Ing Juergen Heckel, VP, Medical Business, Sales & Marketing, Global, Certified Medical Device Advisor, EIZO Corporation, gives an insight about contents of quality control process
Accuracy and stability are the most important targets we have to achieve in healthcare industry for the best patient treatments. The visibility of cancer is very difficult and depends very much on the visible image contents and used equipment at the hospital. The doctors are only able to diagnose what is visible in special on the medical grade monitor so called image diagnostic device. Why Quality Control (QC) is important and what exactly will be controlled? For image diagnostic devices quality control means to check the ‘stability or also called constancy’ of the image device. Medical diagnostic monitors are already pre-calibrated at the factory side to DICOM Part 14 GSDF Standard in an optimum reading room environment (mainly dark rooms of 0lx). Most of the medical monitor manufactures offer their own optional special QC Software and sensors to periodically control and adjust the device onsite. Such QC is mandatory and highly recommended and unfortunately often forgotten. Having only the medical certification like CE mark label for medical or FDA510K certification does not replace the need of QC. It just shows the device is declared as medical device but does not show the accuracy.
Let us understand step by step the contents of the QC process. At first the ‘Acceptance’ test will be performed. This is the test when the medical monitor will be installed at the first time and also depends on the working environment. Here the room ambient light will be measured and set between 0 and 100lx (Lux) for diagnostic. (for mammography it should be even darker between 0-50lx). By knowing the exact ambient room-light the brightness of the monitor will be set as next via calibration. This means it is not enough just to unpack the new medical monitor and expect that the device works perfect in all environments all the time. The client environment is maybe different to the one the device manufacturer used at the factory side.
For calibration there are various sensors available (inbuilt or external). After such calibration process is done the acceptance test can be performed. The test includes a visual check (here various DICOM test patterns will be shown to check the geometry but also contrast visibility), a greyscale test (the DICOM GSDF greyscale levels will be measured), a luminance test (the calibrated luminance will be controlled if reached or not) and finally the uniformity test (it controls the corner to centre uniformity of luminance and greyscale). Such an acceptance test is required one time at the first installation and will be repeated again only in case the working environment will be changed or in service cases. For dual monitor solutions the uniformity test also compares the performance on one and to both medical monitors to each other.
The second QC control function is called ‘Constancy’ test. With the constancy test the stability of the medical monitor could be understood. Here the actual performance of the medical monitor will be checked and compared with the one done during the acceptance test and aligned with the selected medical standard (e.g. AAPM, IEC or DIN). Constancy tests include more or less the same four steps as the acceptance test but require this periodically (at least every six months). In case the medical monitor does not pass the constancy test, the medical monitor requires some adjustment also so called ‘Calibration.’ With the calibration procedure, the medical monitor will be re-adjusted and corrected.
Normally after such adjustment method the medical monitor pass then the needed requirement following the selected medical standard. Medical monitors have several components embedded which deteriorates over the life time and because of such parts a ‘maintenance’ and calibration is mandatory to keep the accuracy for diagnostic purpose.
Some components are, say for example, the LCD panel module and backlight. If such calibration and QC testing process are missed, the brightness may drop or the uniformity decrease which will end in a dramatic impact on the medical DICOM image and small details may not be seen anymore. It can cause a misreading from the doctor. In such cases, the doctor has no chance to proceed an accurate patient treatment. QC is also extremely important because doctors exchange images within their hospital network but also with tele-radiologists. Even the patient image data will be periodically compared on the image diagnostic devices and have to appear in same contents even after years. The QC is taking care of geometry issues like flicker, artefacts, pixel failure check etc. For such tests, various test patterns are available and embedded in medical standards. The QC Software of the medical monitor manufacturer supports all medical standards.
There are various medical global standards available for example from IEC (worldwide), the USA QC Guideline of AAPM /ACR or the German industry standard DIN and others. In their contents, they are all very similar and matched. The test patterns for the visual check are DICOM based and most of the cases from AAPM TG18 or SMPTE. In terms of brightness, they are almost the same by recommendation of 350cd/m2 for general diagnostic and 450cd/m2 for mammography. There are currently initiatives worldwide to harmonise several existing standards into one global reference standard. Thanks to the existing and future medical standards, the image diagnostic devices can be better understood in their benefits and limitations for better patient healthcare. Medical standards needs to be updated periodically because the equipment is improving so fast. Such standards will be created by several stake holders like medical physicists, industrial experts, doctors and legal experts. Standards will help to improve the accuracy in diagnostic.
Some Links:
AAPM (AAPM TG18/ACR) http://www.aapm.org
DIN (6868-157) https://www.din.de/en/
IEC (62563-1) http://www.iec.ch
Contact Details:
EIZO Corporation
A-5101 Bergheim,
Dorfstrasse 15/2
Mob: +43 664 8440782,
Mob (UAE): +971523381264
E-mail: juergen.heckel@eizo.com
Website: www.eizoglobal.com