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A modified titanium spinal pedicle screw 4.5 mm diameter, 35 mm length, marked with two 1.0mm tantalum beads, one inside the head and one near the screw tip was inserted into a bovinetibia segment. Six additional 1.0 mm tantalum beads were inserted into the bonesegment superiorly, distally and adjacent to the pedicle screw.The phantom was placed on a standard clinical diagnostic imaging bed above a custom RSAcarbon fiber calibration cage (Halifax Biomedical Inc.). A pair of DR or CR imaging plateswere placed below the calibration cage and irradiated 8 times at 100, 125 kV at 2.5 mAs. ForDR additional test were performed at 150 kV, and again at 100 kV at 0.5 mAs. At the time ofabstract submission CR results at these settings were not available.To determine precision, the standard deviation of 3D vector distances between beads wasdetermined using RSA for each of the different imaging parameters.ResultsStandard deviations of the inter-bead distances measured in the pedicle screw were 44.4 and32.1 µm (N=8) respectively for the 100 and 125 kV settings at 2.5 mAs using the DR system,compared to 109.0, 55.8 µm for CR [Fig. 1]. The distances between the bone implanted beadsprovided standard deviations of 24.4 and 22.7 µm respectively for the 100 and 125 kV settingsat 2.5 mAs using the DR system, compared to 33.1 and 33.0 µm with the CR system. Furtherincreasing the photon energy to 150 kV with the DR system reduces the precision error to 22.4µm in the pedicle screw and remains approximately the same at 21.0 µm in bone. Lowering themAs while maintaining 100 kV increases the precision error in the pedicle screw (64 µm) andshowed no significant difference in bone (24.4 µm).ConclusionThe current phantom design is basic in nature and does not account for any soft tissue scatter.However, initial results indicate a considerable reduction in precision error when using DRcompared to CR imaging equipment for RSA analysis. Increasing the kV did not significantlyinfluence the precision in measuring bead locations in bone. For embedded tantalum beadswithin a titanium pedicle screw, imaging at higher kV values with the described DR imagingsystem did allow more precise localization. This approach may be useful in assessing the invivo position of spine or other titanium implants.FiguresThursday, October 7, 2010, 16:30-17:20Session A8: Periprosthetic Fractures in THAPeriprosthetic Fractures Around Exeter Stems: A New Injury?*Jonathan Phillips - Queen's Medical Centre, Nottingham University Hospitals - Nottingham,UKChris Boulton - Queen's Medical Centre, Nottingham - Nottingham, UKfile:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]