Radiation Safety

Fluoroscopy machine settings and dose

Optimizing Machine Settings in Fluoroscopy: Balancing Accuracy and Exposure

When radiation is involved in our work, we take steps to minimize the exposure of our staff to radiation using protective gear. In addition to the equipment itself, machine-specific settings can also be used to minimize patient and staff exposure. There are several factors that can affect the amount of dose exposed, including the size of the field, the chosen kVp, and the rate of pulse per second. When actions are taken to minimize patient exposure, staff exposure is also minimized.

In order to adjust the machine settings to minimize our exposure while maintaining adequate image quality in line with the ALARA (as low as reasonably achievable) principle, we must fully understand their effects.

One simple approach to minimizing the patient and staff exposure is the collimated field size. The exposure is directly related to it; this means collimating tightly to the area of interest. Working with a rectangular field it is sometimes useful to rotate the field so that it covers the entire area of interest without having to widen it. Furthermore, in fluoroscopy the use of electronic magnification can add to the dose exposure and should not be applied more than practically necessary [1].

It is also possible to influence exposure in fluoroscopy by reducing the pulse rate and the fluoroscopic film rate. You can do this more or less easily depending on the procedure. Coronary angiography, for example, usually has pulse rates between 7.5 and 15 pps. According to some studies, you can get away with 3 pps if you change the post processing parameters [2].

The tube current (mA) and exposure time (s) effectively have the same effect on the dose, as one sets the amount of photons generated and the other decides for how long this happens. Finding the right balance for tube current and exposure time is decided by the tube's technical limitations (the higher the current the quicker the tube wears) and the patient's ability to hold still ( e.g. children are often exposed for shorter times with a higher tube current). Changes in kVp affect radiation dose, exposure, and image contrast.

Increasing the kV reduces the exposure of the patient and especially to the skin exposed by the beam. This is because the higher kV produces radiation with increased penetration through the patient’s body and less radiation is required at the entrance surface to produce the necessary exposure to the image receptor. The other factor that must be considered in selecting the appropriate kV value is the effect on image contrast. In general, lower kV values produce increased image contrast. This can be especially significant in fluoroscopy when using iodine contrast media. 

The points mentioned above show that there is a fine balance between improving the image quality and unnecessary patient/ staff exposure. It is our responsibility as professionals to find the accurate balance and minimize exposure while being able to perform successfully.

Education is a key to ensure practitioners remain well aware of these factors. Along with theoretical and clinical training, Virtual Reality provides a safe and accessible environment for students to test themself and explore those boundaries. Studies have shown that simulation training increases the ability and confidence of students to protect themselves. The availability of operating theaters is also very limited, so having a virtual room can provide students with more regular exposure. [3] With Virtual Medical Coaching's radiation safety simulation, current and future medical professionals can learn about interventional radiology and visualize radiation and its dose in the operating room. Research from University College Dublin using our simulation found that radiography and medical students experienced increased confidence through VR learning, particularly in understanding radiation safety matters [4]. Through immersive and engaging experiences, learners are able to visualize the practical application of theoretical concepts in a realistic setting, overcoming some of the common challenges to learning.

[1] https://www.iaea.org/resources/rpop/health-professionals/radiology/radiation-protection-in-fluoroscopy/good-practices-in-fluoroscopy

[2] Badawy MK, Scott M, Farouque O, Horrigan M, Clark DJ, Chan RK. Feasibility of using ultra‐low pulse rate fluoroscopy during routine diagnostic coronary angiography. J Med Radiat Sci 2018; 65: 252–8. 

[3] “Time for a simulation strategy?” by Naomi Shiner, NTF, SFHEA, DPrac, PgCert, PgCert, BSc, J Med Radiat Sci 70 (2023) 106–108

[4] Rainford, L., Tcacenco, A., Potocnik, J., Brophy, C., Lunney, A., Kearney, D., & O'Connor, M. (2023). Student perceptions of the use of three-dimensional (3-D) virtual reality (VR) simulation in the delivery of radiation protection training for radiography and medical students. Radiography (London, England. 1995), 29(4), 777-785. https://doi.org/10.1016/j.radi.2023.05.009

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