Postcontrast application of single breath-hold three-dimensional variable flip-angle fast spin-echo breath-hold magnetic resonance cholangiopancreatography for evaluating the pancreaticobiliary ductal system

Introduction

Magnetic resonance cholangiopancreatography (MRCP) is a noninvasive imaging technique that has become a cornerstone in the diagnosis of diseases involving the pancreatobiliary ductal system (1,2). For 3.0 T magnetic resonance imaging (MRI) systems, three-dimensional (3D) MRCP sequences acquired during breath-holding are particularly favored due to their superior image quality and diagnostic efficacy (3-5). In clinical practice, when pancreaticobiliary lesions are suspected, both upper abdominal contrast-enhanced imaging and MRCP are often required to comprehensively assess the pathology. However, on MRCP images, tissues with T2 hyperintense signals, such as vessels, lymphatics, and nerves, can potentially interfere with the visualization of the pancreatobiliary ductal system.

The use of gadolinium-based contrast agents has been shown to improve the depiction of background tissues, such as vessels, and enhance the visualization of T2 hyperintense signals at neural roots on MR neurography (6,7), involving a principle analogous to that of T2-weighted imaging being used in MRCP (4). Given that the contrast agent is excreted through the liver and kidneys, its impact on the visualization of the biliary system in postcontrast MRCP remains a topic of ongoing debate, with conflicting findings being reported across studies (8,9).

Three-dimensional variable flip-angle fast spin-echo breath-hold MRCP (3D SPACE BH MRCP) is capable of completing image acquisition within 18 s (5,10,11). Performing this sequence during the portal venous phase and equilibrium phase of the upper abdominal three-phase dynamic enhancement scan (between 60 and 180 s after contrast injection) can optimize the overall scanning workflow. The aim of this study was to compare image quality between precontrast and postcontrast conventional 3D SPACE BH MRCP in examinations of the pancreatobiliary ductal system. We present this article in accordance with the STROBE reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1657/rc).

Methods

Patients

This prospective study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments and was approved by the Ethics Committee of Wuhan No. 1 Hospital {approval No. [2024] 56}. Informed consent was obtained from all individual participants. From March to May 2024, 40 patients (19 men and 21 women; mean age 57.5±13.08 years; age range 31–77 years) with clinically suspected pancreaticobiliary lesions undergoing upper abdominal contrast-enhanced MRI and MRCP were enrolled. The exclusion criteria were MR contraindications, hypersensitivity to gadolinium, and inability to BH for 18 s.

MRI acquisition

All imaging was performed with a Siemens 3.0T MR scanner (Siemens Healthineers, Erlangen, Germany) equipped with a 16-channel phased-array abdominal coil. Patients were instructed to fast for at least 6 h prior to the examination. Single BH 3D SPACE BH MRCP sequences were acquired both pre-contrast and postcontrast, specifically between the portal venous and equilibrium phases of the dynamic contrast-enhanced MRI. Identical acquisition parameters were used for both pre- and postcontrast 3D SPACE BH MRCP sequences.

The imaging parameters were as follows: field of view (FOV), 350 mm × 350 mm; matrix size, 320×240; repetition time (TR), 2,000 ms; echo time (TE), 501 ms; flip angle, 100°; echo train length, 338; bandwidth, 651 Hz/pixel; parallel imaging with generalized autocalibrating partial parallel acquisition (GRAPPA) and an acceleration factor of 4; signal averaging, 1.4; spatial resolution, 0.5 mm × 0.5 mm × 1.3 mm; section thickness, 1.3 mm; number of sections, 48; phase oversampling, 20%; slice oversampling, 25%; and acquisition time, 18 s.

Gadobenate dimeglumine (MultiHance, Bracco Diagnostics, Princeton, NJ, USA) was administered intravenously at a dose of 0.1 mmol/kg body weight. Dynamic contrast-enhanced MRI was performed in three phases: arterial phase (range, 25–35 s), portal venous phase (range, 55–65 s), and equilibrium phase (range, 180–200 s). The postcontrast 3D SPACE BH MRCP sequence was acquired 90–120 s after contrast agent administration.

Image analysis

After image acquisition, the data were transferred to the picture archiving and communication system (PACS), with patient identifiers and acquisition parameters anonymized to ensure blinding during analysis.

