Patient population
A retrospective comparative analysis was done over a period of 20 months for patients who were referred for MRCP at the Department of Radiology,
John Radcliffe Hospital,
Oxford Radcliffe Hospitals NHS Trust.
Patients who did not undergo US were excluded from the study.
Accordingly,
a primary study group was obtained which was composed of patients with both MRCP and US of the abdomen.
Depending on the diagnosis made by MRCP and US,
patients were again excluded if neither technique could diagnose stone in the bile duct and the primary study group was turned into a smaller,
final study group in which all patients were diagnosed by MRCP and/or US as having choledocholithiasis.
In the final study group,
Patients' presentations were varied; they presented with right upper quadrant (RUQ) pain (44%),
clinical jaundice (29%),
cholangitis (5%),
acute pancreatitis (12%) and abnormal liver function tests (LFTs) (40%) (table 1).
Table 1: Clinical presentations
Presentation
|
Number (No.)
|
Percentage (%)
|
RUQ pain
Clinical jaundice
Cholangitis
Pancreatitis
Abnormal LFTs
|
40
26
5
11
36
|
44
29
5
12
40
|
RUQ= Right upper quadrent,
LFTs=liver function tests
A subgroup analysis was performed for patients in whom choledocholithiases escaped detection by US and were exclusively diagnosed using MRCP.
Their common bile duct size and bile duct stone characteristics such as the number,
site and size of stones were studied.
Examination techniques
MRCP. All patients underwent MRCP examination using 1.5-T system (Ge Signa).
A phased array torso coil was used.
Contrast agent (gadolinium) was administered at a dose of 0.1 mmol/kg b.w.
when a pancreatic pathology was suspected like a tumor mass.
Patients were fasted for 6-8 hours to reduce gastrointestinal fluids.
Negative oral contrast agents were rarely used.
Techniques used were standard MRCP protocol with coronal and axial T2,
thin slice and thick slab MRCP.
Gradient echo images were obtained through the upper abdomen and one of these images through the porta hepatis was chosen for localization,
using this; contiguous coronal images were obtained through the region of the biliopancreatic ducts with the application of frequency-selective fat suppression.
Details of pulse sequences used in this study are mentioned in table 2.
Table 2: Details of pulse sequences used in this study
Parameter
|
T2-coronal
|
T2-axial
|
Thin slice
|
Thick slab
|
TR,
ms
|
2000
|
2000
|
2000
|
2000
|
TE,
ms
|
90
|
90
|
38
|
1500
|
Matrix size,
pixels
|
320 × 224
|
256 × 224
|
384 × 224
|
384 × 256
|
FOV,
mm
|
480
|
440
|
480
|
300
|
Section thickness,
mm
|
8
|
8
|
4
|
60
|
Interspace gap,
mm
|
2
|
2
|
---
|
---
|
Receive bandwidth,
KHz
|
62.5
|
41.67
|
62.5
|
31.25
|
Echo train length
|
---
|
23
|
---
|
---
|
Breath hold,
sec
|
20
|
2 × 20
|
3 × 20
|
3
|
MRCP reports were analysed for degree of biliary duct visualization,
presence of bile duct dilatation (maximum extrahepatic duct diameter) and the presence of stones.
Stones were diagnosed at MRCP as rounded,
ovoid or faceted areas of signal void on T2 weighted sequences surrounded by high signal bile in at least 2 imaging planes.
US. Grey-scale US equipment utilizing 3.5-5 MHz curvilinear probes were used (Sequoia,
Siemens,
Germany).
The patients were fasted for 4-6 hours and examined in the supine and right anterior oblique positions to visualize optimally the gall bladder and biliary ducts.
The extra-hepatic bile duct was visualized in its longitudinal direction and the anteroposterior diameter measured at the level of the common hepatic duct (where the right hepatic artery crosses the duct) when the diameter of the duct was within the normal limits,
but if the duct was found to be dilated,
the diameter was measured at the maximal point of dilatation.
The diameter of the normal common duct,
as measured on US scans,
is regarded within normal if it is less than 5 mm in its upper portion,
although this figure can be increased to 6 mm for a measurement at its lower end,
and 10 mm in patients who have had a cholecystectomy [7] with additional 1 mm increase per decade after the age of 50 years [8].
A stone was identified as an intraductal echogenic focus,
with or without shadowing.
Once detected,
the number,
size and site of stones were determined as well.