1 Introduction

Cholelithiasis is a common disease in China, and cholelithiasis is the eternal theme of biliary surgery. It is crucial to discover and locate cholelithiasis、clinical diagnosis of the disease, adopt suitable and reliable treatment before the operation (Quan et al., 2018). Therefore, analyze the imaging before operation and pay attention to the risk factors of Biliary tract injury play an important role (Quan et al., 2018). MRCP, color Doppler ultrasound, CT, have been widespread used among cholelithiasis. The data of MRCP, color Doppler ultrasound and CT examination in 1000 patients with cholelithiasis before operation were retrospectively analyzed, in order to investigate the optimal preoperative examination of cholelithiasis and the clinical value of reducing the occurrence of biliary tract injury.

2 Patients and Methods

2.1 Patients

We randomly assigned 1000 patients with cholelithiasis from The First Hospital of Hohhot City since 2011, of whom 451 are males and 549 are females. The distribution of age is 25 to 85, with an average age of 51.8. All the 1000 patients were given MRCP before operation. While 947 of the patients were examined with Liver and gallbladder color Doppler ultrasound at least once before operation, the remaining 53 were examined by CT of midsection. Among the 1000 patients,914 cases proved to be cholelithiasis by surgery (Including 2 cases with Roux-Y cholangiojejunostomy); 31 cases proved by ERCP; 55 cases Abandonment of surgical treatment for various reasons. The main clinical symptoms of the patients were: obviously celiodynia 736 (73.6%)、Fever and chills 56 (5.6%)、Jaundice and dark urine 41 (4.1%)、Nausea and vomiting 513(51.3%), GGT (galactosylhydroxylysyl glucosyltransferase) is 55.6 mol/L on average, TBIL (total bilirubin) is 16.1 mol/L.

2.2 MRCP image analysis

MRCP diagnostic criteria for cholelithiasis：Calculus of bile duct and cholecystolithiasis on MRCP image is usually low signal, oval or round, target sign, inverted cup sign or cast pattern of bile duct. All MRCP images were recorded on film, physician or above in imaging department read the film with double blind method to evaluate the lesion. If there were differences, a consensus was reached after discussion. Postoperative cholecystectomy dissect gallbladder to identify the cholecystolithiasis; Direct exploration of common bile duct by choledochoscope to identify Calculus of bile duct; ERCP before or after surgery; The above three methods are the final examination of all kinds of imaging examination before operation.

2.3 Biliary tract variation

Both the MRCP that the patients with cholelithiasis taken before operation and the imaging taken during operation were read by at least two chief physicians, one from Imaging department and one from General surgery department. If there were differences, a consensus was reached after discussion.

2.4 Statistical analysis

With the software SPSS 13.0, chi-square test was used to compare the detection rate difference of CT, Doppler, and MRCP of cholelithiasis, α=0.05.

3 Results

Among 1000 cases of cholelithiasis patients, patients with only Calculus of bile duct was 177, 676 cases of patients with only cholecystolithiasis,185 cases of patients with both (Including 45 cases of muddy stone).

3.1 Comparison of detection rate of cholecystolithiasis

The total number of patients with cholecystolithiasis was 698.676 gain color Doppler examination, 30 of them did not detected; 22 gain CT examination, 9 of them did not detected; all the 698 patients gain MRCP,109 of them did not detected. The detection rate of cholecystolithiasis were 95.56% (doppler), 59.09% (CT) and 87.50% (MRCP). Owing to the Low inspection rate of CT, there is no statistical significance. The detection rate of cholecystolithiasis comparison among groups show the detection rate of cholecystolithiasis of color Doppler ultrasound was significantly higher than that of MRCP.

