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Role of magnetic resonance cholangiopancreatography in conjunction with 3D assessment in patients of different billiary obstruction causes

Sonography is most commonly employed as the primary imaging tool because of its high sensitivity for the presence of gallstones, it enables us to accurately evaluate the status of the intra and extra hepatic biliary ducts, and the sonographic examination can be performed relatively rapidly and at a very low cost , but occasionally imaging pitfalls or because of some unusual presentations the sonographic evaluation may be difficult.


INTRODUCTION
Obstructive jaundice is defined as a condition occurring due to block in the pathway between the site of bile conjugation in hepatocytes and the entry of bile into the second part of duodenum through the ampulla. 1 Obstructive jaundice is more prevalent in 5th and 6th decade of life with male to female ratio of 1:1.5. 2 The most common cause of biliary obstruction is gall stone disease. 3 With biliary obstruction, the proximal biliary tree gets dilated and there is increase in intrabiliary pressure with the result cellular microvilli in biliary canaliculi become distorted and dysfunctional. 4,5

Imaging of biliary obstruction
Biliary obstruction can pose problems in diagnosis and management especially because of the wide etiology. So, it is mandatory to determine preoperatively the existence, the nature and site of obstruction because an ill-chosen therapeutic approach can be dangerous. 6 As imaging techniques have improved, radiologists have increasingly studied images of the biliary tract by novel methods.
Sonography is most commonly employed as the primary imaging tool because of its high sensitivity for the presence of gallstones, it enables us to accurately evaluate the status of the intra and extra hepatic biliary ducts, and the sonographic examination can be performed relatively rapidly and at a very low cost , but occasionally imaging pitfalls or because of some unusual presentations the sonographic evaluation may be difficult. 7 MRCP was introduced in 1991 by Wallner et al as a noninvasive method of imaging of biliary tree.8 MRCP uses heavily weighted T2 sequences, as a result the static and slow-moving fluid filled structures such as bile and pancreatic duct are greatly intensified, resulting in intensified duct to the background contrast. MRCP combines the advantages of both projectional imaging and cross-sectional imaging and is an established diagnostic technique that has replaced direct cholangiopancreatography for diagnostic purposes. MRCP provides an efficient alternation when diagnostic ERCP or PTC is unsuccessful or inadequate. 9 MRCP can visualize biliary tract above and below the level of the obstruction, which is essential for treatment planning and one that is neither provided by ERCP nor PTC. 10 Conventional 2D MRCP also has pitfalls which may stimulate or mask various pathologic conditions of extra hepatic ducts or pancreatic duct and may be caused by a variety of reasons and to overcome this, number of new modern techniques including fast imaging sequence, parallel imaging techniques, phased array coils, 3D turbo spin echo techniques are being used, which allow the acquisitions of higher quality diagnostic imaging. 3D imaging techniques provide better image quality compared to 2D sequences even though the combinations of different MRCP sequences have proven to be valuable in the assessment of biliary anatomy and pathology. 11 Three dimensional respiratory triggered T2 weighted fast spin echo techniques have been used in several applications for some time. As compared with 2D dimensional techniques, they offer higher signal to noise ratio, contrast to noise ratio, improved spatial resolution and thinner imaging sections without intersection gaps allowing more robust post processing manipulation, but are disadvantaged by the long acquisition times [generally 8 to 10 minutes]. 12 For post processing techniques of 3D MRCP, maximum intensity projection [MIP] and volume rendering VRT has been commonly used because of its handiness. 13 The potential advantages of 3D T2weighted MRCP techniques over 2D imaging include the capacity for use of thinner sections without inter slice gap and a higher SNR and for post processing manipulation of the images with techniques such as multiplanar reconstruction, maximum intensity projection, and volume rendering. With these tools, unlimited projectional views in any arbitrary plane can be obtained to clarify anatomic relationships. 14

Aims and objectives of study
To evaluate the patients with clinical suspicion of biliary tract obstruction and USG documented biliary obstruction with 3D MRCP and compare it with conventional MRCP.

METHODS
This is an observational study carried out in the Department of Radiodiagnosis and Imaging and Department of Gastroenterology, Government Medical College Srinagar from June 2019 to January 2021 over a period of 18 months after obtaining ethical clearance from Institutional Ethical Committee. Study group consisted of 50 cases (patients) of biliary obstruction.

Inclusion criteria
The study includes cases of biliary obstruction referred to the department of radio diagnosis and imaging from the department of medical and surgical gastroenterology for imaging investigations.

Exclusion criteria
This study will exclude, patients with MRI incompatible cardiac pacemakers, stents, coils, cochlear implants and other devices, patients with claustrophobia and other contraindications to MRI.

Instrument and technique used
MRCP Magnetic Resonance Cholangiopancreatography (MRCP) was carried out on a superconductive 3 .0Tesla scanner (Magneton, Skyra, Siemens) using phased array body coils. Patients were instructed to fast for 4 hours prior to the study in order to reduce fluid secretions within the stomach and duodenum to reduce bowel peristalsis and promote gallbladder distension.
Protocol followed was: Localizer to localize the pancreaticobiliary duct. This was accomplished by acquiring a scout MRCP obtained in a slice thickness of 3-4 mm. MRCP images were acquired using half-Fourier single shot turbo-spin-echo (HASTE) sequence.