Quantitative image analysis

On the PACS workstation, two board-certified radiologists (reader 1, Di Tian, and reader 2, Hongfen Peng, with 1 year and 20 years of experience in interpreting MRCP images, respectively) independently evaluated the original two-dimensional (2D) coronal thin-slice MRCP images using fixed window settings (window width/level: 350/150). On these images, the widest portion of the common bile duct (CBD) was selected, and regions of interest (ROIs) were placed within the left periductal background tissue and the liver parenchyma in the right hepatic lobe, avoiding large intrahepatic bile ducts and vessels. Images were enlarged to ensure full coverage of the CBD lumen. The mean ROI area for the CBD was 70.19±41.30 mm², while the background ROI (50 mm²) was positioned to exclude vascular structures, gastrointestinal tract, ascites, and artifacts. Three repeated measurements were performed, and the mean values were calculated. ROIs were copied to ensure consistency in placement and size between pre- and postcontrast scans. The signal intensity (S) and standard deviation (SD) were recorded for the CBD (S_CBD and SD_CBD), the adjacent periductal background tissue (S_background and SD_background), and the liver parenchyma. Quantitative parameters for MRCP image quality were evaluated as per the methodology described by Shiraishi et al. (12). The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and contrast ratio (CR) were calculated with the following formulae:

SNR=SCBD/SDCBD[1]

CNR=(SCBD−Sbackground)/(SDCBD2+SDbackground2)/2[2]

CR=(SCBD−Sbackground)/(SCBD+Sbackground)[3]

The original oblique coronal MRCP images from both pre- and postcontrast scans were analyzed for each patient to assess the image quality parameters.

Qualitative image analysis

Thick-slab maximum intensity projection (MIP) images, which were automatically reconstructed postscan, were evaluated with fixed window settings (window width/level: 150/350). Image quality was scored on a 4-point Likert scale based on the depiction of intrahepatic bile duct branches, extrahepatic bile ducts, main pancreatic duct, and background suppression [modified from previous work (10,13)]. Points were assigned according to the following scheme: 1 point, poor image quality (severe blurring of ductal margins, significant artifacts, nondiagnostic); 2 points, fair image quality (major artifacts); 3 points, good image quality (minor artifacts); and 4 points, excellent image quality (no artifacts interfering with interpretation). Interobserver discrepancies were resolved through discussion.

Statistical analysis

Statistical analyses were performed with SPSS version 26 (IBM Corp., Armonk, NY, USA). The Shapiro-Wilk test was used to assess the normality of continuous quantitative variables. Data that conformed to a normal distribution are expressed as the mean ± SD, while nonnormally distributed data are expressed as the median with the interquartile range (IQR). For nonnormally distributed variables, the Wilcoxon signed-rank test was applied to compare differences between pre- and postcontrast measurements. Interrater reliability for subjective scores between the two readers was evaluated with Cohen’s kappa coefficient (κ). Interpretation of κ values followed the established criteria, as follows: κ <0.4, poor agreement; 0.4≤ κ <0.7, moderate agreement; and κ ≥0.7, substantial agreement. A two-tailed P<0.05 was considered statistically significant.

Results

Among the 40 enrolled patients, biliary obstruction was observed in 15 cases (37.5%), with the etiologies including hilar cholangiocarcinoma (n=2), distal CBD carcinoma (n=1), CBD stones (n=11), and pancreatic head cancer (n=1).

Quantitative analysis

Postcontrast 3D SPACE BH MRCP showed a statistically significant 12.77% reduction in liver parenchyma signal intensity (P=0.009) and a 17.98% decrease in periductal background signal (S_background, P<0.001) compared with precontrast imaging, in addition to a 2.17% improvement in CR (P<0.001). However, no significant differences were observed in CBD signal intensity, SNR, or CNR between pre- and postcontrast scans (all P values >0.05). Detailed results are presented in Table 1.

Qualitative analysis

Image quality was diagnostic in all 40 cases before and after contrast administration, with no scan receiving a score of 1 (nondiagnostic). The median subjective quality scores were 4 (IQR, 3–4) for precontrast and 4 (IQR, 4–4) for postcontrast. Postcontrast scores were significantly higher than were precontrast scores (Z =−2.714; P=0.007). Interobserver agreement was substantial for both pre- and postcontrast assessments (precontrast: weighted κ =0.76; postcontrast: weighted κ =0.79; both P values <0.01). The qualitative scoring distributions are presented in Table 2, and representative images are shown in Figure 1.

Figure 1 A 51-year-old female patient with IPMN of the pancreatic body/tail. (A,B) Pre- and postcontrast 3D SPACE BH MRCP source images. (C,D) Pre- and postcontrast 3D SPACE BH MRCP thick-slab maximum intensity projection reformations. Postcontrast images show marked background tissue suppression (arrows), with reduced renal parenchyma and lymphatic vessel signal, whereas the intra- and extrahepatic bile ducts, common bile duct, main pancreatic duct, and the pancreatic body/tail IPMN remained hyperintense, allowing clearer depiction of the biliary and pancreatic ductal systems. 3D SPACE, three-dimensional variable flip-angle fast spin-echo; BH, breath-hold; IPMN, intraductal papillary mucinous neoplasm; MRCP, magnetic resonance cholangiopancreatography.

