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Miniaturised Tracking System

Miniaturised Tracking System for Computer Aided Surgery - A Feasibility Study

Navigated surgery has become a state-of-the-art method in many surgical interventions. The challenge is that tracking systems are integrated into the complex OR environment and the demands on the system are different concerning space accuracy and functionality.
Therefore many existing systems have ergonomic disadvantages like the size, or the “line of sight” problem. With increased accuracy new applications will be available.

MiniTrackingSystem

Method

The objective is to develop a miniaturized handheld tracking system: Optical markers with precise recognizable structures are attached to the tracked objects. Then image processing algorithms recognize the marker structure using three optical cameras and determine the 6D location. To overcome the disadvantages of conventional tracking systems the new device is mounted directly upon the surgical instrument and is automatically situated in the best position concerning the operating situs and the “line of sight” problem is reduced. The new concept makes tool and tracking system form one unit. Therefore reference calculations between them are not needed, which is to the benefit of precision.

The first functional Prototype was developed with commercial cameras for the purpose of:

  • Development of different Image processing algorithms
  • Marker development
  • Evaluation of different camera calibration methods
  • Accuracy tests

The accuracy tests were divided into two steps. In the first step measurements were taken along a 6mm long trajectory in the centre of the measurement volume.

In a second step the accuracy was measured using a XYZ positioning device with an accuracy of 27m (X/Y-axis) and 57m (Z-axis). 50 positions were detected and compared to the known geometry.

For the second configuration, the result is an accuracy deviation of 0.238 mm RMS without lens correction. Using the Tsai algorithm for correction of lens distortion, the deviation was 0.116 mm.

Discussion

The first prototype has proven technically feasible and provided the first useful measurement results to estimate the accuracy potential.

For further measurements in the full XYZ-Volume more accurate camera calibration algorithms, using polynoms of 5th order, were implemented. First results are promising.

The next step is miniaturization. The following CTI project includes these objectives:

  • Development of miniaturized high resolution cameras
  • Small hardware for image processing using FPGA and embedded systems
  • Sterilizable markers
  • Extendable and adaptable IT-structure compatible to existing planning and navigation systems.

Contact:

Erik Schkommodau
phone: +41 61 467 42 46
Email: erik.schkommodau@fhnw.ch

Simone Hemm
phone: +41 61 467 47 96
Email: simone.hemm@fhnw.ch

Roman Ramseyer
phone: +41 61 467 44 13
Email: roman.ramseyer@fhnw.ch

Sandro Fabbri
phone: +41 61 467 47 97
Email: sandro.fabbri@fhnw.ch

Florian Coigny
phone: +41 467 42 25
Email: florian.coigny@fhnw.ch

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