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SU-G-IeP2-07: Investigation of 3D-Printed Phantoms for Synthetic CT Benchmarking in An MR-Only Workflow.

PURPOSE
As we move toward MR-only treatment planning, a need exists to develop multi-modality phantoms to benchmark synthetic CT (synCT) generation. We evaluated candidate materials for CT/MR compatible 3D printed phantoms to support MR-only planning.


METHODS
Overall, 14 different 3D printing molding thermoplastic and UV photopolymer products were evaluated. Product samples (5.35 cm diameter disks) were obtained of urethane and silicone products of varying durometer: ClearFlex (50 and 95), Task 12, Smooth-Cast (45D, 60-61D), ReoFlex (20 through 60), VytaFlex 10, Flex Foam-iT! 17 urethane products as well as DragonSkin 10 and SORTA-Clear 18 silicone rubbers. Standard clinical sequences (T1-weighted FFE, T2-weighted TSE, and balanced turbo field echo) were acquired on a 1.0T open bore MR-simulator. An ultra-short echo-Dixon sequence (TE1= 0.144s) was obtained to identify bone materials for our synCT pipeline. Irregular objects and organs were segmented from CT images and 3D printed using ABS and UV photopolymers. CT images were acquired and compared to MR.


RESULTS
ClearFlex, Task, Smooth-Cast, and Flex Foam-iT! products could not be visualized for any MR sequence. No urethane products were visible using T2-weighted images. VytaFlex 10 (CT range: -2 to 18HU) and Reoflex 20, 30, and 40 (CT range: -35 to -3HU) provided appreciable signal in both T1 and bTFE signals, while ReoFlex 50 and 60 (CT ranges: 8 to 35HU) provided distinguishable signal only in UTE images, thus rendering these materials as possible bone surrogate candidates. Silicone rubbers (DragonSkin 10 (CT range: 185 to 218HU) and SORTA-Clear 18 (CT range: 201 to 224HU)) were visible for all MR sequences used in our synCT pipeline. Irregular objects yielded appreciable signal in MR images with close congruence to CT.


CONCLUSION
Several candidate materials, including bone surrogates, were identified for 3D printed phantoms. Future work includes characterizing MR relaxation properties and performance at other field strengths. The submitting institution has research agreements with Philips Healthcare. Research sponsored by a Henry Ford Health System Internal Mentored Grant.