Congress:
EuroSafe Imaging 2021
Keywords:
Cardiac, Head and neck, Radioprotection / Radiation dose, CT, Diagnostic procedure, Calcifications / Calculi, Dosimetric comparison, Trauma
Authors:
D. P. Ivanova, M. Nedevska, D. Kostova-Lefterova, V. Groudeva, K. Romanova
DOI:
10.26044/esi2021/ESI-10764
Methods or background
The survey is performed with two different CT systems: 320-slice and 16-slice (Figure 1 and Figure 2).
Head and
cardiac CT examinations are involved in the current study.
In order to evaluate the patient exposure - volume computed tomography dose index (CTDIvol) and dose length product (DLP) are used. For additional analyses, the values for the tube voltage, tube current, pitch, beam width (NxT), slice thickness, number of slices and some patient data - sex, age and weight are also recorded. The survey is performed with patient and phantom data with constant exposure parameters for all examinations, except the changes in trot.
The phantom which is involved in the current investigation is used only on the 320-slice CT system. It is filled with water and consists of five cylinders with different density. In order to evaluate the image quality a calculation of the signal to noise ratio (SNR) and contrast to noise ratio (CNR) is made. For the calculations of the SNR and CNR, the Hounsfield units (HU1 and HU2) of two different cylinders from the phantom and the standard deviation (SD) of the water are used (Figure 3) with the following formulas:
- SNR = HU1/SD [2];
- CNR = (HU1 – HU2)/SD [2].
An additional calculation of the effective dose (ED) was made in order to estimate the radiologic risk:
- ED [mSv] = k-factor [mSv.mGy-1.cm-1]*DLP [3].