQ pain, the guideline advises proceeding to upper endoscopy to directly evaluate for gastroduodenal pathology such as erosive esophagitis or ulcer disease. 40

Avoidance of Ineffective or Risky Interventions

• The guideline explicitly cautions against repeating ultrasound or CT scans after the initial negative work‑up, stating that these modalities are inferior to MRCP for detecting subtle biliary abnormalities and therefore add no diagnostic value. 40

MRCP as the Preferred Imaging Modality for Cystic Duct Visualization

Diagnostic Performance

• MRCP provides the highest non‑invasive sensitivity (85‑100 %) and specificity (≈90 %) for visualizing the cystic duct, outperforming other imaging techniques. (Journal of Hepatology, 2009) 41
• The European Association for the Study of the Liver (EASL) endorses MRCP as a safe diagnostic tool for the biliary tree, with accuracy for detecting biliary obstruction that approaches that of ERCP when performed in experienced centers equipped with state‑of‑the‑art technology. (Journal of Hepatology, 2009) 42
• Thin‑slice 3‑D MRCP acquisitions can demonstrate communication between a cyst and the pancreatic duct with sensitivity up to 100 %; the same technique reliably depicts cystic duct anatomy and pathology. (Journal of the American College of Radiology, 2020) 43
• When MRCP is performed in high‑volume, technologically advanced centers, its diagnostic accuracy for biliary obstruction is comparable to that of ERCP. (Journal of Hepatology, 2009) 42

Comparison with Alternative Imaging Modalities

• Ultrasound is limited for visualizing the distal common bile duct and cystic duct because overlying bowel gas obscures these structures; the lower common bile duct and pancreas are often inadequately depicted. (Journal of Hepatology, 2009) 42
• Abdominal computed tomography is less operator‑dependent than ultrasound but involves ionizing radiation and provides inferior delineation of the biliary tree, especially the cystic duct, compared with MRCP. (Journal of Hepatology, 2009) 42
• Endoscopic retrograde cholangiopancreatography (ERCP) remains the gold standard for both visualization and therapeutic intervention of the biliary tract, but it carries notable complication rates: pancreatitis 3‑5 %, bleeding 2 % (when sphincterotomy is performed), cholangitis 1 %, and procedure‑related mortality 0.4 %. (Journal of Hepatology, 2009) 41

Clinical Recommendations

• EASL recommends MRCP as the first‑line advanced imaging modality for suspected cystic duct pathology, reserving ERCP for therapeutic purposes after non‑invasive imaging confirms the need for intervention. (Journal of Hepatology, 2009) 42
• In cases where extra‑hepatic biliary obstruction is suspected but the necessity for endoscopic treatment is uncertain, MRCP should be performed to avoid unnecessary ERCP and its associated risks. (Journal of Hepatology, 2009) 41
• For optimal diagnostic yield, MRCP should be conducted in centers with experienced radiologists and modern MR equipment, ensuring accuracy that rivals ERCP. (Journal of Hepatology, 2009) 42

Diagnostic and Management Strategies for Right Upper Quadrant Pain in Patients Receiving Prednisone

Laboratory Evaluation

• Obtain a complete blood count concurrently with the initial right‑upper‑quadrant ultrasound to detect leukocytosis that may indicate infection, recognizing that corticosteroid therapy can blunt the white‑cell response. 44
• Measure C‑reactive protein (CRP) and erythrocyte sedimentation rate (ESR) when available; these inflammatory markers are often suppressed by prednisone, so low values do not exclude serious pathology. 45, 46

Imaging Strategy

• Computed tomography (CT) should be reserved for patients who are critically ill (e.g., peritoneal signs, suspected perforation or abscess) rather than as a first‑line test for RUQ pain, because CT offers lower sensitivity for gallstones compared with ultrasound. 44

Effects of Prednisone on Clinical Presentation

• Prednisone suppresses fever and inflammatory laboratory markers, which can mask the typical signs of acute cholecystitis, cholangitis, or other intra‑abdominal infections; clinicians must maintain a low threshold for advanced imaging and specialist consultation in steroid‑treated patients. 45, 46

