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DE GRUYTER C u rrent Directions in Biomedical Engineering 2022;8(1): -12 Mareen Allgaier*, Belal Neyazi, I. Erol Sandalcioglu, Bernhard Preim, and Sylvia Saalfeld Immersive VR training system for clipping intracranial aneurysms https://doi.org/10.1515/cdbme-2022-0003 In our proposed immersive VR clipping training, we make use of the motivational benefits of immersive VR. Hereby, the Abstract: Training clipping of intracranial aneurysms is chal- user is surrounded by a virtual environment imitating the real lenging due to less frequent interventions because of minimal- scenario. Furthermore, immersive VR provides intuitive and invasive methods, ethical aspects regarding cadaver training realistic interactions with 3D anatomical models. In virtual and consumption of resources when using 3D printed mod- systems it is also possible to undo single steps, save results, els. By proposing an immersive virtual reality training system, explore anatomical structures without physical limitations, and we make use of increased motivation, engagement and realism to easily compare different strategies and results. when using a virtual operating room. In this simulation, a se- lected microsurgical clip can be applied at the aneurysm neck. Before closing the clip and deforming the vessels, the affected area is visualized to assess the clip position. Our qualitative 2 Related Work evaluation with two neurosurgeons with different levels of ex- perience indicates benefits such as increased motivation, pres- Because of the relevance of additional training for IA clipping, ence, and the possibility to try out different strategies. How- there are several commercial and non-commercial virtual sys- ever, some surgical steps can be refined to increase realism tems. An easy-available but non-immersive system proposed and learning effect, and interactions can be further improved. by Allgaier et al  provides additional visualizations high- The proposed training system benefits from training by trial lighting the vessel deformation during clipping. and error in an engaging environment leading to an improved The commercial Immersive Touch® system (Chicago, IL) training experience. was evaluated by 17 experts . The study was conducted with a semi-immersive stereoscopic monitor-mirror system and a Keywords: Virtual Reality, Surgical Training, Intracranial haptic stylus, the Geomagic Touch (3D Systems, Rock Hill, Aneurysms, Clipping. SC). The procedure includes the drawing of a craniotomy out- line and placing the clip. Exposing the aneurysm by opening 1 Introduction the Dura and Sylvian Fissure was not included. Their results show that the majority of participants believes that the simu- Immersive virtual training (VR) is an easily available and cost- lation is helpful regarding anatomy, education, preparing for effective method to train specific surgical procedures, espe- a surgery and finding an appropriate approach. However, nine cially procedures that are seldom and require anatomical un- participants had difficulties with grasping and interacting with derstanding. Such a procedure is microsurgical clipping of in- the clip because of an unfamiliar depth perception. Further- tracranial aneurysms (IAs), which are pathological dilatations more, only 12% rated the haptic feedback as realistic. of blood vessels in the brain. A clip has to be applied care- Similar to Alaraj et al. , Gmeiner et al.  evaluated a fully at the aneurysm neck to seal it off the blood flow with- semi-immersive clipping system developed at RISC Software out affecting other arteries and thus retaining the normal blood (Hagenberg, Austria) using a stereoscopic display and the Ge- flow. Depending on the access, possible clipping strategies are omagic Touch. However, Gmeiner et al.  applied the real limited. To train the correlation between access and clipping, medical instrument such as a forceps to the haptic device and virtual training is a good way to explore different strategies included blood flow to evaluate the clipping. Their study with without harming someone or having ethical conflicts. 18 experts also revealed similar results. For anatomical educa- tion it is highly appreciated, whereas only one third mentioned that the haptic interaction was truly satisfactory. *Corresponding author: Mareen Allgaier, Otto-von-Guericke Another commercial system is the Dextroscope® (Vol- University, Department of Simulation and Graphics, Universitätsplatz 2, Magdeburg, Germany, e-mail: ume Interactions Pte Ltd, Singapore). Three neurosurgical de- firstname.lastname@example.org partments used this system with either a monitor-mirror sys- Belal Neyazi, I. Erol Sandalcioglu, Department of Neurosurgery, tem or a stereoscopic display . However, this system could University Hospital Magdeburg, Germany only be used to plan the intervention by placing an already Bernhard Preim, Sylvia Saalfeld, Department of Simulation and Graphics, University of Magdeburg, Germany Open Access. © 2022 The Author(s), published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 International License. 