Quantitative MRCP Imaging: Accuracy, Repeatability, Reproducibility, and Cohort-Derived Normative Ranges

Abstract

Background: Magnetic resonance cholangiopancreatography (MRCP) is an important tool for noninvasive imaging of biliary disease, however, its assessment is currently subjective, resulting in the need for objective biomarkers.

Purpose: To investigate the accuracy, scan/rescan repeatability, and cross-scanner reproducibility of a novel quantitative MRCP tool on phantoms and in vivo. Additionally, to report normative ranges derived from the healthy cohort for duct measurements and tree-level summary metrics.

Study type: Prospective.

Phantoms/subjects: Phantoms: two bespoke designs, one with varying tube-width, curvature, and orientation, and one exhibiting a complex structure based on a real biliary tree. Subjects Twenty healthy volunteers, 10 patients with biliary disease, and 10 with nonbiliary liver disease.

Sequence/field strength: MRCP data were acquired using heavily T2 -weighted 3D multishot fast/turbo spin echo acquisitions at 1.5T and 3T.

Assessment: Digital instances of the phantoms were synthesized with varying resolution and signal-to-noise ratio. Physical 3D-printed phantoms were scanned across six scanners (two field strengths for each of three manufacturers). Human subjects were imaged on four scanners (two fieldstrengths for each of two manufacturers).

Statistical tests: Bland-Altman analysis and repeatability coefficient (RC).

Results: Accuracy of the diameter measurement approximated the scanning resolution, with 95% limits of agreement (LoA) from -1.1 to 1.0 mm. Excellent phantom repeatability was observed, with LoA from -0.4 to 0.4 mm. Good reproducibility was observed across the six scanners for both phantoms, with a range of LoA from -1.1 to 0.5 mm. Inter- and intraobserver agreement was high. Quantitative MRCP detected strictures and dilatations in the phantom with 76.6% and 85.9% sensitivity and 100% specificity in both. Patients and healthy volunteers exhibited significant differences in metrics including common bile duct (CBD) maximum diameter (7.6 mm vs. 5.2 mm P = 0.002), and overall biliary tree volume 12.36 mL vs. 4.61 mL, P = 0.0026).

Data conclusion: The results indicate that quantitative MRCP provides accurate, repeatable, and reproducible measurements capable of objectively assessing cholangiopathic change. Evidence Level: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;52:807-820.

Keywords: 3D-printed phantom; biliary disease; magnetic resonance cholangiopancreatography (MRCP); quantitative metrics; repeatability; reproducibility.

Conflict of interest statement

All authors affiliated with Perspectum Diagnostics are employees, and several have stock options within the company. J.M.B. and S.V. are listed on relevant patent applications.

© 2020 The Authors. Journal of Magnetic Resonance Imaging published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Figures

Figure 1

Overview of conventional MRCP and quantitative MRCP for an example case. (a) Coronal slice through a 3D MRCP acquisition, near the bifurcation. (b) Maximum intensity projection (MIP) over all slices. (c) Surface rendering of enhanced ducts. (d) Quantitative MRCP model, with biliary tree and pancreatic duct (PD) colored by diameter. (e) A plot of the modeled diameter profile along the length of the selected PD; the orange and blue arrows denote automatically identified points where the diameter is more than 30% narrower or wider than adjacent regions.

Figure 2

Quantitative MRCP phantoms. (a) Mathematical surface model generated from specified centerline coordinates and tube diameters for the “tubewidth” phantom; synthetic 3D voxel arrays can be generated from this at varying resolutions. (b) A version of the model with the same tubes as hollow voids within a cube. (c) The cube has been 3D‐printed and is bathed in fluid within a 3D‐printed housing that can then be inserted into the scanner. (d) Example results of modeling a scan of the cube; note that the break visible to the right of the crosshair (white arrow) is due to an air bubble trapped in the fluid; the corresponding point will not be counted as a stable match for the evaluation. (e) A modeled surface from a clinical case was used as a starting point for the more anatomically realistic portion of the “clinical” phantom. (f) Example modeled results from a scan of the clinical phantom, showing the additional artificial tubes.

Figure 3

Forest plots summarizing the Bland–Altman analyses for the accuracy of diameter measurements on the (a) digital tubewidth and (b) digital clinical phantoms and (c) 3D‐printed tube‐width and (d) 3D‐printed clinical phantoms

Figure 4

Forest plots summarizing the Bland–Altman analyses of reproducibility across scanners for the (a) tubewidth 3D‐printed phantom and (b) clinical 3D‐printed phantom.

Figure 5

Bland–Altman scatterplots reveal moderate repeatability of biliary tree metrics with examples shown for (a) the CBD median (0.0 mm bias, –1.2 – 1.1 mm LoA, RC = ±1.7 mm) and (b) total biliary tree volume (–0.1 mL bias, –3.5 – 3.4 mL LoA, RC = ±2.2 mL). Reproducibility of quantitative MRCP comparing the results between Siemens Prisma and Siemens AvantoFit in both (c) the CBD median (–0.3 mm bias, –1.9 – 1.3 LoA, RC = ±2.3 mm) and (d) total tree volume (0.2 mL bias, –4.1 – 4.4 mL LoA, RC = ±4.9 mL).

Figure 6

Comparison of healthy and biliary diseased patients (a) healthy participant (i) total tree volume of 4.1 mL, (ii) isolation and analysis of the CBD, with quantitative results: Median: 5.2 Min 2.7 mm Max 6.2 IQR 4.1–5.8, (iii) CBD diameter profile revealing slight increase (>30%) at blue arrow. (b) Participant with biliary disease, (i) total tree volume 22.2 mL, (ii) isolation and analysis of the CBD, with quantitative results: Median 4.8, Min 2.3 Max 7.8, IQR 4.4–5.8, (iii) CBD diameter profile revealing a stricture (blue) and apparent dilatation (orange).

Figure 7

(a) Total biliary tree volume analysis revealed biliary diseased patients to have a larger overall biliary tree compared to healthy volunteers (P = 0.0026). (b) The CBD of individuals with biliary disease were found to be significantly larger than the healthy volunteers (P = 0.005). (c) The total percentage of ducts in the biliary tree whose diameter was between 5–7 mm were significantly increased in individuals with biliary disease (P = 0.0018), (d) whereas the total percentage of ducts in the biliary tree with a diameter of less than 3 mm were found to be significantly greater in healthy volunteers (P = 0.029).