# Ultrasound Navigation for Transcatheter Aortic Stent Deployment Using Global and Local Information
## 2 Materials and Methods
### A Global 3D Navigation Map Based on 2D US-3D MR Image Registration
#### 2.2.1 Multi-Feature Particle Filter Tracking Method for the 3D Trajectory of the Catheter
Therefore, the performance of IVUS segmentation method was evaluated using 500 IVUS images from the sequences of ten patients. These patients' IVUS sequences were collected in Navy PLA General Hospital, China (detailed information of patients is listed in supplementary material Table S1). The MA and lumen borders of 500 images had been manually delineated by an expert in IVUS images interpretation from the Navy PLA General Hospital. Examples of segmented lumen and MA borders of our method are illustrated in Figure 9. Segmentation accuracy was quantified by using standard measurements including Dice indexes and Hausdorff distance. The comparison results of proposed segmentation method and manual delineation are listed in Table 1.

Figure 2:0 3D trajectories of the catheter. Figure 2:1 Segmentation examples of IVUS images; yellow and green contours denote the MA and lumen borders respectively (dotted lines denote detected borders by manual segmentation and full lines denote detected contours by proposed segmentation method, respectively). ### The US Navigation In Vitro Experiment

We presented an in vitro experiment of the catheter intervention for stent deployment, which is conducted on a cardiac and aortic phantom. During the experiment, there was a plaque inside our aortic phantom, and the center of the plaque was identified as the surgical target. The user was asked to insert a catheter into the target inside the vessel to simulate transcatheter stent deployment. During the intervention, two different types of navigation information: (1) a global navigation map alone; (2) a global map plus local navigation information were available to the user, respectively. The image guidance interface and information during the intervention are illustrated in Figure 2:2 Under the guidance of a global navigation map (Figure 10a-c), the relative position between interventional catheter and 3D cardiac structure is displayed intuitively to navigate the catheter to the target. However, there is the limitation that the morphological information of aortic model, especially the lesion's position, is blurred (Figure 10c). On one hand, to evaluate the vessel reconstruction error of global information, we measured the average outer radius of manually reconstructed aortic model from global MR image, and compared the average outer radius with the actual outer radius of aortic phantom (4.5000 mm). We selected 40 transverses of the reconstructed aortic model to acquire an average outer radius. The resolution of MR images is 0.4871 mm and the acquired reconstruction error of global navigation is 1.1241 mm. On the other hand, the catheter was navigated to the target using global information, and the distance between the catheter arrival position and the target was measured by using coronal and sagittal X-ray projections images from C-arm (Fluoroscan Insight, HOLOG, Boston, MA, USA). This distance is treated as targeting error of global navigation (See Figure 11a) and the acquired targeting error is 2.8701 mm. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Index**} & \multicolumn{2}{c}{**MA Border**} & \multicolumn{2}{c}{**Lumen Border**} \\ \cline{2-5}  & **Mean** & **Std** & **Mean** & **Std** \\ \hline Hausdorff distance & 0.65 mm & 0.20 mm & 0.41 mm & 0.27 mm \\ Dice index & 92.30\% & 8.21\% & 89.87\% & 7.12\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mean and standard deviations (Std) of the Dice similarity and Hausdorff distance between the lumen/MA (media-adventitia) border obtained by our method and manual delineation. Figure 10: Image guidance interface and information. (**a**) a global navigation map from 2D US-3D MR registration; (**b**) enlarged view of a global map at the region of aorta, green curve is the preoperative planning path, asterisk denotes the position of interventional catheter; (**c**) collected MR image; (**d**) local navigation information with morphological characteristics of aorta.