Influence Of Image Quality On Dose Optimization In Conventional Radiology

The dose entering the skin (De) is the main parameter used to determine the irradiation
that a patient receives during a radiodiagnostic examination. The dose entering the skin
depends on parameters such as the charge (mAs), the tube voltage (kV), the focus-film
distance (DFF), the focus-skin distance (DFP). Thus the objective of our work is to reduce as much as possible the dose at the entrance of the skin while taking into account the quality of the resulting image. This was done through the determination of the De of four (4) anatomical regions explored, the comparison of these doses obtained with the international diagnostic reference levels (NRD) adopted in Cameroon, then the
comparison of the images obtained according to the dose at the entrance of the skin
used. We conducted a prospective study over a period of five (5) months from May 24
to September 15, 2017 in the imaging department of the Garoua Regional Hospital
(HRG). The data used come from 459 adult patients with a mass between 50 and 90 kg.
The evaluation of the dose at the entrance to the skin of the patients was done through
the Davies model and the determination of the quality of the image using the Michelson
process and the Davies model, then the calculations of the 75th percentiles of the dose
at the entrance and the analysis and processing of the data was done by Excel 2010 and
Sphinx version 4.0. The doses at the entrance to the skin obtained in mGy were
respectively 5.05 ± 0.4 for the thorax, 13.84 ± 0.5 for the pelvis, 21.00 ± 5.1 and 149.18
±9.9 for AP and lateral views of the lumbar spine, 17.85 ± 2.5 for AP views / 10.52 ± 0.9
for skull profile. This study led us to understand that the 75ths the dose at the entrance
to the skin varies very little with the DFF / DFP ratio (the value 1 which translates the
absence of blur) and rather we obtain a maximum contrast with the values elevated by
75ths of the dose on the surface of the skin. The maximum contrast represents the
visibility of each pixel in black and white, whereas with a small value of 75ths of the
dose to the skin, the contrast is zero. The result of all these variations is that the quality
of the image remains clinically diagnostic according to the values considered in our
study.