Discussion

The findings of our study indicate that 3D SPACE BH MRCP enhanced with a gadolinium-based contrast agent following the portal venous phase significantly suppresses background tissue signals as compared to conventional 3D SPACE BH MRCP, with the observed differences being statistically significant. However, no statistically significant differences were detected in the signal intensity of the pancreatic duct between pre- and postcontrast imaging.

The interval of 1 to 2 min between the portal venous phase and equilibrium phase following gadolinium-based contrast agent administration provides a feasible temporal window for 3D SPACE BH MRCP acquisition (18 s), without compromising the overall scanning workflow. This protocol demonstrated significant suppression of T2-hyperintense background tissues surrounding the pancreaticobiliary ducts, including for vascular structures (17.98% reduction), lymphatic tissues (12.77% reduction), periductal fascia, and renal parenchyma, while enhancing the pancreaticobiliary CNR by 2.17%. This phenomenon is consistent with the T2 relaxation shortening induced by gadolinium in tissues (14). Similar T2 contrast-enhanced background suppression mechanisms have been observed in 3D SPACE neurography, with gadolinium-mediated T2 relaxation effects reducing the signal intensity of vascular, lymphatic, and muscular tissues, thereby improving neural tissue visualization (15,16).

In our study, no significant difference in bile duct signal intensity was observed between postcontrast 3D SPACE BH MRCP (acquired at 90–120 s after contrast injection) and precontrast 3D SPACE BH MRCP. This finding contrasts with that of Kanematsu et al. (8), who reported blurred biliary margins and degraded image quality in 2D thick-slab MRCP images acquired 5 to 10 min after gadoxetic acid disodium administration. The T2 signal shortening effect in bile, attributed to the 50% hepatic metabolism of gadoxetic acid, leads to intrabiliary contrast agent excretion at 5 min after injection, causing signal homogenization of the biliary walls. In contrast, our protocol involves conventional gadopentetate dimeglumine, which has a predominant renal excretion pathway and lower hepatic metabolism (3–5%), thereby minimizing its impact on biliary signal intensity.

In the study by Ringe et al. (17), respiratory-triggered 3D MRCP was acquired immediately following the contrast-enhanced (gadobutrol) portal venous phase, with k-space filling occurring approximately 3 min after contrast injection. Despite this approach, both qualitative and quantitative indicators of image quality still exhibited a decline. In our study, an MRCP sequence with a single BH was performed for 18 s and was followed by 3D SPACE BH MRCP acquisition 90 s after contrast injection, significantly earlier than the time window during which the contrast agent would be excreted into the bile ducts. Similarly, Kim et al. (18) reported improved image quality for both 2D and 3D MRCP when acquired within 1.5 min (mean 3 min) after the contrast-enhanced (gadobutrol) portal venous phase.

We further found preserved bile duct visualization in post-portal venous phase 3D SPACE BH MRCP acquired during a single BH (18-s acquisition and 90 s after contrast). This contrasts with the findings of Jin et al. (19), who used a respiratory-triggered 3D SPACE sequence acquired after gadobutrol administration. Their protocol’s k-space filling completion at approximately 5 min after injection coincided with biliary contrast excretion, when intrabiliary gadolinium would theoretically induce T2 signal reduction and compromise ductal visualization. However, Jin et al. observed a consistent bile duct T2 signal intensity despite a 52% rate of obstructive cases (29/56), which is potentially attributable to the delayed bile secretion from obstructive pathologies. In our study, the biliary obstruction rate was 37.5% (15/40), and the preserved image quality likely reflects the earlier imaging timing (90 vs. 300 s after injection), which precedes significant biliary contrast accumulation. This is further compounded by the predominant renal excretion of gadopentetate dimeglumine, which minimizes hepatic-biliary transfer.

Limitations

First, the difference in diagnostic efficacy between pre- and postcontrast 3D SPACE BH MRCP was not evaluated in this study. This represents a critical clinical priority and will be a primary focus of future research. Second, while this study focused on evaluating image quality in gadopentetate dimeglumine-enhanced pre- and postcontrast 3D SPACE BH MRCP, the impact of other gadolinium-based contrast agents, particularly hepatobiliary-specific agents, such as gadoxetic acid disodium, on 3D SPACE BH MRCP image quality was not examined.

Conclusions

The acquisition of 3D SPACE BH MRCP postcontrast effectively suppresses background tissue signals while preserving the visualization of the pancreaticobiliary ductal system. This technique not only enhances the overall image quality of MRCP but also maintains compatibility with upper abdominal enhanced scanning workflows, thereby improving diagnostic efficiency.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1657/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1657/dss

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1657/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the Ethics Committee of Wuhan No. 1 Hospital {approval No. [2024] 56} and informed consent was obtained from all individual participants.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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