FireWire-based Vision System Inspects X-ray Dosimeter Badges; Checks for Potential Radiation Exposure

To check for radiation exposure, a German company developed a FireWire- based camera vision system that helps inspect and analyze film badges, or dosimeters, of individuals with potential exposure.

The Helmholtz-Zentrum Co. of Munich is responsible for the analysis of approximately 120,000 film badge dosimeters a month, a task that once was performed manually and now is done using a machine.

To speed inspection and increase reliability, Helmholtz-Zentrum developed a machine-vision system to automatically inspect these films. The film from each dosimeter is first mounted on a plastic adhesive foil, which is wound into a coil. This coil is then mounted on the vision system so that each film element can be inspected automatically.

Then, to analyze each film, a DX4 285 FireWire camera from Kappa optronics (Gleichen, Germany) is mounted on a bellows stage above the film reel. Data from this camera is then transferred to a PC and processed using Halcon 9.0.

Before the optical density of the film is measured, its presence and orientation must be determined. As each film moves under the camera system’s field of view, this presence and orientation task is computed using Halcon’s shape-based matching algorithm.

Both the camera and a densitometer are used to measure the optical density of the film. The densitometer measures the brightness at each of seven points on the film in high precision and is used to calibrate the camera measurement for every film image.

To increase the dynamic range of the gray-level image of the film, two images with different exposure times are computed and combined into a high-dynamic-range image. Because the background lighting is not homogenous, shading correction is performed to eliminate any lighting variation. Any lens vignetting and variations caused by pixel-to-pixel sensitivity variation is eliminated by flat-field correction.

To pinpoint the specific causes of x-ray exposure, the system is also programmed to detect whether any potential exposure is caused by errors in film developing or x-ray contamination. If the imaging system detects contamination events, these are then reported manually.