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Title: Predictive sensor based x-ray calibration using a physical model

Abstract

Many computer assisted surgery systems are based on intraoperative x-ray images. To achieve reliable and accurate results these images have to be calibrated concerning geometric distortions, which can be distinguished between constant distortions and distortions caused by magnetic fields. Instead of using an intraoperative calibration phantom that has to be visible within each image resulting in overlaying markers, the presented approach directly takes advantage of the physical background of the distortions. Based on a computed physical model of an image intensifier and a magnetic field sensor, an online compensation of distortions can be achieved without the need of an intraoperative calibration phantom. The model has to be adapted once to each specific image intensifier through calibration, which is based on an optimization algorithm systematically altering the physical model parameters, until a minimal error is reached. Once calibrated, the model is able to predict the distortions caused by the measured magnetic field vector and build an appropriate dewarping function. The time needed for model calibration is not yet optimized and takes up to 4 h on a 3 GHz CPU. In contrast, the time needed for distortion correction is less than 1 s and therefore absolutely acceptable for intraoperative use. Firstmore » evaluations showed that by using the model based dewarping algorithm the distortions of an XRII with a 21 cm FOV could be significantly reduced. The model was able to predict and compensate distortions by approximately 80% to a remaining error of 0.45 mm (max) (0.19 mm rms)« less

Authors:
; ; ;  [1];  [2];  [2]
  1. Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Pauwelsstr. 20, 52074 Aachen (Germany)
  2. (Germany)
Publication Date:
OSTI Identifier:
20951136
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 4; Other Information: DOI: 10.1118/1.2558266; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ALGORITHMS; CALIBRATION; CORRECTIONS; IMAGE INTENSIFIERS; IMAGE PROCESSING; IMAGES; MAGNETIC FIELDS; PHANTOMS; SURGERY; X RADIATION

Citation Formats

Fuente, Matias de la, Lutz, Peter, Wirtz, Dieter C., Radermacher, Klaus, Department of Orthopaedic and Trauma Surgery, University Hospital Bonn, Sigmund-Freud-Strasse 25, 53127 Bonn, and Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Pauwelsstr. 20, 52074 Aachen. Predictive sensor based x-ray calibration using a physical model. United States: N. p., 2007. Web. doi:10.1118/1.2558266.
Fuente, Matias de la, Lutz, Peter, Wirtz, Dieter C., Radermacher, Klaus, Department of Orthopaedic and Trauma Surgery, University Hospital Bonn, Sigmund-Freud-Strasse 25, 53127 Bonn, & Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Pauwelsstr. 20, 52074 Aachen. Predictive sensor based x-ray calibration using a physical model. United States. doi:10.1118/1.2558266.
Fuente, Matias de la, Lutz, Peter, Wirtz, Dieter C., Radermacher, Klaus, Department of Orthopaedic and Trauma Surgery, University Hospital Bonn, Sigmund-Freud-Strasse 25, 53127 Bonn, and Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Pauwelsstr. 20, 52074 Aachen. Sun . "Predictive sensor based x-ray calibration using a physical model". United States. doi:10.1118/1.2558266.
@article{osti_20951136,
title = {Predictive sensor based x-ray calibration using a physical model},
author = {Fuente, Matias de la and Lutz, Peter and Wirtz, Dieter C. and Radermacher, Klaus and Department of Orthopaedic and Trauma Surgery, University Hospital Bonn, Sigmund-Freud-Strasse 25, 53127 Bonn and Helmholtz-Institute for Biomedical Engineering, RWTH Aachen University, Pauwelsstr. 20, 52074 Aachen},
abstractNote = {Many computer assisted surgery systems are based on intraoperative x-ray images. To achieve reliable and accurate results these images have to be calibrated concerning geometric distortions, which can be distinguished between constant distortions and distortions caused by magnetic fields. Instead of using an intraoperative calibration phantom that has to be visible within each image resulting in overlaying markers, the presented approach directly takes advantage of the physical background of the distortions. Based on a computed physical model of an image intensifier and a magnetic field sensor, an online compensation of distortions can be achieved without the need of an intraoperative calibration phantom. The model has to be adapted once to each specific image intensifier through calibration, which is based on an optimization algorithm systematically altering the physical model parameters, until a minimal error is reached. Once calibrated, the model is able to predict the distortions caused by the measured magnetic field vector and build an appropriate dewarping function. The time needed for model calibration is not yet optimized and takes up to 4 h on a 3 GHz CPU. In contrast, the time needed for distortion correction is less than 1 s and therefore absolutely acceptable for intraoperative use. First evaluations showed that by using the model based dewarping algorithm the distortions of an XRII with a 21 cm FOV could be significantly reduced. The model was able to predict and compensate distortions by approximately 80% to a remaining error of 0.45 mm (max) (0.19 mm rms)},
doi = {10.1118/1.2558266},
journal = {Medical Physics},
number = 4,
volume = 34,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
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