| Περίληψη: | 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.
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