Eur. Radiol. 6, 147-152 (1996) © Springer-Verlag 1996

Original article

MR cholangiopancreatography (MRCP) at 0.5 T: technique optimisation and preliminary results P. Pavone, A. Laghi, C. Catalano, L. Broglia, A. Messina, A. Scipioni, M. Di Girolamo, R. Passariello

Istituto di Radiologia - II Cattedra, Universit~ degli Studi di Roma "La Sapienza", Policlinico Umberto I, Viale Regina Elena 324, 1-00161, Rome, Italy

Received 2 May 1995; Revision received 13 July 1995; Accepted 21 August 1995

Introduction

MR cholangiopancreatography (MRCP) is becoming increasingly reliable in the evaluation of bilio-pancrea- tic disease. It is a new diagnostic, non-invasive imaging modality allowing complete visualisation of the pan- creatic and biliary system, with images similar to cholan- giographic views. Recent studies report a high accuracy in depicting choledocholithiasis and other causes of bili- ary and pancreatic duct obstruction, with a good corre- lation with the results of endoscopic retrograde cholan- giopancreatography (ERCP) and percutaneous transhe- patic cholangiography (PTC) [1-3].

All previous studies of MRCP have been performed at high field strength (1.0-1.5 T) with different acquisi- tion modalities. Both breath-hold and non-breath-hold sequences are reported in the literature, with very simi- lar different results [4-8]. Thanks to the technological improvement of mid-field strength commercial equip- ment, with higher-intensity gradients (15 mT/m), fast imaging is nowadays available.

The aim of our study was to assess the feasibility of MRCP at mid-field strength (0.5 T), since to our knowl- edge no reports have been published previously. A three-dimensional fat-suppressed, heavily T2-weighted turbo spin-echo (TSE) sequence, with acquisition of sin- gle sections in the coronal plane, was used.

Correspondence to: P. Pavone

Methods

From September 1994 to January 1995, 31 patients with dilated biliary systems (diagnosed by ultrasonography in all patients and by CT in 19 patients) were examined with MRCR The patients were 13 men and 18 women,

148 R Pavone et al.: MR cholangiopancreatography at 0.5 T

Fig.1. Comparison between two images obtained with an acquisition time of 14 rain (left) and 3 rain (right) respectively. Contrast and spatial resolution are similar; a slightly decrease in motion artefacts is obtained by the reduction in the acquisition time

Table 1. A comparison of the results of MR cholangiopancreato- graphy (MRCP) and endoscopic retrograde cholangiopancreato- graphy/percutaneous transhepatic cholangiography (ERCP/PTC) in 31 patients

No. of lesions MRCP ERCP/(PTC) a (n=3) (n=31)

Stones 12 12 11/(-) Strictures 16 16 13/(3) BD above obstruction 31 31 26/(5) BD below obstruction 5 3 5/@) Pancreatic duct 8 8 2/(-) Site of BEA 3 3 1/(2)

BD, bile ducts; BEA, bilio-enteric anastomosis a Five patients underwent PTC: 2 with hepatico-jejunostomia; 3 with previous unsuccessful ERCP

ranging in age from 20 to 83 years (mean age 56.3 years).

The dilatation of the biliary ducts was caused by chronic pancreatitis (4 case), pancreatic head carcinoma (7cases), choledocholithiasis (12cases), iatrogenic stricture following laparoscopic colecystectomy (3 cases), Klatskin tumour (1 case) and carcinoma of the gallbladder invading the main bile duct (1 case). Three patients who had undergone surgery for bilio-en- teric anastomosis were also evaluated. Diagnosis was confirmed at surgery in 11 cases (7 pancreatic carcino- mas and 4 chronic pancreatitis) and at ERCP/PTC in 20 cases.

ERCP was successfully performed in 26 cases; in 3 cases due to an inability to cannulate the ampulla of Vater the patients were subsequently submitted to PTC. Two patients underwent PTC because of bilio-en- teric anastomosis (choledochojejunostomy).

