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Evaluating Image Quality of Cone Beam CT Systems: A Quantitative Approach


Aim: To develop an imaging strategy by evaluating image quality of three different CBCT scanners using a quantitative approach. Method: Hitachi CB MercuRay, iCAT Platinum and NewTom Vgi were selected. Density, water, and wire phantoms were scanned with multiple protocols from each CBCT. Image quality was assessed based on signal quality, noise level, and resolution by measuring voxel value stability, signal-to-noise ratio (SNR), noise, and modulation transfer function (MTF). A custom program was developed in Matlab to calculate MTF. Result: All three systems had Hounsfield (HU) values within the acceptable range for all four density inserts with Hitachi MercuRay had the highest variation in HU values due to consistently larger standard deviation. The SNR for NewTom, iCAT and Hitachi were 45.1, 27.9 and 11.7 respectively (P < 0.001). Hitachi had twice as much noise compare to that of NewTom Vgi and iCAT Platinum scanner (P < 0.001). Uniformity of signal within the volume from the most favorable to least were NewTom Vgi, Hitachi and iCAT Platinum. The approach used in this study to measure uniformity had some limitations. MTF were measured for each protocol to investigate the resolution of each system. The range of spatial frequency at MTF = 0.5 for Hitachi, iCAT and NewTom were 1.39-5.72, 2.95-7.13 and 6.05-7.01 respectively. Overall, NewTom Vgi and iCAT Platinum can resolve higher spatial frequency than Hitachi MercuRay. Conclusion: This project demonstrated that it is feasible to evaluate image quality with a quantitative approach and the objective assessment can aid in development of case-specific imaging strategy.

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