Introduction: Computed tomography devices differ in their technical characteristics. Different indications require the use of unique protocols for each examination. Establishing protocols increases diagnostic efficacy while reducing potential harm to the patient. Due to the risks associated with radiological imaging, the principles of radiation protection must be observed, as well as the ways to reduce patient dose and ensure good image quality. Purpose: The purpose was to determine the difference in image quality on all five CT devices of the Ljubljana Institute of Oncology and to present the findings in connection to the difference in dose of ionizing radiation received by patients in computed tomography diagnostic imaging of the chest. Methods: We have imaged a total of 19 primary and addition protocols using the standard chest and abdomen CT protocol used in the Department of radiology. It was the starting point of scanning parameters on the basis of which we adjusted protocols on other devices in order to obtain the same imaging conditions. We continued scanning with a protocol of our own, for which we determined the imaging parameters ourselves and used it on other devices. 5 radiology specialists evaluated the obtained images according to the European guidelines on qualty criteria for computed tomography. Results: The results show that with the exception of one pair of physicians, there is a similarity of assessment. More than half of the comparisons were statistically significant, meaning that these physicians gave the same estimates. The Philips device protocol no. 7 is the best-rated physician protocol (3.97), and the GE SPECT-CT protocol no. 19 is the worst-rated (1.89). The first protocol of the Siemens AS + device had the lowest dose values (DLP 67 mGy cm, CTDI 1.86 mGy). Philips protocol no. 10 causes the highest dose rate (DLP 568.9 mGy cm, CTDI 16.23 mGy). Discussion and conclusion: We have shown that image quality is influenced by the choice of a single protocol, mainly due to automatic exposure control, iterative reconstruction and voltage selection. Protocol no. 1 Siemens AS + device causes the lowest dose for patients. When we, due to the almost 6x higher dose, ignore the Philips protocol no. 7 which has slightly better image quality, we can say that Siemens AS + also produces the best quality images. The research showed which devices are comparable to each other and with what settings they can be used to obtain the same image quality with the lowest possible radiation dose.
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