Maximum intensity projection (MIP) imaging using slice‐stacking MRIa)

PURPOSE: To evaluate the feasibility of acquiring maximum intensity projection (MIP) images using a novel slice-stacking MRI (SS-MRI) technique. METHODS: The proposed technique employed a steady state acquisition sequence to image multiple axial slices. At each axial slice, the scan is repeated throughout one respiratory cycle. Four objects (small, medium, and large triangles, and a cylinder) moving with a patient breathing trajectory were imaged repeatedly for six times using the slice-stacking MRI and 4D-CT. MIP(SS-MRI) and MIP(4D-CT) were reconstructed. The internal target volume (ITV) was segmented for each object on the six scans and compared between MIP(SS-MRI) and MIP(4D-CT). The medium triangle was also imaged with various motion patterns using slice-stacking MRI, 4D-CT, and sagittal cine-MRI. The corresponding MIP images were reconstructed and volume/area measurements were performed and compared between different imaging methods. Three healthy volunteers underwent the slice-stacking MRI and sagittal cine-MRI scans. A region of interest (ROI) was selected and contoured for each subject in both MIP(SS-MRI) and MIP(cine-MRI). The area of the selected ROI was computed and compared. RESULTS: Volume comparison between MIP(SS-MRI) and MIP(4D-CT) showed statistically insignificant (p > 0.05 in all cases) difference in the mean ITVs for all four objects. For the study of the medium triangle with multiple motion patterns, there was a good agreement in the measured ITVs between MIP(SS-MRI) and MIP(4D-CT) (p = 0.46, correlation coefficient = 0.91), with a mean difference of 1.4% +/- 4.4%. The area measurements between MIP(SS-MRI) and MIP(cine-MRI) also showed good agreement (p=0.47, correlation coefficient = 0.97), with a mean difference of 0.2% +/- 2.9%. For the healthy volunteer study, the average difference in the area of selected ROI was -2.5% +/- 2.5% between MIP(SS-MRI) and MIP(cine-MRI). CONCLUSIONS: These preliminary results showed good agreement in volume/area measurements between the slice-stacking MRI technique and 4D-CT/cine-MRI, indicating that it is feasible to use this technique for MIP imaging.