## 4 Discussion  
The ability to accurately and safely deploy an embolization device is a cornerstone of a successful embolization procedure. While many embolic agents are available, they are often limited in their ability to achieve distal control and immediate occlusion, not re-sheathable, and difficult to place in tortuous or small target vessels. The Caterpillar Arterial Embolization Device (Caterpillar) appears to address many of these limitations. The Caterpillar with its dual nitinol fibers and occlusion membrane allows for accurate placement and improves occlusion timing. However, no clinical comparison studies have been performed to evaluate their embolic efficacy. In this study, we compared the embolic effects of the Caterpillar to the fibered endovascular coils in a variety of arterial embolic procedures. Overall, the Caterpillar device demonstrated a significantly shorter relative time to occlusion, significantly decreased cost, and potentially decreased radiation and procedure time compared to the fibered coil embolization in arterial procedures. As the primary outcome, the Caterpillar embolization procedures were found to have a significantly reduced relative time to complete vessel occlusion in all procedures compared to fibered coil embolization procedures in our matched cohort. In all procedures, the Caterpillar achieved an overall 92% reduction in occlusion time from an average of 12 min to 1 min. This was due to (1) the decrease in the number of devices (one Caterpillar per procedure compared to multiple fibered coils) required for complete vessel occlusion, and (2) the proprietary occlusive membrane that is a part of the Caterpillar. This reduction in occlusion time was further analyzed in subgroups based on the vessel size (>2 or <2 mm). In the larger vessel group (2.1 to 5.1 mm), a similar reduction in occlusion time in the Caterpillar group was observed as expected, as many coils (up to 11) were needed in some cases. Similar findings were noted in the small vessel group (1.3 to 2 mm). The average occlusion time was significantly reduced in the Caterpillar group by 84% (from 9 min 49 s in the coil group to 1 min 56 s in Caterpillar group). Even though embolizing small vessels did not require as many coils or as much procedure time, more time was still needed for occlusion compared to a single device occlusion with Caterpillar. Future studies with a larger number of procedures with various vessel sizes should be performed to confirm these findings. Shorter vascular occlusion times also translated to decreased overall procedure times. In addition to saving procedure time and radiation dose by simply requiring fewer devices (less time to open packages and deploy coils), using fewer embolic devices produces procedure time by decreasing the number of \"judgement calls\" required by the operator (for example, determining the size, number, and packing density of coils). Ref. [12] In our study, mean procedure times were significantly shorter in the Caterpillar patients (81.0 \(\pm\) 36 min), compared to the mean procedure time for the control group of 111.5 \(\pm\) 49 min. Fluoroscopy time was chosen as the surrogate for relative radiation dose. The Caterpillar group had a significantly lower mean fluoroscopy time at 19.2 \(\pm\) 14 min compared to the control group at 30.7 \(\pm\) 15 min. Saving radiation dose for both the patient and the operator has a significant clinical impact for both parties, decreasing both deterministic and stochastic radiation effects. However, we believe that the overall procedure time or radiation time assessment is not an accurate assessment, as there are many other factors involved in increasing the procedure or radiation time such as the anatomical complexity of the target vessels for embolization, operators' experience, additional time spent on other parts of the procedure such as additional angiograms during Y90 mapping, or multiple catheter and wire exchanges.