In medical imaging, there are 2 main monitor types: diagnostic and clinical review.
- Are primarily included in radiologists' workstations.
- Are mission-critical and often perform 8-12 and sometimes 24 hours a day, indicating a strong need for high reliability.
- Have high resolution, which by today's standards is at least 3 megapixels (5 megapixels for mammography).
- Have a small pixel pitch. The pixel pitch is the distance in millimeters from the center of a pixel to the center of the adjacent pixel. A smaller pixel pitch means there is less empty space between pixels; this equals higher pixel density and higher screen resolution. Pixel pitch in diagnostic monitors is usually no more than 0.21mm for X-Ray, CT or MRI; it should not be more than 0.25 mm for ultrasound, fluoroscopy and nuclear medicine. For mammography, the pixel pitch should be no more than 0.17 mm.
- Have a low ambient luminance (Lamb). When the power to the monitor is off, the screen will still have some brightness due to diffusely reflected room lighting. This is called the ambient luminance. Lamb should be less than one-fourth of the luminance of the darkest gray level.
- Have an appropriate minimum luminance (Lmin). Monitor luminance is measured in Candelas per square meter. If Lmin is too low, human eye will not perceive much in the dark regions of the image. If Lmin is too high, the dynamic range of the display will decrease, degrading performance. Minimum luminance should be 1 cd/m2 for X-Ray, CT or MRI; it should be 0.8 cd/m2 for ultrasound, fluoroscopy and nuclear medicine. For mammography, the minimum luminance should be 1 to 1.2 cd/m2.
- Have a high maximum luminance (Lmax). Lmax in diagnostic monitors should be at least 350 cd/m2 for X-Ray, CT or MRI; it should at least 250 cd/m2 for ultrasound, fluoroscopy and nuclear medicine. For mammography, the Lmax should be at least 400 cd/m2.
- Formal hardware calibration to within 10% of Grayscale DICOM Diagnostic Function (GSDF) is required and must be maintained over the lifespan of the display. The best diagnostic displays are self-calibrating and include all software and hardware required to perform this function.
Clinical review monitors:
- Are included in workstations for non-radiology physicians and radiologic technologists.
- Are used episodically, in bursts rather than continuously.
- High resolution and small pixel pitch are not as critical. At least 2 megapixel monitors are acceptable here. Pixel pitch of 0.25 mm is acceptable for most clinical review monitors.
- Luminance range should be at least 0.8 - 250 cd/m2.
- Display calibration to within 20% of Grayscale DICOM Diagnostic Function (GSDF) should be performed at least annually.
An important distinction
Diagnostic displays for radiologists' use are designed to a much higher standard than clinical review monitors, which in turn are built to a higher standard than many commercial off-the-shelf (COTS) units. Failure to select a task-appropriate display could result in adverse outcomes:
- Failure to detect a clinically significant finding;
- Down time related to display failure, resulting in loss of productivity and/or treatment delay;
- Loss of productivity and additional expense attempting to calibrate a monitor that cannot self-calibrate or maintain calibration;
- Legal liability related to adverse patient outcomes.
Remember: your eye cannot see what the display does not show. Using suitable equipment is critical to getting the job done. Select the appropriate medical imaging monitor for your needs, and avoid down time, frustration, loss of reputation and legal liability.