Tracking systems are critical to all types of computer-assisted image-guided intervention. Many technologies exist; however, only optical and electromagnetic systems are widely used commercially. In orthopaedic applications, optical systems dominate because of the large working volume and accuracy, but these systems suffer from deficiencies due to line of sight. Electromagnetic trackers can be made much smaller but are less accurate and are affected by metal, although current-generation systems are less affected by metal artifacts than were the earlier ones, which were more widely reported in the literature.
"2013b ) with encouraging results . The tracking error of our tracking system has been reported to have a root mean square error of approximately 0 . 2 mm when tracking a passive rigid body , although typi - cally the tip of a stylus - like tool that is subject to lever - arm effects can be localized at 1 to 2 mm ( Glossop 2009 ; Wiles et al . 2004 ) . "
[Show abstract][Hide abstract] ABSTRACT: Acquisition of ultrasound data negatively affects image registration accuracy during image-guided therapy because of tissue compression by the probe. We present a novel compression correction method that models sub-surface tissue displacement resulting from application of a tracked probe to the tissue surface. Patient landmarks are first used to register the probe pose to pre-operative imaging. The ultrasound probe geometry is used to provide boundary conditions to a biomechanical model of the tissue. The deformation field solution of the model is inverted to non-rigidly transform the ultrasound images to an estimation of the tissue geometry before compression. Experimental results with gel phantoms indicated that the proposed method reduced the tumor margin modified Hausdorff distance (MHD) from 5.0 ± 1.6 to 1.9 ± 0.6 mm, and reduced tumor centroid alignment error from 7.6 ± 2.6 to 2.0 ± 0.9 mm. The method was applied to a clinical case and reduced the tumor margin MHD error from 5.4 ± 0.1 to 2.6 ± 0.1 mm and the centroid alignment error from 7.2 ± 0.2 to 3.5 ± 0.4 mm.
Ultrasound in medicine & biology 01/2014; 40(4). DOI:10.1016/j.ultrasmedbio.2013.11.003 · 2.21 Impact Factor
"Optical tracking systems offer a larger working volume and higher accuracy than EM tracking devices (EM systems are potentially affected by large ferromagnetic objects) (Birkfellner et al 2008, Stevens et al 2010, Seeberger et al 2012). Most optical tracking systems make use of a relatively small number of cameras (two or three) (Glossop 2009, Willoughby et al 2012), thus reducing calibration requirements but limiting their practical use in complex clinical scenarios, where the required line-of-sight between the tracked objects and the cameras is easily obstructed. To overcome this limitation, we propose the use of a multi-camera optical tracking system to ensure correct tracking of the applicator in a real IOERT setting, in which several actors and objects are moving around. "
[Show abstract][Hide abstract] ABSTRACT: Intra-operative electron radiation therapy (IOERT) combines surgery and ionizing radiation applied directly to an exposed unresected tumour mass or to a post-resection tumour bed. The radiation is collimated and conducted by a specific applicator docked to the linear accelerator. The dose distribution in tissues to be irradiated and in organs at risk can be planned through a pre-operative computed tomography (CT) study. However, surgical retraction of structures and resection of a tumour affecting normal tissues significantly modify the patient's geometry. Therefore, the treatment parameters (applicator dimension, pose (position and orientation), bevel angle, and beam energy) may require the original IOERT treatment plan to be modified depending on the actual surgical scenario. We propose the use of a multi-camera optical tracking system to reliably record the actual pose of the IOERT applicator in relation to the patient's anatomy in an environment prone to occlusion problems. This information can be integrated in the radio-surgical treatment planning system in order to generate a real-time accurate description of the IOERT scenario. We assessed the accuracy of the applicator pose by performing a phantom-based study that resembled three real clinical IOERT scenarios. The error obtained (2 mm) was below the acceptance threshold for external radiotherapy practice, thus encouraging future implementation of this approach in real clinical IOERT scenarios.
Physics in Medicine and Biology 12/2013; 58(24):8769-8782. DOI:10.1088/0031-9155/58/24/8769 · 2.76 Impact Factor
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