3.2 Comparison of detection rate of Calculus of bile duct

The total number of patients with Calculus of bile duct was 302.289 gain color Doppler examination，79 of them did not detected;53 gain CT examination，14 of them did not detected; all the 302 patients gain MRCP,78 of them did not detected. (These include intraoperative choledochos copy for the detection of inflammatory flocculants and non-calculi, and the indication of suspected calculi cases by nuclear magnetic resonance before operation). The detection rate of cholecystolithiasis were 72.65% (doppler), 73.58% (CT) and 92.13% (MRCP). Owing to the Low inspection rate of CT, there is no statistical significance. The detection rate of cholecystolithiasis comparison among groups show the detection rate of Calculus of bile duct of MRCP was significantly higher than that of color Doppler ultrasound.

3.3 Preoperative nuclear magnetic image analysis

The analysis shows extrahepatic biliary tract variation 120 cases, among whom 11 cases with ductus cysticus Long and twisted,77cases with ductus cysticus calculus incarcerated,3 cases with Mirizzi syndrome,13cases with Low confluence of ductus cysticus,4cases with ductus cysticus join with right hepatic duct,1case with Accessory bile duct,2cases with choledochocyst,9cases with Intrahepatic atrophy gallbladder. Preoperative MRCP findings of Biliary tract variation in 117 cases confirmed by Operation，the aberration rate is 11.7%.

4 Discussion

Cholelithiasis is one of the most common diseases in general surgery. It includes cholecystolithiasis, intrahepatic bile duct and extrahepatic bile duct calculus. The main clinical symptoms of the patients were：obviously celiodynia, Fever and chills, Jaundice and dark urine, Nausea and vomiting. MRCP, color Doppler ultrasound, CT, have been widespread used among cholelithiasis Color Doppler ultrasound is convenient, inexpensive and radiation-free, but its low sensitivity to choledocholithiasis , and it is vulnerable to the influence of the patient's intestinal flatulence, the operator's personal experience and the performance of the equipment .Ct is an examination with great density resolution and  high specificity for the diagnosis of high-density calculus, but it is hard to diagnose iso-density, low-density and silt-like calculus. MRCP Imaging was carried out using single-shot fast spin-echo sequences to obtain heavy T2-weighted images, which resulted in an obvious comparison between static fluids flowing interstitially or slowly in the human body and peripheral soft tissues. MRCP is an simple and rapid examination wide indications, high success rate and few complications. It is suitable for patients who cannot be clearly diagnosed by CT or doppler but highly suspected of choledocholithiasis, as well as the patients who were failure in ERCP examination (Mainly include patients who were obesity, claustrophobia, or with pacemakers) (Ji et al., 2012).

This study finds that the detection rate of cholecystolithiasis comparison among groups show the detection rate of cholecystolithiasis of color Doppler ultrasound (95.56%) was significantly higher than that of MRCP (87.50%). Color Doppler ultrasound is inexpensive and can be repeated many times, and especially in the finding of small calculus and cholesterol crystal which stick to gall bladder wall, doppler is significantly better than CT and MRCP.As an experience Ultrasound doctor. The diagnostic rate of cholecystolithiasis could achieve 98.4% or more (Tang, 2016). CT does well in density resolution, but limited to the slice thickness of cross-sectional imaging and the size of calculus. The diagnostic rate of cholecystolithiasis is about 75% to 85% (Cai, 2014). Owing to the Low inspection rate of CT in this study, there is no statistical significance. In our analysis, due to the limitation of color Doppler ultrasound and CT, combined with MRCP, the detection rate of cholelithiasis will be improved obviously. Cholecystolithiasis usually shows low signal filling defect (signal loss) on MRCP image and high signal intensity (target sign) in the center of the cholecystolithiasis. Cast pattern of bile duct are often accompanied by high internal signal intensity. Due to the different structure and composition of the calculus, the pigmented calculus can produce a longer T2, because it contains more liquid components in the bile mud. MRCP 3D images can cause small calculus in the bile duct to be submerged in high signal biliary fluid. In the process of 3D reconstruction, some information is lost due to technical factors, but the original image is better in displaying the details of calculus. Therefore, analysis of MRCP images combing with T2W1, the diagnosis of cholecystolithiasis could catch higher accuracy. The date of this study is 87.50%, which was consistent with the literature.