All patients were studied with a 0.5 T superconduct- ing magnet. The body coil was used for both excitation and signal reception. A T2-weighted TSE sequence (TR = 3000 ms, TE = 120 ms, NEX = 4) in the axial plane was performed to localise the dilated biliary and

pancreatic ducts. For MRCP imaging, a three-dimen- sional TSE sequence was acquired with the following imaging parameters: TR -- 5000 ms, TE = 244 ms, echo train length (ETL) = 45, acquisition time = 14 min 10 s. Images were obtained in the coronal plane with a 3- mm section thickness and no interslice gap; image ma- trix size was 83 x 128, and four signal averages were used for all images. Respiratory compensation was used for all images. Coronal images were post-processed with the MIP algorithm to produce 12 projections rota- ted about 15 ° on the coronal axis. Recently, the scan parameters have been optimised, reducing the acquisi- tion time to 3 min (Fig. 1). The new parameters are: TR = 3000 ms, TE -- 700 ms, E T L = 128; however, in all the cases repor ted here MRCP was done with a 14-rain acquisition time.

In cases of extrinsic compression of the biliary system conventional MRI images in the axial plane were ac- quired: Tl-weighted (TR -- 350 ms, TE = 10 ms, NEX = 6) SE, both with and without fat suppression, and T2- weighted (TR = 3000 ms, TE = 120 ms, NEX = 6) TSE.

MRCP and ERCP images were evaluated by an ex- perienced radiologist and an endoscopist with the ima- ges placed side by side on the viewing boxes. The filling defects inside the duct, the level of the stricture, the vi- sualisation of the ducts above and below the stricture, the visualisation of the pancreatic duct and finally the site of bilio-enteric anastomosis were assessed on the MR images and conventional cholangiograms. MR ima- ges were evaluated both after MIP reconstruction and as single slices. In difficult cases additional rotations of the images in the coronal plane were available.

Resul t s

MRCP of diagnostic quality was acquired in all patients. In 2 cases the examination was compromised by the poor clinical condition of the patients; however, the stu-

E Pavone et al.: M R cholangiopancreatography at 0.5 T 149

Fig.2a, b. Choledocholithiasis in a 64-year-old woman. a MRCP shows a filling defect at the distal third of the main bile duct with wide dilatation above, b Single slice depicts well the 2-cm stone, wedged in the papilla

Fig. 3 a, b. Choledocholithiasis in a 52-year-old woman. a MRCP MIP shows a 5-mm stone in the distal third of the main bile duct. b Single M R slices, as a " tomographic view", allow a bet ter depiction of the stone

Fig. 4 a, b. Carcinoma of the head of the pancreas in a 53-year- old woman, a E R C P shows the obstruction at the distal third of the main bile duct, with wide dilatation above the obstruction. b MRCP exhibits a good correlation with the E R C E In addi- t ion the gallbladder and the pancreatic duct are well demon- strated

150 P. Pavone et al.: MR cholangiopancreatography at 0.5 T

Fig.5 a-c. Cholangiocarcinoma of the common hepatic duct in an 83-year-old woman, a ERCP after the placement of a biliary endo- prosthesis. The dilated biliary system is well demonstrated. The anteroposterior (AP) view does not allow a good depiction of the carrefour, b MRCP shows a good correspondence with ERCP in AP view. c Rotation on the longitudinal axis permits visualisation of the carrefour

Fig.6. Chronic pancreatitis in a 62-year-old man. MRCP shows the wide dilatation of the Wirsung duct and the small pancreatic duct of the tail

dies were considered of diagnostic quality. Results are summarised in Table 1.

MRCP correctly identified the presence of stones ranging in diameter from 0.5 to 2.5 cm in 12 of 12 pa- tients (Fig. 2). The findings of MRCP and ERCP regard- ing the size and the site of the stone were in agreement

in 11 cases. A discrepancy occurred in 1 case where ERCP failed to demonstrate a small 0.5-cm stone, clear- ly visible on MRCP coronal slices (Fig. 3). Stones were depicted as oval-shaped, low-intensity structures within the bile ducts. In 1 patient the main bile duct was com- pletely filled with small calculi, resulting in an inhomo-

E Pavone et aI.: MR cholangiopancreatography at 0.5 T

geneous signal on MIP reconstruction. The analysis of the single slices allowed a better depiction of the stones.

