TU‐F‐17A‐04: Respiratory Phase‐Resolved 3D MRI with Isotropic High Spatial Resolution: Determination of the Average Breathing Motion Pattern for Abdominal Radiotherapy Planning

Abstract

Purpose:To develop a retrospective 4D‐MRI technique (respiratory phase‐resolved 3D‐MRI) for providing an accurate assessment of tumor motion secondary to respiration.Methods:A 3D projection reconstruction (PR) sequence with self‐gating (SG) was developed for 4D‐MRI on a 3.0T MRI scanner. The respiration‐induced shift of the imaging target was recorded by SG signals acquired in the superior‐inferior direction every 15 radial projections (i.e. temporal resolution 98 ms). A total of 73000 radial projections obtained in 8‐min were retrospectively sorted into 10 time‐domain evenly distributed respiratory phases based on the SG information. Ten 3D image sets were then reconstructed offline. The technique was validated on a motion phantom (gadolinium‐doped water‐filled box, frequency of 10 and 18 cycles/min) and humans (4 healthy and 2 patients with liver tumors). Imaging protocol included 8‐min 4D‐MRI followed by 1‐min 2D‐realtime (498 ms/frame) MRI as a reference.Results:The multiphase 3D image sets with isotropic high spatial resolution (1.56 mm) permits flexible image reformatting and visualization. No intra‐phase motion‐induced blurring was observed. Comparing to 2D‐realtime, 4D‐MRI yielded similar motion range (phantom: 10.46 vs. 11.27 mm; healthy subject: 25.20 vs. 17.9 mm; patient: 11.38 vs. 9.30 mm), reasonable displacement difference averaged over the 10 phases (0.74mm; 3.63mm; 1.65mm), and excellent cross‐correlation (0.98; 0.96; 0.94) between the two displacement series.Conclusion:Our preliminary study has demonstrated that the 4D‐MRI technique can provide high‐quality respiratory phase‐resolved 3D images that feature: a) isotropic high spatial resolution, b) a fixed scan time of 8 minutes, c) an accurate estimate of average motion pattern, and d) minimal intra‐phase motion artifact. This approach has the potential to become a viable alternative solution to assess the impact of breathing on tumor motion and determine appropriate treatment margins. Comparison with 4D‐CT in a clinical setting is warranted to assess the value of 4D‐MRI in radiotherapy planning.This work supported in part by grant 1R03CA173273‐01