PHSOR11 Presentation Time: 9:50 AM

Purpose

This study focuses on determining the optimal MRI scanning parameters for precise localization of MR-line markers, and to investigate their apical reconstruction error.

Materials and Methods

In the study, it was assumed that the front seal of each MR-line marker was identical. Three MR-line markers were individually placed at the tips inside the tubes of plastic sharp needles. The position of the plastic-tipped sharp needles was marked with three additional MR-line markers. These needles, along with the markers, were then fixed into the same L-shaped (rectangular) mold to ensure that the plastic sharp needles and their corresponding MR-line markers maintained a stable, horizontal alignment and were immobilized during the process. The physical distance measured between the tips of the two MR line markers, one located inside and the other outside the plastic sharp needle, was approximately 2.30mm. To evaluate the apical reconstruction error of the MR-line marker,10 sets of MR images were acquired with varying slice thicknesses, including T1-weighted images with thicknesses of 3 mm, 2 mm, and 1.4 mm, and T2 -weighted images with thicknesses of 3 mm, 2 mm, and 1 mm.

Results

The analysis of the image distance between the MR-line marker tips, both inside and outside plastic sharp needle, revealed that the probability of the measurement of the MR-line marker being within 1 mm accuracy was 92.59%. It was observed that the thickness of the MR images positively correlated with both the mean and standard deviation of the image measurement value in T1-weighted scans. Additionally, the standard deviation of MR-line marker image measurements in T2-weighted scans showed a slight increase as the layer thickness was reduced to 2mm. Upon comparing the results from the three sets of MR-line marker image measurements, it was found that the overall results of T2-weighted scans at 3 mm and T1-weighted scans at 1.4 mm were similar. However, it is important to note that the thinner slice parameter not only restricts the length of the scan, but also leads to increased scanning time and additional time required for contouring before brachytherapy treatment, resulting in increased discomfort for the patient. Therefore, a scanning parameter of T2-weighted scans at 3 mm is recommended for the reconstruction of the MR-line marker.

Conclusions

The study demonstrated that the MR-line marker possesses significant potential for clinical application, particularly in the precise localization of plastic sharp needles. This finding is pivotal as it provides a crucial experimental foundation for the implementation of an MR-only workflow in interstitial gynecologic brachytherapy.