A retrospective 4D-MRI based on 2D diaphragm profiles for lung cancer patients.

Abstract

4D-MRI, compared to 4D-CT, provides better soft-tissue contrast for target delineation. However, motion artefacts are often observed due to residual breathing variations. This study is to present a retrospective 4D-MRI reconstruction method based on 2D diaphragm profiles to improve the quality of 4D-MR images in the presence of significant breathing variations. The proposed 4D-MRI reconstruction method utilized diaphragm profiles (2D cine images on a single sagittal plan at the peak diaphragm) in conjunction with 4D-MR scans (2D-cine images on multiple pre-determined coronal planes along the anterior-posterior direction over a volume of interest). The diaphragm profile images were exploited to sort the 4D-MR scans by matching respiratory amplitude of diaphragm on the 4D-MR scans to the diaphragm profiles. To evaluate reconstructed 4D-MR images (ten 3D-MR images), sagittal images on ten 3D-MR images under free breathing (FB) and respiratory guidance (GB) were compared with diaphragm profile images (reference) from 13 healthy volunteers. Forty-four 4D-MR scan datasets were successfully reconstructed without distinct respiratory-related motion artefacts even with the presence of breathing variation. The differences in diaphragm profiles between the reference and corresponding reconstructed images in the mean of root mean square were similar between FB (3.5mm) and GB (3.0mm), confirming that the 4D-MRI reconstruction method was effective even with significant breathing variation. The diaphragm profiles were utilized to reconstruct 4D-MR images with spatial reliability and a fixed scan time under FB and GB. Our method can provide reliable 4D information of thoracic and abdominal regions for MRI-guided radiotherapy.