Mixed Reality Applied to Surgical Planning and Tailoring of Carotid Endarterectomies

doi:10.21203/rs.3.rs-7722134/v1

Download PDF

Research Article

Mixed Reality Applied to Surgical Planning and Tailoring of Carotid Endarterectomies

https://doi.org/10.21203/rs.3.rs-7722134/v1

This work is licensed under a CC BY 4.0 License

You are reading this latest preprint version

Purpose

Perioperative three-dimensional (3D) anatomical visualization with mixed reality (MxR) may have a relevant impact on adequate carotid endarterectomy (CEA) planning compared to standard imaging studies, by highlighting patient specific anatomical features and allowing the rehearsal of the relevant surgical steps in 3D.

Methods

All consecutive CEAs planned with MxR between January 2022 and July 2024 were prospectively included. Using the preoperative head and neck CT-angiography (CTA) and/or MR-angiography (MRA), skin, skull, cervical spine and vascular anatomy including plaques were segmented. The resulting 3D interactive hologram was matched on the patient with MxR glasses in the operating room after patient positioning and drawing initial skin incision. The impact of 3D visualization on surgical planning and anatomical understanding was documented and usability testing was performed.

Results

Forty-nine CEAs were included. Mean hologram’s preparation time was 17+/-8 minutes. Mean duration of intraoperative hologram’s use was 5 +/- 2 minutes. The supervising surgeon significantly altered (shortening) the skin incision in 16 cases (33%). Higher scores were given to the domains Ease of Use and Satisfaction.

Conclusions

CEA planning with MxR seems to have an impact on anatomical understanding for both less experienced neurosurgeons and highly experienced neurosurgeons performing more than 25 CEAs per year. Future research should focus on quantification of the benefits in surgical training and assess the impact on surgical outcomes.

mixed reality

carotid endarterectomy

surgical revascularization

cerebral ischemia

3D visualization

surgical planning

Carotid endarterectomy (CEA) represents the first line of treatment for high-grade symptomatic and asymptomatic carotid artery stenosis worldwide.¹ This surgical procedure has been introduced in the 1950s and has been developed and extensively studied worldwide. The optimal performance of CEA requires experience and training as well as a precise knowledge and understanding of the patient neck anatomy.²

The carotid bifurcation lies normally at the level of the vertebral bodies of C3-C4.³ However this is highly variable and cases of high or low bifurcation must be carefully examined to choose the best therapy (surgery or endovascular, in case of very high or very low carotid location of the plaque).^2,4Also vessels’ tortuosity (i.e.: loop or kinking) or anomalies (i.e.: side-by-side carotid) and variations in its branching pattern can occur. Surgeons should take these variations into consideration for surgical planning. However, all these variations may not be adequately projected in three dimensions (3D) by viewing only two-dimensional (2D) imaging.⁴

Mixed Reality (MxR) could be a suitable technology for better 3D visualization and anatomical understanding and could lead to better surgical planning as well as intraoperative visualization of the patient-specific anatomy.⁵ MxR is a form of Augmented Reality (AR) featured by the overlay of a 3D stereoscopic interactive reconstruction of the patient anatomy, a so-called hologram, over the real world’s anatomy using a head mounted display (HMD), thus without losing the perception of the reality around the hologram. This connection substantially augments not only the anatomical appreciation, but also the spatial orientation and comprehension of the anatomical relationships among healthy and pathologic structures.⁶ Therefore, MxR could optimize the surgical planning, increase intraoperative efficiency, decrease intraoperative adverse events and improve surgical outcomes.

The authors present in this study the experience gathered on MxR application for carotid endarterectomies (CEAs), focusing on the impact on patient-specific anatomical understanding and surgical planning.

The local review board approved the present study before its performance. All included patients signed an informed consent to give permission to the surgical procedure and to the publication of their clinical and radiological data under general KEK PB_2017_00093/NCT01628406 (Kanton of Zurich Ethical Committee). The present study has been performed in accordance to the principle of the Declaration of Helsinki.

Patient clinical and radiological data

Consecutive patients who underwent CEA surgery planned with MxR between January 2022 and July 2024 at our institution were included in the analysis.

