What are the display requirements for diagnostic interpretation of radiology images?
Display requirements include luminance response, pixel pitch, and display size.
- • Luminance response: Brightness and contrast of gray scale medical images result from luminance related to image gray level values.
- • Maximum luminance: Perceived contrast of image depends on ratio of luminance (LR) for maximum gray value (L max ) to luminance of lowest gray value (L min ). Note that this is different from the contrast ratio often reported by monitor manufacturers. All display devices in one facility should have the same LR.
- • L max of diagnostic monitors should be at least 350 cd/m 2 , although monitors for interpretation of mammograms should have L max of at least 420 cd/m 2 . Monitors for other purposes should have L max of at least 250 cd/m 2 .
- • DICOM gray scale display function (GSDF) should be used to set intermediate gray values with similar response functions among all monitors in a facility.
- • Calibration: Luminance response, LR, and GSDF can be selected using the monitor on-screen display controls, although some devices may require software from the monitor manufacturer to set luminances of each gray level.
- • Quality control: Display devices should be periodically checked to verify the luminance response. Both basic and advanced verification tests may be utilized. Contrast response of monitors for diagnostic interpretation should be within 10% of the GSDF over the full LR and the contrast response should be within 20% of the GSDF over the full LR for other purposes.
- • Pixel pitch: Spacing of pixel structures, which determines amount of detail that can be presented. Determines maximum spatial frequency that can be presented in an image. The maximum spatial frequency that can be described by digital signals with a constant pitch P is 1/(2P) cycles/mm. Optimal pixel pitch should be small to present all spatial frequencies within human visual perception. The pixel pitch should be about 0.200 mm but not larger than 0.210 mm for diagnostic interpretation.
- • Display size: Visualization of the full scene is optimal when the diagonal display distance is about 80% of the viewing distance, which corresponds to approximately 21 inches (53 cm) when there is an arm’s length viewing distance of about 60 cm. An aspect ratio (width to height) of 3 : 4 or 4 : 5 works well for presentation of radiographic images.