Abstract
Computed Tomography scanners equipped with system for Automatic Exposure Control (AEC) have been recently installed into clinical practice in Macedonia. Assessment of their AEC settings and performances is important task from patient doses and images quality point of view. This study was done by analyzing of CT examinations in patients in the City Hospital "8 September" in Skopje. The examinations were carried out by GE Bright Speed 16 slices scanner equipped with AEC system. In all patients were applied the same protocol with constant acquisition parameters was applied, and images were reconstructed by standard mode. Patient dimensions and image noise were measured from the scouts and axial images. From DICOM header the information related to dose, TCM and slice position were extracted. It was found that scanner automatic exposure system adjusts exposure mainly according to maximal patient lateral dimension (LR) and applying the same Noise Index (NI) value in patients with different size does not provides necessarily the same image noise level. In patients which LR dimension was less than 30 cm it was found that AEC adjusts tube current at the minimum of mA interval with no modulation throughout different body parts.
Highlights
In the last ten to fifteen years, there is a sharp increase in the number of installed CT scanners in the Republic of Macedonia
While in 2000 there were less than ten CT scanners, in 2013 there were more than 35 CT scanners installed on the territory of the Republic of Macedonia
It was found that scanner automatic exposure system adjusts exposure mainly according to maximal patient lateral dimension (Figure 3) with coefficient of correlation of 0.79 between CTDI value and LR dimension
Summary
In the last ten to fifteen years, there is a sharp increase in the number of installed CT scanners in the Republic of Macedonia. According to a European survey conducted in 2011 on the population doses from medical procedures, the number of available CT scanners in the Republic of Macedonia per million populations is higher than that of the United Kingdom or of Slovenia, for example [1]. This leaded to significant increase of the number and the type of performed CT examinations, as well as of the number of patients with multiple studies and follow-up examinations. With the introduction of faster multidetector CT scanners, various techniques have been developed to reduce the radiation dose to the patients. A key parameter affecting dose to the patient is the selected tube current–time product (mAs)
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