Review

The Role of Thermography in the Management ofEquine Lameness

A. L. EDDY*, L. M. VAN HOOGMOED and J. R. SNYDER

Veterinary Medical Teaching Hospital* and the Department of Surgical & Radiological Sciences (Van Hoogmoed, Snyder),School of Veterinary Medicine, University of California Davis, Davis CA 95616, USA

SUMMARY

Equine thermography has increased in popularity recently because of improvements in thermal cameras andadvances in image-processing software. The basic principle of thermography involves the transformation ofsurface heat from an object into a pictorial representation. The colour gradients generated reflect differencesin the emitted heat. Variations from normal can be used to detect lameness or regions of inflammationin horses. Units can be so sensitive that flexor tendon injuries can be detected before the horse developsclinical lameness. Thermography has been used to evaluate several different clinical syndromes not only in thediagnosis of inflammation but also to monitor the progression of healing. Thermography has importantapplications in research for the detection of illegal performance-enhancing procedures at athletic events.

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KEYWORDS: Equine; thermography principles; lameness; research.

The Veterinary Journal 2001, 162, 172±181doi: 10.1053/tvjl.2001.0618, available online at http://www.idealibrary.com on

INTRODUCTION

The electromagnetic spectrum is composed of wave-lengths that range from the shortest gamma rays, toX-rays, ultraviolet light, visible, infrared, microwave,and the longest radio waves. Within this spectrum,humans perceive only a very small region known asvisible light. Infrared radiation, which is detected bythermal cameras, is emitted by all objects propor-tional to their temperature. This radiation can beabsorbed, emitted, reflected, or transmitted. Emis-sivity refers to the object's ability to absorb and emitinfrared radiation and is considered more significantthan reflection, which is the ability to simply reflectthe infrared radiation. An object's classification asreflector or emitted is a function of its inherentmaterial properties. Brick, for example, has excellentemissivity but is a poor reflector, while metals gen-erally have the opposite properties. Emissivity isimportant in considering thermal images since the

Correspondence to: J. R. Snyder, E-mail: jrsnyder@ucdavis.edu

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ability of a material to emit or reflect heat should beconsidered in the interpretation of an image. Ther-mal cameras generate images based on the amount ofheat generated rather than reflected. More specifi-cally, they actually detect differences in temperaturesof the target and surroundings. This is important indesigning the time and environment in which ther-mal scans are performed. For example, at midday, ahorse may appear to blend into the backgroundbecause its body temperature is similar to that of thewooden stall door in the background. However, afternightfall, the stall door will have liberated themajority of its heat and the horse will exhibit a muchmore striking contrast to the background.

Similar to visible light, infrared radiation can beoptically focused, collected, and transformed viadetector arrays to an electronic signal. The detectorswithin the camera are complex arrays composedof barium strontium titanate (BST), which is tem-perature sensitive. These detectors have pyroelectricproperties that are influenced by the temperatureand infrared radiation generated by an object. Whentemperature changes occur in the BST, a pyroelectric

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Fig. 1. Thermographic images are a pictorial summary ofthe heat gradients generated by an object. Variations inheat are represented by different colours. The hottest areasare white and red while the cooler regions are representedby the darker blues and black.

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signal is interpreted by intricate circuitry within thedetector and an electronic signal is generated. Thissignal can then be translated via integrated circuitsand software into a video signal and displayed withvarying colours reflecting differences in the heatemissions gathered from the target. Since the vari-able measured is heat and not light, thermal camerasare not affected by the intensity or quantity of lightin the scene. This property is also enhanced sinceinfrared cameras generally operate in the long-waveinfrared region (7±14 mm) which is less affected bysunlight compared to the shorter waves.

Objects transfer heat energy to their surroundingenvironment via three mechanisms. Conductionrefers to the transfer of energy between two solidbodies with different temperatures that are in directcontact. Heat can also be conducted within the samebody when there is a discrepancy in temperaturefrom one regional area to another. The second mech-anism is convection, whereby heat is transferred viathe movement of a liquid or gas such as water or air.Finally, radiation refers to heat transfer by the elec-tromagnetic radiation that an object emits in alldirections without the need for any solid or fluidmedium. The thermographic cameras now availableto veterinary practitioners are state-of-the-art devicesthat generate detailed images with exquisite sensi-tivity to temperature variation. The common cam-eras used include the DTIS-500 camera (EmergeVision Systems), ThermaCam (Inframetrics), andThermacam PM595 (Flir Systems). Thermographyis a non-invasive, non-contact diagnostic techniquethat measures heat emitted from a targeted surfaceand displays the information as a pictorial repre-sentation. Variations in the colour pattern reflectthermal gradients (Fig. 1). The warmest areas aredepicted as white or red, while the coolest regionsappear blue or black. It can augment other mod-alities in diagnosing equine lameness and back pain.While thermography does not reveal specificpathologies, it facilitates the localization of increased(inflammation and/or injury) or decreased heat(reduced blood flow or vasomotor tone).