Statistical methods
The recorded data was compiled and entered in a spreadsheet (Microsoft excel) and then exported to data editor of Statistical package for social sciences (SPSS) version 20.0 (SPSS Inc., Chicago, Illinois, USA). Statistical software SPSS (version 20.0) and Microsoft excel were used to carry out the statistical analysis of data. Continuous variables were expressed as Mean±SD and categorical variables were summarized as percentages. Graphically, the data was presented by bar and pie diagrams. Diagnostic accuracy (sensitivity, specificity, positive predicted value and negative predicted value) of conventional 2D MRCP and 3D MRCP with MIP and VRT was obtained for detection of various causes of biliary obstruction, taking ERCP, surgical findings and histopathology as gold standard. Table 1 showing age distribution of cases. The mean age in our study was 47.5 years (range 7-76 years) with standard deviation of 16.57 years. The maximum number of patients were in the age group of 51 to 60 years (32%).     Table 2 showing the distribution of patients with respect to gender. In our study out of the total 50 patients, 21 (42%) patients were males and 29(58%) were females.       Table 7 shows that the Sensitivity, Specificity, PPV and NPV of 3D MRCP with MIP and VRT and it is 100% for each. Table 8 shows the sensitivity, specificity, PPV, NPV of 3D MRCP with MIP and VRT and it is 100% for each. Table 9 shows 100% sensitivity, 100% specificity, 100% PPV and 100% NPV of conventional 2D MRCP for pancreatic Divisum.  12 24 Total 50 100

DISCUSSION
Biliary obstruction because of the wide etiology possesses a significant challenge in diagnosis. Imaging plays a key role in diagnosis, helps in accurate evaluation and management of the patient with biliary obstruction.
Even though MRCP offers many advantages currently it still has a few drawbacks like, low spatial resolution, imaging in the physiologic non-distended state, which decreases the sensitivity to subtle ductal abnormalities, image artifacts of various types and lack of therapeutic option.
To overcome some of these drawbacks, a number of new modern techniques are being used, which allow the acquisitions of higher quality diagnostic imaging with lower incidence of technical pitfalls. 3D MRCP is one of the breakthrough improvements in the MRCP techniques.
In our study we studied 50 patients out of which 21 were men and 29 were women. The average age of patients was 47.5 years with a range of 7 to 76 years. Most cases were seen in the age group of 51 to 60 years of age. In our study females were affected more commonly with a female to male ratio of approximately 1.4: 1.
Mean age in our study was 47.5 years which is similar to the study done by Shukla et al where it was 48.5 years. 2 Similarly, Agal et al who studied 62 patients and Meena Set al who studied 75 patients of both benign and malignant etiology of biliary obstruction, there is more or less equal age incidence in present study. 15 In our study, females were predominantly affected which is similar to study done by Hasan et al where 62% of patients were females. 16 Out of a total 29 patients, 18 were male and 11 were females with a female to male ratio of 1.63:1.
Gallstone disease was the commonest etiology responsible for biliary obstruction in 40% of the patients. These results were comparable to the study done by Prabakar et al. 17 16,23 In addition, the 3D reconstructed images were helpful in identifying the extent of common bile duct infiltration as well as the intra-hepatic duct infiltration, and were considered as an excellent preoperative drawer of the biliary system anatomy.

CONCLUSION
From the present study we concluded, in patients with biliary obstruction, MRCP aims at finding the pathology. It also helps in planning of surgical or interventional management and serves to guide these procedures. For malignant stricture, both conventional 2D MRCP and 3D MRCP with MIP and VRT have equal diagnostic accuracy in detecting and categorizing malignant strictures. However, 3D MRCP with MIP and VRT performed better for small benign strictures and intrahepatic strictures. For CBD stones and gallbladder stones, both 2D MRCP and 3D MRCP showed similar sensitivity and specificity and were highly accurate in detecting the location and size of stones. 3D MRCP with MIP and VRT out performed conventional 2D MRCP in detecting pancreatic dilatation and IHBR dilatation. 3D MRCP with MIP not only detected MPD dilatation but it was very sensitive in detecting early changes of chronic pancreatitis. Image quality of 3D MRCP was better than 2D MRCP with less frequency of technical pitfalls on 3D MRCP as compared to 2D MRCP. Conventional 2D MRCP imaging gives us a Comprehensive view of biliary and pancreatic system anatomy and pathology, however sometimes it is not enough to make a decision. By using 3D reconstructions, multiplanar and reformatted images (MIP, VRT) of the biliary tract, it provides quick and clear visualization of the complex relationships between the anatomy and pathologic changes. Furthermore, it increases our confidence in the diagnosis and contribution to understand the disease process. In fact, in most cases 3D imaging does not add quantitative information but the main advantage is that cross sectional imaging is depicted in pattern which is easier to interpret.