Infrared (IR) imaging involves the accurate detection of infrared radiation from an object’s surface using specialist technology. The method of IR imaging is harmless, non invasive and requires no sedation lending itself perfectly to imaging a wide range of species.
In the case of veterinary IR imaging, we are measuring the emitted thermal radiation from the skin’s surface. The amount of infrared radiation detected by the technology is dependent on both the animal’s physiological state at the time of scanning, and numerous environmental factors that need to be considered in order to achieve accurate results.
Within a healthy individual, the body’s ability to regulate and stabilise its own physiology is dependent on a number of factors all working in harmony to achieve balance within what is a complex biological system.
Physiological dysfunction as a result of diseases that affect the vascular system, nervous system, musculoskeletal function and connective tissues will result in temperature changes to the skin’s surface that can be detected by IR imaging. IR imaging is therefore a test of physiology, and unlike MRI or X-ray which reveals structural changes, is a functional imaging modality.
Being able to visualise physiological dysfunction throughout the whole body of an animal is critical to our understanding of how disease affects not only the primary area of concern, but the resulting secondary issues that may go unnoticed. If you want to know how it all works, check out the Science Hit section.
To medical professionals, the skin can provide an insight into the diagnosis of systemic diseases, but also enables the monitoring of the health of blood vessels and nerves. The skin is a complex organ with structures that allows blood to be shunted and moved away from the surface layers to the deeper areas of the skin.
The flow of blood through the skin helps in the regulation of body temperature and blood pressure and is controlled by the autonomic nervous system (ANS). One arm of the ANS is the sympathetic nervous system (SNS), which has nerve fibres running to and from the central nervous system (CNS). The specialised areas of the skin that shunt blood away from the surface contain modified smooth muscle which is innervated by the SNS. Inflammation at any tissue depth is detected by sensory fibres.
This information is processed by the CNS and leads to a sympathetic response in the area of skin corresponding to the affected site (dermatome). This reflex arc causes a decrease in the sympathetic motor tone of capillary bed sphincters, leading to increased dermal bloodflow. Other than assessment of dermatomes that represent deep inflammation, superficial, localized inflammation can also be detected to a temperature sensitivity of 0.01°C by modern IR cameras. Further, abnormally low surface temperatures can indicate poorly perfused or compromised tissues, or nerve dysfunction.
Modern IR cameras accurately detect thermal (IR) radiation emitted by the skin’s surface. However, they do not capture colour information, they record thermal information which is then displayed in a way that we can visually interpret. The image is visualised using false colors representing the difference in temperature. The color tones correspond to the apparent surface temperatures of the target and this is what makes up a thermogram, where each pixel has a corresponding temperature measurement.
In a healthy subject, there is a symmetrical ‘dermal pattern’ within a thermogram that is consistent and reproducible for any individual providing environmental factors are controlled. A subject with physiological dysfunction will present with thermal asymmetry, and it is this asymmetry that we are looking for.
Applications, where you are dealing in small differences in temperature, are easier to see and analyze by applying a rich color palette to the image such as rainbow or high contrast palettes; this is routinely utilised by the medical and veterinary sciences for diagnostic
imaging where detecting thermal asymmetry is crucial.
Applications of infrared Imaging are ever increasing due to more comprehensive investigations following imaging, improved diagnostics, research and result correlations. There are 4 key areas to work within when using the technology and we have provided a synopsis below, linking you to helpful case selections.
Lameness & Poor Performance
Lameness and poor performance investigation are the technology’s leading applications. Infrared Imaging can review the whole patient, non-invasivley and within a short space of time, evaluating both chronic and acute conditions.
Full body imaging helps clinicians to connect their patients, enabling better evaluation of secondary and primary issues, leading to a holistic approach to lameness and poor performance investigation.
Areas of the body that are difficult to image with other modalities can be easily reviewed helping to warrant more expensive, localised diagnostics. This technology supports smaller practices when investigating complex cases, helping them to do more in house, reducing referral and offering a cost effective option for uninsured animals.