Surgical indication to CEA was given on the basis of ICA stenosis percentage, calculated according to the NASCET criteria, vessel angioanatomy and clinical presentation.⁷ All the surgical indications were discussed interdisciplinary either at the cerebrovascular board of our Institution (neurologists, neurosurgeons and neurointerventionalists) or case by case. Preoperative and postoperative modified Rankin scale (mRS) and National Institute of Health Stroke Score (NIHSS) were collected for every patient. Each CEA was performed according to the state of art microsurgical technique.^8–11 Using the preoperative imaging (head and neck CTA and/or MRA), data on plaque presence as well as its position and morphology, carotid bifurcation level (based on cervical vertebral bodies), anatomical variations (side-by-side carotid or abnormal ECA branch origin, i.e. anatomical variations of thyroid artery), carotid vessels’ tortuosity (kinking and loops) were recorded. Data on postoperative imaging control (CTA) performed within 48 hours from the procedure and postoperative adverse events during the hospital stay were also gathered.

Segmentation process and hologram preparation

Using the preoperative radiological studies as source imaging source in the form of Digital Images and Communication in Medicine (DICOM), the CCA, ECA and ICA, as well as the plaques presenting calcifications (when clearly evident) were semi-automatically and manually segmented. (3D Slicer image computing platform | 3D Slicer) Automatic segmentation of skull and cervical spine, as well as skin were performed in dedicated software (LumiNE, Augmedit bv, Netherlands), In this software a visualization scene was automatically deployed including source medical imaging and superimposed 3D segmentation.^12,13 The software generates automatically a format viewable with a stereoscopic head up display (HoloLens 2, Microsoft, Richmond, USA). The total active time required for the hologram’s preparation, i.e. the time demanded to perform manual and semi-automatic segmentations since the automatic segmentations did not require any active time, was recorded.

Intraoperative hologram use

Just before skin disinfection and draping, after patient positioning and a first planning of the skin incision, a manual matching between the hologram, visualized through MxR glasses was performed (Fig. 1). Hereby anatomical landmarks (i.e. mandibular angle, sternal notch, external acoustic meatus and glabella) were used as anatomical landmarks for positioning. Anatomical correspondence was verified by the supervising surgeon. The superimposition of the hologram on the surgical situs was utilized by the neurosurgeon to study the position of the carotid bifurcation and its relation to the incision made previously. Then each supervising surgeon was given the opportunity to shorten the surgical incision according to the 3D visualization and each modification was documented. After the usage of the hologram, the operating neurosurgeon was questioned on the impact of the 3D visualization on the anatomical understanding and the use of the MxR system. The interview was performed on the following domains: Usefulness, Ease of Use, Ease of Learning, and Satisfaction. Table 1 describes in more details how the domains mentioned above were defined.

Table 1
Definition of the Evaluation Domains
Domain	Definition	Meaning of a high score
Ease of Use	How naturally users can interact with the MxR system	The interface feels straightforward and intuitive
Ease of Learning	How quickly and comfortably users can get up to speed with the MR tool	The system can be mastered by those new to it with little effort
Satisfaction	How users feel about their overall experience with the MR system	The system allows the user to achieve the expected goals for its use.
Usefulness	How valuable the MR system is, whether it adds meaningful support	The technology is seen as genuinely helpful in surgical planning and anatomical understanding.

Each domain was given a score from 1, lowest score, to 7, highest score; as score from 5 and above was deemed to be positive¹⁴. All included neurosurgeons had at least 6 months of exposure to the MxR system and their level of experience in CEA surgery was rated according to the annual number of surgeries performed as experienced (>/= 25 CEA/year as supervising surgeon) and inexperienced¹⁵.

Statistical analysis and comparison with non-MxR CEAs

A descriptive analysis was used to analyze the included prospective cohort of patients and characterize the application of MxR on surgical preparation. Data were expressed as percentages, means and standard deviations (SD). All statistical analyses have been performed with Excel 2016 (version 10.0.5491.1000) and R Studio (version 2023.09.0 + 463).

Demographic and surgical data

The study included forty-nine patients with a mean age of 75+/-8 years. The cohort included 28 left (57%) and 21 right (43%) CEAs.

Preoperatively, 38 patients (78%) presented symptomatic stenosis. All the patients but one, who demonstrated a NIHSS of 7 points, showed a NIHSS<7, and 43 patients (88%) demonstrated a mRS≤2. After surgery, all patients but one demonstrated no worsening of the scores. Forty-one patients (84%) received a preoperative CTA, 6 patients (12%) an MRA only and 2 patients (4%) underwent both imaging studies. Immediate postoperative imaging control with head and neck CTA was performed for 48 patients (98%), in one patient a doppler-ultrasound was performed instead. All patients showed a successful postoperative result with patent internal carotid artery.

