Supervisors info:
Ιωάννης Δαμηλάκης, Καθηγητής Ιατρικής Φυσικής, Πανεπιστήμιο Κρήτης
Κώστας Περισυνάκης, Αναπληρωτής Καθηγητής Ιατρικής Φυσικής, Πανεπιστήμιο Κρήτης
Μιχάλης Μαζωνάκης, Επίκουρος Καθηγητής Ιατρικής Φυσικής, Πανεπιστήμιο Κρήτης
Summary:
Over the past years, along with the growth rate, the number of CT examinations has also increased, thereby burdening patients with radiation dose. The dosimetric quantities used are CTDIvol and DLP, which are used as dose “indexes” and “descriptors”. The quantity that is the most closely associated with cancer risk (due to CT examination dose) is the effective dose. It allows comparison of radial risk associated with partial or whole body exposure, and takes into account the difference in radiosensitivity of various organs of the human body, as well as the type of radiation that is absorbed by each organ.
Apart from the radiation dose, an important parameter in the evaluation of a CT system is the image quality, which is associated with features such as image noise, signal-to-noise ratio (SNR), spatial resolution and artefacts.
In this study, we made a comparison between the two CT systems that are installed at General University Hospital of Heraklion (Siemens Somatom Sensation 16: 16 slices CT and GE Revolution GSI: 64 slices CT) in terms of dose (CTDIvol , DLP, effective dose) and also in terms of image quality (image noise, SNR) for the following examinations: head, thorax, abdomen, thorax and abdomen (together). The patients for these examinations were exclusively adults. For studying image quality, some specific regions
were selected (identical for all the patients) by using ROI, for each anatomical region to be imaged.
Οne of the main results obtained, is that the radiation dose is greater for the Siemens machine only for head examinations. For the other types of CT examinations, GE’s CT system burdened the patients with higher radiation dose. Concerning image quality, for head examinations, both sequential and helical scanning, image noise is lower and signal-to-noise ratio is higher for the Siemens machine, in comparison to the corresponding values of that of GE. For thorax examinations, image noise is lower and signal-to-noise ratio higher for the Siemens’ scanner in the aorta, while noise and SNR values in the heart and in the breast, vary approximately at the same level without great discrepancies for the two in-comparison CT systems. Moreover, for abdomen examinations, noise in aorta, liver and spleen is lower for the Siemens machine with simultaneous superiority on SNR values for examinations with contrast and simple examinations (without contrast). In regards to the last type of examination that was studied, thorax and abdomen together, seemed that in case of the thorax, the Siemens machine may had increased noise levels compared with that of GE’s in the aorta, heart and breast, but at the same time signal-to-noise ratio was also increased, except in the heart. In general, in case of abdomen, SNR is higher for the Siemens CT system, while the noise of this machine is lower compared with that of GE scanner.
