Purpose: We have previously developed a 4D‐MRI technique using the fast imaging sequence employing steady‐state acquisition (FIESTA) sequence, which has suboptimal tumor‐to‐tissue contrast‐to‐noise ratio (CNR) due to its T2*/T1 weighting. This study investigated the feasibility of enhancing the tumor‐to‐tissue CNR using deformable image registration (DIR). Methods: Five patients with cancers in the liver were included in an IRB‐approved study. 4D‐MRI images were acquired on a 1.5T GE scanner and reconstructed off line using in‐house developed program. All patients were also imaged with a T2‐w fast recovery fast spin‐echo (FRFSE) sequence at the end‐of‐exhalation phase. Deformation vectors between respiratory phases of the 4D‐MRI were determined using commercial software. Pseudo ‘enhanced’ 4D‐MRI was then generated by applying the deformation vectors to the T2‐w FRFSE MR images. Motion trajectories of tumor and diaphragm and tumor‐to‐tissue CNR were compared between the original T2*/T1‐w 4D‐MRI and the ‘enhanced’ T2‐w 4D‐MRI. To validate our method, we performed a simulation study based on a 4D digital human phantom. MR images with T2*/T1‐w and T2‐w with were generated by assigning organ intensities corresponding to those in FIESTA and FRFSE images, respectively. Results: In the phantom study, motion trajectories of the hypothesized ‘tumor’ matched excellently between the original T2*/T1‐w 4D‐MRI and the ‘enhanced’ T2‐w 4D‐MRI. Mean(±SD) absolute difference in motion amplitude was 0.66 (±0.62) mm. In the patient study, tumor and diaphragm motion trajectories closely matched between the two 4D‐MRIs: mean correlation coefficient was great than 0.97 in all directions; the mean (±SD) absolute difference in motion amplitude was smaller than 0.55(±0.19) mm. Tumor‐to‐tissue CNR was significantly improved from 7.57(±5.6) in the original 4D‐MRI to 23.75(±15.8) in the ‘enhanced’ 4D‐MRI. Conclusion: It is feasible to improve tumor‐to‐tissue CNR of T2*/T1‐w 4D‐MRI using the DIR method. The ‘enhanced’ 4D‐MRI retained comparable tumor motion information as the original 4D‐MRI. This work is partly supported by funding from NIH (1R21CA165384‐01A1) and a research grant from the Golfers Against Cancer (GAC) Foundation.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging