# Image Quality Assessment of Augmented Reality Glasses as Medical Display Devices (HoloLens 2)
## 1 Introduction  
### Use and Evaluation of Medical Display Devices  
Imaging modalities such as radiography, computed tomography (CT), and magnetic resonance imaging are essential pillars of modern medicine. They provide critical information regarding the condition of bones, organs, and other tissues, which is vital for diagnosing and treating various diseases and injuries. Without these imaging procedures, accurate medical care would be unattainable in many domains. For physicians to effectively utilize the acquired image data, it must be presented on medical-grade display devices. The quality of these displays is paramount, as it influences the reliability of diagnostic and therapeutic decisions [1,2]. Subpar image quality can lead to misinterpretations and compromise patient safety [3]. Therefore, medical display devices must adhere to stringent standards across various technical parameters, including overall image quality, luminance, luminance-to-grayscale conformance, and color uniformity.  
Standardized testing procedures were used to ensure compliance with these requirements. The overall image quality is typically assessed using a standardized test pattern comprising various elements, including fine line pairs, regions with different shades of gray, and text. An examiner evaluates whether these elements are recognizable and distinguishable on a display device [4, 5, 6].  
Brightness is another critical parameter, defined by the luminance a display device can produce. Using a luminance meter, the examiner measures the minimum luminance of a black test pattern and the maximum luminance of a white test pattern [4, 5, 6].  
Luminance-to-grayscale conformance refers to the relationship between the designated gray level of an image and the resulting luminance of the display device, thereby assessing the ability to discriminate between different shades of gray. This conformance is evaluated by measuring the luminance of multiple test patterns with graduated gray values. The measured values are compared to a standardized luminance curve to ensure that individual gray levels are distinguishable and consistently rendered across different display devices [4,5]. In the medical field, the gray scale standard display function (GSDF) has been established as a reference. This reference curve, defined in the Digital Imaging and Communications in Medicine (DICOM) guidelines, provides a uniform standard for accurate grayscale displays [7].  
Finally, the color uniformity of the display device was assessed to ensure consistent color reproduction. The test measured the red, green, and blue color coordinates at multiple points on the screen [8], and the results were compared according to ISO standards [9]. This assessment evaluates whether the display device consistently reproduces colors uniformly across the entire screen area.  
Manufacturers of medical display devices must demonstrate the performance of these parameters to secure approval as medical devices [8,10]. Post-deployment, healthcare facilities are mandated to conduct regular constancy tests to ensure continued image quality [6]. The stringency of display requirements varies according to their intended application. A fundamental distinction exists between primary and secondary display devices [4]. Primary displays, predominantly utilized in radiology, support diagnostic processes by presenting image data. These devices are subject to stringent requirements since diagnostic accuracy is heavily reliant on the quality of displayed images. Conversely, secondary display devices replicate confirmed findings and are not employed for initial diagnoses. They are used for purposes such as patient education, peer review, and preoperative planning. Since they only display image data previously assessed on primary displays, their requirements are less stringent.