C-arm rotation encoding with accelerometers.
OBJECTIVE
Fluoroscopic C-arms are being incorporated in computer-assisted interventions in increasing number. For these applications to work, the relative poses of imaging must be known. To find the pose, tracking methods such as optical cameras, electromagnetic trackers, and radiographic fiducials have been used-all hampered by significant shortcomings.


METHODS
We propose to recover the rotational pose of the C-arm using the angle-sensing ability of accelerometers, by exploiting the capability of the accelerometer to measure tilt angles. By affixing the accelerometer to a C-arm, the accelerometer tracks the C-arm pose during rotations of the C-arm. To demonstrate this concept, a C-arm analogue was constructed with a webcam device affixed to the C-arm model to mimic X-ray imaging. Then, measuring the offset between the accelerometer angle readings to the webcam pose angle, an angle correction equation (ACE) was created to properly tracking the C-arm rotational pose.


RESULTS
Several tests were performed on the webcam C-arm model using the ACEs to tracking the primary and secondary angle rotations of the model. We evaluated the capability of linear and polynomial ACEs to tracking the webcam C-arm pose angle for different rotational scenarios. The test results showed that the accelerometer could track the pose of the webcam C-arm model with an accuracy of less than 1.0 degree.


CONCLUSIONS
The accelerometer was successful in sensing the C-arm's rotation with clinically adequate accuracy in the C-arm webcam model.
Grzeda
Victor
V
Queen's University, Kingston, ON, Canada. grzeda@cs.queensu.ca
Fichtinger
Gabor
G
D000054:Acceleration; D002138:Calibration; D004867:Equipment Design; D005471:Fluoroscopy / Q000295:instrumentation*; D006801:Humans; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D012399:Rotation; D012984:Software
Comput Aided Surg. 2000;5(6):373-90
11295851
Med Phys. 2005 Oct;32(10):3185-98
16279072
Med Image Comput Comput Assist Interv. 2006;9(Pt 1):494-502
17354927
Med Image Comput Comput Assist Interv. 2007;10(Pt 2):9-17
18044547
IEEE Trans Med Imaging. 2009 Dec;28(12):1955-68
19605321