Characterization and modeling of a CT scanner by experimental measurements and software simulations

• Κύριος συγγραφέας: Αλεξανδροπούλου, Ολυμπία
• Άλλοι συγγραφείς: Καγκάδης, Γεώργιος
• Μορφή: Thesis
• Γλώσσα: English
• Έκδοση: 2021
• Θέματα: Equivalent source model; Computed tomography (CT); Μοντέλο ισοδύναμης πηγής; Αξονικός τομογράφος

In the present thesis, a method which generates X-ray source models is used for performing simulations of the multidetector row Canon Aquilion One Prism Edition scanner. The equivalent source model, as it is called, consists of an X-ray energy spectrum and filtration profile that are based entirely on measured values and can replace proprietary manufacturer’s data in simulations. Required measurements include the first half value layer (HVL1) and the bowtie description (dose values across the fan beam) for the Canon Aquilion One Prism Edition CT scanner. Using these measured values, we generate a spectrum with the HVLs approximately equal to those measured and this is the equivalent spectrum and then we determine a filtration shape and this is the equivalent filter that attenuates the equivalent spectrum the same way the actual filtration attenuates the actual X-ray beam. So, an equivalent source model is generated, using the spectrum based on HVL1 measurements and its respective filtration scheme. Then, simulations using the DukeSim CT simulation platform were evaluated using thissource model and through the comparison of CT dose index (CTDI) simulations to measured CTDI values for the specific Canon scanner using each kVp available and the large and medium filter. CTDI experiments were performed for both 16 cm in diameter (head) and 32 cm in diameter (body) CTDI phantoms. Then we calculated the percent error between each simulation and measurement result in order to evaluate the accuracy of the simulations that performed using the equivalent source model. The average error between the simulated and measured values is 2.1 % across both filters, all kVps and both phantom sizes. From the results we can say that the equivalent source model we created based on measured values can be used in place of manufacturer’s data for dosimetry simulations of a CT scanner. Additionally, real experiments were performed and evaluated. Real projection images of the Catphan phantom were acquired on the Canon Aquilion One Prism Edition CT scanner, under 40 and 150 mAs at 120 kV. CT number linearity, spatial linearity in x and y axes, low contrast detectability, uniformity and spatial resolution were assessed as image quality metrics to be evaluated in this thesis.