For the diagnosis of Calculus of bile duct, color Doppler ultrasound can be used as the first choice of screening in clinical. Some studies have shown that the accuracy of color ultrasound examination for the calculus in intrahepatic bile duct and choledocholithiasis is 98% and 76% (Liu, 2015). The diagnosis of intrahepatic bile duct calculus by color Doppler ultrasound is not affected by intestinal gas. The accuracy of diagnosis is much higher than extrahepatic bile duct calculus. Most of the calculus were hyperechoic, the characteristics of its distribution along the bile duct tree can be found when observed from different angles. However, there are many branches of intrahepatic bile duct, so it is easy to miss diagnosis without careful scanning, and it is necessary to distinguish it from the calcification point in the liver. The accumulation of gas in bile duct is easily misdiagnosed as calculus in ultrasonic examination. Especially in patients after Cholangiojejunostomy and complicated with biliary tract infection, the number and range of calculus may exceed the actual situation. However, for the diagnosis of low density calculus which approximate to bile and cholecystolithiasis, color Doppler ultrasound has shown its superiority  (He and Yang, 2011).The date of this study is 72.65%.CT is not the first choice for  diagnose, because it is as sensitive as color Doppler and MRCP to the intrahepatic bile duct calculus, Especially for those whose diameter is less than 0.5 ~ 1.0 cm without intrahepatic bile duct stenosis and distal hepatic duct dilatation, it is difficult to diagnose. CT can lead to definite diagnosis for patients with intrahepatic bile duct stone diameter > 1.0 cm, intrahepatic bile duct stenosis and distal hepatic duct dilatation. MRCP can clearly show the number of bile duct calculus, the location of obstruction and the degree and scope of bile duct dilatation. It can not only clearly diagnose, but also provide the specific location, involvement and location of dilated bile duct, as well as provide reliable diagnostic basis for clinical treatment. Especially suitable for patients with no dilatation of extrahepatic bile duct. The positive rate of MRCP for choledocholithiasis was significantly higher than that of other methods, which can reach 94%-97%. The date of this study is 92.13%. MRCP should be the first choice for those suspected of cholelithiasis, regardless of whether the color Doppler ultrasound or CT is positive or not. Especially when the patient is unable to tolerate or refuse to undergo invasive examination and surgical exploration, the possibility of cholelithiasis cannot be ruled out solely by the negative results of ultrasound and CT. There has been study of the comparison of MRCP and CT in diagnosis of cholelithiasis, which show that MRCP is superior to CT (Xiao, 2014).

All in all, the results of this study indicate that MRCP is more suitable for the diagnosis of cholelithiasis and the diagnosis of biliary tract variation before operation. The study shows that MRCP is the most ideal and reliable diagnostic method for cholelithiasis (Bahram and Gaballa, 2010; Cheng et al., 2014). MRCP has a high clinical value in the diagnosis of biliary tract system tumor and liver tumor before operation. It also has some reference value for the diagnosis of preoperative indication of acute cholecystitis and the feasibility of cholecystitis. The diagnosis of mrcp in polyps of gallbladder, the diagnosis of gallbladder carcinoma, and the application value of Chol cystolithotomy are still controversial (Guo and Zhang, 2015).

Authors’ contributions

L.A participated in the design of the study and performed the statistical analysis and wrote this manuscript. L.J and L.ZY diagnosed the Image and analyzed the variation .Y.H and C.YM participated in the design of the study and performed the statistical analysis. Z.JY participated in the study and revised the manuscript. W.G conceived of the study and revised the manuscript. All authors read and approved the final manuscript.

Acknowledgments

The project is funded by the Natural Science Foundation of Inner Mongolia Autonomous region (No. 2016MS08118).

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