9 M. Allgaier et al., Immersive VR training system for clipping intracranial aneurysms closed clip at the desired location. The clip could not be opened and closed and no vessel deformation was simulated. In contrast to the previously mentioned approaches, Shono et al.  proposed a virtual simulation that comprises dissecting the arachnoid membrane and trabecula, and retract- ing the brain. In the clipping phase, clips can be applied at a de- formable aneurysm. For the deformation, they use NVIDIA’s PhysX engine, which is integrated in the game engine Unity. Like the previous approaches they use a stereoscopic display. For interactions they employ the motion capture device Leap Motion® (Leap Motion, San Francisco, CA) with a 3D-printed Fig. 1: Virtual operating room. forceps. Additionally, they include usual sounds of an operat- ing room to increase the sensation. Tab. 1: Parameters used for NVIDIA Flex soft container for vessel Besides virtual simulations, there are also hybrid simula- deformation. tions combining realistic physical cases with VR. Theodoro- Vite et al.  use a physical workstation with a patient skull Simulation Parameters Common Parameters and Mayfield clamp in combination with a VR simulation us- Substep Count 9 Static Friction 3 ing a VR headset to explore and clip an aneurysm. The user Iteration Count 15 Dynamic Friction 2 can interact with the virtual instruments with the help of the Gravity (0,0,0) Particle Friction 1 Radius 0.002 Max Speed 340282.3 Geomagic Touch. Solid Rest 0.0005 Max Acceleration 340282.3 In contrast to the above-mentioned approaches, we want Fluid Rest 0.0002 Damping 50 to provide an immersive training experience. To achieve this, Collision Distance 0.0002 we use a VR headset in combination with a pen-like device to imitate a real surgical instrument. Furthermore, the experience is improved by using a virtual operating room including vir- to choose a clip from an inventory menu where the clip proper- tual staff. During clipping, a real-time deformation is used to ties such as opening angle and length can be seen. The chosen deform the vessels according to the applied clip. Finally, ad- clip can then be applied to the aneurysm. Since the navigation ditional visual support to increase the usability and training is is difficult due to a lack of depth cues because of missing sur- included. rounding structures, rays indicating distances between the clip and vessels are included  (see Fig. 2 1b). Once the clip is placed, closing is visualized by highlighting the area the clip would hit (see Fig. 2 2b). By this, the user can asses whether 3 Material and Methods the clip is placed in the desired way and which parts of the ves- sels and aneurysm are affected. Finally, the clip can be closed The immersive VR simulation was implemented with the leading to a deformation of the vessels. For this, an NVIDIA game engine Unity (Unity Technologies: https://unity.com, Flex softbody surface representation with the physical param- San Francisco U.S.). For the implementation and evaluation eters summarized in Tab 1 is applied to the vessels. an HTC Vive Pro Eye (HTC Corporation, Taiwan) was used. As input device, the VR Ink (Logitech, Switzerland) was cho- sen because a pen-like device is more similar to the medical instrument than a device held in power-grip, such as a VR 4 Evaluation controller, and thus more appropriate . The same clip and middle cerebral artery aneurysm models as in previous work The virtual clipping was qualitatively assessed by two neuro- were used . surgeons: One male senior neurosurgeon (S) with 13 years of In the following the simulation workflow is described. Af- neurosurgical experience who often used VR, and one female ter one of the predefined aneurysms is selected, the user en- novice neurosurgeon (N) with one year of neurosurgical expe- ters a virtual operating room (see Fig. 1) adapted from Hu- rience who has used VR a few times. The evaluation started ber et al. . According to the use case, the patient’s head is with a short description of the tasks and interactions. Before approximated by a skull, since skin incision is not included using the application, they were asked to complete the Simula- in the workflow. The positioning of the head, craniotomy and tor Sickness Questionnaire (SSQ-pre) . Subsequently, they brain retraction are described in . Afterwards, the user has had to go through the application. Thereby, they were verbally 10 M. Allgaier et al., Immersive VR training system for clipping intracranial aneurysms to real micorsurgical procedures. However, the senior neuro- Navigation surgeon emphasized that the virtual clipping is much