Infrared imaging can help to identify dysfunction at an early stage. The ability to measure subtle inflammatory processes enables the detection of sub-clinical injuries and the early onset of disease. Soft tissue degeneration and the early stages of osteoarthritis can be isolated during imaging sessions providing the opportunity to monitor the areas and intervene earlier.
Often infrared imaging can detect responses before structural imaging is able to correlate as the condition is still physiological in basis, but with clinical examination and the correct monitoring strategy it is a helpful modality for the veterinary surgeon’s tool box.
Pain can be a result of a structural issue but it can also be physiological without a structural involvement. Much research has been done to improve the detection of pain in animals, and as a test of function, infrared imaging enables clinicians to objectively quantify the animal’s subjective feeling of pain. Through the identification of physiological (autonomic) dysfunction we are able to correlate with regions of potential pain.
Infrared imaging is therefore a beneficial modality when evaluating complaints that may be related to poor performance or behaviour. The real time visual images can help to communicate with clients during investigation and encourage the appropriate treatment plans.
Infrared imaging is effective when monitoring recovery and the patient’s response to treatment. It objectively measures inflammatory and neurological processes over a period of time helping to guide rehabilitation programmes.
It is used to examine the site of injury along with observing secondary issues that may be developing due to an uneven gait/ compensation; a helpful indicator when returning the patient to work or exercise.
DR LIAT WICKS
The electromagnetic (EM) spectrum comprises the entire distribution of electromagnetic radiation according to frequency or wavelength.
Electromagnetic waves form a spectrum of different wavelengths divided into sub-ranges, commonly termed portions. These portions include visible light, X-ray, Infrared and ultraviolet radiation among others. The wavebands within the EM spectrum overlap each other with no clear boundaries. The visible part of the spectrum is limited to a small portion of the EM spectrum and is the part which we can see,
however this varies between individuals and between different species of animal
IR radiation (which includes thermal energy) has a longer wavelength than the visible portion reaching beyond the visible range, so we are unable to see it. Everything with a temperature above absolute zero emits thermal energy, even very cold objects like ice.
IR cameras allow us to see into this invisible portion enabling us to visualise and measure the thermal energy emitted from any object. Our eyes predominantly see reflections, as only a few objects emit light. IR cameras detect both reflected and emitted IR radiation.
Emissivity is a crucial measure in thermography, it is the ability of an object to efficiently emit IR radiation and ranges from 0 to 1. Shiny smooth surfaces have a low emissivity, but skin has an emissivity close to 1 (0.95-0.98) which makes it an almost perfect emitter of IR radiation.
However, an object not only emits IR radiation, but absorbs and reflects it from the immediate environment, and other objects close by. The accuracy of the resulting thermogram is also influenced by other environmental factors such as solar loading, draughts, ambient temperature and humidity. All these factors can cause inaccurate and misleading results if not taken into consideration during image capture stages and is why standardised imaging protocols are crucial in practice.
Credit – Ibarrac at English Wikipedia
Pointing you in the right direction
There is a vast array of thermal imaging devices on the market, ranging from low-resolution plug-in devices for your smartphone, to high-end high definition cameras. Choosing the right technology for an application is wrought with issues, but for physiological imaging there are a few specifications that must be met in order to achieve what is considered clinical accuracy in both the medical and veterinary professions.
Using the wrong specification of equipment in the wrong way and without suitable training or experienced veterinary interpretation, results in inaccurate, unreliable results which reduces the power and validity of this technology within the profession.
At Vet-IR we have over 60 years of of collective experience in using IR devices, ranging from devices specifically designed for physiological imaging, to the more modern FLIR science grade cameras which have the correct specifications and thermal sensitivity to undertake accurate
physiological imaging. We can advise on the kind of equipment and minimum specification that is required to undertake clinical standard physiological imaging and, where needed, point you in the right direction of experienced suppliers.
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