gallstones are among the most prevalent clinical problems all around the world . based on published studies , the prevalence of gall stones in europe is about 5 - 20% in the general population , rising with age . the incidence of gallstones is three times more common in women than in men ( 13 ) . twelve percent of patients with symptomatic gall stone disease have common bile duct stones ( 4 ) . choledocholithiasis may be asymptomatic ; or it may cause serious problems , such as obstructive jaundice , pancreatitis and cholangitis , which can complicate disease management , especially in older patients . according to previous studies , it is recommended that common bile duct investigation should be done in order to rule out choledocholithiasis in all patients with symptomatic cholelithiasis . bile duct calculi in majority of cases are predictable on the basis of clinical , biochemical and radiological examinations . ultra - sonography ( uss ) is an available , low cost , non - invasive test , with no need for ionizing radiation . uss can measure the diameter of intra and extra hepatic bile ducts , indicating whether it is dilated or not . however , it misses approximately 65% of bile duct stones because of the interference with bowel gas and also because ultra - sonography is a procedure highly operator dependent ( 36 ) . intra - operative cholangiography ( ioc ) is the gold standard procedure in the diagnosis of bile duct stones . but it is invasive , needs anesthesia , elongate the duration of operation and anesthesia and may increase intra and post - operative complications . studies recommend trying to move to a procedure much safer , more cost effective with less complication . magnetic resonance cholangiopancreatography ( mrcp ) is a non - invasive procedure that gives high resolution images of the biliary tree without any exposure to ionizing radiation ( 3 , 7 ) . its role in identifying uncertain anatomy and visualizing the bile duct stones is well - established ( 8) . investigations show that comparing to direct cholangiography , mrcp has found to be sensitive and specific ( 3 , 7 , 9 , 10 ) . therefore , given that ioc is an invasive procedure with probable complications , it would seem that mrcp could replace the direct cholangiography when it used for diagnostic purposes based on studies indicate that it is a sensitive and specific diagnostic procedure ( 7 ) . we performed this study to compare the efficacy of ioc and mrcp in patients thought to have biliary stones , considering the sensitivity , specificity , positive predictive value and negative predictive value of these two procedures . through this study we can help answering the question below : can pre - operative mrcp obviate the need for ioc ? fifty - nine consecutive inpatients with suspected common bile duct ( cbd ) stones admitted to the surgery unit of imam hossein medical center , tehran , iran , were recruited in the study over a period of 24 months . patients had the mean age of 556 sd years ( range 36 - 68 ) . we studied them after obtaining their approval from the ethics committee of the university hospital , imam hossein hospital , tehran , iran . after taking a history and examination , blood tests and routine biochemical assays including serum liver enzymes , bilirubin , amylase and alkaline phosphatase an abdominal uss was performed to look for the presence of gallstones and any signs of a cbd stone or bile duct dilation . patients included in this study all had normal sonography but higher than normal alkaline phosphatase level ( alph > 200 ) and were clinically suspicious to common bile duct ( cbd ) stones . any patient with derangement in other liver tests ( such as bilirubin ) or documented biliary stone diagnosed by uss were excluded from the study . if in a patient scheduled for cholecystectomy according to these investigations there was a strong suspicion to choledocholithiasis , the patient received preoperative mrcp , and then undergone ioc along with subsequent cholecystectomy . all mrcp scans were analyzed by a radiologist who was unaware of ioc and lab test results . cholecystectomies were performed in a standard manner by one surgeon , the operating surgeon initially assessed ioc , and the film was subsequently reported by one , blinded radiologist who was unaware of mrcp scan results either . based on recorded data , specificity , sensitivity , positive and negative predictive values were individually calculated for both procedures ( mrcp and ioc ) . sensitivity was the ability to identify patients with cbd stones using the number of positive mrcp diagnoses divided by the total number of patients with confirmed cbd stones by ioc . specificity was the ability to identify patients without cbd stones using the number of negative mrc diagnoses as a percentage of the total number of patients without ioc - proven cbd stones . positive and negative predictive values of mrc were determined by the proportion of mrcp diagnoses ( positive or negative ) confirmed by ioc . fifty - nine consecutive inpatients with suspected common bile duct ( cbd ) stones admitted to the surgery unit of imam hossein medical center , tehran , iran , were recruited in the study over a period of 24 months . patients had the mean age of 556 sd years ( range 36 - 68 ) . we studied them after obtaining their approval from the ethics committee of the university hospital , imam hossein hospital , tehran , iran . after taking a history and examination , blood tests and routine biochemical assays including serum liver enzymes , bilirubin , amylase and alkaline phosphatase an abdominal uss was performed to look for the presence of gallstones and any signs of a cbd stone or bile duct dilation . patients included in this study all had normal sonography but higher than normal alkaline phosphatase level ( alph > 200 ) and were clinically suspicious to common bile duct ( cbd ) stones . any patient with derangement in other liver tests ( such as bilirubin ) or documented biliary stone diagnosed by uss were excluded from the study . if in a patient scheduled for cholecystectomy according to these investigations