FLIR thermal imaging cameras used to detect small nerve fiber dysfunction
It is estimated that about 2% of the world population suffers from small nerve fiber dysfunction, which can result in neuropathic pain; diabetic patients represent a large portion of this population. While the dysfunction of large nerve fibers can be assessed using standard neurological examination and electromyography (EMG), currently no non-invasive techniques exist to detect and quantify small fiber dysfunction.
In research funded by the Dutch Technology Foundation STW, thermal imaging technology is used to develop an experimental setup that can detect this neuropathic phenomenon. To stimulate the development of new ways of employing thermal imaging cameras for medical purposes FLIR Systems has donated a high quality cooled FLIR SC5000 Series thermal imaging camera and the dedication of its experienced personnel to this research project.
The current method used to detect small nerve fiber dysfunction is skin biopsy, but this method has serious limitations, explains Dr. Ir. Sjoerd Niehof, thermography expert at the Anesthesiology Department of the Erasmus University Medical Center. "Skin biopsy is an invasive method. The skin of the patient is locally sedated and a small portion of skin has to be removed for analysis in the lab. This method is relatively slow and it only reveals information about a small area of skin. We aim to prove that thermal imaging can be used to identify small nerve dysfunction in larger areas quickly and in a non-invasive manner. This would speed up assessment, saving time and money, while imposing minimal stress on the patient."
The theory: blood flow regulation
The theory behind this method is based on changes in blood flow. The body has a thermoregulatory control system that responds to thermal stimuli by increasing or decreasing local blood flow. This can be detected using thermal imaging technology.
For a pilot study the thermal stimulus was delivered using a cold plate. Although this pilot study proved the concept, the cold plate method was uncomfortable for the patient. The current setup therefore employs an infrared lamp to deliver the thermal stimulus. The infrared lamp produces only infrared radiation of a specific spectral frequency, so a spectral band filter can be used to block that part of the infrared spectrum before it reaches the thermal imaging camera. This ensures that the measured skin temperatures are accurate.
The hypothesis is that the way the body responds to thermal stimuli can indicate the function and integrity of small nerve fibers. In ill conditions such as small nerve fiber dysfunction the reaction of the body's control mechanism are likely altered. The earlier pilot study proved that a patient with small nerve fiber dysfunction shows a slower response to the thermal stimulus than a healthy subject; or in some cases no response at all.
Physics and technical knowhow
Developing the setup requires extensive knowhow of the physics and technical details involved. The BioMechanical Engineering Department of the Technical University of Delft, the Netherlands, was therefore involved in the research. To help with observational software development and integration the research also includes Noldus Information Technology.
FLIR SC5000: sensitive and accurate
One part of the system was readily available: the thermal imaging camera. FLIR Systems provided the researchers with a FLIR SC5000 Series thermal imaging camera, which is specifically designed for the most demanding scientific applications. The Indium Antimonide (InSb) focal plane array detector provides thermal images of 640x512 pixels at a sensitivity of below 20 mK (0.02 °C). The external triggering feature also allows it to synchronize with the most fleeting of events.
"FLIR Systems has been very supportive", says Wu. "We get really good data from the FLIR SC5000 Series thermal imaging camera and due to the support we received from the FLIR Advanced Thermal Solutions Department we were able to relatively easily incorporate the FLIR SC5000 into our setup."
Testing on real patients
After system development the next step in the process is testing it on real patients, explains Niehof. "During this phase of the process we will investigate both healthy test subjects and patients with small nerve fiber dysfunction using the newly developed test method and compare the results with the current gold standard: conventional skin biopsy."
At the end of the road this research project will hopefully deliver a new method to detect small nerve fiber dysfunction, but according to Niehof it doesn't end there. "We aim to make a system that can be used with other types of disease as well. Although the measurement set-up needs to be tested separately for each disease, we think that it can also be used with burn injuries, Raynaud's disease, vascularisation of skin flaps and skin cancer to name just a few examples."
Niehof thinks that thermal imaging technology has a promising future in medical applications. "The use of thermal imaging technology in medicine is currently limited by the lack of standardization in recording methods and a lack of knowledge regarding the underlying mechanisms that result in the measured temperature differences. With this research we hope to at least partially fill those gaps and hopefully future research projects will help to further develop thermal imaging technology into an accepted medical technique."
Disclaimer: all statements in this application story are based on the above-mentioned research. FLIR Systems cannot be held responsible for the use or misuse of any of its thermal imaging cameras in a medical environment.
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