Equine Thermography - Hot or not?
Updated: Jun 16, 2020
The potential uses for thermography in equestrian care have been outlined historically, as far back as Von Schweinitz (1999) its sensitivity in equine pathophysiological detection was highlighted, it stated thermography as the most sensitive screening modality for back pathology in the horse (Fig.1), but why has it not become part of mainstream diagnostics?
Fig.1 Thermogram of a horses spine.
Thermography is the least invasive of any equine diagnostic modality (Readelli et al 2014), this is an obvious advantage, however this benefit creates certain downfalls of the modality: It is not regulated, anyone who decides to go out and purchase a thermographic tool can point it at an animal and provide a “Thermography service”, without any training or understanding of how the images need to be acquired in order to make them reliable; There is a plethora of different grades of equipment available, some designed for industrial use, some low spec some high spec, again, this lack of industry standardisation creates an unreliability; Vets receive very limited training in thermography, so when these unqualified people use non-standardised equipment to acquire unreliably taken images, they then give those images to a vet who has no training in reading them, over time this has given thermography a reputation for being a non-tool amongst the veterinary community, however we can see that in the medical world the modality is widely used (Lahiri et al 2012), so is thermography a useful tool in equestrian care or not?
Temperature has been used as an indication of pathology for thousands of years, since 400BC it has been used as a diagnostic tool, Galileo invented the thermoscope in the 17th century which was later adapted to become the thermometer and today radiometers are widely used in the measurement of inner ear temperatures. In 1868 Carl Wunderlich studied the temperatures of fever sufferers and found increased temperatures to correlate with illness, it was with the discovery of infrared radiation in 1800 that the path to thermography as a diagnostic tool began (Lahiri et al 2012), Hardy (1934) described the emissivity of the human body and confirmed the efficacy of reading surface body temperatures by way of a radiometer. Lahiri et al (2012) outlined the science behind creating a thermal image, using Boltzmann’s constant the emissivity of the skin can be measured and turned into a colourful image representing the differences in surface temperature, it was in 1963 that these differences in colour were identified as potentials for recognising physical illness (Barnes 1963), since then its uses have become more numerous as human medicinal research studied its potentials and applications, these are extensively outlined in Lahiri et al (2012), which concluded that the use of thermography is likely to see a surge in the medical field as the equipment and interpretation becomes more precise. The unique applications of thermography have also been studied in human medicine, its use in diagnosing neurological pathologies is outlined in Neves et al (2015) and many other studies have proven its applications in pathologies that are often difficult to detect with other screening modalities (Fig.2).
Fig.2 Unique applications of Thermography in human medicine include vascular issues such as thrombosis, hormonal issues such as thyroid dysfunction, neurological issues such as Reflex Sympathetic Dystrophy, complex regional pain syndrome and paralysis (Shaydakov and Diaz (2017),Cojocarul et al (2015),Hooshmand (2018),Moran et al (2018).
These pathologies often do not show structural changes therefore can be difficult to diagnose through other screening modalities, however as thermography is a test of physiological dysfunction it can see the bodies response. Thermography is often thought of as showing “hot spots” however as you can see from this Fig.2 often abnormal thermal patterns and in fact “cold spots” can present as indications of pathology.
So again we ask, with this wide use of the technology in the medical field, why are we not more widely utilising the technology to care for our horses? Lets address the questions most frequently asked of the modality, the reliability and the science, furthering on from what was outlined earlier in this article.
Dyson (2013) expressed the complexity of equine diagnostics, emphasising the systematic, correct selection of diagnostic tools, the precise and reliable acquisition of diagnostic imagery and the specialist, experienced interpretation of those images, this set of necessary protocols in achieving valuable diagnostics also applies to thermography, it is a veterinary diagnostic tool and should be treated as such. To assess thermography’s place in equine care and veterinary medicine we must understand diagnostics in general (see my article on common diagnostics), no diagnostic modality is perfect, artefacts are common place and are a result of equipment and human error, even in the most established of diagnostic modalities. Jimenez et al (2008) produced 5 tables of potential artefacts in the process of producing and reading radiographs, Thrall et al (2013) expressed the importance of correct image acquisition and how radiographs can become unreliable in the event of inexperienced acquisition and interpretation (Fig. 3).
Fig.3 Poor image acquisition can mean the images are sub-clinical even in established modalities such as radiographs, this is the same for every modality including thermography.
