The technology behind medical monitors

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Did you know that regular monitors should not be used for viewing medical images? Medical monitors have their own specifications to ensure the quality of the images to be analyzed. This subject came up when talking to some company colleagues. Venturus is partner of a multinational company that develops this type of monitor and currently has a project in this area: it is an application capable of calibrating medical monitors. That’s why I decided to write this article to talk a little more about what are medical monitors and how this project is being developed here. 

Before talking about medical monitors and their differences from ordinary monitors, I will talk a little about the technical characteristics of monitors in general.  The key features that define the quality of a monitor are: 

  • Luminance: The measure of the density of the intensity of a light reflected in a given direction. It is measured in candela units per m2. A candela (meaning Latin candle) roughly equates to the intensity of light a candle emits; 
  • Contrast Ratio: The ratio that measures the variation between the maximum brightness emitted by an all-white image and the minimum emitted by an all-black image. That is, for a contrast ratio of 100:1, 100 each white we see is 100 times brighter than the black we see; 
  • Size: Physical measure that defines the dimension, in inches, of the diagonal of the monitor screen; 
  • Resolution: Number of horizontal and vertical lines a monitor can display, given in pixels. 

There are some other features like refresh rate, response time, color support and angle of view, but we won’t go into detail in this article.  

What is a medical monitor? 

A medical monitor has an image quality control system that must meet the specifications set by health regulatory agencies and must be maintained throughout the life of the monitor. 

Medical monitors should ensure uniformity of screen luminance. The luminance value of standard monitors is between 200 to 250 cd / m², gaming monitors are now around 300 cd / m² and medical monitors are above 350 cd / m². 

With respect to the contrast ratio, monitors should be able to adjust and maintain the proportion evenly across the monitor area. Medical monitors generally have a house contrast ratio of 10,000:1. 

On ordinary monitors, we have no major problems if some of the features presented in the previous section vary over time. However, for medical monitors, any variation in any of these characteristics may lead to incorrect diagnosis or analysis. 

What are the types of medical monitors? 

There are three types of medical monitors, which are: clinical, diagnostic and surgical. Clinical monitors are used for viewing images when the doctor will not issue a report from it. They are commonly used in medical offices for quick viewing. Diagnostic-type monitors are those used for issuing imaging reports such as X-ray, tomography, etc. Finally, the surgical type monitor is used during invasive procedures such as endoscopy and surgery.  

What are their technical specifications? 

Although we have three types of monitors defined by application, there are still, within each type, peculiarities depending on the type of medical image to be evaluated. For example, a monitor that is used to report a mammogram may not necessarily be used to report a simple X-ray analysis. Why? Because each medical image has its particularities, which can be affected by characteristics such as the luminance, brightness or resolution of the monitor.  

In the case of CT scans, for example, a resolution of 1M pixels (≥1280 x 1024) is sufficient. For X-ray analysis, a resolution of 3M pixel (≥1920 × 1440) is required and, for mammography, the resolution is 5M pixel (≥2560 × 2048). The standard resolution of a monitor is directly related to the complexity of the exam that will be analyzed on it. The higher the specificities of the image characteristics to be evaluated, the higher the resolution required.  

 

In this image we can see the difference between the images with and without calibration in the DICOM standard. (source: https://epson.com/faq/SPT_V11H348020~faq-178734) 

 

In order to ensure the quality of medical images and thus procedures, examinations and diagnostics, calibration and validation standards of the images were created. Two examples of standards are the DICOM® (Digital Imaging and Communications in Medicine) standard 1 and the TG18 (AAPM Task Group 1818 standard.  

DICOM® is an international standard for transmitting, storing, retrieving, printing, processing and displaying medical images. The DICOM® standard defines various standards to ensure the necessary quality of medical imaging for clinical practice. 

DICOM® standards include part 14, called the Grayscale Standard Display Function (GSDF) DICOM, which defines the grayscale image display standard for medical monitors.   

TG18, defines test standards that are used to evaluate the performance of medical monitors. This standard is defined by the AAPM (American Association of Physical Medicine). 

And how does Venturus contribute to it? 

Venturus has a very significant stake in the quality of our multinational partner’s medical monitors. In this project, the team iresponsible for researching and implementing the monitor’s luminance, contrast and color calibration and validation software.  

To calibrate colors (red, green, blue as well as grayscale), luminance and contrast, part 14 of the DICOM® standard was used.  

To perform the calibration acceptance tests, the standards of the TG18 were followed. In this acceptance step, it was necessary to use a specific hardware, the probe (model i1Display Pro) that captures the pixels of the generated image, together with their coordinates, and then compares the image generated by the monitor with a reference image. Based on calibration and acceptance tests, ICC (International Color Consortium) 4 color profiles were then generated, which will be used as the basis for adjusting the monitors to be manufactured. 

The first part of this project has already been delivered and we are moving to the second phase. The idea now is to manage the monitors remotely, allowing to perform an analysis of the reports generated by the process types (Calibration, Acceptance Testing, Calibration Compliance, etc.), as well as allowing the maintenance scheduling, calibration, which has to be done on site. 

This second part of the project is of the utmost importance since such equipment being down for maintenance implies many examinations having to be postponed, which can often be crucial. Remotely monitoring the status of monitors will allow the administrator to more quickly and analyze more reliably the performance of each medical monitor on the network, so they can schedule or even request action, such as a new calibration or acceptance test, anticipating potential problems. 

Conclusions 

As much as we have great commercial monitors being sold on the market, they should not be used in the medical field since they can lead to errors in imaging analysis and diagnosis. Medical monitors have specifications and international standards for this purpose that guarantee that the equipment delivers the best results and quality in images and thus in procedures, analysis and diagnostics.  

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