![]() Using 3D bone reconstructions from the CT data, a pair of digitally reconstructed radiographs was generated using model- based tracking software. The total number of frames for each exam was 331 ± 60.7 (average ± SD). Specimen 2 was imaged at 73 kVp/ 2.9 mA (fluoro 1) and 74 kVp/2.5 mA (fluoro 2). Specimen 1 was imaged at 83 kVp/3.1 mA (fluoro 1) and 85 kVp/3.2 mA (fluoro 2). Fluoroscopy video was acquired for the impingement exam (Supplemental Video 1 please see the appendix, at the end of this article, for Web access to the videos and for captions that describe them), FABER test, and supine straight-legged int/external rota- tional profile. The pelvis was secured to the radiolucent table with Velcro straps. Pixels representing the implanted beads were automatically segmented and fit to a sphere to define bead centroids in CT coordinates. 16 Bones were segmented semiautomatically using Amira (5.4.1, Visage Imaging, San Diego, CA). Data were upsampled to 3× resolution to reduce staircase artifact. CT images of the entire pelvis, proximal femurs, and knees were acquired with a Siemens Somatom CT Scanner (0.7 mm slice thickness, Specimen 1/Specimen 2: 405/424 mm FOV, 512 × 512 matrix). Bead locations were chosen so as to minimize disruption of soft tissue. At least five beads were implanted into each bone. Steel beads (2 mm diameter) were implanted into the left hemipelvis and femur with a minimally invasive approach preserving all soft tissue (Figure 2). Two pelvis-toe cadaveric specimens were acquired (Specimen 1: male, 57 years old, 170 cm, 70 kg, BMI 24.2 Specimen 2: female, 59 years old, 168 cm, 50 kg, BMI 17.7). Bias and precision was defined by the average and standard deviation of the differences for 400 frames, respectively. 15 Tracked bead intercentroid distances were compared with known distances to quantify accuracy. 15 3D positions of the beads in laboratory coordinates were calculated using direct linear transform theory. An acrylic plate with steel beads spaced 30 mm (2 mm diameter, positional uncertainty 0.0013 mm) was imaged during random motion. the accuracy of dynamic radiostereometric analysis (DRSA) under optimal conditions.
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