Intravascular treatment is known as one of effective treatment methods for cerebral aneurysms. One problem of this therapy is that an intravascular treatment device unexpectedly moves and a tip of the device strongly contacts on a vessel wall. This unexpected movement of the device causes vascular injury. In actual treatment, 2D X-ray image is used. It is difficult for an operator to estimate 3D position of the device from the 2D X-ray image. In this study, we propose estimation methods for 3D position of devices using a X-ray image and a 3D blood vessel model.
At the first step of estimation procedure, a 3D position of X-ray image, a 3D blood vessel model and X-ray source (Xs) are determined by 2D/3D registration method. The actual 3D position of the device tip (P) is placed on the straight line between Xs and P. Moreover, its position is limited within the 3D vessel model. From characteristics, the 3D position of the device tip is estimated. In this study, two methods to estimate the 3D position of the device are proposed. First: A closest point to the straight line from the center line of the blood vessel model is defined as the position in 3D space of the guidewire (one-point estimation method). Second: A mean value of points on the straight line inside the blood vessel model is defined as the position in 3D space of the guidewire (average estimation method). The accuracy of estimation methods depends on angle of X-ray irradiation. In this study, the relationship between the accuracy of estimation methods and the angle of X-ray irradiation. The estimation accuracy was investigated using numerical calculation.
In the case of a simple blood vessel shape, the error of the estimation was proportional to the angular difference between an ideal and an actual. The errors of the estimated arc length parameter at the ideal angle of X-ray irradiation were 0.002 mm and 0.078 mm, respectively. This result shows that this method is effective for simple blood vessel shape. In future work, other factors to affect the accuracy are also investigated.