Medical physics evaluation of different portable dental X-ray units

Introduction
Recently developed portable dental X-ray units increase the mobility of the forensic odontologists and allow more efficient X-ray work in a disaster field, especially when used in combination with digital sensors. This type of machines might also have potential for application in remote areas, military and humanitarian missions, dental care of patients with mobility limitation, as well as imaging in operating rooms.

Objective
To evaluate radiographic image quality acquired by three portable X-ray devices in combination with four image receptors and to evaluate their medical physics parameters.

Materials and methods
Images of five samples consisting of four teeth and one formalin-fixed mandible were acquired by one conventional wall-mounted X-ray unit, MinRay® 60/70 kVp, used as a clinical standard, and three portable dental X-ray devices: AnyRay® 60 kVp, Nomad® 60 kVp and Rextar® 70 kVp, in combination with a phosphor image plate (PSP), a CCD, or a CMOS sensor. Three observers evaluated images for standard image quality besides forensic diagnostic quality on a 4-point rating scale.

Furthermore, all machines underwent tests for occupational as well as patient dosimetry.

Results
Statistical analysis showed good quality imaging for all system, with the combination of Nomad® and PSP yielding the best score. A significant difference in image quality between the combination of the four X-ray devices and four sensors was established (p < 0.05).

For patient safety, the exposure rate was determined and exit dose rates for MinRay® at 60 kVp, MinRay® at 70 kVp, AnyRay®, Nomad® and Rextar® were 3.4 mGy/s, 4.5 mGy/s, 13.5 mGy/s, 3.8 mGy/s and 2.6 mGy/s respectively. The kVp of the AnyRay® system was the most stable, with a ripple of 3.7%. Short-term variations in the tube output of all the devices were less than 10%. AnyRay® presented higher estimated effective dose than other machines.

Occupational dosimetry showed doses at the operator's hand being lowest with protective shielding (Nomad®: 0.1 μGy). It was also low while using remote control (distance > 1 m: Rextar® <0.2 μGy, MinRay® <0.1 μGy).

Conclusions
The present study demonstrated the feasibility of three portable X-ray systems to be used for specific indications, based on acceptable image quality and sufficient accuracy of the machines and following the standard guidelines for radiation hygiene.

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