more difficult due to jittering, leading to a higher frustration. The reason for this is probably because of a missing physical skull with which they usually stable their hands. Regarding clipping, both participants liked the deforma- 1a) 1b) tion and rated it as realistic enough. They also emphasized that it is a crucial part of a training system. However, it would Positioning and assessment be good to have the possibility to modulate the speed of the clip application. Usually surgeons do not just apply the clip but close it carefully, observing the deformation and open it again to replace it if necessary. Showing the area affected by the clip helped the surgeons to discern the clip location in the 2a) 2b) 3D space. Furthermore, it should be possible to apply multiple clips. Application and deformation Regarding clip assessment, different possibilities were discussed. The first possibility would be to include visual ex- ploration of the clipped aneurysm. Both rated this approach as very useful, as this would be similar to an angiography with which one can check whether the aneurysm is sealed off 3a) completely. Furthermore, they would appreciate an additional numeric output indicating how much (e.g. percentage) of the Fig. 2: Virtual clipping of an aneurysm (marked with the yellow aneurysm ostium is closed. The third possibility was rated a rectangle in 1a). bit less helpful than the others. Here, it was proposed to fill the vessels with blood. One participant mentioned that with this one can see whether the parent artery is still open. However, it assisted and reminded which buttons they have to use. After is currently not possible to simulate realistic blood flow during they completed the workflow, they were asked to fill out a runtime of a real-time application. It can only be approximated questionnaire comprising the following parts: by a fluid simulation e.g using NVIDIA Flex. Further aspects 1. Simulator Sickness Questionnaire (SSQ-post)  that can be used to evaluate and compare the clipping results 2. NASA Task Load Index (NASA-TLX) to assess mental are time and how strong the brain is retracted. and physical demand  Furthermore, general improvements were discussed. First, 3. Questions referring to clipping we proposed collaborative VR, where two or more users can 4. Questions referring to further improvements use the simulation at the same time. They can either work to- 5. Igroup Presence Questionnaire  and additional ques- gether and discuss different approaches, or work in a compet- tions to assess presence and immersion itive mode where the users compete against each other. Both participants think that both modes would lead to an increased motivation and learning effect. However, the feedback and re- 5 Results actions of the senior neurosurgeon show that he would prefer the competitive mode. In the SSQ one participant (S) mentioned an increase from Moreover, the brain retraction should be limited as such ’none’ to ’slight’ regarding the symptoms ’general discomfort’ large deformations are not possible in reality. The novice neu- and ’eye strain’ after using the VR system. rosurgeon stated the consistence and volume of the brain as a The results of the NASA-TLX, where usually a 20-point challenge of the access during clipping surgery. A further as- Likert scale is used, show that for one participant the task was pect that could be included is pulssynchronous clipping. In this more mentally demanding (N: 15/20, S: 15/20) than physically context, the novice neurosurgeon also mentioned that includ- demanding (N: 11/20, S: 18/20). Both of them had to work ing EKG sound would make the experience more realistic. hard to accomplish their level of performance (N: 14/20, S: The last part of the questionnaire was about immersion. 19/20). The question of how frustrated they were (N: 2/20, S: Both participants agreed that they felt present in the virtual 14/20) and following up questions indicate that the novice sur- space and they were captivated by the virtual world. However, geon did not have more difficulties placing the clip compared they were aware of the real world and paid attention to it. 11 M. Allgaier et al., Immersive VR training system for clipping intracranial aneurysms Additionally, three questions were added to get an im- tions, institutional policies and was performed in accordance pression whether the participants think that immersion can im- with the tenets of the Helsinki Declaration, and has been ap- prove the training experience. The statement ’Due to immer- proved by the authors’ institutional review board or equivalent sion I can concentrate better on the exercise’ was rated with 4 committee. (S) and 5 (N) (1=fully disagree, 5=completely agree). Whether they take the exercise more seriously was rated with 3 (S) and 5 (N) and ’Due to immersion I’m more motivated to solve the References exercise well’ was rated with 4 (S) and 5 (N).  