MRCP correctly showed the presence and the site of biliary stenosis in 16 patients. Among the 13 patients who underwent both ERCP and MRCR the findings of MR and conventional cholangiography were in agree- ment about the site of the stenosis in all cases (Fig. 4). In the remaining 3 patients ERCP was not successful. PTC performed in these cases was of superior diagnostic value in only i case, due to poor cooperation of the pa- tient, and was in agreement with MRCP in the other cases.

In the 5 cases where strictures were located in the proximal bile duct, visualisation of the distal portions of the bile duct, below the level of the stricture, was pos- sible at MRCP in 3 cases and at ERCP in 5 patients (Fig. 5).

The dilated biliary tree above the stenosis was visua- lised by MRCP in all 31 patients, and by ERCP in only 26 patients. In all cases a better and clearer depiction of the ducts was obtained with MRCR

A dilated pancreatic duct was present in 8 patients, and observed on MRCP images in all cases; at ERCP it was visualised in 2 cases (Fig. 6).

In 3 patients with bilio-enteric anastomosis, a correct evaluation of the site of the anastomosis was always pos- sible with MRCR The MRCP findings were in agree- ment with ERCP in 1 (submitted to choledoco-duode- nostomy) and with PTC in the other 2 patients (pre- viously submitted to hepatico-jejuno-anastomosis).

D i s c u s s i o n

MRCP is a new diagnostic technique for the visualisa- tion of the biliary and pancreatic ducts with images simi- lar to ERCP and PTC. It requires neither contrast med- ium injection nor any biliary intervention. All the pre- vious studies have been performed at high field strength and have suggested a good correlation with ERCP and PTC [3, 9-11]. The wide availability of 0.5 T magnets, especially in Italy and in many European countries, due to their lower costs in terms of management and pur- chase, led us to assess the feasibility of MRCP at 0.5 T, using a new generation commercially available magnet with 15 mT/m gradients.

Various techniques have been used by the other in- vestigators, based on GRE and FSE sequences, with the common aim of improving contrast between static fluid (bile) and background (hepatic parenchyma and peritoneal fat). Both breath-hold and non-breath-hold techniques have been employed [4-8]. From our experi- ence we prefer to use a heavily T2-weighted TSE se- quence, with fat signal suppression, to improve fluid/ background contrast. A non-breath-hold technique was preferred as our patient population included some who were elderly. With a breath-hold technique the active cooperation of the patient is required and, according to other authors, oxygen support is sometimes necessary [7]. Thus, respiratory compensation may represent a va- lid method of avoiding artefacts due to respiratory m o -

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tion. With this technique MRCP was successfully per- formed in all patients studied, including 2 who were un- well and elderly.

Our results are similar to those reported in corre- sponding comparative studies performed at high field strength [3]. In cases of choledocholithiasis a better eva- luation of small stones (< 5 mm in diameter) was ob- tained by MRCR in agreement with the results obtained by other authors [1, 2]. In this group of patients an eva- luation of the single slices rather than only the MIP re- construction was very helpful in detecting small filling defects. In this way a "tomographic" evaluation of the main bile duct is obtained. In fact in 1 case a stone, smal- ler than 5 ram, visible only on one coronal slice, could hardly be demonstrated on the MIP reconstruction; the finding was subsequently confirmed at MRCR Regard- ing the possible clinical implications of the technique it is important not to underestimate cases that could be treated endoscopically or surgically. In choledocholi- thiasis no false negative cases occurred, resulting in a high specificity of the technique.

