# Intraoperative Use of Mixed Reality Technology in Median Neck and Branchial Cyst Excision
## 4 Conclusions  
Overall, these proposed solutions can be used for treatments using MR technology on a daily basis. However, the most effective solutions were the radiopaque marks used (in the second and third cases), which allowed us to automate the calibration process. In both cases, the additional time spent on patient preparation was no more than 10 min (excluding the 3D segmentation process). On the other hand, in the first case where face mask was used, the total time for preparation was about an hour due to difficulties with the patient's positioning.  
Resulting hologram positioning accuracy depends on:  
* Marker-based 3D visual localization [17]. Translation error from 1 m distance is about 2-3 mm;
* Manufacturing accuracy of fabricated marker holder. For FDM technology, this is about 0.2 mm;
* CT data slice thickness. In our case, all datasets have 1 mm thickness;
* Marker placement.  
In the first case, the overall error was approximately 7-15 mm due to our inability to precisely measure the mask's complex shape. On the other hand, in the second and third cases, we used our own marker holders, so the total error decreased for both cases down to 3-7 mm. Thus, the most significant amount of error was caused by the marker placement. For future development, we are planning to focus on a more accurate marker positioning system that uses multiple smaller markers.  
In addition, based on these cases, we compiled a list of benefits and drawbacks for using MR technologies in the operating room:  
1. The MR technology can be applied in the operating room as an additional auxiliary technique to assess the adequacy of surgical exposure as well as for intraoperative navigation;
2. The bloodstream visualization eliminates the risk of great arterial and venous trunks intersection. Additional ligation is almost completely excluded;
3. At the current stage of technological development, there is a competition between the brightness of the operating room lighting and the brightness of the hologram, which makes their simultaneous use impossible. Therefore, the MR technology can  
Figure 10: Construction of 3D model of anatomical structures using 3D Slicer. Standardization of the patient’s position in the operating room and intraoperative image in mixed reality glasses (Microsoft HoloLens 2).  
be implemented for periodic navigation of the wound with the lights dimmed as well as for postoperative follow-up of cysts and fistula excision;
4. The direct use of mixed reality technology during surgical manipulations based on the problem of \"focal rivalry\" [25] is difficult. Therefore, glasses were used only in the process of planning and marking access, as well as in checking the results with the preoperative state.
5. Despite the rigid fixation of the patient in Case 1, Cases 2 and 3, which involved no rigid immobilization of the patient relative to the operating table, demonstrated the best accuracy for hologram referencing. We attribute the obtained results to the variants of the reference marker's attachment to the patients' body parts and its relation to the surgery area. The closer they were to each other, the more accurately the hologram could reference to the real landmarks.  
Conceptualization, V.M.I., S.V.S. and M.N.P.; methodology S.V.S. and M.N.P.; project administration, V.M.I., A.M.K. and A.I.Y.; resources, A.M.K., N.V.K. and A.I.Y.; software, S.V.S.; supervision, V.M.I.; Visualization, S.V.S., O.V.L. and A.P.L.; writing--original draft, S.V.S., N.V.K., M.Y.P. and M.N.P.; writing--review & editing, V.M.I. and A.M.K. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.