# Image Quality Assessment of Augmented Reality Glasses as Medical Display Devices (HoloLens 2)
## 1 Introduction
### Use of Augmented Reality Glasses as Medical Display Device  
Beyond traditional display technologies, augmented reality (AR) glasses are becoming increasingly prevalent in the medical sector. These head-worn devices typically feature optically transparent see-through displays, enabling digital images or information to overlay the user's view without obstructing environmental perception. The primary advantage of AR glasses lies in their capacity to seamlessly integrate virtual content into the user's physical surroundings. In a medical setting, this integration facilitates the projection of medical images, markers, or instructions directly onto the field of view during patient care.  
HoloLens 2 (Microsoft Corp., Redmond, WA, USA) is a premier AR device featuring a see-through display. It utilizes laser beam technology to generate images on a screen by sequentially moving three distinct lasers--red, green, and blue--line by line. By modulating the intensity of each laser beam, it can render a spectrum of colors and grayscale shades. This technology enables HoloLens 2 to project holographic images directly within the user's visual field.  
Figure 1 illustrates HoloLens 2 (left) and demonstrates its capability to display medical images within the user's field of view (right).  
HoloLens 2 has been evaluated and implemented in medical environments, particularly during surgical procedures [11]. Moreover, [PERSON] et al. [12] developed an AR system to assist minimally invasive cardiac surgeries by projecting three-dimensional electroanatomical heart maps onto a surgeon's field of view to visualize cardiac conduction. Similarly, [PERSON] et al. [13] utilized HoloLens 2 for preoperative planning in liver transplantation, converting CT image data into a three-dimensional liver model displayed within the surgeon's field of view in the operating room. Both studies have demonstrated that AR significantly improves the precision and efficiency of surgical procedures.  
The adoption of AR in surgery is increasing with the initial commercial applications already available. In surgical settings, overlaid images must precisely align with a patient's actual anatomy, leading surgical research to frequently stress the spatial accuracy of virtual overlays [14; 15; 16]. Nevertheless, AR adoption in radiology--a field where image quality is critical--remains limited. This limitation may stem from the lack of appropriate testing methodologies to evaluate the image quality of AR glasses.  
Existing test methods for AR glasses are not tailored for assessing medical devices [17; 18] and do not establish acceptance criteria for medical display systems. Without such standards, the suitability and specific applications of AR glasses in medical settings remain uncertain. Furthermore, existing methods are designed exclusively for AR glasses  
Figure 1: Illustration of HoloLens 2 and its use for the visualization of medical images.  
with fixed pixel grids. However, it remains unclear whether these methods are applicable to HoloLens 2 [19; 20; 21].  
In contrast, conventional medical display devices have established acceptance criteria. Nonetheless, it is uncertain whether these test methods can be adapted for AR glasses, such as HoloLens 2 [22; 23]. Transferability would be beneficial, as manufacturers and healthcare providers already have experience with these procedures.  
This study aimed to determine whether the established test methods for medical display devices are suitable for assessing the image quality of HoloLens 2. Additionally, we evaluated whether HoloLens 2 satisfies the criteria for primary and secondary display devices.