Hologram preparation

The mean time to achieve complete semi-automatic and manual segmentation was 17+/-6 minutes. While for the majority of the included cases the arterial structures of interest were segmented semi-automatically (38 cases, 76%), the CCA, ICA and ECA were segmented manually in 12 cases (24%). The determination of the level of the bifurcation on the hologram using the level of the vertebral bodies showed that the most represented bifurcation level was between C4 and C5 vertebral body (14 cases, 29%), followed by level C3-C4 (12 cases, 24%). In all cases included in the present cohort, the plaque’s localization included the level of the bifurcation. An overview of the steps of hologram’s preparation is illustrated in Figure 2.

Impact of intraoperative use

Mean duration of intra-operative (i.e. during the non-sterile phase of the operation, after positioning and before disinfection and draping), hologram’s use was 5 +/- 2 minutes. Moderate kinking of the affected ICA was observed in 3 cases (6%): In one case (2%), a side-to-side anatomy was reported. Tailoring the skin incision, i.e. shortening it to focus on the position of the bifurcation, based on intraoperative hologram visualization was performed in 16 cases (33%).

After being questioned on their experience with MxR, by 3 of the 5 neurosurgeons the mean score of all the domains was above 5. The best scores were given to the domains Ease of Use and Satisfaction, while the worst score was given by an inexperienced surgeon in the domain Usefulness. More details on the results of the interviews are provided in Table 2.

Table 2: Summary of the interview’s results showing a color-coded representation of the mean values for each domain and a general mean value with standard deviation

Illustrative case with ordinary anatomical features

A 68-years-old male patient presenting with a transitory ischemic attack (TIA) showed a 50%-stenosis of the right ICA at a Doppler-Ultrasound. A preoperative head and neck CTA documented a carotid bifurcation at C3 vertebral body level and a partially calcified plaque localized at the level of the CCA bifurcation and at the origin of the ICA. Starting from the preoperative CTA as source imaging, a holographic rendering of the plaque and of the CCA, ICA and ECA, as well as the single thyroid artery was performed. After intraoperative patient positioning, the hologram was manually matched with the patient’s head and neck providing a 3D visualization of the carotid bifurcation and plaque, confirming the correct incision planning. The anatomical correctness of the matching of the hologram, the incision planning, the holographic plaque extension and the origin of the thyroid artery was then confirmed intraoperatively after reaching the carotid sheath and opening the CCA and ICA (Figure 3).

Illustrative case with complex anatomical features

The case of a 78-years-old female patient was presented to the institutional interdisciplinary vascular board to discuss the indication of a left CEA. She presented a fluctuating paresis of the right hemibody as well as right hemodynamic watershed strokes on CT and an 80%-stenosis of the left ICA at Doppler-Ultrasound. The indication of a CEA over a stenting was given, driven by the presence of a floating thrombus at the level of the calcified plaque. The preoperative holographic reconstruction of the anatomy of the patient could demonstrate clearly plaque and thrombus, and it highlighted the presence of a severe kinking (110°) of the ICA distal of the stenosis (Figure 4). Due to the relevant kinking of the ICA and with the aim to correct it surgically, the supervising surgeon decided to remove the plaque using the eversion technique. The eversion of the stenotic left ICA allowed indeed a complete removal of the plaque and a correction of the kinking.

In this case, the interactive holographic reconstruction helped by increasing the anatomical appreciation of relevant patient-specific features and endorsed the intraoperative decision to perform the eversion technique.

This study aimed to evaluate the applicability of MxR on surgical planning of CEA and anatomical understanding.

In our opinion, the added value of MxR lies in the direct transfer of 2D anatomical details in 3D and the overlay of the 3D reconstruction on the surgical field. This overlay has the potential to enhance the intraoperative identification of relevant morphological details, i.e. height of the bifurcation, loops or kinking, twisted anatomy, as well as the morphology of the plaque and its extension. The impact of an improved intraoperative visualization may be relevant on the effectiveness of the surgical isolation of the carotid sheath and identification of the bifurcation and ICA. The improved anatomical appreciation may be beneficial for less experienced neurosurgeons and but also for expert ones. Less experienced surgeons could profit from the 3D visualization to increase spatial orientation improving their intraoperative understanding. On the other hand, experienced ones may benefit from the clearer depiction of details to further improve and tailor their surgical strategy. Furthermore, the relatively low cost of the system could thereby increase its use for this indication. This study is a first exploration of the effects of the technology and cannot be used to study reduction of complications or improvement of outcome.

