Retrospective four-dimensional magnetic resonance imaging with image-based respiratory surrogate: a sagittal–coronal–diaphragm point of intersection motion tracking method

Abstract. A four-dimensional magnetic resonance imaging (4-D-MRI) technique with Sagittal–Coronal–Diaphragm Point-of-Intersection (SCD-PoI) as a respiratory surrogate is proposed. To develop an image-based respiratory surrogate, the SCD-PoI motion tracking method is used for retrospective 4-D-MRI reconstruction. Single-slice sagittal MR cine was acquired at a location near the center of the diaphragmatic dome. Multiple-slice coronal MR cines were acquired for 4-D-MRI reconstruction. As a motion surrogate, the diaphragm motion was measured from the PoI among the sagittal MRI cine plane, coronal MRI cine planes, and the diaphragm surface. These points were defined as the SCD-PoI. This point is used as a one-dimensional diaphragmatic navigator in our study. The 4-D-MRI technique was evaluated on a 4-D digital extended cardiac-torso (XCAT) human phantom, a motion phantom, and seven human subjects (five healthy volunteers and two cancer patients). Motion trajectories of a selected region of interest were measured on 4-D-MRI and compared with the known XCAT motion that served as references. The mean absolute amplitude difference (D) and the cross-correlation coefficient (CC) of the comparisons were determined. 4-D-MRI of the XCAT phantom demonstrated highly accurate motion information (D=1.13  mm, CC=0.98). Motion trajectories of the motion phantom measured on 4-D-MRI matched well with the references (D=0.54  mm, CC=0.99). 4-D-MRI of human subjects showed minimal artifacts and clearly revealed the respiratory motion of organs and tumor (mean D=1.08±1.03  mm; mean CC=0.96). A 4-D-MRI technique with image-based respiratory surrogate has been developed and tested on phantoms and human subjects.