# Evaluation of HMDs by QFD for Augmented Reality Applications in the Maxillofacial Surgery Domain
## 3 Results
### Scenario n. 3--Maxillofacial Trauma Surgery  
This application proves to be the less challenging between the evaluated scenarios. In trauma treatment, the preoperatorary planning, where the skull fragments puzzle is recomposed, is as important as correctly shaping the fixing plates. The complete QFD table has been supplied in the Supplementary Material (Table S4).  
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 subtraction of 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 message for real-time surgical assistance.
* Robust voice control: the number of people in the operating room should not condition the voice command's 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.
* Display and navigate face DICOM: the face is important as the site of the implant; therefore, all available medical data are necessary to be displayed at the surgeon's request.
* Display and handle 3D models of bones: it is fundamental that bone resection models are displayed.
* Display and handle non-standard tools 3D models (guides, splints, plates): tailored surgical tools must be easily managed.
* 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, while a digital zoom may alter the images.
* Add-on accessories: a modular device allows the device to be customized.  
The specification relative importance is shown in Figure 6. Computing power, resolution, and cameras, like the previous case, are still relatively the most important specifications; all the other features are significantly less important.  
Figure 7 shows which device, between those evaluated, can better fulfil the maxill-facial trauma requirements. The best-case device is represented by a white background element to improve the contrast with the market devices coloured lines; this makes it easier to identify the best-performing devices. The reduced gap between devices scores, with respect to the previous scenarios, is a consequence of the easier requirement list.  
Figure 6: Device specification relative importance for maxillofacial trauma surgery.  
Figure 7: Device evaluation chart for maxillofacial trauma surgery.