Are low-dose CT scans a satisfactory substitute for stereoradiographs for migration studies? A preclinical test of low-dose CT scanning protocols and their application in a pilot patient.

BACKGROUND: Computed tomography (CT) has the potential to acquire the data needed for migration studies of orthopedic joint implants of patients who have had tantalum beads implanted at the time of joint replacement surgery. This can be accomplished with the same precision as radiostereometric analysis (RSA). Switching to CT would increase availability without the need for the specific facilities required for RSA. However, higher effective dose is a concern.

PURPOSE: To investigate if migration measurements can be done with CT with an accuracy and effective dose comparable to that of conventional RSA.

MATERIAL AND METHODS: Fourteen scanning protocols were tested in a hip phantom that incorporated tantalum beads and an uncemented femoral stem. The protocols were graded for clinical practice according to the three parameters of image quality, effective dose, and robustness of numerical data. After grading, the two protocols that graded best overall were applied to a pilot patient.

RESULTS: All protocols produced scans in which the numerical data were sufficient for a migration analysis at least as precise as would be expected using RSA. A protocol with an effective dose of 0.70 mSv was shown to be applicable in a pilot patient.

CONCLUSION: Low-dose CT scans with an effective dose comparable to a set of routine plain radiographs can be used for precise migration measurements.