June 2020, Vol. 12, No. 2  AJHPE         50

Short Communication

Why was the idea necessary?
Digital X-ray imaging systems have a wide, dynamic exposure latitude that 
allows almost 500 times the exposure necessary to produce optimal diagnostic 
images.[1,2] Consequentially, patients may receive more exposure to ionising 
radiation than necessary to produce an image of optimal diagnostic quality. 
A recent study showed that ~54% of radiographers understood and used 
indicators of exposure in digital X-ray imaging systems.[3] With just more 
than half of radiographers understanding and using indicators of exposure 
in digital X-ray imaging systems, enhancing radiographers’ understanding 
of exposure technique factors (kilovoltage peak (kVp), milliampere and the 
exposure time (mAs)) in digital X-ray imaging systems is needed to curtail 
unnecessary exposure to ionising radiation. 

Ethical approval for the study was obtained from the Faculty of Health 
Sciences Research Ethics Committee, University of Johannesburg (ref. no. 
REC-234-2019).

What was tried?
A structured tutorial demonstrating the effect of mAs on image quality in 
digital X-ray imaging systems was tried. Four radiographs were taken of a 
hand phantom, using a constant kVp, focal film distance (FFD), focal spot 
size, 4-sided collimation and the same computed radiography (CR) (a type 
of digital X-ray imaging system) cassette. Only the mAs changed for each 
exposure (exposure refers to each time the radiograph is taken and the 
phantom hand is ‘exposed’ to ionising radiation) (Fig. 1A-D). Before the 
tutorial, students needed to predict the image quality for each exposure. After 
the tutorial, students compared their predicted outcomes with the actual 
outcomes. Dose area products (DAPs), exposure indicators (EIs) and image 
quality for each exposure without any image post-processing were tabulated. 
Students then evaluated and reported the effect of mAs. The resultant images 
and exposure technique factors are indicated in Fig. 1.

The effect of mAs on image quality in digital X-ray imaging systems was 
observed. It was noticeable that at higher than standard optimum mAs, the 
image quality was preserved (acceptable mAs for a posteroanterior (PA) 
projection of a hand for the X-ray unit used in the tutorial was 2.5 mAs 
(Fig. 1B)). However, with higher mAs, there was a congruent increase in the 
dose to the phantom (DAP). Students predicted that for the exposure technique 
factors used in Fig. 1C and Fig. 1D, they would not be able to observe an 
image, but acceptable images were obtained. Students predicted a contrary 
outcome, despite learning the theory of the wide dynamic exposure latitude 
of digital X-ray imaging systems and seeing images similar to those in Fig. 1 
in the literature. Therefore, using a blended teaching approach provided an 
opportunity for students to experiment with varied mAs to enhance their 
understanding of the effect of mAs on image quality in digital X-ray imaging 
systems. 

Declaration. None.

Acknowledgements. Thank you to the students who voluntarily participated in 
the tutorials.
Author contributions. Sole author.
Funding. None.
Conflicts of interest. The author lectures the students who participated in the 
tutorial. 

1. Moore QT, Don S, Goske MJ, et al. Image gently: Using exposure indicators to improve pediatric digital 
radiography. Radiol Technol 2012;84(1):93-99. 

2. Don S, Whiting BR, Rutz LJ, Apgar BK. New exposure indicators for digital radiography simplified for radiologists 
and technologists. Am J Radiol 2012;199(6):1337-1341. https://doi.org/10.2214/AJR.12.8678

3. Lewis S, Pieterse T, Lawrence H. Evaluating the use of detector dose indicators in digital X-ray imaging systems. 
Radiography (Lond) 2019;25(3):e58-e62. https://doi.org/10.1016/j.radi.2019.01.003

Accepted 28 January 2020.

Afr J Health Professions Educ 2020;12(2):50. https://doi.org/10.7196/AJHPE.2020.v12i2.1261

Exposure technique factors in digital X-ray imaging systems:  
Demonstrating the effect of mAs
S Lewis, MTech: Radiography

Department of Medical Imaging and Radiation Sciences, Faculty of Health Sciences, University of Johannesburg, South Africa

Corresponding author: S Lewis (shantell@uj.ac.za )

This open-access article is distributed under 
Creative Commons licence CC-BY-NC 4.0.

A B

C D

Fig. 1. Images from the demonstration: (A) 45 kVp/0.5 mAs. (B) 45 kVp/2.5 mAs. 
(C) 45 kVp/200 mAs. (D) 45 kVp/400 mAs.

https://doi.org/10.2214/AJR.12.8678
https://doi.org/10.1016/j.radi.2019.01.003