# Medical Augmented-Reality Visualizer for Surgical Training and Education in Medicine
## 1 Introduction  
Medical applications of virtual and augmented reality (AR) have been extensively developed during the last decade [1; 2]. In the current era of data fusion, AR provides an ideal approach for educational purposes [3], especially those related to medicine [4; 5; 6], as it supports the training of surgeons without risk to patients. Virtual reality and AR techniques may also be employed to shorten the learning curves [7] related to surgical procedures and increase the overall educational efficiency, thereby providing increased patient safety. Shortening the learning curves for surgical personnel is a societally important and widely researched issue. It aims to improve the accuracy and performance of surgical procedures in the most effective manner. Key factors related to learning of surgical procedures include proper real-time feedback and trial evaluation [8]. Studies have shown that the preferred feedback type is haptic (e.g., tool vibration) [9], suggesting that the success of surgical training is notably influenced by the degree of realism of the implemented haptic feedback [10]. In addition, surgeons may prefer additional haptic feedback, as it can provide valuable tactile information during surgery [9]. More generally, haptic feedback is believed to enhance perception by providing another mode of sensorial information. A review of simulation platforms available within endourology [11] presents a set of outcome measures for the validation of simulation and assessment tools. They include such parameters as:  
* face validity (i.e., extent to which the examination resembles the situation in the real world),
* content validity (i.e., extent to which the intended content domain is being measured by the assessment exercise),* construct validity (i.e., extent to which a test is able to differentiate between a good and bad performer),
* concurrent validity (i.e., extent to which the results of the test correlate with gold-standard tests known to measure the same domain),
* predictive validity (i.e., extent to which this assessment will predict future performance),
* acceptability (i.e., extent to which assessment procedure is accepted by subjects in assessment),
* educational impact (i.e., extent to which test results and feedback contribute to improve the learning strategy on behalf of the trainer and the trainee),
* cost effectiveness (i.e., technical and nontechnical requirements for implementation of test into clinical practice)  
An initial validation of the system described in this paper with regard to the aforementioned parameters will be presented in further sections. Currently available systems that support surgical procedures by means of augmented visualization utilize virtual reality headsets, goggles with translucent displays [12], or external computer displays [13]. For instance, head-mounted displays like Google Glass or Microsoft Hololens are being used in research on medical procedure training [14; 15]. Although the headsets are often reported to be useful, they create a physical barrier between the surgeons and their environment, imposing an undesirable situation during medical procedures. Moreover, most translucent devices require additional markers for external tracking to achieve precise positioning of the virtual structures [16], especially in changing environments. Most of these devices are uncomfortable to wear and use for prolonged periods and often cause eye strain, headaches, and substantial discomfort [17; 18; 19]. Likewise, external screens can cause discomfort by the frequent switching of the surgeon's focus between the patient and screen, thus prolonging operation time. Another known disadvantage is that stereoscopic AR projection systems can exhibit the vergence-accommodation conflict. Conventional 3D displays present images on a surface, requiring both eyes to focus at a certain distance regardless of the intended distance to the virtual object. Hence, it is essential to properly set the depth of the display considering the depth of the depicted scene.