Semester of Graduation

Spring 2026

Degree

Master of Science (MS)

Department

Physics and Astronomy

Document Type

Thesis

Abstract

Purpose: Four-dimensional computed tomography (4D-CT) is the current clinical standard for respiratory motion assessment, but it contributes to cumulative imaging dose and offers limited soft-tissue contrast. Four-dimensional magnetic resonance imaging (4D-MR) provides a radiation-free alternative with superior soft-tissue visualization. The purpose of this thesis was to evaluate the feasibility and limitations associated with using 4D-MR as an alternative to 4D-CT for respiratory motion assessment in patients treated with abdominal compression belts (CB).

Methods: Three complementary studies were performed. First, respiratory motion measured using 4D-MR and 4D-CT was compared in a retrospective cohort of CB patients using a validated mutual information–based, box-assisted registration approach. Second, interfraction reproducibility of CB placement was evaluated using daily treatment MR images, assessing external contour stability, organ positional variability, and demographic predictors relative to a non-CB cohort. Third, a programmable respiratory motion phantom was used to quantify fundamental three-dimensional motion recovery differences between 4D-MR and 4D-CT under known ground-truth conditions to isolate modality- and reconstruction-related baseline discrepancies.

Results: Box-assisted registration demonstrated strong agreement with contour-based motion measurements for both CT and MR, supporting its use for respiratory motion quantification. CB placement exhibited greater interfractional variability over the PTV region as well as organ positional displacements compared to the non-CB cohort. In patient data, 4D-MR consistently measured larger respiratory motion than 4D-CT in all dimensions. Phantom experiments showed that intrinsic modality and reconstruction effects greatly affect motion recovery capabilities, showing 4D-CT is able to recover closer to ground truth values in idealistic conditions.

Conclusions: 4D-MR can reliably quantify respiratory motion in CB patients but exhibits systematic differences relative to 4D-CT due to modality-specific sampling and reconstruction characteristics. MR can recover the full range of motion as it continuously acquires 3D data, not just a 2D slice. While 4D-CT accurately characterizes motion at the time of acquisition, it may underrepresent the full range of motion present during treatment delivery.

Date

3-26-2026

Committee Chair

Krystal Kirby

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

Download

Available for download on Friday, March 26, 2027

Share

COinS