Skin temperature directly reflects the underlyingcirculation and tissue metabolism; therefore, normalthermographic patterns can be mapped to corre-spond to the horse's superficial vascularity and bodycontour (Turner, 1991). An understanding of thenormal variations in equine thermal patterns is cru-cial to interpretation of the scans in clinical cases.Skin overlying or in close proximity to major vessels(cephalic and saphenous veins, for example) willgenerally appear warmer. Areas distant from a major

blood supply, such as the dorsal metacarpus/meta-tarsus, fetlock, and pastern, appear cooler. Becauseof its arterio-venous plexus, the coronary and lami-nar corium just proximal to the hoof wall is thewarmest region of the distal limb. The route ofthe median palmar vein in the forelimbs (Fig. 2) andthe metatarsal vein in the hind limbs produces awarm region between the third metacarpus/meta-tarsus and the flexor tendons. The tendons arerelatively cool from the palmar/plantar view, withthe area between the bulbs of the heels emitting themost heat (Turner, 1991).

The use of thermography to assist in the diagnosisand prognosis of inflammatory conditions has beenavailable to the human and equine practitioner forseveral years. Recent technological advancements inthe design and image processing of the equipmenthave made the technology more attractive to equineprivate practitioners such that the equipment is nolonger reserved for affluent practices or universities.With horses, thermography has proved useful in thediagnosis, prognosis, and evaluation of soft tissueinjury or disease, and superficial orthopaediclesions, where the bone is covered by minimal softtissues (Turner, 1991). Some recent innovationsinclude improved resolution, more user-friendlyimage processing software, and uncooled cameratechnology (von Schweinitz, 1999). A system suitablefor evaluating horses should include a camera witha 20�±30� lens angle, the capability to position thecamera 1.5 to 2 m above the horse's back, and tem-perature band gradients adjustable to 0.5�±0.6�C(von Schweinitz, 1999; Fig. 3).

Fig. 2. Regions in close proximity to large vessels will appear to be warmer than more distant regions. Therefore, themedial aspect (A) of the limbs will normally appear warmer than the lateral aspect (B) of the limb.

Fig. 3. The thermographic camera is a lightweight hand-held portable device which can be connected to a laptopcomputer or monitor for image projection. Using integrated software, the images can also be downloaded and processed inthe laptop and subsequently stored for data analysis or printed immediately. (The image on the left is reprinted withpermission from the Equine Veterinary Education).

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A controlled environment is essential to a suc-cessful thermographic scan (Fig. 4). If available,stocks can be used to facilitate immobilization of thehorse and ensure the safety of the personnel andequipment. Scans should be performed in a draught-free area with low light, a temperature of lessthan 30�C (ideal temperature about 20�C), and a 10±20 min acclimation period (Turner, 1991). Thehorse must have a clean, dry hair coat and skin, andshould not be groomed within 2 h before the scan.

Topical agents should not be applied prior to thescan and any residues should be washed off theprevious day. The patient should not receivephysical therapy within 24 h of the exam andshould not have acupuncture in the region of thethermographic scan during the previous week.Exercise and sedation (especially �2 agonists) shouldbe avoided because of their effects on blood flowand superficial perfusion. Information that shouldbe recorded includes presence of focal lesions,

Fig. 4. Thermographic image taken of a horse immediately following exposure to the sun on the right side of the body(arrow).

Fig.5. Injuries totheflexortendonswillcauseanincreasedthermal pattern relative to the adjacent regions (arrow).

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recent injections, and ambient temperature andhumidity if excessive (von Schweinitz, 1999).

Before scanning, the thermal sensitivity must beadjusted to detect hairless sites, such as the muzzle oreye, at the uppermost range. Hairless or clippedregions will appear warmer because hair insulatesagainst the emission of infrared radiation. With thehorse standing straight and square, the minimumviews include the following regions: cranial pectoral,lateral neck and body, lateral pelvic limb, dorsallimbs (all four), caudal hind limbs, thoracolumbardorsal spine, and lumbosacral dorsal spine (vonSchweinitz, 1999). Repeated scans of suspect areasto assure reproducibility will yield more reliableinformation. Two to three scans should be per-formed at least one minute apart (Turner, 1991).

