# Review of Microsoft HoloLens Applications over the Past Five Years
## 3 Results
### Applications in Medical and Healthcare Fields
#### 3.1.1 Medical and Surgical Aids and Systems
The frustum of the flexible endoscope is rendered as an AR overlay, to provide surgical guidance. They developed a prototype FlexiVision integrating robotic flexible endoscope based on the da Vinci Research Kit and Microsoft HoloLens. Additionally, the AR surgical guidance was evaluated in the lesion targeting task; it was confirmed that the completion time, number of errors and subjective task load level could be significantly reduced. [PERSON] et al. [44] proposed a balance rehabilitation method based on AR. This method measures the movement of the head through an inertial measurement unit sensor mounted on an AR HMD and quantitatively assesses the individual's postural stability. Moreover, it provides visual feedback to the user through holographic objects that interact with the head position in real time (Figure 5). The proposed method was validated using eight participants, who performed three postural tasks three times, depending on the presence or absence of AR. The center of pressure (COP) displacement was measured using the Wii Balance Board and the displacement of the head was measured through the HoloLens. Consequently, significant correlations were observed between the COP and head displacement. Additionally, there were significant differences between patients with and without AR feedback. However, the experiments performed were not statistically significant because the sample size was small. Figure 5: Conceptual diagram of an AR HMD-based rehabilitation management method that can support both therapists and patients [44] (IMU, inertial measurement unit). [PERSON] et al. [45] proposed the first wearable AR application for shoulder rehabilitation based on Microsoft HoloLens, which can track a user's hand in real time. A serious game that maximizes the user's comfort was designed--starting with the analysis of traditional rehabilitation exercises, while accounting for HoloLens specifications--and an immersive AR application was implemented. The proposed application was evaluated by rehabilitation specialists and healthy subjects. Consequently, ergonomics and motivational values were positively evaluated. [PERSON] et al. [46] comprehensively evaluated the HoloLens as a tool to quantify gait parameters from position data, by determining the reliability and concurrent validity of repeated tests. The HoloLens measurement system was able to quantify walking speed, step length and cadence reliably and effectively for a broad range of speeds used by healthy young adults, as well as for self-selected comfortable speeds used by people with [PERSON]'s disease. Table 2 summarizes the literature reviewed on the use of Microsoft HoloLens in medical and surgical aids and systems. Except for one of the 19 papers, all studies were conducted using HoloLens 1. Thirteen used AR technology, while the rest used MR technology. Moreover, three studies provided users with a simple visualization of virtual objects and 13 studies allowed interactions between users and virtual objects. The remaining studies provided the users with an opportunity to immerse themselves in VR and interact with objects.