Despite the wide diffusion of MxR in the neurosurgical field and the presence of multiple studies endorsing the positive impact of this technology on anatomical comprehension, surgical planning and training, to our knowledge no study specific on MxR for CEA planning has been published yet. Preliminary experience on the potential positive impact of this technology on CEA was previously published by our group in a more comprehensive cohort of neurosurgical cases.⁵ Neuronavigation technology or ultrasound have not found its way to this procedure because the absence of head fixation and a high cost/benefit ratio.

In spite of its merits, the present study has several limitations. First, this study is an initial exploration of the potential benefits of MxR on CEAs and cannot be used to study reduction of complications or improvement of outcome. Furthermore, the nature of the present cohort, including a small number of cases from a tertiary referral center and no control group, may fail to clearly demonstrate the benefits of the application of the technology. A major theoretical limitation of the technology thereby is the absence of rotation in the hologram. Head rotation during operative positioning could provide a change in the intraoperative anatomy compared to the anatomy during scanning which is performed in straight supine position. However, we did not find this of relevant impact for the purposes of this study. Matching was still possible on the combination of anatomical landmarks and the intraoperatively found level of bifurcation was adequate in all cases, although intraoperative hologram-head matching was operator-dependent and the correspondence’s check between hologram and patience anatomy was still subjective. Formal objective measurement of the registration error is therefore a good step for future research. Other intrinsic limitations could also limit its wide adaptation. Its workflow is influenced by the quality of the internet connection, thus, it may not be easy to implement in operating rooms. Also preoperative imaging quality impacts heavily hologram quality. A bad scan will result in an ugly hologram.

Future developments should focus primarily on the improvement and automatization of the MxR workflow dedicated to CEA procedures: the head to hologram matching should be made automatic and not operator-dependent, and the hologram should become adaptable to the specific head and neck positioning. Furthermore, in order to increase the reproducibility and applicability of the results, a more numerous and diverse cohort of cases should be examined and matched with a control group. Moreover, the integration of hemodynamic parameters into the holographic rendering, in order to combine patient-specific 3D interactive anatomical information to vessel-specific volume flow rates, flow velocity turbulences and shear stresses should be investigated. MxR could then be integrated in the diagnostic workup for carotid artery stenosis and influence the therapeutic decision making.

Another relevant application is the training of surgeons to perform CEAs. MxR could represent a valuable simulation model for CEAs giving the possibility of training different surgical scenarios in a non-threatening environment, and allowing less experienced surgeons to appreciate the nuances and variations of the anatomy of the carotid artery at the neck. This role of MxR should be further explored.

CEA planning with MxR seems to have an impact on incision planning and preoperative anatomical understanding. Future research should focus on quantification of the benefits in surgical training.

Funding: the present study was performed as part of the PhD of Dr. med. E. Colombo and received funding through the SURGENT Consortium, University of Zurich (UZH). https://www.hochschulmedizin.uzh.ch/en/projekte/surgent.html

Disclosures: Tristan van Doormaal is the Chief Medical Officer of Augmedit, and received a grant from Hanarth foundation, paid to UMC Utrecht. Giuseppe Esposito is a member of the Board of Trustees for the Brain Disease Foundation and is a consultant for Aesculap B. Braun. Luca Regli owns shares of Augmedit. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