There are many factors that can compromisethe quality of the scan. In addition to extreme cli-mates, anxious or active patients can have significantskin temperature reductions due to increases insympathetic tone. Variation in time given to equili-brate the patient after transport, arrival into atemperature-controlled environment, or removalof blankets and bandages can also alter results.Variables in winter hair coats and clipping patternsconfound interpretation (von Schweinitz, 1999).

CLINICAL APPLICATIONS

Tendons and ligamentsIn the acute phase, tendonitis is detected as a focalincreased area of heat in the normally elliptical iso-thermic zone (Fig. 5). As lesions heal, the patternbecomes more normal, but the overall temperatureof the tendon remains elevated. `Hot spots' can bedetected thermographically up to two weeks beforeclinical evidence of swelling or pain. This permits

early detection of lesions and appropriate changesin training routines (Turner, 1991). Ligament inju-ries such as suspensory desmitis can also produce`hot spots', and thermography can be used in con-junction with the physical examination to detect and/or confirm areas of palpable pain (Turner, 1991).

FeetThermography can aid in the detection of numerousdiseases of the foot including laminitis, naviculardisease, abscesses and corns. It may help reveal dis-ease in the early phase or when physical and radio-graphic findings are inconclusive. Temperaturedifferences greater than 1�C between any of the

Fig. 6. The caudal aspect of the foot is best imaged with the limb extended slightly caudally (A). The warmest regions in thecaudal foot are between the bulbs of the heel (B).

Fig. 7. Thermal image of normal feet. The hottest regionis located on the coronary band which corresponds to thesuperficial blood flow patterns.

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hooves are abnormal (Figs 7 & 8). If all four feet areinvolved, the temperature of the feet between theheel bulbs should be measured. A difference of morethan 1�C between the feet is significant (Turner,1991).

Laminitis is detected as an increased temperaturechange between the warmer coronary band and thehoof wall. Normally this difference is between 1�Cand 2�C. Thermography can be useful in detectinglaminitis before clinical signs appear and can beused to monitor patients at high risk of becominglaminitic (Turner, 1991). Navicular disease, unlikemost foot abnormalities, is characterized by a reduc-tion in blood flow and temperature rather than byinflammation and a temperature increase. Normallythere is a 0.5�C increase in temperature in the footafter exercise. Horses with navicular disease do nothave this increase because of compromised bloodflow (Turner, 1991).

Joint diseaseWhile radiography is the preferred method forevaluating osseous changes, thermography reveals

inflammation associated with capsulitis and synovitis(Fig. 9). Most inflamed joints exhibit an oval area ofincreased heat centered over the joint when viewedfrom lateral to medial. The pastern is an exceptionto this rule. It exhibits a circle of decreased heatsurrounded by a peripheral area of increased heat.Thermography of joints can reveal alteration inthermal patterns two weeks prior to onset of clinicalsigns. This permits alteration in training and closeobservation to prevent more serious disease (Turner,1982).

Long bone injuryThermography has limited use in evaluating bonyabnormalities because the majority of bone is sepa-rated from the skin by soft tissues. However, thermo-graphy is very useful in the diagnosis of dorsalmetacarpal disease (sore shins or bucked shin com-plex). Grade 1 (pain, but no radiographic pathol-ogy) and grade 2 (pain with radiographic evidenceof callus) disease appears as a hot spot over thedorsal third metacarpal bone that is 1±2� warmerthan surrounding tissue. Grade 3 lesions (pain andradiographic evidence of a stress or fatigue fracture)appear as hot spots on the lateral or medial aspect ofthe third metacarpal bone rather than on the dorsalaspect. Grade 3 lesions are 2±3� warmer than sur-rounding tissue. Since thermographic changes pre-cede radiographic changes by two weeks, detectinggrade 3 disease early may prevent a stress fracturefrom becoming complete with continued training(Turner, 1991).

Hind limb myopathyHind limb myopathy can be difficult to documentand monitor objectively. Myositis can be detected asa generalized increased thermal pattern over theaffected gluteal region (Fig. 10). Inflammation inthe cranial thigh appears as hot spots associated withthe quadriceps proximal to their insertion of the

Fig. 8. A: Thermal image of a foot abscess which eventually drained at the coronary band. Notice the increased heatpattern located on the lateral aspect (arrow). B: Thermal image displaying the heat pattern of laminitis. Notice the increasedpattern on the coronary band as well as the bands of heat on the dorsal aspect of the hoof (arrow).

