Abstract
BackgroundRadiostereometric analysis (RSA) is often used for evaluating implanted devices over time. Following patients who have had tantalum beads implanted as markers in conjunction with joint replacements is important for longitudinal evaluation of these patients and for those with similar implants. As doing traditional RSA imaging is exacting and limited to specialized centers, it is important to consider alternative techniques for this ongoing evaluation. This paper studies the use of computed tomography (CT) to evaluate over time tantalum beads which have been implanted as markers.MethodsThe project uses both a hip model implanted with tantalum beads, acquired in several orientations, at two different CT energy levels, and a cohort of seven patients. The model was evaluated twice by the same observer with a 1-week interval. All CT volumes were analyzed using a semi-automated 3D volume fusion (spatial registration) tool which provides landmark-based fusion of two volumes, registering a target volume with a reference volume using a rigid body 3D algorithm. The mean registration errors as well as the accuracy and repeatability of the method were evaluated.ResultsThe mean registration error, maximum value of repeatability, and accuracy for the relative movement in the model were 0.16 mm, 0.02° and 0.1 mm, and 0.36° and 0.13 mm for 120 kVp and 0.21 mm, 0.04° and 0.01 mm, and 0.39° and 0.12 mm for 100 kVp. For the patients, the mean registration errors per patient ranged from 0.08 to 0.35 mm. These results are comparable to those in typical clinical RSA trials. This technique successfully evaluated two patients who would have been lost from the cohort if only RSA were used.ConclusionsThe proposed technique can be used to evaluate patients with tantalum beads over time without the need for stereoradiographs. Further, the effective dose associated with CT is decreasing.
Highlights
Radiostereometric analysis (RSA) is often used for evaluating implanted devices over time
We divide the results into those associated with the measurements of the model and those derived from the patient studies
The mean 3D-difference in individual landmarks in the original and registered volumes between repeated trials was 0.16 mm for the 120-kilovoltage peak (kVp) series and 0.20 mm for the 100-kVp series. This demonstrates that the effect of user input in this system is minimal and that there was only a small increase in the standard deviation when using the lowerdose computed tomography (CT) scan
Summary
Radiostereometric analysis (RSA) is often used for evaluating implanted devices over time. Radiostereometric analysis (RSA) is considered the gold standard [1, 2] for precise monitoring of small movements of orthopedic joint implants This monitoring is important because small movements of the implant early after implantation give an early indication of an increased risk for aseptic loosening and subsequent revision [3]. Traditional RSA imaging must be performed very exactly [6], as it requires that the patient be positioned precisely with respect to a calibration cage and two X-ray tubes which must be used simultaneously to produce a usable steroradiograph This radiograph must include a sufficient number of fixed tantalum beads (i.e., tantalum beads which have not moved) in the patient, which have a fixed and reproducible relation to the markers in the cage so that the examination can be correctly duplicated over time. It is important to consider alternative techniques for following all of these patients over time
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