Kernan WN, Ovbiagele B, Black HR, et al. Guidelines for the prevention of stroke in patients with stroke and transient ischemic attack: a guideline for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2014;45(7):2160-2236. doi:10.1161/STR.0000000000000024
Michalinos A, Chatzimarkos M, Arkadopoulos N, Safioleas M, Troupis T. Anatomical Considerations on Surgical Anatomy of the Carotid Bifurcation. Anat Res Int. 2016;2016:6907472. doi:10.1155/2016/6907472
Alves Ribeiro R, de Souza Ribeiro JA, Omar ARF, Goncalves Caetano A. (PDF) Common Carotid Artery Bifurcation Levels Related to Clinical Relevant Anatomical Landmarks. International Journal of Morphology. 2006;24(3). doi:10.4067/S0717-95022006000400019
Schulz UG, Rothwell PM. Major variation in carotid bifurcation anatomy: a possible risk factor for plaque development? Stroke. 2001;32(11):2522-2529. doi:10.1161/hs1101.097391
Colombo E, Regli L, Esposito G, et al. Mixed Reality for Cranial Neurosurgical Planning: A Single-Center Applicability Study With the First 107 Subsequent Holograms. Oper Neurosurg (Hagerstown). 2023;26(5):551-558. doi:10.1227/ons.0000000000001033
Kos TM, Colombo E, Bartels LW, Robe PA, van Doormaal TPC. Evaluation Metrics for Augmented Reality in Neurosurgical Preoperative Planning, Surgical Navigation, and Surgical Treatment Guidance: A Systematic Review. Oper Neurosurg (Hagerstown). 2023;26(5):491-501. doi:10.1227/ons.0000000000001009
Ferguson GG, Eliasziw M, Barr HW, et al. The North American Symptomatic Carotid Endarterectomy Trial : surgical results in 1415 patients. Stroke. 1999;30(9):1751-1758. doi:10.1161/01.str.30.9.1751
Velz J, Esposito G, Wegener S, Kulcsar Z, Luft A, Regli L. [Diagnostic and Therapeutic Management of Carotid Artery Disease]. Praxis (Bern 1994). 2020;109(9):705-723. doi:10.1024/1661-8157/a003475
Uno M, Takai H, Yagi K, Matsubara S. Surgical Technique for Carotid Endarterectomy: Current Methods and Problems. Neurol Med Chir (Tokyo). 2020;60(9):419-428. doi:10.2176/nmc.ra.2020-0111
Rothwell PM. Endarterectomy for symptomatic and asymptomatic carotid stenosis. Neurol Clin. 2008;26(4):1079-1097, x. doi:10.1016/j.ncl.2008.09.013
Fode NC, Sundt TM, Robertson JT, Peerless SJ, Shields CB. Multicenter retrospective review of results and complications of carotid endarterectomy in 1981. Stroke. 1986;17(3):370-376. doi:10.1161/01.str.17.3.370
van Doormaal JAM, Fick T, Ali M, Köllen M, van der Kuijp V, van Doormaal TPC. Fully Automatic Adaptive Meshing Based Segmentation of the Ventricular System for Augmented Reality Visualization and Navigation. World Neurosurg. 2021;156:e9-e24. doi:10.1016/j.wneu.2021.07.099
Fick T, van Doormaal JAM, Tosic L, et al. Fully automatic brain tumor segmentation for 3D evaluation in augmented reality. Neurosurg Focus. 2021;51(2):E14. doi:10.3171/2021.5.FOCUS21200
Lund A. Measuring Usability with the USE Questionnaire. ResearchGate. Accessed July 14, 2025. https://www.researchgate.net/publication/230786746_Measuring_Usability_with_the_USE_Questionnaire
Breite MD, Breite CN, Sheaffer WW, et al. Carotid endarterectomy surgeon volumes in contemporary practice: A comparison to randomized trial inclusion criteria. Am J Surg. 2021;222(1):241-244. doi:10.1016/j.amjsurg.2020.11.004

Competing interest reported. Tristan van Doormaal is the Chief Medical Officer of Augmedit, and received a grant from Hanarth foundation, paid to UMC Utrecht. Giuseppe Esposito is a member of the Board of Trustees for the Brain Disease Foundation, and is a consultant for Aesculap B. Braun. Luca Regli owns shares of Augmedit. The other authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.

Download PDF

Reviewers agreed at journal
26 Oct, 2025
Reviewers invited by journal
16 Oct, 2025
Editor assigned by journal
03 Oct, 2025
Submission checks completed at journal
03 Oct, 2025
First submitted to journal
26 Sep, 2025

You are reading this latest preprint version

Mixed Reality Applied to Surgical Planning and Tailoring of Carotid Endarterectomies

Status:

Version 1

Abstract

Purpose

Methods

Results

Conclusions

Figures

Introduction

Materials and Methods

Patient clinical and radiological data

Segmentation process and hologram preparation

Intraoperative hologram use

Statistical analysis and comparison with non-MxR CEAs

Results

Discussion

Conclusion

Statements and Declarations

References

Additional Declarations

Status:

Version 1