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Digital stereophotogrammetry based on circular markers and zooming cameras: evaluation of a method for 3D analysis of small motions in orthopaedic research.

Bobrowitsch E, Hurschler C, Olender G, Plaass C, Waizy H, Arnold H, Stukenborg-Colsman C - Biomed Eng Online (2011)

Bottom Line: The first experiment of the 10 mm distances measurement showed a total accuracy of 0.0086 mm and precision of ± 0.1002 mm.In the second experiment, translations from 0.5 mm to 5 mm were measured with total accuracy of 0.0038 mm and precision of ± 0.0461 mm.The rotations of 2.25° amount were measured with the entire accuracy of 0.058° and the precision was of ± 0.172°.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory for Biomechanics and Biomaterials, Department of Orthopaedic Surgery, Hannover Medical School, Germany. evgenij.bobrowitsch@yahoo.de

ABSTRACT

Background: Orthopaedic research projects focusing on small displacements in a small measurement volume require a radiation free, three dimensional motion analysis system. A stereophotogrammetrical motion analysis system can track wireless, small, light-weight markers attached to the objects. Thereby the disturbance of the measured objects through the marker tracking can be kept at minimum. The purpose of this study was to develop and evaluate a non-position fixed compact motion analysis system configured for a small measurement volume and able to zoom while tracking small round flat markers in respect to a fiducial marker which was used for the camera pose estimation.

Methods: The system consisted of two web cameras and the fiducial marker placed in front of them. The markers to track were black circles on a white background. The algorithm to detect a centre of the projected circle on the image plane was described and applied. In order to evaluate the accuracy (mean measurement error) and precision (standard deviation of the measurement error) of the optical measurement system, two experiments were performed: 1) inter-marker distance measurement and 2) marker displacement measurement.

Results: The first experiment of the 10 mm distances measurement showed a total accuracy of 0.0086 mm and precision of ± 0.1002 mm. In the second experiment, translations from 0.5 mm to 5 mm were measured with total accuracy of 0.0038 mm and precision of ± 0.0461 mm. The rotations of 2.25° amount were measured with the entire accuracy of 0.058° and the precision was of ± 0.172°.

Conclusions: The description of the non-proprietary measurement device with very good levels of accuracy and precision may provide opportunities for new, cost effective applications of stereophotogrammetrical analysis in musculoskeletal research projects, focusing on kinematics of small displacements in a small measurement volume.

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Marker test on the cadaveric foot specimen. The single right camera picture. The nine markers were attached on the first metatarsal bone fragments fixing with a locking screw plate after a proximal osteotomy. The fiducial marker was placed in the middle of the lower image part.
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Figure 4: Marker test on the cadaveric foot specimen. The single right camera picture. The nine markers were attached on the first metatarsal bone fragments fixing with a locking screw plate after a proximal osteotomy. The fiducial marker was placed in the middle of the lower image part.

Mentions: In order to test how the background colours of the connective tissue influence the precision of marker detection, a human foot specimen was used. The foot was fresh frozen and stored in a plastic bag at -20°C. The specimen (left, female, 79 years old, without degenerative changes of the connective tissue) was thawed at room temperature for 24 hours. Then the first metatarsal bone was prepared free of the surrounding tissue, proximally osteotomized and fixed with a locking screw plate. Nine markers were attached by means of acrylic superglue on the parts of the first metatarsal bone. The markers were 2 mm black circles on a white water resistant background (0.5 mm thin pieces approximately of a 4 mm diameter, Figure 4).


Digital stereophotogrammetry based on circular markers and zooming cameras: evaluation of a method for 3D analysis of small motions in orthopaedic research.

Bobrowitsch E, Hurschler C, Olender G, Plaass C, Waizy H, Arnold H, Stukenborg-Colsman C - Biomed Eng Online (2011)

Marker test on the cadaveric foot specimen. The single right camera picture. The nine markers were attached on the first metatarsal bone fragments fixing with a locking screw plate after a proximal osteotomy. The fiducial marker was placed in the middle of the lower image part.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3038981&req=5

Figure 4: Marker test on the cadaveric foot specimen. The single right camera picture. The nine markers were attached on the first metatarsal bone fragments fixing with a locking screw plate after a proximal osteotomy. The fiducial marker was placed in the middle of the lower image part.
Mentions: In order to test how the background colours of the connective tissue influence the precision of marker detection, a human foot specimen was used. The foot was fresh frozen and stored in a plastic bag at -20°C. The specimen (left, female, 79 years old, without degenerative changes of the connective tissue) was thawed at room temperature for 24 hours. Then the first metatarsal bone was prepared free of the surrounding tissue, proximally osteotomized and fixed with a locking screw plate. Nine markers were attached by means of acrylic superglue on the parts of the first metatarsal bone. The markers were 2 mm black circles on a white water resistant background (0.5 mm thin pieces approximately of a 4 mm diameter, Figure 4).

Bottom Line: The first experiment of the 10 mm distances measurement showed a total accuracy of 0.0086 mm and precision of ± 0.1002 mm.In the second experiment, translations from 0.5 mm to 5 mm were measured with total accuracy of 0.0038 mm and precision of ± 0.0461 mm.The rotations of 2.25° amount were measured with the entire accuracy of 0.058° and the precision was of ± 0.172°.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory for Biomechanics and Biomaterials, Department of Orthopaedic Surgery, Hannover Medical School, Germany. evgenij.bobrowitsch@yahoo.de

ABSTRACT

Background: Orthopaedic research projects focusing on small displacements in a small measurement volume require a radiation free, three dimensional motion analysis system. A stereophotogrammetrical motion analysis system can track wireless, small, light-weight markers attached to the objects. Thereby the disturbance of the measured objects through the marker tracking can be kept at minimum. The purpose of this study was to develop and evaluate a non-position fixed compact motion analysis system configured for a small measurement volume and able to zoom while tracking small round flat markers in respect to a fiducial marker which was used for the camera pose estimation.

Methods: The system consisted of two web cameras and the fiducial marker placed in front of them. The markers to track were black circles on a white background. The algorithm to detect a centre of the projected circle on the image plane was described and applied. In order to evaluate the accuracy (mean measurement error) and precision (standard deviation of the measurement error) of the optical measurement system, two experiments were performed: 1) inter-marker distance measurement and 2) marker displacement measurement.

Results: The first experiment of the 10 mm distances measurement showed a total accuracy of 0.0086 mm and precision of ± 0.1002 mm. In the second experiment, translations from 0.5 mm to 5 mm were measured with total accuracy of 0.0038 mm and precision of ± 0.0461 mm. The rotations of 2.25° amount were measured with the entire accuracy of 0.058° and the precision was of ± 0.172°.

Conclusions: The description of the non-proprietary measurement device with very good levels of accuracy and precision may provide opportunities for new, cost effective applications of stereophotogrammetrical analysis in musculoskeletal research projects, focusing on kinematics of small displacements in a small measurement volume.

Show MeSH