Meditherm is an FDA registered medical device manufacturer and the Meditherm 520 Fever screen system is listed as a class I medical device. (FDA Certificate to Foreign Government is available on request). The systems also carry the CE mark as a class I medical device and comply with the European MDD conformity.
Industrial cameras have a wide range of temperature measurement and as a consequence the sensitiv-ity and accuracy is also spread over a wide range. A medical camera like the Meditherm system has a very narrow range of detection (within the range of human physiology) and so our sensitivity and accuracy is concentrated in this narrow range of IR emissivity and temperature..... which provides higher sensitivity and easier protocols which are not as affected by the outside environmental factors as an industrial camera will be (because of the wide range detected in all industrial applications, emissivity from electrical equipment, lighting, reflective surfaces, sunlight, and other IR sources in the immediate area will affect the results and require the operator to be very skilled as a thermography technician).
Our system is designed and built specifically for clinical use and the detection of physiological IR.
Industrial cameras have many features and functions that are irrelevant to medical applications and actually work against the sensitivity and objectivity of results. Many of these features like edge enhance-ment, auto averaging and emissivity correction have to be disabled before the camera can be used for applications like fever screening. Many industrial cameras without internal temperature reference calibration require an additional external black body calibration unit (at extra cost).
All industrial cameras have a lens correction built in. This is because they use actual lenses (just like normal cameras) to focus and zoom. (in industrial applications they have to look at objects at all distances from very close to very far away) the industrial camera lens will absorb about 17% of the emitted radiation (IR) so this needs to be corrected for by the software. The Meditherm camera does not use standard camera lens, so there is no loss of signal from the object emitting the radiation. We use a small germanium window which does not absorb measurable amounts of the emitted radiation, so we are detecting close to 100% of the IR being emitted from the human body. (no lens correction = better accuracy)
Industrial cameras all have a % of thermal drift. Which they use software 'averaging' to compensate for. This does not make much difference to most industrial applications but it is very important when using thermography for clinical applications.
The only way to counter the problems of thermal drift is to have a reference temperature. Industrial cameras do not have a stable reference temperature point. All industrial cameras being used in airports for fever screening should have an outside temperature reference source (black body emitter or calibra-tion emitter) that is seen within each view. (basically an accurate temperature that can be seen by the camera and used to calibrate each frame)
Meditherm has proprietary technology which gives us an internal reference temperature accurate to 1/100th deg c. This handles any thermal drift and calibrates the results on a frame by frame basis End result: more stable results, repeatability, better accuracy and less need to continually alter the range and scale of detection like the industrial cameras which give higher percentages of false positive and false negative results and demand a higher level of training to be operated efficiently.
Our med520 software has developed from over 20 years of medical research and is specific to the appli-cation of mass screening for physiological abnormality. Industrial camera software has been adapted (at best) for fever screening from the industrial application software which is in most instances not suitable or easy to use by untrained operators. Meditherm operating guidelines are available at : http://www.compix.com/TemperatureMonitoring Help Meditherm technical support is available world wide.
Interpolation is when you process the number of available pixels with the software. You can increase the number or decrease the number with software. It can be very confusing to the layman in terms of real definition, resolution and thermography images. The pixel count in normal photographic cameras (mega pixel) tells you how smooth the picture is .... more pixels are generally better (higher definition). This is not the case with thermography.
When talking about thermal definition we need to know not only how many individual temperature measurements have been taken in an image but are they all individually accurate and sensitive to the claimed specifications.
You can have a single temperature measurement (one pixel) which is split into 4 by the software, this affectively increases the definition x4 but you still only have the same amount of temperature data, it just looks smoother visibly.
If a camera is claiming 76,800 pixels (320x240) ...... are all of those pixels individual temperature measurements that are accurate and sensitive to the claimed specifications ? Meditherms are. Industrial camera definition is also prone to averaging bad pixels (which have no temperature), and thermal drift, which again averages temperature range pixel to pixel but most significantly there is a trade off between the speed of temperature measurement and the accuracy of measurement of each pixel.
