A year and a half ago, an Adora RSA was installed at Sahlgrenska University Hospital/Mölndal Hospital for stereo and regular X-ray examinations. Adora RSA has two X-ray tubes along with two detectors plus a smaller size detector.
RSA is an abbreviation for RadioStereometric Analysis. It is called stereo as two X-ray tubes are angulated to make the beams cross. The object needs to be in the crossing point and the detectors are placed in a calibration cage. The calibration cage defines a three-dimensional coordinate system which is used in the analysis of the images. Despite the double exposure, stereo examinations give considerably lower X-ray dose as the images are exposed at very high kV.
Stereo examinations are made on research patients with tantalum markers placed adjacent to a prosthesis, most commonly a hip prosthesis, but it can also be performed on e.g. knees and shoulders. By using stereo X-ray it is possible to determine if the prosthesis is worn, has moved or if there is instability in the joint. The advantage is an accuracy of 0.1 mm compared to 5 mm in regular X-ray.
X-ray nurses can change between regular X-ray and stereo examinations through pre-programmed auto-positions and a few manual steps. The patient table is turned aside and the calibration cage holding the detectors is placed under the table and brought into position. The table is turned back, and as the table is floating, it is easy to adjust the position of the patient. When the room isn’t used for research patients, the master tube is used for regular X-ray. The flexibility in regular X-ray examinations is equal to other Adora solutions even if the RSA tube is positioned in the ceiling unit and moves along the system.
Last Summer, the Adora RSA was upgraded to Adora RSA+RF thus adding fluoroscopy and serial imaging functionality. Fluoroscopy is a great advantage with regular X-ray examinations as certain prosthesis need to be projected in exact perpendicular angle which saves dose for the patient. Serial imaging enables dynamic examinations in stereo where the patient moves whilst images are exposed in a series.
Previously, a normal examination room and a mobile X-ray unit was used to set up manually for stereo examinations – it took a long time and required much accuracy. The exposure was done by pressing two exposure buttons at the same time, but the Adora RSA features one single exposure button to activate both tubes within milliseconds. After stereo examination, the patient had to be moved to a different room for regular X-ray, but now it is just a matter of selecting an auto-position, and the Adora automatically shifts between regular a stereo X-ray. Correct and accurate each time.
Professor Johan Kärrholm is responsible for the research and finds the new equipment promising. The simplified operation gives considerable time gains and an improved working environment. The performance of the detectors in terms of image quality is as good as the digital cassettes. Preliminary studies of the detectors’ resolution show that they are at least at the level of our former equipment. The possibility to perform dynamic RSA examinations by means of detectors instead of film changers has resulted in time savings of several hours per examination if including the analysis process. Furthermore, the image quality is better. These factors will make studies of dynamic sequences such as joint movements, joint instability, movements of implants, and movements of fractures in healing much easier to perform. Therefore, the new technique holds considerable potential to improve our knowledge within these interesting and important areas.
Text: Maria Mårtensson and Johan Kärrholm
Translated from the original Swedish article published in Mediel Magasinet Nr. 1/2013
Doc. nr: 14200497.1817