Does altering the exposure parameters (kV and mAs) affect the entrance skin dose and image quality of paediatric patients undergoing extremity imaging using DR equipment?

Abstract

Background
The field of radiography has seen tremendous advancement in the technologies used to capture and store images. The radiation dose received by patients is kept As Low As Reasonably Achievable (ALARA), whilst producing a diagnostic X-ray. The introduction of
Direct Radiography (DR) has been reported to reduce the image quality, and manufacturers are promoting a change in practice from historical imaging techniques. Limited literature is available to support changing practice, causing unrest within the radiographic workforce.

Aim
Identify how radiology departments can achieve optimum image quality at the lowest radiation dose to the paediatric patient. The study aimed to firstly evaluate current practice by measuring the effect that manipulating exposure parameters (kV and mAs) has on
Entrance Skin Dose (ESD) and image quality (IQ) for paediatric patients undergoing DR imaging of their extremities; and secondly to compare the performance (as defined by ESD and image quality across a range of kV and mAs settings) of two different pieces of DR equipment currently in service within the researchers NHS Trust.

Method
A local evaluation of current practice was undertaken on two different DR systems (DR1 and DR2). Quantitative experiments across a range of exposure parameters (40-63kV and 0.63-
3.1mAs) assessed the effects on ESD and image quality. A patient phantom enabled simulation of a paediatric extremity skin surface. IQ was assessed by three consultant radiologists. Both ESD and IQ results were statistically analysed using a combination of
parametric and non-parametric tests.

Results
All images assessed were of diagnostic image quality. DR1 produced lower ESD and improved image quality compared to DR2. ESD was lowest at 63kV / 0.63mAs on both DR1 and DR2. Optimum contrast was achieved at 42kV / 3.1mAs on DR1 and 40kV / 2.5mAs on DR2. Resolution was highest at 63kV / 0.63mAs for DR1, and did not vary for DR2.

Conclusion
Image contrast was improved with little increase to the ESD on both DR1 and DR2 when using a low kV, high mAs combination. This study has highlighted differences in both radiation output and image quality between the two DR systems currently in service. Further clinical evaluation is warranted to investigate the reasons for this.

Date of Award	2017
Original language	English
Awarding Institution	Coventry University
Supervisor	Doug Thake (Supervisor), Jane Coad (Supervisor) & Theresa Morton (Supervisor)