Interpolation can be done in both directions..... making more pixels by splitting them into multiples to show the appearance of higher definition or combining multiple pixels into a single temperature measurement (pixel) with better accuracy.
The longer you leave the detector looking at each pixel the better the accuracy. The faster you run the detector (to take more pixels) the lower the accuracy.
Industrial cameras scan at 30 + frames per second so the accuracy of each pixel is low......(in medical terms) which is why they have the software perform averaging and edge enhancement.
We have slowed our frame rate down to 7.5 frames per second for the specific reason that this is the speed that we can measure each individual pixel (temperature measurement) to the required accuracy ..... so every one of our pixels is a real temperature (and can be counted). There is a ‘trade-off’ between ‘speed’ and "sensitivity".
Faster is not always better!
First, there are a couple of resolutions that apply to IR cameras. There's spatial resolution and there's thermal resolution. Spatial resolution is related to the number of pixels in an image. This is analogous to today's digital cameras and their number of pixels/picture, e.g. 2 megapixel vs. 3 megapixel vs. 4 megapixel, etc. For many or most applications 2 megapixels will provide excellent pictures for most set-tings in fact unless you try to zoom in you would be hard pressed to tell the difference between 2, 3 or 4 megapixels. However, you will find a significant difference in image file sizes and camera costs. The point here is that the 2 megapixel camera will work perfectly well for routine picture taking. Using IR cameras for scanning humans works much the same. (you cant tell the visible difference)
The focal length of industrial cameras is generally short and using optical lens (25 degrees is com-mon) to zoom in for distance reduces the accuracy by simply making the pixels bigger and reducing the field of view.
For fever screening we recommend the med520 using an 11 degree field of view which make the tem-perature measurements more accurate at distance. We do not use an optical or digital zoom lens. We can supply the med520 with optional field of view, 11 degree, 17 degree, 25 degree, 32, degree. 50 degree and are happy to advise on the best options for specific requirements.
The focal ability of the Meditherm 520 with an 11 degree FOV is 1 meter (39 inches) to infinity. The opti-mum focal length for fever screening is 7.3 meters (24 foot). The focal length to stay within specification for fever screening is 6 foot to 35 foot. (accurate measurements can still be made up to 70 feet but the area of the face will be so small that sensitivity will be low due to the number of pixels, ‘individual tem-perature measurements’ on the face.
Not with the Meditherm 520. People should walk at normal speed and the camera should be facing the people or at most be at 20 degrees angle to the people being scanned.
The frame rate will detect anyone within 1/7th of a second who is moving in the field of view. The alarm will continue the whole time that a person with fever is in the view of the camera, (average time it takes for people to pass by the camera is 15 to 30 seconds).
The time a person is being imaged as they walk towards the camera depends on how far away they are when we start imaging.... the optimum distance of 7.3 meters (24 feet) can be used as the target area and imaging can begin at 21 meters (70 feet), the time it takes a person to walk from 21 Meters to 2 meters from the camera is the time we have to detect fever.
There is plenty of time to identify a target person, the image on the screen will set off an alarm and circle the person as he or she walks towards the camera. They can be identified and stopped by the time they reach the fever screening station. This works well in practice and has been found to be affective. The software also has a 'freeze frame' mode which saves the image for replay if there is any question about who set off the alarm.
The Meditherm 520 is the most economic system available today. The price includes all system componants : Camera, Heavy duty stand, Laptop or PC, with all operating software..
The system can be operated by a non-technical person and with the auto averaging function engaged, can run unattended. The threshold alarm can be heard by attendants within a wide proximity range.
The camera is supplied with a universal adapter for mains power in any country and uses very little power (5v) and can also be run from a re-chargeable power pack with 13 hour continuous operating.
Each camera is calibrated before it leaves the factory and a calibration certificate accompanies each unit to certify that it meets or exceeds its published specifications.
The software can be easily loaded onto any laptop or PC and will run on any MS windows operating sys-tem.
Meditherm is the world leader in physiological testing and leads the field in fever screen-ing applications.
With experience spanning over 17 years and 43 coun-tries Meditherm is best placed to supply and support your screening equipment require-ments.