SU-E-J-68: Evaluation of Liver Deformation During Breathing Using Deformable Image Registration: A Comparison Between 4D CT and 4D MRI




It is of clinical interest to study liver deformation during breathing by applying deformable image registration (DIR) on respiratory correlated 4D images. This study aims to evaluate and compare the accuracy of DIR-derived liver deformation based on 4D CT and 4D MRI.


4D CT, 4D MR and cine MR images of liver region were acquired from 5 patients with liver cancer under an IRB-approved protocol. Tumor trajectories were tracked from cine MR images. DVFs from 4D CT and 4D MR were generated via DIR implemented in Velocity AI. To enable comparison between DVFs and tumor trajectories from cine images, deformation vectors from each frame were linked together, forming DVF-based trajectories. All DVF-based trajectories within each tumor region were averaged. Absolute difference, relative difference and correlation coefficient between each pair of averaged DVF-based trajectory and trajectory from cine MR images were calculated.


All metrics did not give consistent indications of which modality can provide more accurate DVFs. In superior-inferior (SI) direction, averaging over all the five patients, 4D CT trajectories exhibited smaller absolute (2.05±0.52mm) and relative difference (0.43±0.14) and larger correlation coefficient (0.92±0.06) than 4D MR trajectories (2.54±1.45mm, 0.47±0.18, 0.88±0.10) whereas 4D MR (1.02±1.20mm, 0.90±0.69, 0.59±0.30) surpassed 4D CT (1.35±1.42mm, 1.35±1.25, 0.12±0.64) in every metric in right-left direction. In anterior-posterior direction, 4D MR trajectories has smaller absolute (1.17±0.74mm) and relative difference (0.50±0.18) with slightly smaller correlation coefficient (0.72±0.23) than 4D CT trajectories (1.51±0.64mm, 0.69±0.09, 0.75±0.26).


We have implemented a novel approach for evaluating accuracy of DVFs based on 4D imaging for studying liver deformation. Initial results indicate that DVFs from 4D CT and 4D MRI are comparable. Further study on more patients is warranted and is undergoing to determine whether there is significant difference between 4D CT and 4D MRI.