Improving the quality of reconstructed X-ray CT images of polymer gel dosimeters: zero-scan coupled with adaptive mean filtering.
This study evaluated the feasibility of combining the 'zero-scan' (ZS) X-ray computed tomography (CT) based polymer gel dosimeter (PGD) readout with adaptive mean (AM) filtering for improving the signal to noise ratio (SNR), and to compare these results with available average scan (AS) X-ray CT readout techniques. NIPAM PGD were manufactured, irradiated with 6 MV photons, CT imaged and processed in Matlab. AM filter for two iterations, with 3 × 3 and 5 × 5 pixels (kernel size), was used in two scenarios (a) the CT images were subjected to AM filtering (pre-processing) and these were further employed to generate AS and ZS gel images, and (b) the AS and ZS images were first reconstructed from the CT images and then AM filtering was carried out (post-processing). SNR was computed in an ROI of 30 × 30 for different pre and post processing cases. Results showed that the ZS technique combined with AM filtering resulted in improved SNR. Using the previously-recommended 25 images for reconstruction the ZS pre-processed protocol can give an increase of 44% and 80% in SNR for 3 × 3 and 5 × 5 kernel sizes respectively. However, post processing using both techniques and filter sizes introduced blur and a reduction in the spatial resolution. Based on this work, it is possible to recommend that the ZS method may be combined with pre-processed AM filtering using appropriate kernel size, to produce a large increase in the SNR of the reconstructed PGD images.
Department of Physics and Applied Mathematics (DPAM), Pakistan Institute of Engineering and Applied Sciences, Nilore, 45450, Islamabad, Pakistan.
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Kakakhel
I.K. Barber School of Arts and Science, University of British Columbia, Okanagan Campus, Vancouver, BC, Canada.
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Jirasek
Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 2Y2, Canada.
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Johnston
Genesis Cancer Care Queensland, Brisbane, QLD, Australia. t.kairn@gmail.com.|Science and Engineering Faculty, Queensland University of Technology, Brisbane, QLD, Australia. t.kairn@gmail.com.
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Kairn
Science and Engineering Faculty, Queensland University of Technology, Brisbane, QLD, Australia.
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D000465:Algorithms; D005782:Gels / Q000737:chemistry*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000592:standards*; D011108:Polymers / Q000737:chemistry*; D000072232:Radiation Dosimeters / Q000592:standards*; D012015:Reference Standards; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed / Q000592:standards*
D005782:Gels; D011108:Polymers
Adaptive mean filtering; Average scan; Gel dosimetry; Radiation therapy; X-ray CT; Zero-scan image