Teo, Siti Humairah Mohd Razlan
(2020)
Study on the effects of patient miscentring on radiation dose and image quality in CT imaging.
Masters thesis, Universiti Sains Malaysia.
Abstract
Incorrect setting of patient positioning on the treatment table always happened in
diagnostic imaging which leads to misinterpretation of data and degrades the image
quality. This study focuses to evaluate the effects of patient miscentring on patient dose
and image quality in CT imaging. The CT scan parameter, patient positioning information
was taken from the head and thorax-abdomen-pelvic protocols acquired in 128-slice
Siemens SOMATOM Definition AS + CT system. This study started with the
retrospective survey on patient miscentring shifting data by using data registration
(DoseWatch, version 1.2, GE Healthcare) to collect information about patient isocenter
shifting. The range of miscentring for minimum and maximum had been obtained and
will be used as guidelines in phantom studies. CTDI phantom and water phantom were
used in dose measurement and image quality assessment respectively. CTDIw is used to
calculate the dose across FOV of the phantom. In this study, isocentre shifting of both
axes (positive or negative axis) can cause an increase or a decrease of CTDIw across the
FOV. This research showed that the shift x- and y- axes and the phantom dose (CTDIw)
have weak correlation which is 0.1796 and -0.2127 respectively for the 16cm CTDI
phantom. While for 32 cm, the correlation is -0.3555 (weak) and 0.5582 (strong) between
both variables. In image quality assessment, SNR is observed. Miscentring of both axes
also associated with the quality of the image produced. There is no correlation between
x-axis shifting and SNR (r = -0.0267). However, the correlation between mean HU and
mean SD with the shift x-axis is weak. There is a strong positive association between the
y-axis shifting and the SNR (r = 0.8156). The correlation between mean HU and mean
SD also good with the y-axis.
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