Room: AAPM ePoster Library
Purpose: To compare image quality of the 2D true fast imaging with steady-state precession (TrueFISP) cine Cartesian and radial sequences available on a 0.35 T MRI-Linac.
Methods: We compared the default 4 frames/s (fps) 2D Cartesian TrueFISP cine MRI with the new 8 fps 2D radial TrueFISP cine MRI using the 0.35 T MRI-Linac (ViewRay, Mountain View). Sequences were compared using a QUASAR MRI4D (Modus Medical Devices Inc.) phantom and in healthy volunteers. The moving phantom cylinder was filled with gelatin and included a peeled hard-boiled egg and mortadella (pork, cheese, and pistachios) for image contrast. Radial TrueFISP parameters were: TE/TR: 1.38; 500 ms (2.8 ms echo spacing); FA: 110°; FOV: 350 mm; Voxel: 2.4x2.4x7 mm; Matrix: 144; Radials: 176; frames are updated each 1/4 of k-space (44 radials); BW: 890 Hz/pixel. Cartesian TrueFISP parameters were: TE/TR: 0.91/2.1 ms (asymmetric echo); FA: 60°; FOV: 350 mm; Voxel: 3.5x3.5x7 mm; Matrix: 100x100; BW: 1351 Hz/pixel; GRAPPA 2; Averages: 2.
Results: Image quality and contrast differed between the two sequences. The radial images had higher resolution and better image quality except in the presence of rapid motion where signal dephasing and blurring were observed. Both Cartesian and radial images looked highly smoothed on the treatment delivery system versus the MRI subsystem which reduced the image dynamic range and inherent contrast.
Conclusion: There are tradeoffs between the radial and Cartesian images. The radial acquisitions are superior for stationary or slow moving targets. The Cartesian image signals are more stable for rapid moving targets. Further work is required to assess the effects of the image acquisition method on target tracking accuracy and gating latency.
Funding Support, Disclosures, and Conflict of Interest: Dr. Mutic has previously consulted for ViewRay. He currently consults for Varian Medical Systems. Dr. Green has received speaking fees from ViewRay. Washington University in St. Louis has a Master Research Agreement with, and may receive financial support from, Viewray.
MRI, Image-guided Therapy, Low-field MRI