# Evaluation of HMDs by QFD for Augmented Reality Applications in the Maxillofacial Surgery Domain
## 3 Results
### Scenario n. 1--Onological and Reconstructive Surgery  
This application resulted as the most challenging because involves two different operation sites. This means having two medical teams working at the same time with an increase in medical data needed to meet the requirements of the increased number of 3D models. Moreover, in the oncological scenario, there is the possibility to visualise soft tissue in addition to bones. The complete QFD table has been supplied in the Supplementary Material (Table S2). The explanation of qualitative requirements is as follows:  
* Simple and smart user interface: smooth navigation through menus and an intuitive layout for tools and information. * Custom user interface: custom interface layout for user comfort. * Lightweight and comfortable: the device must not hinder or weary the surgeon. * Ample and unobstructed field of view: the device must not hinder the surgeon's field of view. The AR is an addition to, and not a substitution for, human view. * Real-world colour fidelity: the device must not alter the aspect of real objects. * User feedback: using visual (colour maps, vector maps, etc.) or audio messaging for real-time surgical assistance. * Robust voice control: the number of people in the operating room should not condition the voice command functionality. * Robust to occlusions: the device must keep track of operation site, surgical tools, and surgeon's hand independently from any visual hindrance. * Robust to contrast: the device must not be influenced by any light sources (e.g., surgical lights, headlights) present in the operating room. * Robust face tracking: the device must never lose the operation site tracking. The face is a sensitive site in case of head repositioning due to the number of joints in the head/neck area. * Robust leg tracking: the device must never lose the tracking of the leg operation site irrespective of how much soft tissue is involved. * Display and navigate face DICOM: the face is important as the site of the implant, then all available medical data are necessary to be displayed on surgeon's request. * Display and navigate leg DICOM: the leg, as the donor site for the fibula-free flap procedure, needs all available medical data to be displayed on surgeon's request. * Display and handle 3D models of bones: it is fundamental that bone resection models are displayed. * Display and handle soft tissue 3D models: in oncologic and reconstructive surgery, soft tissue may be included in the collected graft. * Display and handle non-standard tools 3D models (guides, splints, plates): tailored surgical tools must be easily managed. * Display osteotomy cut lines: virtual guides to help the surgeon to identify the position and orientation of the resection planes. * Choice for every 3D model the display style: solid, wireframe or hidden. Many objects are visualised in mixed reality; choosing the best display style for each one is, therefore, necessary. * Share live images on other devices: viewing the operation site from a user's point-of-view aids teamwork and is useful as a training method. * Record images for training and evaluation: recorded images from the surgeon's point-of-view are useful for training and postoperative checks. * Device autonomy must be adequate for the required task: in battery-powered devices, the autonomy must be adequate to last the duration of the operation. * Cordless device: many people and devices are present in the operating room; therefore, easy-to-manoeuvre solutions are preferable. * Optical zoom: some structures and vessels are too small to be seen by the human eye; therefore, a digital zoom may alter the images. * Add-on accessories: a modular device allows the device to be customized. The specifications' relative importance is shown in Figure 2. The radar chart underlines the importance of computing power due to the number and complexity of 3D models handled. The resolution is also important to have a proper fusion between the real scene and virtual models.