Medical Monitor

How to Choose
Featured in aycan’s April 2011 issue of “News and Views”

With numerous monitors available on the market, varying needs of users, and ever-increasing budget pressure, its important to select the right monitor for your needs. Below is a basic overview of how to go about selecting a monitor along with detailed guidelines from the industry’s leading bodies.

First, Determine the Application

Choosing a medical monitor depends first on what you plan to use it for. Outside of general office monitors, there are two categories of monitors in the digital medical environment: Clinical and Diagnostic.

• Clinical Monitors, used for displaying clinical records and DICOM images, are a cost efficient option to a full-fledged diagnostic monitor, with many of them delivering calibration that is compliant with DICOM Part 14.

• Diagnostic Monitors have higher performance values than Clinical Monitors with brightness and grayscale being especially important as they provide greater image detail which is essential for readings.
  

Consider Key Performance Factors

No matter which category you fall in, determining a monitor’s performance for productivity and accuracy is based on the same key factors:

• Contrast. Contrast is simply the ratio of the luminosity of the brightest color (white) to that of the darkest color (black) that the monitor is capable of producing. The greater the contrast, the greater the detail.

• Dependability. A monitor should be stable so that what a user sees today is the same as what they’ll see tomorrow. FDA clearance and warranties are two items that indicate a monitor’s dependability.

• Grayscale. For black and white images, being able to render every shade of gray as defined by Digital Imaging and Communications in Medicine (DICOM), the American College of Radiology (ACR), and the American Association of Physicists in Medicine (AAPM) guidelines, is essential for accurate readings. The greater the grayscale, the more detail you will see in the image, which is particularly important when viewing mammography and CR images. A DICOM grayscale look-up table is also important so that grayscale output is optimized to the human visual system.

• Luminance. Luminance is used to characterize the brightness of displays. A typical computer display emits between 50 and 300 cd/m2. For diagnostic displays, between 400 and 900 is recommended. In general, the greater the luminance the better.

• Resolution. Resolution refers to the pixel density—the number of pixels per-unit distance or area. As a general rule, the higher the resolution the sharper the image will appear. This means less clicking, panning and zooming a user will need to do to see what they need to see.

• Uniformity. An image should look the same on any monitor connected to the same network. This is particularly critical when a user views images on multiple monitors, or when sharing or collaboration is needed. Uniformity depends on the quality of the monitor’s software and hardware.

• Viewing Angle. Viewing Angle is the maximum angle at which images on the monitor can be viewed without excessive degradation to the image. It is measured in degrees horizontally and vertically. The average viewing angle found in medical monitors is 170 degrees. And again, as a general rule, more is better. The greater the angle, the better the view.

Understand Legal Requirements and Standards

While there are no legal requirements on which medical monitor to use, the Federal Drug Administration (FDA), the ACR, and the AAPM have all created guidelines for the electronic viewing of medical images. These guidelines cover the performance factors discussed above as well as test patterns for sharpness at the center of the four corners, visibility of rectangles, and tests to determine if the display is free of shadows and image movements. Uniformity test criteria for luminance, and grayscale are also provided. All toll, the guidelines set best practices for creating an optimal diagnostic reading environment. Key industry guidelines can be found at the links below:

• AAPM: http://deckard.mc.duke.edu/~samei/tg18

• ACR: http://www.acr.org/SecondaryMainMenuCategories/quality_safety/guidelines/med_phys/electronic_practice.aspx

• NEMA: http://medical.nema.org/dicom/2004/04_14PU.PDF This guideline, DICOM Part 14: Grayscale Standard Display Function, from the National Electrical Manufacturers Association (NEMA) specifies a standardized Display Function for display of grayscale images. Both the ACR and AAPM standards recommend the use of DICOM Part 14.

• FDA: http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/default.htm Although not required, for quality and liability reasons, it’s recommended to go with an FDA-cleared monitor.

Consider Cost

Of course, cost is also a key factor. Because the price difference between the three types of monitors is significant, it’s important to choose the right one for your application. On average, good quality General Office Monitors range in price from $200 to $500; Clinical Monitors range from $1,500 to $5,000, and Diagnostic Monitors price from $6,000 on up. The important thing is not to over buy or under buy for the intended application.

Watch Technology Trends

As technology continues to advance at a rapid pace, its important to understand the trends so you acquire a monitor that will give you the performance you need today and well into the future. Some trends to consider when selecting a monitor are:

• DisplayPort. DisplayPort is the new standard for connecting monitors to graphic cards–replacing the Digital Video Interface (DVI) for this purpose. It’s a small, easy-to-use connector with a simple locking mechanism that eliminates the need for screws. DisplayPort works with longer cable lengths and has potential for daisy chaining monitors (an interconnection of monitors, one after another) and other advanced features. DisplayPort can provide the same functionality as a High-Definition Multimedia Interface (HDMI) but is not expected to displace HDMI in high-definition consumer electronics devices. Most new graphics cards have DisplayPort connectors.

• Eco-Friendly Monitors. Combining ergonomic and environmental features, Eco-Friendly Monitors deliver increased comfort for improved productivity, reduced environmental burden, and ultimately lower running costs.

• 3D Stereoscopic Imaging. This technique creates/enhances the illusion of depth in an image in one of three ways: by viewing separate images from two offset sources using glasses; using glasses that filter offset images from a single source separated to each eye; or viewing without glasses as the light source splits the images directionally into the viewer’s eyes.

• Quad HD Monitors. Quad HD is the next step in high-resolution large screen monitors. Instead of using many small monitors, interventional suites and operating rooms can now use one Quad HD Monitor that can be configured and optimized for image presentation from multiple inputs and uniquely configured for best-image presentation by doctor preference or procedure.

• OLEDs, E ink, and Portables (iPads, iPods, Tablets). OLED and E ink are new display technologies that could replace the LCD display. E ink is used in the Kindle, for example, and has superb viewing characteristics under daylight conditions. OLED is currently being used in some phones and small displays. Known for vibrant color reproduction and a slim form factor, OLEDs are still very expensive and there are concerns about degradation over time. iPads and iPods are appreciated for their portability, superb image quality, and providing instant access to information anytime, anywhere. Of course they have some drawbacks when compared to the criteria established by ACR and AAPM.

Look at Maintenance and Warranty

Once you’ve chosen the right monitor for the job, you’ll want to be sure it is maintained for optimal performance. This means ongoing monitoring and calibration. To minimize time and expense and ensure consistency, Quality Assurance (QA) software is available from many monitor vendors that can automate QA tests such as calibration as well as provide evidence of compliance with laws.

To protect your investment, it’s best to obtain a warranty that provides a minimum of three to five years of comprehensive coverage. The warranty should also guarantee the total image quality including brightness and color temperature.

Summary

While reading-environment conditions and a variety of software and hardware components affect image quality and interpretation, the most influential component is the monitor. To ensure you choose the right one, first determine the use of the monitor, either Clinical or Diagnostic, and then select one that aligns with the guidelines set by the industry’s key governing bodies. Be sure to also review and consider both warranty and maintenance plans as well as future technology trends as both of these can present added expense if not factored into your initial purchasing decision.

Related Readings:

There has and will continue to be much written on this subject. Below are a few articles, in addition to the industry links above, that you may find helpful as you research your monitor needs:

• http://www.healthimaginghub.com/what-monitor-to-use-for-viewing-medical-images.html

• http://www.auntminnie.com/index.aspx?sec=sup&sub=ris&pag=dis&ItemID=93832