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Evaluation of Phantoms Used in Image Quality Performance Testing of Dental Cone Beam CT Systems

H Alahmad

H Alahmad1*, K Krugh2 , (1) University of Florida, Gainesville, FL, (1) University of Toledo Medical Center, Toledo, OH (2) University of Toledo Medical Center, Toledo, OH


SU-H4-GePD-I-6 (Sunday, July 30, 2017) 4:30 PM - 5:00 PM Room: Imaging ePoster Lounge

Purpose: To evaluate the available phantoms as a tool for image quality assessment of dental CBCT units.

Methods: Two commercially available phantoms were evaluated; ACR CT phantom (Gammex 464) and CATPHAN (Phantom Laboratory). Additionally, A prototype dental CT phantom (CIRS Inc.) was evaluated. Scans were made on three different machines; i-CAT Classic (Imaging Sciences International), ILUMA (IMTEC/3M) and GALILEOS Comfort (Sirona). A total of eight protocols with different parameters were used. A CT scan of the phantoms were also performed with a conventional CT (Toshiba Aquilion 16) to verify the pixel values. Image noise and uniformity, pixel value accuracy and linearity, contrast scale, and high contrast spatial resolution of the images were evaluated. The image analysis was done using ImageJ software (NIH).

Results: The image noise in the ACR and CATPHAN phantoms was found to be approximately double that in the prototype phantom. For the uniformity test, the average difference in the pixel values between center and periphery was the least for the prototype phantom. While pixel values were found to be linear as compared to CT number, the larger diameter phantoms demonstrated an overall decreased pixel value (-500 for water) and a diminished contrast scale. The prototype phantom was found to maintain CT number accuracy and a 1.0 contrast scale. The CATPHAN provided the best measure of high-contrast resolution (8 lp/cm for the 20 second scan).

Conclusion: There is not one phantom evaluated that provided superior results for all image quality tests. The prototype phantom was adequate for all tests with the exception of the high contrast resolution test whereas the ACR phantom and the CATPHAN due to larger diameter relative to the prototype demonstrated higher noise and non-uniformity, pixel value inaccuracy, and lower contrast scale because of more beam hardening artifact occurring with the large diameter.

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