Scattering of X-rays in diagnostic radiology : computed radiography, digital radiography, mobile digital radiography and mobile C-arm fluoroscopy

Abstract

The medical use of X-ray-based imaging modalities has increased in the last decade. During imaging scattered radiation is generated, and the staff can be exposed to it in various situations, including when holding the patient or conducting an interventional operation. To be able to minimize the exposure it is essential to have knowledge of the distribution of the scattered radiation. In this study scattered radiation maps where implemented based on direct measurements with dosimeters in various distances, angles and heights using an anthropomorphic phantom as a scattering object. Measurements were done using multiple imaging modalities and parameters. Maps were intended for educational purposes to be used in the radiation protection training of the staff.

Thorax PA and LAT measurements in a standing position demonstrated that the scattered radiation is directed strongly back from the phantom towards the X-ray tube. Scatter intensity being stronger in the LAT imaging. On the other hand, pelvis AP measurements in a supine position demonstrated that the radiation is directed relatively equally to all directions when the horizontal plane perpendicular to the primary beam central axis is considered. The use of the pelvic shield in Thorax measurements and the radiation protection blanket in Pelvis measurements did not affect scattering with the applied measurement method. Also using 50kg weighing child’s imaging parameters did not have effect on the scattering as the same phantom was used.

Measurements done using fluoroscopy with urological experiment parameters demonstrated that the scattered radiation is directed relatively equally to all directions when the horizontal plane perpendicular to the primary beam central axis is considered. However, there is an emphasis on the scatter at the end of the patient table where the operating physician would be positioned, and accordingly a decrease on the scatter at the opposite end. The use of the lamella radiation protection curtain on the physician’s end of the operation table decreased the measured dose rates of the dosimeter, that was placed lower than patient table surface level and therefore was shielded by the curtain.

Bedside Thorax measurements with a mobile imaging system demonstrated that the scattered radiation is directed relatively equally to all direction when the horizontal plane perpendicular to the primary beam central axis is considered. Also, when these measurements are compared to the previous stationary Thorax measurements, it is evident that scattered radiation dose rates with the mobile system are lower.

As the used dosimeter system measures personal dose equivalent Hp(10) rate, the cumulative dose values calculated based on the exposure time can be used as an estimate of the overall effective dose. Dose received by the healthcare professionals is small in Thorax and Pelvis imaging in a possible holding situation when compared to the annual dose limit of radiation workers. On the other hand, the estimated dose of the physician is clearly higher in a fluoroscopy-guided urological operation. Yet the magnitude of the physician’s dose is on the level that it is unlikely to exceed the annual dose limit. Lowest estimated effective doses were gotten in the bedside Thorax examination, where the dose received by the personnel correspond to 12 and 8 seconds of background radiation on 0.7- and 1-meter distances to the scatter radiation origin, respectively.