All veterinary diagnostic processes have a careful set of protocols to minimise error, however artefacts and generally poor images are sometimes inevitable, it is only an experienced eye that can recognise these and not make the mistake of them becoming part of their interpretation. Thermography is a highly sensitive modality, again this is an obvious benefit of the technology, however as well as internal influences on temperature readings, environmental factors can hugely effect reliability of results (Soroko and Howell 2018) from mud, sweat and water, to scars, recent veterinary care and even tack and boots, if these environmental factors are not addressed by strict protocols artefacts are created. Fernandez-cuevas et al (2015) outlined the potential influencing factors, expressing the importance of a controlled environment and an equilibration period to ensure stabilised measurements, 8-10 min was recommended for human equilibration. Studies found that humidity levels didn’t have significant effect on skin temperature as long as the ambient temperature was within a comfortable range (Atmaca and Yigit 2006), however it is clear that outside of this range, if sweating or shivering occur the reliability of results can become questioned.
Thermography will essentially and potentially detect any and all physiological dysfunctions occurring within the patient, once again a huge benefit, however when addressing a particular lameness for example, which of these findings is clinically relevant? Let’s take an MRI, MRI’s produce highly detailed images and will inevitably show evidence of multiple pathological changes (Fig 4-5)
Fig4. MRI enables a high tissue contrast image and provides both structural and physiological data, it can be presented as a 2D “slice” of the subject enabling the viewer to see intended structures without the possible superimposition of superficial structures (Murray 2011).
Fig.5 MRI findings will often show pathological changes that are not clinically significant.
Experienced specialised veterinarians can distinguish between clinically relevant findings and non-relevant findings by understanding the pathogenesis of the clinical history presented, this is also true of thermography, without the clinical history and veterinary knowledge the relevance of thermographic findings can not be established and misdiagnosis is probable.
The importance of veterinary knowledge in interpretation goes beyond clinical relevance, thermography is often thought of as “looking for hotspots” this is inaccurate as thermography is a test of physiological dysfunction by assessing the autonomic, sympathetic and parasympathetic nervous systems effect on dermal tone and the study of the disruption in homeostasis. Von Schweinitz (1999) highlighted the importance of understanding neuroanatomy and neurophysiology, outlined in detail the interpretational considerations in particularly spinal thermograms and stated thermography as portraying the physiological status of neural outflow and reading the bodies control of vasomotor tone.
Fig.6 Diagram expressing the sympathetic nervous systems influence on the peripheral vascular system. Interactive-biology.com
The mammalian inflammatory response to injury and disease has been widely studied and documented and is similar in systemic and musculoskeletal systems, this inflammatory response creates heat (Fig. 7) and this heat can be detected by thermography, either by direct heat transference in superficial musculoskeletal injury or by the sympathetic nervous system in deeper pathologies as described previously.
Fig. 7 The inflammatory process in osteoarthritis. All inflammatory processes create heat. Dovepress.com.
The common misconception that all hotspots are pathological indications is another cause for a loss in veterinary faith in the modality, specialised interpretation vets understand the potential bias a thermogram can imprint and often utilise other images to further assess the visual patterns (Fig.8).
Fig.8 The different images available to specialised interpretation vets, normal thermogram, greyscale and spatial derivative. These take the bias of hotspots out of the equation. These images are from Vet-IR interpretation system.
Above we have addressed protocols, image acquisition, veterinary knowledge, clinical history and specialised experienced interpretation as possible limiting factors depending on how they are done, one limiting factor that is not down to how its done is the fact that thermography can not see structure and is therefore most often a pre-requisite to further investigations, however this is no way lessens its usefulness. Diagnostics often follow a line of investigation (see my article on diagnostics), from clinical observation and diagnostic analgesia through to further paired modalities, with each tool adding a part to the picture (Fig.9). Thermography provides localization and physiological information however it lacks structural specificity and can not outline aetiology and so has its place amongst other diagnostics as a piece of the puzzle (Eddy et al 2001).
Fig.9 Thermogram vs radiograph.
Thermography can save a lot of time in pin pointing areas of dysfunction and experienced interpretation vets can give detailed indications as to the structures most likely affected (Fig.10) however the structural damage assessment will need further diagnostic modalities.
Fig.10 Veterinary report by Vet-IR
Fig.10 clearly shows that thermography, with experienced veterinary interpretation can provide vital and extensive physiological information relevant to the clinical signs. In the authors opinion this (in conjunction with all the other factors expressed) is what outlines a thermography service as being useful. The subtle complexities of thermographic acquisition and interpretation express that the reliability of thermography as a diagnostic modality depend on it being respected and utilised as a veterinary tool, it requires medical grade biological screening cameras, with images taken in a controlled environment after clinical preparation by a trained technician who understands its potential artefacts and then interpreted by a specialised veterinarian who understands the cases clinical history. Without these points in place you are essentially paying for some pretty pictures!
So having addressed the questions asked of the modality and establishing what makes it a useful tool, we can now look at its potential applications in equine veterinary care. Von Schweinitz (1999) clearly outlined thermography as a highly sensitive diagnostic tool for back pathology, Eddy et al (2001), Radaelli et al (2014) and Soroko and Howell (2018) all list many applications and potential uses for the modality, unfortunately there is limited evidence based research in comparison to human medicine on thermography’s application in specific pathologies, but these reviews clearly express that its applications are widespread and will become more established as more research is completed.