Alaraj A, Luciano CJ, Bailey DP, Elsenousi A, Roitberg BZ, Bernardo A, et al. Virtual reality cerebral aneurysm clipping simulation with real-time haptic feedback. Neurosurg 2015;11 6 Discussion and Conclusion Suppl 2(0 2):52-8.  Allgaier M, Amini A, Neyazi B, Sandalcioglu IE, Preim B, Our proposed training system differs from previous ap- Saalfeld S. VR-based training of craniotomy for intracra- nial aneurysm surgery. Int J Comput Assist Radiol Surg proaches on the basis of providing an immersive environment 2022;17(3):449-456. using a virtual operating room for aneurysm clipping train-  Allgaier M, Neyazi B, Preim B, Saalfeld S. Distance and ing. Consequently, we provide a motivating and engaging ex- force visualisations for improved simulation of intracra- perience, which is essential for an effective training. With the nial aneurysm clipping. Int J Comput Assist Radiol Surg presented prototype we combine the immersive environment 2021;16(8):1297-1304. with the clipping of aneurysms using a soft body deformation.  Allgaier M, Chheang V, Saalfeld P, Apilla V, Huber T, Huettl F, et al. A comparison of input devices for precise interaction Thus, users can try out different strategies in a more realistic tasks in VR-based surgical planning and training. Comput scenario. Although the device is no medical instrument, we Biol Med 2022;145(2):105429. put emphasis on providing a similar device regarding the hand  Gmeiner M, Dirnberger J, Fenz W, Gollwitzer M, Wurm G, position. However, having a completely virtual system without Trenkler J, et al. Virtual Cerebral Aneurysm Clipping with grounded haptic devices has the drawback of having no sup- Real-Time Haptic Force Feedback in Neurosurgical Educa- tion. World Neurosurg 2018;112:e313-e323. portive surface which is available in a real clipping procedure.  Hart SG, Staveland LE. Development of NASA-TLX (Task To solve this, a 3D printed skull with a large craniotomy hole Load Index): Results of Empirical and Theoretical Research. can be used. This physical model has to be adjusted according Adv Psychol 1988;52:139-183. to the virtual head placement or the virtual head has to be reg-  Huber T, Wunderling T, Paschold M, Lang H, Kneist W, istered with the physical skull after placement. If the virtual Hansen C. Highly immersive virtual reality laparoscopy simu- instrument still jitters more than a real instrument, it is likely lation: development and future aspects. Int J Comput Assist Radiol Surg 2018;13(2):281-290. due to tracking inaccuracy.  Kennedy RS, Lane NE, Berbaum KS, Lilienthal MG. Sim- Our evaluation focused on qualitative feedback, which also ulator Sickness Questionnaire: An enhanced method provides important feedback for further developments. How- for quantifying simulator sickness. Int J Aviat Psychol ever, having more participants would lead to statistical results. 1993;3(3):203–220 The main challenge in this case is to get that many participants,  Kockro RA, Killeen T, Ayyad A, Glaser M, Stadie A, Reisch R, et al. Aneurysm Surgery with Preoperative Three- as the target group is limited to neurosurgeons. Dimensional Planning in a Virtual Reality Environment: Tech- In conclusion, we have presented an immersive VR train- nique and Outcome Analysis. World Neurosurg 2016;96:489- ing system for the clipping of intracranial aneurysms. Our sys- tem benefits from an immersive virtual operating room, realis-  Schubert T, Friedmann F, Regenbrecht H. The Experience tic interactions with a pen-like device and real-time deforma- of Presence: Factor Analytic Insights. Presence: Teleoper tion of the vessels. Virtual Environ 2001;10(3):266–281.  Shono N, Kin T, Nomura S, Miyawaki S, Saito T, Imai H, et Author Statement al. Microsurgery Simulator of Cerebral Aneurysm Clipping Research funding: This study was funded by the Federal Min- with Interactive Cerebral Deformation Featuring a Virtual istry of Education and Research within the Forschungscampus Arachnoid. Oper Neurosurg 2018;14(5):579-589. STIMULATE (grant number 13GW0473A) and the German  Teodoro-Vite S, Pérez-Lomelí JS, Domínguez-Velasco Research Foundation (grant number SA 3461/3-1). Conflict of CF, Hernández-Valencia AF, Capurso-García MA, Padilla- Castañeda MA. A High-Fidelity Hybrid Virtual Reality Sim- interest: Authors state no conflict of interest. Informed con- ulator of Aneurysm Clipping Repair With Brain Sylvian Fis- sent: Informed consent has been obtained from all individuals sure Exploration for Vascular Neurosurgery Training. Simul included in this study. Ethical approval: The research related Healthc 2021;16(4):285-294. to human use complies with all the relevant national regula-
Current Directions in Biomedical Engineering – de Gruyter
Published: Jul 1, 2022
Keywords: Virtual Reality; Surgical Training; Intracranial Aneurysms; Clipping
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