Effect of Calibration Error on Bone Tracking Accuracy With Fluoroscopy

Model-based 3D-fluoroscopy can quantify joint kinematics with 1mm and 1 deg accuracy level. A calibration based on the acquisition of devices of known geometry is usually applied to size the system. This study aimed at quantifying the sensitivity of the fluoroscopic pose estimation accuracy specifically to errors in the calibration process, excluding other sources of error. X-ray focus calibration error was quantified for different calibration setups, and its propagation to the pose estimation was characterized insilico. Focus reference position influenced the calibration error dispersion, while calibration cage pose affected its bias. In the worst-case scenario, the estimation error of the principal point and of the focus distance was lower than 1mm and 2 mm, respectively. The consequent estimation of joint angles was scarcely influenced by calibration errors. A linear trend was highlighted for joint translations, with a sensitivity proportional to the distance between the model and the image plane, resulting in a submillimeter error for realistic calibration errors. The biased component of the error is compensated when computing relative joint kinematics between two segments. Copyright \ua9 2014 by ASME

Characterization of 3D Fluoroscopy calibration: joint kinematics quantification sensitivity to calibration errors

Model based 3D fluoroscopy can quantify joint kinematics with a mm/deg accuracy level. A calibration based on the acquisition of specific devices is usually applied to size the system. This study aimed at the characterization of the sensitivity of the pose estimation accuracy to errors in the calibration process, in order to evaluate a possible simplification of the calibration procedure. In-silico simulations were performed to analyze a data-set obtained adding controlled perturbation in the calibration process. The estimation of the rotations was scarcely influenced by calibration errors, while a linear trend was highlighted for translations with a sensitivity of 20% correspondent to approximately a 1 mm error for realistic calibration errors. This error is compensated when computing relative kinematics between two joint segments

3D Elbow Kinematics with Monoplanar Fluoroscopy: <it>In Silico</it> Evaluation

An in-silico assessment of the performance of 3D video-fluoroscopy for the analysis of the kinematics of long bones is proposed. A reliable knowledge of in-vivo joints kinematics in physiological conditions is fundamental in the clinical field. 3D video-fluoroscopy theoretically permits a mm/deg level of accuracy in joint motion analysis, but the optimization algorithm for the pose estimation is highly dependent on the geometry of the bone segment analyzed. An automated technique based on distance maps and tangency condition was applied to the elbow bones. The convergence domain was explored to quantify and optimize measurement accuracy in terms of bias and precision. By conditioning the optimization algorithm using simple image features, the estimation error had small dispersion (interquartile range within 0.5 and 0.025&#8201;mm/deg for out-of-plane and in-plane pose parameters, resp.), but with occasional bias and outliers. 3D video-fluoroscopy produced promising results for the elbow joint, but further in-vitro validation studies should be carried out.</p

Functional reaching discloses perceptive impairment in diplegia children with cerebral palsy

The currently accepted definition classifies Cerebral Palsy (CP) as a mere posture and movement disorder. Conversely, some authors have recently associated the presence of several motor dysfunctions exhibited by diplegic children with CP to an impairment in the perceptive system. The aim of the present study was to investigate the influence of the Perceptive Impairment (PI) on motor control and to appraise if the PI can be revealed by a reaching task. A functional reach and touch experiment was accomplished from sitting posture considering different directions and distances. Typically developing and diplegic children with CP were enrolled and, the latter, a priori divided in two subgroups considering a positive or negative diagnosis of PI. The reaching trials were quantified by means of centre of pressure analysis in terms of the overall quality of the task, and accuracy and effectiveness of postural adjustments and Anticipatory Postural Adjustments (APAs). The three groups showed statistically significant differences in terms of percentage of touched target, and of time spent and maximum distance covered to reach the target. In particular, PI caused a major difficulty in accomplishing the reaching tasks, thus a lower autonomy level in action. Overall, the PI strongly affected the anticipatory control system. Children with PI, rarely recruited APAs, each of which was characterized by small amplitude and inaccuracy in direction. The lack of effective APAs indicated how PI strongly influenced the motor control strategy. The present study demonstrates that the PI is a primary syndrome responsible for the long-term prognosis beside the motor and the postural disorders in CP

Effects of calibration errors on 3D kinematics quantification with fluoroscopy

Model based 3D fluoroscopy can quantify joint kinematics with a mm/deg accuracy level. A calibration based on the acquisition of specific devices is usually applied to size the system. This study aimed at the characterization of the sensitivity of the pose estimation accuracy to errors in the calibration process, in order to evaluate a possible simplification of the calibration procedure. In-silico simulations were performed to analyse a data-set obtained adding controlled perturbation in the calibration process. The estimation of the rotations was scarcely influenced by calibration errors, while a linear trend was high- lighted for translations with a sensitivity of 20% correspondent to approximately a 1 mm error for realistic calibration errors. This error is compensated when computing relative kinematics between two joint segments

Fluoroscopic analysis for the estimation of in-vivo elbow kinematics: influence of 3D model

The reliable knowledge that model-based three-dimensional (3D) fluoroscopy can provide about in vivo joints kinematics is essential to diagnose orthopedic pathologies, develop new prosthesis, and evaluate clinical procedures. To exploit 3D fluoroscopy for the analysis of elbow kinematics, its use was evaluated considering a single model for the forearm or two different models for the ulna and radius. Active elbow flexion-extension and prono-supination motor tasks of a healthy male subject were acquired by means of fluoroscopy. The 3D bone models were automatically aligned to the relevant projections. The pose estimation algorithm sought the tangency condition of the projection rays with the model surface, minimizing a cost function and exploiting an adaptive distance map. Five iterative guided alignments were performed to avoid the final convergence to a local minimum. The results highlighted the critical alignment of the ulna/radius model, particularly when prono-supination is performed. From the physiological motion patterns and given the values of the cost function, 3D fluoroscopy was proven to be applicable to the analysis of the elbow kinematics when single bone models for the ulna and radius are used. \ua9 2012 World Scientific Publishing Company