Fig. 9. Increased heat patterns associated with an inflammed fetlock joint.

Fig. 10. Increased pattern present on the medial andlateral aspects of the gluteal regions in a horse withmyositis.

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patella. Caudal thigh inflammation is most com-monly visualized at the musculotendinous junctionof the semitendinosus muscle, and less frequently asinflammation caudal to the third trocanter of thefemur. The loin, sacroiliac region, body of the glu-teal muscle, and the biceps femoris appear hot whenthe croup region is injured (Turner, 1996). In astudy of horses with croup or caudal thigh myopathy,20 of 23 horses with palpable areas of pain had cor-responding abnormal areas noted during thermo-graphic scans. Once areas of inflammation have beenobserved, thermography can be used to evaluateprogress in the convalescence period (Turner, 1989).

Neck and backThermography is also useful in identifying andlocalizing spine-related disease (von Schweinitz,

Fig. 11. A: Lateral thermal pattern of the back of horse with palpable pain caused by a poorly fitted saddle. Increased heatis present in the saddle location (arrow). B: Dorsal view of the same horse showing increased heat (arrow) over the dorsalspinous processes in the saddle region.

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1999; Fig. 11). Such problems may manifest aspalpable back pain, training difficulties, or beha-vioural abnormalities. In addition to depicting thephysiological status of local tissues, thermographyalso relates information about neural outflow fromthe spine. Other tools, including radiology, ultra-sound, and nuclear scintigraphy, are limited in theirability to reveal information about equine spinaldisease. In a recent study (von Schweinitz, 1999),53 horses with vague locomotion or behavioralabnormalities and clinical signs consistent with backdisease had neuromuscular disease of the thoraco-lumbar region. Clinical signs in these cases includedpain on palpation, pain elicited at acupuncture andtrigger points, spinal distortion, restricted flexion,abnormal posture or movement, muscular abnorm-alities (irritability, asymmetry, atrophy, spasm), andpoor hair and skin in the affected areas (vonSchweinitz, 1999).

Thermography is useful in these cases becausealteration in skin temperature corresponds tochanges in the sympathetic autonomic nervous sys-tem (i.e. vasomotor tone). Vasomotor tone alterationis often associated with back pain and shows upthermographically as a region of decreased temp-erature (cold spot). Rather than being inflammatoryin origin, chronic back disease in the horse is nowconsidered to be a sympathetic associated painsyndrome. These disorders seem more amenable totreatment with acupuncture, exercise management,and other physical therapies than conventional anti-inflammatory medications (von Schweinitz, 1999).

LIMITATIONS/ADVANTAGES

Like other diagnostic tools, thermography is mostuseful when its limitations are recognized. Equip-ment is expensive, and therefore may not be within

the financial means of all practices. While thermo-graphy provides localization and physiological infor-mation, it lacks specificity and cannot defineaetiologies. Generally, thermography is best used incombination with other modalities rather than as areplacement for them.

Even with these limitations, however, thermo-graphy has much to offer. It is non-invasive andinvolves no radiation exposure. When used for serialevaluations, it helps monitor response to treatment.It is more sensitive than palpation for detectingsubtle temperature variations. This high sensitivitymakes it useful in conjunction with other modalitiesthat provide more specific information (such asradiography, nuclear scintigraphy, and ultrasound).Thermography often reveals physiological changesbefore they appear as clinical signs or radiographicabnormalities, thus providing early warning and achance to alter training schedules or initiate treat-ment. At the University of California Davis Veter-inary School, we attempted to correlate the findingsof thermographic scans with other diagnostic mod-alities ± specifically ultrasound, nuclear scintigraphy,and radiology. We were interested in determiningwhether we could detect injuries or lesions withthermography that could then be confirmed or dis-puted with another diagnostic procedure. Horsesthat presented to the teaching hospital for variousorthopaedic or musculoskeletal injuries were eval-uated thermographically using routine scanningprotocols. Although we were unable consistently toevaluate the horses at a specific time, we attemptedto minimize temporal variation by scanning thehorses within an enclosed room which generally wasmaintained at a constant temperature. The horsesincluded in this preliminary study included thosepresented for nuclear scintigraphy of limbs forpotential humeral and tibial stress fractures,

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ultrasound examination of the distal limbs fortendon or ligament injury, and horses where aradiographic examination was performed based onthe findings of a lameness examination. Horses wereincluded only if they displayed a current lameness.