There were no false negative or false positive find- ings of obstruction, and the level of obstruction was cor- rectly identified in all patients. Due to difficulties in vi- sualising normal bile ducts which are below the level of obstruction, the extent of the stenosis could not be eval- uated well in all cases using MRCR A further limitation of MRCP is the poor depiction of the ampulla of Vater, which could result in a misdiagnosis in the case of in- flammatory or neoplastic lesions.

In all the patients with a dilatation of the pancreatic duct MRCP was able to define the level of the obstruc- tion. In fact, the main advantage of MRCP is the con- temporaneous visualisation of both the main bile duct and the pancreatic duct, if dilated; on MRCR in con- trast, this needs two different cannulations, which is sometimes technically difficult.

In our experience we have always obtained images of diagnostic value. However, there are a few disadvan- tages of MRCP compared with conventional studies; these limitations are similar to those observed at 1.5 T. Spatial resolution is limited by section thickness and the small matrix. We used a 3 mm slice thickness, the same as that used at 1.5 T. Satisfactory contrast-to- noise (C/N) and signal-to-noise (S/N) ratios were ob- tained, comparable with those at 1.5 T. Further reduc- tion in slice thickness would improve spatial resolution, but with the mid-field strength equipment available would lead to inadequate S/N and C/N ratios. More- over we used a 83 x 128 matrix, consistently smaller than that used in previous studies, due to the need to reduce acquisition time. Despite this the overall resolu- tion of the images was considered satisfactory and simi- lar to that of published images obtained at high field strength.

Our clinical series was obtained with an acquisition time of 14 min. We considered this long acquisition time necessary to obtain good image quality, because of the increased number of signal averages required due to the lower S/N ratio, as compared with high field strength equipment. More recently, as referred to in

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me thods , we have b e e n ab le to op t imi se our t echn ique , r educ ing the acqu i s i t ion t ime to 3 min.

M R C P at 0.5 T canno t d e m o n s t r a t e n o n - d i l a t e d bi l i - a ry ducts well. This is no t a cr i t ica l p r o b l e m f rom the c l in ical po in t of v iew due to the fact tha t this e x a m i n a - t ion can be c o n s i d e r e d as a s econd- l eve l t e c h n i q u e per- f o r m e d a f te r an u l t r a s o u n d e x a m i n a t i o n . In the case of n o r m a l f indings at u l t r a s o n o g r a p h y t h e r e is no indica- t ion for M R C R

In conclus ion , M R C P p e r f o r m e d at m id - f i e ld s t r eng th cou ld have the same c l in ica l va lue as high f ie ld s t r eng th M R C R F u r t h e r r a n d o m i s e d s tudies a re neces- sa ry for a b e t t e r eva lua t i on of the va l id i ty of the techni - que. I t is e x p e c t e d tha t t echn ica l i m p r o v e m e n t will be poss ib le wi th the i n t r o d u c t i o n of n e w devices such as p h a s e - a r r a y and d e d i c a t e d sur face coils.

R e f e r e n c e s

1. Guibaud L, Bret PM, Reinhold C, Atri M, Barkun ANG (1994) Diagnosis of choledocholithiasis: value of MR cholangiogra- phy. AJR 163:847-850

2. Guibaud L, Bret PM, Reinhold C, Atri M, Barkun ANG (1994) Diagnostic accuracy of MR cholangiography in the detection of choledocholithiasis. Radiology 193: 134P

3. Hall-Crags MA, Allen CM, Owens CM, et al (1993) MR cholangiography: clinical evaluation in 40 cases. Radiology 189:423-427

R Pavone et al.: MR cholangiopancreatography at 0.5 T

4. Wallner BK, Schumacher KA, Weidenmaier W, Friedrich JM (1991) Dilated biliary tract: evaluation with MR cholangiogra- phy with a T2 weighted CE-FAST sequence. Radiology 181: 805-808

5. Morimoto K, Shimoi M, Shirakawa T, et al (1992) Biliary ob- struction: evaluation with three-dimensional MR cholangiogra- phy. Radiology 183:578-580

6. Laubenberger J, Buechert M, Guiler H, et al (1995) MR cholangiography with the RARE technique: a new projection method for examination of the bile and pancreatic ducts. Magn Reson Med 33:18-23

