In vitro measurement of tissue integrity during saccular aneurysm embolizations for simulator-based training.

In the domain of endovascular neurosurgery, the measurement of tissue integrity is needed for simulator-based training and for the development of new intravascular instruments and treatment techniques. In vitro evaluation of tissue manipulation can be achieved using photoelastic stress analysis and vasculature modeling with photoelastic materials. In this research we constructed two types of vasculature models of saccular aneurysms for differentiation of embolization techniques according to the respect for tissue integrity measurements based on the stress within the blood vessel model wall. In an aneurysm model with 5 mm dome diameter, embolization using MicroPlex 10 (Complex 1D, with 4 mm diameter loops), a maximum area of 3.97 mm² with stress above 1 kPa was measured. This area increased to 5.50 mm² when the dome was touched deliberately with the release mechanism of the coil, and to 4.87 mm² for an embolization using Micrusphere, (Spherical 18 Platinum Coil). In a similar way trans-cell stent-assisted coil embolization was also compared to human blood pressure simulation using a model of a wide-necked saccular aneurysm with 7 mm diameter. The area with stress above 1kPa was below 1 mm² for the pressure simulation and maximized at 3.79 mm² during the trans-cell insertion of the micro-catheter and at 8.92 mm² during the embolization. The presented results show that this measurement system is useful for identifying techniques compromising tissue integrity, comparing and studying coils and embolization techniques for a specific vasculature morphology and comparing their natural stress variations such as that produced by blood pressure.

Photoelastic stress analysis in blood vessel phantoms: three-dimensional visualization and saccular aneurysm with bleb.

BACKGROUND: The photoelastic effect is used for stress measurement during endovascular surgery simulation for quantitative evaluation of catheter trajectory in in vitro environments. By extending the capabilities of this sensing technology, its potential for intravascular tools evaluation will increase. METHODS: In this research the error introduced by stress direction on magnitude measurements was studied, then stress measurements were made in the phantom modelling of a saccular aneurysm with bleb. To visualize three-dimensionally the stress field changes produced by a guide wire in a phantom wall, a scanner and an algorithm relying on maximum likelihood-expectation maximization are proposed. Three-dimensional fields at different pressure level were compared with the stress field surrounding the guide wire. RESULTS: The maximum error in stress magnitude measurements due to stress direction was 2.52%. Stress local maximum was detected in the bleb phantom before rupture. Three-dimensional visualization was obtained in vasculature phantom with average errors of 10.73%, 4.55%, 3.18% for inner pressures of 80, 120, 160 mmHg, respectively. Stress measurement in the neighbourhood of the guide wire is equivalent to applying an inner pressure of 120 mmHg. CONCLUSIONS: For the presented polariscope, the weak influence of stress direction in magnitude measurements was confirmed. In vasculature phantoms, the three-dimensional visualization of stress eliminated birefringence visualization distortion and enabled more comprehensive comparison of stress produced by intravascular tools with stress produced by normal blood pressure.

Autonomous catheter insertion system using magnetic motion capture sensor for endovascular surgery.

BACKGROUND: In order to reduce fluoroscope usage in endovascular surgery, there is a need to develop autonomous catheter insertion systems. METHODS: We propose a system for tracking the position and speed of a catheter using a magnetic motion capture sensor to provide feedback to a catheter-driving mechanism, to perform autonomous catheter insertion in major vasculature. Catheter insertion speed control and path reconstruction experiments were performed with the system inside a silicone model of major vasculature to simulate surgery. RESULTS: The system controlled the catheter for speeds of 6.14 mm/s and reproduced a two-dimensional path inside the silicone blood vessel phantom with less than 7 mm of error. CONCLUSIONS: We found that error in speed control rises as a result of friction between the catheter and the model wall. Path reconstruction error depends on the model's cross-sectional diameter, the properties of the catheter insertion mechanism, the magnetic sensor and the system guidance technique.

Numerical evaluation method for catheter prototypes using photo-elastic stress analysis on patient-specific vascular model.

BACKGROUND: To date, no quantitative analysis has been developed to evaluate catheter performance inside the vascular lumen. METHODS: An evaluation system for endovascular tools was built with a polyurethane elastomer vascular model inside a polariscope and a catheter driving system. This robotic system reproduced a catheter insertion trajectory inside the vascular model, using a surgical catheter and three catheter prototypes used for motion capture on endovascular surgery simulation. Birefringence is produced by photo-elastic characteristics of the polyurethane elastomer when the material is submitted external stress. The birefringence produced by the catheter on the vascular model wall was recorded and represented numerically by the correlation between consecutive frames of the registered video. RESULTS: Correlation values between frames showed that the performance of the prototypes was lower than that of the medical use catheter. The performance of prototypes was reduced by microcoils on their tips. CONCLUSIONS: This methodology opens new options to evaluate medical catheters and physicians skills. opyright