there was a strong suspicion to choledocholithiasis , the patient received preoperative mrcp , and then undergone ioc along with subsequent cholecystectomy . all mrcp scans were analyzed by a radiologist who was unaware of ioc and lab test results . cholecystectomies were performed in a standard manner by one surgeon , the operating surgeon initially assessed ioc , and the film was subsequently reported by one , blinded radiologist who was unaware of mrcp scan results either . based on recorded data , specificity , sensitivity , positive and negative predictive values were individually calculated for both procedures ( mrcp and ioc ) . sensitivity was the ability to identify patients with cbd stones using the number of positive mrcp diagnoses divided by the total number of patients with confirmed cbd stones by ioc . specificity was the ability to identify patients without cbd stones using the number of negative mrc diagnoses as a percentage of the total number of patients without ioc - proven cbd stones . positive and negative predictive values of mrc were determined by the proportion of mrcp diagnoses ( positive or negative ) confirmed by ioc . in this study the mean age of the patients was 55 with the standard deviation of 6 years . mean level of alkaline phosphtase was 492 with the standard deviation of 26 ( table 1 ) . statistics and its relative 95% confidence interval tp= true positive , tn= true negative , fp = false positive , fn = false negative , ppv= positive predictive value , npv = negative predictive value , da= diagnostic accuracy , lr= likelihood ratio , do= diagnostic odds the positive predictive value for ioc was 88% , comparing to mrcp which was 43% . the difference was significant with the p - value less than 0.05 ( p = 0.04 ) . these findings show that we had lots of false positive results performing mrcp comparing with ioc . the diagnostic accuracy difference of these two procedures were significant either ( p = 0.02 ) which means ioc is much more accurate . there were no significant and meaningful differences between the sensitivity and specificity statistics based on statistical analysis ( table 2 ) . the incidence of common bile duct ( cbd ) stones among the patients undergoing cholecystectomy is reported as approximately 12% . there are some symptoms , signs and invesigations that should arouse suspicion of a cbd stones including derangement in liver function test ( lft)s , dilated cbd in ultrasound ( us ) . routine intra - operative cholangiography ( ioc ) is performed , by some surgeons , for several reasons . firstly through this procedure we can confirm that cbd is clear and find unsuspected stones in cbd . but according to the evidences 1% of patients with normal lft and ultra - sonography have stones in their cbd and 75% of these stones passes spontaneously ( 4 , 1921 ) . the disadvantage of this procedure is that we force an unnecessary cbd exploration to the patient and prolongation of the operation , because of the radiography and also because of surgical dissection and cannulation . preoperative evaluation of the biliary tree has assumed a great importance in patients suspicious to choledocolithiasis and may help us avoiding intra - operative difficulties . performing a confident assessment of the cbd prior to the surgery may reduce or obviate the need for hazardous and timeconsuming ioc ( 3 , 11 ) . several diagnostic and therapeutic strategies have been suggested for clinical diagnosis and management of cbd stones such as routine mrcp , selective endoscopic retrograde cholangiopancreatography ( ercp ) , routine ioc or endoscopic us with cbd exploration . however no single method is both risk free , highly sensitive and specific currently in use(1114 ) . results from different studies demonstrate that sensitivity and specificity of mrcp for detection of cbd stones is high and the resolution of the biliary tree images is excellent . these investigations confirm the accuracy of mrcp in diagnosis of cbd stones ( 1517 ) . recent studies comparing mrcp with ioc or ercp confirmed that mrcp has the accuracy up to 95% ( 7 , 22 , 23 ) . studies comparing ercp with mrcp indicates that reliance upon mrcp findings may have reduced the requirement for ercp and sphincterotomy by up to 75% ( 22 , 24 ) . in our study there were no significant differences in sensitivity , specificity between the two procedures mrcp and ioc . but based on our study the diagnostic accuracy of ioc was higher than mrcp ( 98% vs 85% ) and this difference was statistically significant ( p = 0.02 ) . the positive predictive value of ioc was 88% , compared to mrcp that was 43% ( p = 0.04 ) . these findings indicates that mrcp has significant false positive results compare to the ioc and based on mrcp only , we may perform unnecessary operations to a few number of patients . considering these results , we feel that although using pre operative mrcp reduces the duration of operation and is less invasive comparing with routine ioc ( 7 , 9 , 10 , 18 ) , it does not have the diagnostic accuracy of the ioc . it may reduce unpredictable damages to the cbd during the ioc but it has significant false positive cases . dalton et al ( 7 ) reported that mrcp should be the only modality used to exclude cbd stones so individual centers must design their own strategies based on local factors including geographical location , personnel , equipment and facilities such as ercp and mrcp , economic factors ( time resources , private or teaching hospital ) and the experience of the operating team . in conclusion the suggestion advocating routine use of mrcp instead of ioc or as a substitute for ioc needs further investigations on more patients . not only should we consider all the advantages and disadvantages of these two procedures ( ioc , mrcp ) but also we should perform some further investigations in order to find out which of these two procedures is the most cost - effective based on local circumstances in different centers . with further studies we may be able to choose a procedure less invasive , less expensive , with lower rate of complications and of course more diagnostic accuracy