7. Takehara Y, Ichijo K, Tooyama N, et al (1994) Breath hold MR cholangiopancreatography with a long-echo-train fast spin echo sequence and a surface coil in chronic pancreatitis. Radi- ology 192:73-78

8. Soto JA, Yucel EK, Barrish M, Chuttani M, Ferrucci JT Jr, Shah J (1994) MR cholangiopancreatography: sequence opti- mization, new techniques and early clinical experience. Radiol- ogy 193: 433P

9. Reinhold C, Bret PM, Guibaud L, Genin G, Atri M (1994) MR cholangiopancreatography: comparison with endoscopic retro- grade cholangiopancreatography. Radiology 193: 434P Soto JA, Yucel EK, Barrish M, Chuttani M, Ferrucci JT Jr, Shah J (1994) MR cholangiopancreatography: correlation with endoscopic retrograde cholangiopancreatography. Radiology 193: 133P Macaulay SE, Schulte SJ, Obregon RG, et al (1994) Non- breath-hold MR cholangiography: comparison with endoscopic retrograde cholangiography and percutaneous transhepatic cholangiography. Radiology 193: 133P

10.

11.

Fornage B.D. (ed.): Musculoskeletal ultrasound. Clinics in Diag- nostic Ultrasound, vol 30. Churchill Livingstone, 1995, 246 pages, £ 65.00,-

This is the 30th volume of the series of Clinics in Diagnostic Ultra- sound edited by Churchill Livingstone since the end of the 1970s, and the quality of the book continues an already established tradi- tion of publishing excellence. The issue, edited by B. D. Fornage, is devoted to the clinical applications of ultrasound in the musculo- skeletal system, a well established but still expanding field of appli- cation of this diagnostic technique.

Four chapters deal with the most important clinical indications for the use of ultrasonography in this field: muscular trauma, soft tissue masses, neuromuscular diseases, and of soft tissues foreign bodies. Next, the book is divided along anatomical structures and sites that can be examined with ultrasound, from the synovium, to the ankle and foot.

Each chapter starts with brief technical considerations on sug- gested instrumentation, best scan planes, necessity of dynamic studies, and usefulness of comparison with the contralateral side. Next, the normal anatomy is presented, followed by a description of the ultrasonographie appearance of the various pathological conditions detectable by ultrasound. All figures are of high quality. In the chapters on evaluation of the rotator cuff and the infant hip, explanatory schematic drawings have been added to ultrasound images and are quite helpful in understanding the many anatomi- cal structures encountered. Pathological findings are presented in detail and are often correlated with the results of experimental

studies performed in vitro. In many cases the results of ultrasound are accompanied by radiographic images or CT scans. However, this is not a book on correlative imaging, and such illustrations are added only when necessary to enhance presentation of ultra- sound findings.

All possible applications of ultrasound in the evaluation of the musculoskeletal system are presented with, in most chapters, a good balance between widely diffuse and relatively new ones. The clinical role of ultrasound and its impact on the management of pa- tients with musculoskeletal problems is well clarified in each case.

In some chapters special attention has been paid to the most advanced fields, with presentation of uses of ultrasonography which are still to be fully evaluated in terms of clinical efficiency, such as the study of the menisci and the cruciate ligaments of the knee. In the chapter on the ankle and foot only one page has been reserved to the well established study of the Achilles tendon, whereas greater attention has been paid to evaluation of peroneal and tibial tendons and soft tissue masses.

This book is a good summary of well established applications of ultrasound in the study of the musculoskeletal system, as well as a presentation of new uses of the technique in this field, and even a source of possible research studies. It can be a useful addition to the library of the general radiologist who has to integrate X-ray studies of the musculoskeletal system with findings provided by ul- trasonography, as well as the expert in ultrasound wishing to have a concise overview of this field. It can even indicate possible new ap- plications and suggest new developments in this rapidly expanding area of ultrasonography. L.E. Derchi, Genova