Development of a T2-Weighted MR Marker for Interstitial Gynecological Brachytherapy
Abstract
Purpose
Magnetic resonance (MR) imaging is increasingly used for image guidance in interstitial gynecological brachytherapy due to its superior soft-tissue contrast; however, accurate reconstruction of implanted plastic needles remains challenging. Plastic needles appear as signal voids on MR images, while metallic components introduce susceptibility artifacts. Existing MR marker solutions are often bulky, primarily designed for applicators, or require combined T1- and T2-weighted imaging. This work aimed to develop and evaluate a compact, in-house MR marker optimized exclusively for T2-weighted imaging to enable reliable MR-only reconstruction of interstitial brachytherapy needles
Methods
An in-house MR marker was developed for MR-only reconstruction of 6F interstitial plastic brachytherapy needles (Elekta). The marker consists of a hydrogel-based core integrated with custom 3D-printed structural components. Needles containing the marker were inserted into animal tissue, and T2-weighted MR images were acquired on a Philips 3T MR simulator. Reference CT imaging using commercial CT markers was performed for comparison. Needle trajectories and tip locations reconstructed from MR images were quantitatively compared with CT-based reconstructions.
Results
The proposed marker produced a continuous, well-defined signal along the needle trajectory on T2-weighted MR images, enabling reliable visualization of both the needle path and tip. Across the evaluated needle trajectories, the mean Euclidean distance between MR- and CT-based reconstructions was 0.76 ± 0.48 mm, with a root mean square error of 0.87 mm. The mean Euclidean distance at the needle tip was 0.54 mm. No signal voids due to air entrapment or susceptibility-related distortions were observed.
Conclusion
A compact, hydrogel-based MR line marker was successfully developed for MR-only reconstruction of interstitial plastic brachytherapy needles. The marker enables accurate needle visualization on T2-weighted MR imaging with sub-millimetre agreement with CT-based localization and without susceptibility artifacts. This approach supports streamlined MR-only workflows for interstitial gynecological brachytherapy, and clinical evaluation is underway.