Soroko and Howell (2018) most recently outlined the applications and limitations of the modality appertaining to the equine, essentially any musculoskeletal pathology involving an inflammatory process can be detected, as well as hypothermic neurological pathologies, there are of course pathologies that are non-inflammatory, such as proximal suspensory desmopathy and chronic osseous changes that have past their inflammatory phase, this is a potential limitation of the modality but is in no way different to any other diagnostic tool, as each one has its applications, for instance you would not use ultrasound to look for a broken bone. This fact can often be overlooked and can add to the scepticism in cases where the final diagnosis of a non-inflammatory pathology does not correlate with thermographic findings.
The various pathologies and applications listed by the reviews can be summed up into a few categories, lameness detection and localization, poor performance and behavioural assessment, preventative care, rehabilitation and complimentary physiological information.
Most horses will need a certain amount of lameness investigation done to ascertain areas of pain, this can be a long, complexed and often nonspecific process (Dyson 2013), thermography’s ability to quickly and non-invasively assess the whole horse can be a huge benefit in quicker localization of causality. Studies by Sue Dyson have shown a large number of working equines presumed sound are in fact lame, her study on the ethogram of facial and other bodily expressions also highlighted that a vast amount of behavioural issues are also linked to pain, horses will work through a lot of discomfort but should they have to? Lameness investigations and diagnostic analgesia can not be effective unless the horse is lame enough to detect a difference, but with the findings of Sue Dyson we can see that there has to be a way of assessing sub clinical pathologies because our horses shouldn’t have to wait until they are broken to be fixed. Thermography can be a valuable tool in preventative care, due to its early stage detective ability (Fig.11), sub clinical pathological causes of pain can be assessed and treated before they become full blown veterinary issues.
Fig.11 Thermography can detect inflammatory process associated with developing pathology and therefore help to prevent injury. Its use in distal parts of the limb as well as the rest of the musculoskeletal system could be a valuable preventative tool.
Soroko and Howell (2018) expressed how thermography could be used in monitoring the training programmes of performance horses to help keep them at peak performance and prevent injury, stating that thermography can detect the physiological response to progressing injury before any other modality could pick up structural change, in the authors opinion this benefit should be more widely utilised, as an equine care professional, horses with performance issues are a subject of daily discussion and as a person who has equine welfare at the heart of practice the author believes we should be using this modality to help keep our horses pain free when they do so much for us. As discussed previously lameness diagnostics can be a difficult and complexed process, often many pathologies are present and complimentary issues arise as horses compensate for discomfort, as thermography can be used to assess the horse in its entirety, each route and complimentary issue can be treated in unison, therefore giving the horse a more wholistic treatment that ends perpetuation, this complimentary physiological information can Sync the work of each professional working on the horse, from the vet to the physio, the trainer to the farrier resulting in a more comprehensive care package.
As well as preventing injury, thermography can be a great tool in monitoring rehabilitation (Fig 12), its ability to monitor the inflammatory process can give information on how a pathology is regressing.
Fig.12 Thermography is used in human medicine to monitor the treatment of breast cancer and can be used to monitor the rehabilitation of many inflammatory pathologies in the equine post-surgery and during physio and other treatment.
To conclude answering our original question, is thermography a useful tool in equine care?
One of the biggest limitations of the modality is its lack of research, Vet-IR and the author have started to address this and the author is personally embarking on research projects to further establish the modality, as these studies become more widespread we can expect to see a surge in its veterinary use as we can see in human medicine. The potential benefits of thermography for horses and the equestrian world are huge, it could help keep horses at peak performance, help prevent injury and be a valuable diagnostic tool. IF the modality is applied correctly, by trained technicians and interpreted by qualified veterinary professionals, it could go a long way in helping provide better and more comprehensive care for our horses and at a much earlier and preventative stage. The author has taken a personal interest in the use of thermography, its ability to help that huge percentage of horses that are in sub-clinical undiagnosed pain is something that can not be ignored.
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THERMOGRAPHIC DIAGNOSTICS IN EQUINE BACK PAIN
Dietrich Graf von Schweinitz, BSc, DVM, MRCVS, 1999,
VETERINARY CLINICS OF NORTH AMERICA: EQUINE PRACTICE VOLUME 15 • NUMBER
u Soroko and Howell 2018, Infrared Thermography: Current Applications in Equine Medicine, Journal of Equine Veterinary Science Vol 60
The Role of Thermography in the Management of Equine Lameness
A. L. EDDY*, L. M. VAN HOOGMOED and J. R. SNYDER, The VeterinaryJoumal2001, 162, 172-181 doi: 1O.1053/t\j1.2001.0618, available online at http://www.idealibrary.com on IDE ~l® •