Management of Acute Cholangitis

• In patients meeting the classic triad of RUQ pain, jaundice, and fever (acute cholangitis), initiate intravenous antibiotics immediately and obtain urgent gastroenterology consultation for therapeutic ERCP. 44

Evaluation and Management of Suspected Biliary Pancreatitis and Choledocholithiasis

Diagnostic Laboratory Evaluation

• Serum lipase or amylase > 3 × upper limit of normal confirms acute pancreatitis in patients presenting with epigastric pain radiating to the back. 47
• Comprehensive liver function tests (AST, ALT, alkaline phosphatase, total/direct bilirubin, GGT) are required to assess for biliary obstruction when gallstones are known. 48
• A complete metabolic panel should be obtained to identify electrolyte disturbances and renal impairment that may accompany pancreatitis. 47

Imaging Strategy

• Ultrasound alone is insufficient for detecting common bile duct stones (sensitivity 22.5‑75 %) even after confirming cholelithiasis; MRCP provides superior visualization of the distal biliary tree. 47
• CT abdomen should be reserved for critically ill patients with peritoneal signs or suspected complications (e.g., perforation, abscess) because it has limited sensitivity for gallstones and biliary pathology. 49

Indications and Timing for Therapeutic ERCP

• Urgent ERCP (within 24 h) is indicated when acute cholangitis is present (fever, jaundice, right‑upper‑quadrant pain). 47
• Early ERCP (within 72 h) is recommended when imaging shows a visible common bile duct stone or a persistently dilated common bile duct. 47

Definitive Management Based on MRCP Findings

• If common bile duct stones are identified, perform ERCP with sphincterotomy and stone extraction. [47] [49] 48
• If biliary pancreatitis is confirmed, schedule laparoscopic cholecystectomy during the same hospital admission (ideally within 2 weeks) to prevent recurrence. 47

Epidemiology Relevant to Clinical Decision‑Making

• Gallstones occur in approximately 10‑15 % of adults, and about 10 % of those individuals develop common bile duct stones. This prevalence underscores the need for prompt biliary evaluation in the described presentation. 49

Risks of Delaying Biliary Evaluation

• Postponing MRCP and definitive biliary decompression can lead to recurrent pancreatitis, ascending cholangitis, secondary biliary cirrhosis, and increased morbidity and mortality. 47

Abdominal Ultrasound as the First‑Line Imaging Modality for Suspected Biliary Obstruction

Initial Imaging Recommendation

• The American College of Radiology mandates abdominal ultrasound as the mandatory first‑line study for patients presenting with jaundice, right‑upper‑quadrant tenderness, and elevated liver function tests or bilirubin. 50
• The American College of Radiology designates ultrasound as the initial evaluation for jaundice with suspected biliary obstruction, achieving specificities of 71 %–97 % for confirming or excluding mechanical obstruction. 50
• The American College of Gastroenterology designates ultrasound as the initial diagnostic test of choice in patients with suspected common‑duct obstruction. 50
• A normal common bile duct (CBD) caliber on ultrasound provides a 95 %–96 % negative predictive value for choledocholithiasis, making it an excellent screening tool. 50

Practical Implementation

• Clinicians should order abdominal ultrasound immediately to assess for biliary ductal dilatation, gallstones or choledocholithiasis, gallbladder wall thickening, and signs of cirrhosis. 50

Role of Computed Tomography (CT)

• CT imaging should be reserved for critically ill patients who exhibit peritoneal signs or suspected complications such as perforation or abscess, rather than for initial diagnostic evaluation of uncomplicated biliary obstruction. 50
• CT should also be used when complications beyond simple biliary obstruction are suspected. 50

Limitations of Ultrasound

• Ultrasound has reduced sensitivity for detecting distal CBD stones due to overlying bowel gas, with reported sensitivities ranging from 22.5 % to 75 % for CBD stone detection. 50