Towards fluoro-free interventions: Using radial intracardiac ultrasound for vascular navigation

Transcatheter cardio-vascular interventions have the advantage of patient safety, reduced surgery time, and minimal trauma to the patient’s body. Transcathether interventions, which are performed percutaneously are limited by the lack of direct line-of-sight with the surgical tools and the patient anatomy. Therefore, such interventional procedures rely heavily on image guidance for navigating towards and delivering therapy at the target site. Vascular navigation via the inferior vena cava (IVC), from the groin to the heart, is an imperative part of most transcatheter cardiovascular interventions including heart valve repair surgeries and ablation therapy. Traditionally, the IVC is navigated using fluoroscopic techniques such as angiography or CT venography. These X-ray based techniques can have detrimental effects on the patient as well as the surgical team, causing increased radiation exposure, leading to risk of cancer, fetal defects, and eye cataracts. The use ∗Corresponding Author: Hareem Nisar, Robarts Research Institute, 1151 Richmond St. N. London, ON N6A 5B7; Email, hnisar3@uwo.ca; Phone, 519.931.5777 Preprint submitted to Ultrasound in Medicine and Biology August 19, 2021 Manuscript in pdf Click here to view linked References

guidance for navigating towards and delivering therapy at the target site.
Vascular navigation via the inferior vena cava (IVC), from the groin to the heart, is an imperative part of most transcatheter cardiovascular interventions including heart valve repair surgeries and ablation therapy. Traditionally, the IVC is navigated using fluoroscopic techniques such as angiography or CT venography. These X-ray based techniques can have detrimental effects on the patient as well as the surgical team, causing increased radiation exposure, leading to risk of cancer, fetal defects, and eye cataracts. The use  Interventionalists rely heavily on image-guidance to navigate and position 8 their tools to deliver therapy at the target region. Common imaging modal-9 ities used for transcatheter-based interventions include X-ray fluoroscopy,   during an ablation procedure and perform transseptal puncture using ICE.

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Alternative imaging modalities such as MR, and US are also considered.   US image represent an artifact inherent to the ICE probe (Fig. 2a). This  and ICE imaging. The first few millimeters of ICE imaging are corrupted by 174 a ring artifact inherent to the radial ICE probe (Fig. 2a). As such, when the 175 ICE catheter is clinging to the vessel wall, the reflection is interrupted close to 176 the center of the image (Fig. 2a) and the vessel boundary appears C-shaped. 177 Therefore, in this study, an edge-based approach was used to segment the  The performance of the segmentation algorithm is highly dependent on 186 the size and placement of the initial seed. Therefore, for the algorithm to 187 be effective, it is necessary to have an initial seed, closely fitted to and com-   represents the 3D model of the vessel scanned from our phantom (Fig. 3b), 215 spatially present in the EM tracker's coordinate system.

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The absolute distance between the US reconstrcuted vessel and the reg-241 istered CT segmenetd vessel was computed and presented as a heatmap on 242 the vessel surface in Fig. 3c. The average distance between the surface of 243 the two models comes out to be 1.7 ±1.12 mm. A maximum error of 5.86 mm 244 between the two surface models was observed. The spatial overlap between 245 the registered US and CT models was evaluated using the Dice coefficient, 246 sensitivity and specificity measures using: 247 Dice = T P overlap between CT and U S vessels (num voxels CT vessel) * (num voxels U Svessel) (2) where T P , T N , F P and F N represent the true positive, true negative, 248 fasle positive and false negative spatial overlap between the US and CT 249 segmented vessels respectively.

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The spatial distance between the two model boundaries was evaluated 251 using the Hausdorff distance (HD). The geometric accuracy results are re-252 ported in Table 1. Comparison showed that the US model had 12.93 % false 253 negative and 6.60 % false positive spatial overlap.

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The x-ray imaging of our phantom, along with a guidewire, is represented 255 in Fig. 4a. In comparison, we can also achieve tool guidance using an US-256 guided vascular navigation system. Fig. 4b shows how the US reconstructed In this study, we present an vascular reconstruction-based surgical navi-261 gation system, which provides a safe and radiation-free method for guiding 262 tools for X procedure. An EM-tracked ICE US probe was used to reconstruct 263 the vascular path in a phantom, such that it can be visualized in a common  concept demonstration (Fig. 4) shows side by side that an US-guided system 337 can provide the same level of information and in three dimensions without 338 the hazards of radiation and lead shielding.