Introduction

Magnetic resonance cholangiopancreatography (MRCP) is a standard imaging technique that provides detailed information of the pancreaticobiliary anatomy and pathology. Most initial study focused on 2D MRCP technique using breath-hold (BH) acquisition sequences, while they suffered from decreased spatial resolution and acquired non-isotropic voxel datasets. Therefore, for the purpose of obtaining high-resolution isotropic images, 3D navigator-triggered with Application-optimized Contrasts by using different flip angle Evolutions (NT-3D-SPACE) MRCP sequences have been performed principally with a respiratory-triggered technique during the last 10 years¹. However, there is a clinical burden that the acquisition time of the respiratory-triggered 3D MRCP sequence often need take more than 6 minutes despite the use of parallel acquisition technique². Breath-hold 3D SPACE(BH-3D-SPACE) is modified from product NT-3D-SPACE which need just about 18 seconds for breath-hold and have good image quality. The aim of this study was to compare the MRCP image quality between BH-3D-SPACE and NT 3D-SPACE, and furthermore to evaluate the diagnosis of choledocholithiasis in a routine clinical setting.

Methods

Seventy-eight patients (41 males and 37 females, age range 24-76 years) were enrolled in this study. All the patients underwent conventional NT-3D-SPACE and BH-3D-SPACE sequence on a 1.5T MR scanner (MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany) using 6-channel body coil and 24-channel spine coil. The parameters about two different types of SPCAE sequences were as bellow: NT-3D-SPACE and BH-3D-SPACE. Two radiologists with five years of experience in abdominal radiology assessed the images independently. They evaluated the image quality of predefined segments of the pancreaticobiliary tree using a 5-point scale:1 = not displayed; 2 = incompletely displayed, not diagnostic;3 = all parts of the segments are uncertainly definable, still diagnostic; 4 = all parts of the segments are included, some are uncertainly definable, still diagnostic; 5 = all parts of the segments are completely and reliably definable. In a second step, the diagnostic confidence was rated on a 5-point scale from –2 to 2: –2 = reliably no concrement; –1 = most likely no concrement; 0 = not evaluable; 1 = most likely concrement; 2 = reliably recognized concrement. Evaluation of image quality and diagnostic confidence was done on the pancreaticobiliary tree which was subdivided into 9 segments. They were scored and statistically evaluated separately for visibility and diagnostic certainty by two blinded radiologists with differing levels of experience on a five-point scale of 1 to 5 and -2 to 2, respectively. Student t-test was performed, and the interobserver agreement was also calculated. Interobserver agreement was assessed by calculating the Cohen kappa statistic (kappa< 0.00: poor agreement, kappa = 0.00-0.20: slight agreement, kappa = 0.21-0.40: fair agreement, kappa = 0.40-0.60: moderate agreement, kappa = 0.61-0.80: substantial agreement; kappa = 0.81-1.00: almost complete agreement).

Results

The mean acquisition time of BH-3D-SPACE MRCP was significantly shorter than that of NT-3D-SPACE MRCP (18 seconds vs 169.3±46.3 seconds; p< 0.001, Table 1). Image quality for each segment was significantly better for the BH-3D-SPACE sequence compared to the NT-3D-SPACE sequence (average score: BH 3D-SPACE 4.48±0.94 vs. NT-3D-SPACE 3.98±1.20, p< 0.01). Diagnostic confidence for the reporting radiologist was also significantly better for BH 3D-SPACE than for NT-3D-SPACE (average score: BH-3D-SPACE 1.67±0.53 vs. NT-3D-SPACE 1.41±0.67, p< 0.01). The interobserver agreement was high in both sequences, 0.68-0.91 and 0.61-0.83, respectively.

Discussion and Conclusion

The study discovered that the BH-3D-SPACE sequence allows for better image quality and shorter data acquisition time in 1.5 T MRCP examinations and leads to a higher diagnostic confidence for choledocholithiasis compared to conventional NT-3D-SPACE sequence. It is known that navigator-triggered 3D-MRCP sequence have been widely used in clinical practice³. However, in patients with irregular or shallow respiratory rhythms, respiratory-gated acquisitions may fail to trigger correctly, prolonging scan times, or may result in images with substantial motion artifact. Our study confirmed that optimized BH-3D-SPACE MRCP is superior to conventional NT-3D-SPACE MRCP regarding the image quality and the level of diagnostic confidence for choledocholithiasis (Fig. 1). Because of the significantly better imaging results, we recommend replacing the conventional NT-3D-SPACE sequence with a BH-3D-SPACE protocol for patients with good BH capacity in 1.5 T MRCP examinations.

Acknowledgements

We thank Shaoyu Wang of Siemens Healthcare, Ltd., Xi’an, China, for technical support.