# 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
By comparing the subsurface location of vascular perforators through AR overlay and the positions obtained by audible Doppler ultrasound, it was determined that the HoloLens allows the surgeon to locate the perforating vessels precisely and efficiently. Figure 3: Original CTA imaging, segmentation and corresponding polygonal models. **(a)** CTA imaging indicating the location of the perforating arteries with yellow arrows. **(b)** Example of a HoloLens rendering of the segmented polygonal models [37]. [PERSON] et al. [38] evaluated the precision of a HoloLens-based vascular localization system. Thus, a 3D printing model for the vascular map was developed and the precision was tested in a simulated operating room under different conditions. They detected five pairs of point coordinates with a probe on the vascular map, which could be identified in the 3D printing and virtual models, and calculated the distance between the points as a navigation error. Consequently, the mean error was reported to be within the clinically acceptable range. This precision evaluation showed that the HoloLens system precisely localizes the perforator and can potentially assist the surgeon in performing the operation. [PERSON] et al. [39] evaluated the possibility of using an optical see-through HMD to navigate lumbar pedicle screw placement. A novel navigation method--tailored to run on the HoloLens--involves capturing the intraoperatively reachable surface of the vertebrae to achieve registration and tool tracking with real-time visualizations, without the need for intraoperative imaging. Fiducial markers are mounted on both surface sampling and navigation; furthermore, 3D printing is possible. [PERSON] et al. [40] evaluated the surgical accuracy of holographic pedicle screw navigation using an HMD via 3D intraoperative fluoroscopy. The accuracy of surgical navigation using an HMD was evaluated by comparing its results with those obtained from navigation using a state-of-the-art pose-tracking system. Holographic navigation using the device proposed in their study showed an accuracy comparable to that of a high-end pose-tracking system. [PERSON] et al. [41] performed a prospective trial on CT-guided lesions targeting an abdominal phantom with and without AR guidance using HoloLens. Eight operators performed needle passes and the total needle redirections, radiation dose, procedure time and puncture rates of non-targeted lesions were compared with and without AR. Consequently, the operators were able to trace their ideal trajectory easily using real needles via virtual guides. Furthermore, it was confirmed that the needle passes, radiation dose and puncture rate of a non-targeted lesion were significantly reduced when using AR. Figure 4 shows an example of using AR-assisted navigation with HoloLens. Figure 4: AR-assisted navigation using HoloLens 2. (**A**) Participant inserts the needle while wearing HoloLens 2. (**B**) View of the needle insertion without AR, (**C**) View of needle insertion through HoloLens 2 with a 3D model and virtual needle guide projected onto the phantom [41]. [PERSON] et al. [42] designed a marker-less image-based registration pipeline using HoloLens and built-in sensors--to guide glenoid drilling during the total shoulder arthroplasty (TSA) procedure--and performed a feasibility analysis. They evaluated the performance of inside-out image-based registration on the HoloLens using a short-throw time-of-flight (ToF) camera and conducted a pilot study on its application to TSA. Although the evaluation results were promising, the current end-to-end error of the system does not appear to meet the surgical accuracy requirements. [PERSON] et al. [43] proposed an automatic flexible endoscopy control method that tracks the surgeon's head with respect to the object in the surgical scene. The robotic flexible endoscope captures the surgical scene from the same perspective as the surgeon and the surgeon wears an HMD to observe the endoscopic video.