## 4 Discussion
Hence, although the embolic deployment time is somewhat related to the overall procedure and radiation time, it is not truly correlative in some cases. Perhaps one of the most important implications of our study is cost. Overall, the embolic device cost was significantly reduced in the Caterpillar group compared to the coil group by 54%. In subgroup analysis, coil embolization in larger vessels (>2 mm) would cost 150% more than Caterpillar embolization. This significant decrease in cost allows for better utilization of resources and cost efficiency. This is a small part of cost saving as the Caterpillar group also had significant time savings in embolization, which can translate toless room time. In summary, it is more cost-effective to use Caterpillar than fibered coils in the embolization of selective vessel sizes. Several limitations existed for this retrospective study, which relied on electronic medical records as its primary information source. However, only objective data, such as time and laboratory values, were collected, and all information was collated by two reviewers, limiting the risk of misclassification bias. In addition, the study was limited by its small sample size (16 Caterpillars and 32 matched controls). As the use of the device becomes more widespread, this concern may be addressed in a future study with a larger cohort. Additionally, inconsistent documentation may have affected the analysis of data from three institutions. Lastly, as mentioned above, the true effects on the procedure time and radiation time are not fully reliable as they were indirectly related to vessel occlusion time. Other procedural and anatomical factors can affect the procedure and radiation time. Hence, only relative outcomes of these parameters should be considered. In conclusion, this is the first reported study comparing the efficacy and cost-effectiveness of the Caterpillar device (or any vascular plug) to conventional coils in terms of time to occlusion, as well as radiation and procedure time. Overall, the use of the Caterpillar devices allowed for accurate placement and rapid occlusion of the target vessel in every case in which they were used. Compared to coil embolization, the Caterpillar device demonstrated a significant decrease in time to vessel occlusion, relative radiation and procedure time, and embolic device cost. Conceptualization, E.W.L., T.T.L. and P.-X.D. ; methodology, E.W.L., T.T.L. and P.-X.D. ; validation, E.W.L., M.J.S., J.P., F.H. and N.E. ; formal analysis, E.W.L., M.J.S. and J.P.; investigation, E.W.L., M.J.S., J.P., P.-X.D. and N.E. ; writing--original draft preparation, M.J.S. and E.W.L. ; writing--review and editing, M.J.S., T.T.L., J.P., P.-X.D., F.H., N.E. and E.W.L. ; supervision, E.W.L. ; funding acquisition, E.W.L. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The retrospective clinical study was approved by the Institutional Review Board (or Ethics Committee) of the University of California, Los Angeles (IRB#21-000278, approved on 23 March 2021). This study received a waiver of informed consent; the UCLA IRB waived the requirement for informed consent under 45 CFR 46.116(f) for the entire study. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy restrictions and HIPAA compliance. E.W.L. has received consulting and research support from BD, consulting from Boston Scientifics Co., and consulting from Cook Medical; N.E. has received consulting from Boston Scientific Co.