Introduction: There are two different ways of collecting data with computed tomography, the sequential and spiral. In the sequential mode a single rotation of the X-ray tube enables to acquire the image of as many numbers of slices as there are different types of detectors, but after every X-ray tube rotation, we have to reposition the patient to the next desired cut. The spiral mode brought a shorter examination time through the development of the computed tomography technology. Purpose: The purpose of our thesis is to describe the protocol for the sequential and spiral imaging, the differences between them and to evaluate obtained differences in acquired values of DLP for both methods of imaging. Methods: We used a retrospective descriptive or descriptive method of collecting data for our thesis, since we obtained our data from previously performed imaging, that was conducted on a 16-slice machine Siemens CT Sensation at University Medical Centre Ljubljana, Institute of Radiology. We will analyse twenty patients referred for thorax CT, half of which (five women, five men) were referred for a sequential CT imaging and the other half for a spiral CT imaging. Results: In interpreting and analysing acquired CT images, we were able to compare the radiation dose that the patients obtained with the help of certain parameters that determine the interpretation of the patient’s dose load at CT imaging; DLP, CTDIvol and the length of the scan. We verified the DLP values that are given on the computer screen at the end of the imaging with the help of a known equation for calculating DLP. In average the DLP in spiral imaging is 164% higher in comparison to sequential imaging. Kolmogorov-Smirnov’s test of normality showed the significance p > 0,05, the t-test for independent samples showed the significance less than 10-3. Discussion: Spiral method of imaging thorax is used in cases of tumours and sequential in discussion about interstitial lung diseases. Because there are significant differences in DLP values between both methods and since CT imaging is an increasingly used diagnostic imaging method, it is important that as radiological engineers we pay attention to all the parameters that determine the patient’s dose load in accordance with ALARA principles. The most important part is choosing suitable method of imaging according to the referred diagnosis and primarily to assure justification of every CT imaging. This research could be used in further examinations of the protocols and doses in thorax area thus their optimisation.
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