In some cases, the regions of the lameness wasknown (e.g. the horse improved with a low 4 pointnerve block), but in others, such as the nuclearscintigraphy cases, no specific site was designated.For this study, we evaluated a total of 64 horsesdivided into 15 with ultrasound, 20 with nuclearscintigraphy, and 29 with radiographic examina-tions. Thermography was 62.5% successful in colla-borating the location/source of the injury with thesethree diagnostic modalities. In horses presentingfor ultrasound examination, the affected site waswarmer than the surrounding area or contralateralstructure in 10/15 (66.7%) cases. Thermographycorrelated with nuclear scintigraphy in 15/20 (75%)cases. Horses with stress fractures of the tibia wereidentified fairly consistently while humeral stressfractures were less reliably noted. This is likely due tothe increased muscle mass over the humerus com-pared to the medial aspect of the tibia which wouldblunt heat transmission from a stress fracture andassociated soft tissue inflammation. Compared to theother two diagnostics, thermography correlated lesseffectively with radiography (15/29; 51.7%). This isprobably the result of a reduced ability of thermo-graphy to detect subtle or chronic bony lesionscausing lameness. For example, horses with degen-erative joint disease of the hock (bone spavin) whilelame, did not exhibit an increased thermal differ-ence. Potentially, the amount of heat generatedfrom chronic and low grade arthritis is not sufficientto reveal a detectable difference. Other lesions suchas degenerative joint disease of the pastern andcoffin joints (ringbone) did not exhibit a consistentthermal difference. Again, it is possible the asso-ciated inflammation may not be sufficient to detect.

RESEARCH APPLICATIONS

In addition to diagnosis of clinical disease, thermo-graphy is also useful for evaluating the effects ofvarious topical treatments (such as cold, biomagnets,and ultrasound) on skin temperature (Turner et al.,1989). In this study, a gel wrap cooled to 4�C andheated to 40�C was applied to the metacarpus. Withcold therapy, the treated limb remained 2.5�C coolerthan the untreated leg by 2 h, and by 4 h thedorsal metacarpus remained 4�C cooler than thecontrol leg. The heated wrap produced temperature

differences between the limbs which actuallyincreased with time. Thirty minutes after removal ofthe wrap, the difference was 2.8�C and increased to3.7�C after 75 min. No significant difference wasseen between biomagnets and placebos applied tothe flexor tendon region for 24 h. Finally, therapeuticultrasound applied to the flexor tendon region for10 min significantly increased the thermal patternon the treated limbs in an intensity-dependentfashion which was sustained for more than one hour.

An area which has received increased interestrecently is the use of thermography to detect illegalactivity at performance events. Intense pressure towin can, unfortunately, promote the use of illegalperformance-enhancing techniques designed toenhance a horse's athletic ability or appearanceartifically. Although pharmaceutical screening atcompetitions reduces the overt use of chemicalperformance-enhancing agents, some competitorshave become creative at evading detection usingprocedures which would not be detected on a rou-tine drug screen. Examples of these techniques mayinclude the application of counter-irritants suchas mercuric iodide to the dorsal aspect of the pasternor metacarpus, subdermal injection of irritants toaccentuate limb flexion, regional nerve blocks,infiltration of the injured area with potent analgesicagents, and palmar digital neurectomies since footpain is a common cause of lameness in performancehorses.

Thermography has recently been evaluated as apotential screening device in studies that recreatedsome of the illegal methods used at competitions. Anearly study by Turner and Scroggins (1989) foundthermography could successfully detect the applica-tion of irritants on the perineal region to accentuatetail carriage. An investigation of the ability of ther-mography to detect illegal procedures was recentlypublished (van Hoogmoed et al., 2000). This studywas designed to evaluate the ability of thermographyto identify irritants applied to a horse's limb anddetermine how long these effects could be detected.Specifically, counter-irritants were applied topicallyand injected subdermally on the dorsal aspect of thepastern, and metallic irritants in limb bandages wereapplied to the limbs to induce metacarpal hyper-sensitivity. In this study, we found thermographydetected changes in skin temperature followingsubdermal injection of hypodermin for up to eightdays. The topical application of mercuric iodide onthe pastern produced an increased heat patternwhich remained significantly elevated for six days.Metallic bottle caps in the leg wraps produced

Table ISummary of the mean (�SD) of the temperaturedifference between the treated and control limb

following three hypersensitization techniques.(Reprinted with permission from

Equine Veterinary Education).

