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Infrared (IR) Imaging Searches Flu-Ravaged Populations
by Winn Hardin, Contributing Editor - AIA Posted 06/03/2009
In late 2002, countries around the world were terrified by the spread of Severe Acute Respiratory Syndrom (SARS). Within 1 year, 650 people died from SARS in China and Hong Kong alone. Two years later, the H5N1, or “bird flu” virus killed another 262 around the world. This year, in April of 2009, just 2 months since the first cases were reported, the H1N1 “swine flu” virus has already claimed 115 lives, most of them in Mexico. As frightening as these numbers are, they pale in comparison to the influenza outbreak of 1918, which killed more than 600,000 just in the United States.
In addition to the tragic loss of human life, influenza outbreaks can cripple industries – travel in particular. According to Frost and Sullivan’s commercial aviation consultant, Diogenis Papiomytis, airports can lose up to 50% of their revenues and 80% of their travelers during the average 6-7 month outbreak of a new flu virus.
If history teaches us anything, it seems to be: influenza will continue to threaten the world’s population as it has for hundreds of years. Diligence is the only protection against spreading influenza, as evidenced by criticism of the Chinese government’s handling of the SARS outbreak, keeping the condition secret until the disease had spread beyond its own borders. Similar conditions in Mexico may have given the swine flu momentum this year.
So how can an imaging system keep viral sickness at bay? While a camera connected to a computer cannot cure the sick, infrared imaging with thermal analysis software can help contain the disease by quickly scanning groups of people in public areas and identifying potential carriers with elevated temperatures – fevers – of 1 to 1.5 degrees or less.
FLIR’s Victory in Taiwan
After the SARS outbreak of 2003, the Taiwan Center of Disease Control fielded several FLIR Systems Inc., (North Billerica, Massachusetts) T360 and A320 IR cameras with built in temperature display and audible temperature alarms in addition to asking travelers to voluntarily fill out a ‘Communicable Disease Survey Form.’ The form, which became mandatory during the SARS outbreak of 2003, identified approximately 15 cases of malaria, dengue fever and similar conditions on average per year. After moving to IR imaging at borders and airports, the CDC identified 60 cases of infectious disease between April and December of 2003, and 93 cases between January and October 2004. Out of those 153 cases, only one had been ‘voluntarily’ reported on the form. Shortly after, the CDC discontinued the use of the form and depended exclusively on IR cameras to catch sick travelers entering Taiwan.
FLIR’s microbolometer-based cameras operate at 50 frames per second, offer high-spatial resolution for handheld IR cameras, and come with internal thermal analysis software that will issue visual and audible alarms when temperatures in the field of view exceed operator set levels. This allows the camera to be connected directly to an LCD monitor without the need for a PC.
Fevers vs. Furnaces
Most IR camera manufacturers express their product’s thermal sensitivity as a percentage of the temperature – typically 2 % – or an absolute value of 2 C, whichever is greater. This means that at low temperatures, cameras like FLIR’s A320 can be sensitive down to 0.08 C, however room temperature operations pose challenges to the system integrator who needs to be able to determine when a person’s skin temperature is just 1 to 1.5 degrees above normal.
“A standard IR imager is accurate to plus or minus 2 to 3 degrees C with its dynamic range spread across a vast temperature range,” explains Jon Upham, Director of Application Engineering at Coherix Inc. (Ann Arbor, Michigan), the supplier of ThermalSentry, an IR imaging system designed specifically for scanning people for elevated temperature. “But we’re interested in high accuracy because we’re trying to distinguish between a person with normal body temperature and another person whose temperature is just slightly elevated.
“The nice thing about microbolometers is that they are very sensitive and because of this, it is practical to spread their entire dynamic range out over a very narrow temperature band” Upham continued, “but they drift over time, so to make them useful, you need very precise real-time calibration.”
Coherix has developed a dual black body calibration target (see photo). One black body is tuned to the lower end of human body temperature, and the second calibration target is tuned a few degrees higher. The result is fine thermal resolution of 0.15 C. The blackbody unit constantly transmits its temperatures via an RF link to the control PC running Coherix’s ThermalSentry software. The dual blackbody unit is in the field of view of the thermal imager at all times so the system continuously recalibrates itself as ambient and camera temperatures change. In addition to scanning people for potential illnesses, Upham said “dual black body calibration units are useful for any IR imaging application where high-accuracy temperature measurement is required, such as looking at injection molding dies and PC boards under test”.
Coherix first designed this system at the behest of several Taiwan customers during the SARS epidemic. “The interesting thing is that it wasn’t just bus terminals and airports,” said Upham. “It was also shopping malls, hospitals, and corporations. They wanted to be able to screen their workforce and visitors as they came into their buildings.”
Coherix is developing a new system with a thermal senor that operates at 9 fps to comply with U.S. International Traffic in Arms Regulations (ITAR), which heavily governs ‘dual use’ technologies, including the export of infrared imagers. Coherix also offers its dual blackbody calibration units as a separate product.
Getting Mean about Temperature
Real time calibration is critical when imaging groups of people walking in unstructured environments, but when people can be constrained to small areas – such as security lines at airports or exiting an airplane – ‘fever’ scanning systems can look for people with temperatures above the mean, simplifying system design and lowering cost.
According to Justin Renken, Systems Architect for thermal imaging specialist, Ann Arbor Sensor Systems LLC (AAS2), real time calibration cannot solve all the issues involved with scanning people in airports for fevers.
“There’s the question of how core temperatures relate to surface temperatures,” noted Renken.
AAS2 sells a 32x31 element thermopile IR camera that is a cost effective solution for the close quarter aspects of a comprehensive fever detection strategy. It does not require a mechanical shutter for operation since thermopiles are 100 times less sensitive to ambient temperature changes than microbolometers. In its solution AAS2 offers a custom calibrated unit which tightens the thermal range of the camera thereby bringing the accuracy to +/- 1 degree or 1%, which is sufficient for this type of monitoring. The practical use of this lower resolution system is limited to eight feet from the human target. AAS2 suggests its systems, which can be used in ‘human assist’ mode with only a camera and analog TV, be installed where people will pass single file at customs/security inspection stations. The camera is also capable of fully automated detection with relay triggering to an external alarm device of your choice. Due to the cameras Embedded Linux Operating System this is all accomplished autonomously, without the requirement of a support PC. AAS2’s sensors are also locked to operate at 9 fps, giving these systems the ITAR compliance necessary for immediate international shipping.
While flu outbreaks typically do not last long, according to Frost & Sullivan’s Papiomytis, history shows us that new strains impact populations every few years. In today’s globalized economy, international travel is commonplace, and to some regions, critical for economic survival. With trillions of dollars in trade and billions of people at risk, IR scanning systems are not affordable, but necessary. “Scanners, for example, typically cost from between $20,000 and $40,000 each,” says Frost & Sullivan’s papiomytis. “If a normal-sized airport requires eight scanners, then they are looking at an outgoing cost of $500,000. This amount is insignificant compared to revenues being slashed by 50% as we witnessed in some SARS-affected airports in Asia Pacific during 2003.”
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