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a unique thermal pattern that persisted for 24 h.The skin directly under the caps remained coolrelative to the surrounding skin because sweat dropsproduced by the presence of the caps lowered thelocal temperature (Table I).

Time Mean�SD P-value

Control ÿ0.00�0.23 0.95

30 min 0.06�1.06 0.79

60 min 0.60�0.78 0.003

2 h 0.89�0.55 < 0.0001

6 h 0.81�0.75 < 0.0001

Day 1 0.85�0.45 < 0.0001

Day 2 1.62�0.69 < 0.0001

Day 3 1.10�0.62 < 0.0001

Day 4 0.86�0.47 < 0.0001

Day 5 0.45�0.45 < 0.0001

Day 6 0.35�0.44 0.001

Day 7 0.35�0.42 0.0005

Day 8 0.18�0.32 0.01

Day 9 0.15�0.46 0.12

Time Mean�SD P-value

Control ÿ 0.04�0.16 0.24

30 min 0.67�0.48 < 0.0001

60 min 0.24�0.33 0.0013

2 h 0.74�0.87 0.0005

6 h 0.93�0.81 < 0.0001

Day 1 1.24�0.54 < 0.0001

Day 2 1.25�0.62 < 0.0001

Day 3 1.23�0.74 < 0.0001

Day 4 0.87�0.75 < 0.0001

Day 5 0.64�0.77 0.0004

Day 6 0.38�0.38 < 0.0001

Day 7 0.02�0.25 0.75

Day 8 0.05�0.38 10.46

Time Mean�SD P-value

Control ÿ 0.01�0.27 0.91

Immediate 0.90�0.89 < 0.0001

30 min 0.25�0.33 < 0.0001

60 min 0.94�0.53 < 0.0001

90 min 1.15�0.68 < 0.0001

2 h 0.80�0.66 < 0.0001

4 h 1.08�0.90 < 0.0001

6 h 0.74�0.59 < 0.0001

Day 1 0.43�0.58 0.003

Day 2 0.00�0.36 0.967

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One limitation of thermography in this type ofinvestigation is a lack of specificity, since it displaysa thermal pattern which does not necessarily differ-entiate between agents. Although the patterns werenot unique, for example between the hypoderminand the mercuric iodide, it was apparent the scanswere not normal. The results of this study suggestthat infrared thermography is sensitive enough todetect the application/injection of various agents inthe distal limbs of horses. Further investigation isrequired to determine whether thermography candetect other techniques such as the injection of anti-inflammatory agents and, potentially, neurectomies.Realistically, with the exception of techniques likebottle caps, which leave a very definitive trademarkof illegality, it would be difficult to disqualify a horsebased on a single thermographic scan alone. Ifthermography is used as a screening device to detectillegal activity at competitions, we recommend thatit be used in conjuction with other methods such asdetermination of skin sensitivity or physical exam-ination of the area.

REFERENCES

TURNER, T. A. & SCROGGINS R. D. (1989). Thermographicdetection of gingering in horses. Journal of EquineVeterinary Science 5, 8±10.

TURNER, T. A. (1989). Hindlimb muscle strain as a cause oflameness in horses. Proceedings of the 35th AmericanAssociation of Equine Practitioners Symposium, 281±290.

TURNER, T. A. (1991). Thermography as an aid to theclinical lameness evaluation. Veterinary Clinics of NorthAmerica: Equine Practice 7, 311±338.

TURNER, T. A., WOLFSDORF, K. & JOURDENAIS, J. (1991).Effects of heat, cold, biomagnets and ultrasound onskin circulation in the horse. Proceedings of the 37thAmerican Association of Equine Practitioners Symposium,249±257.

TURNER, T. A. (1996). Thermography as an aid in thelocalization of upper hindlimb lameness. Pferdeheilkunde12, 632±634.

VAN HOOGMOED, L. M., SNYDER, J. R., ALLEN, K. A. &WALDSMITH, J. D. (2000). Use of thermography to detectperformance enhancing techniques in horses. EquineVeterinary Education 12, 132±138.

VON SCHWEINITZ, D. G. (1999). Thermographic diagnosticsin equine back pain. Veterinary Clinics of North America:Equine Practice 15, 161±177.