Equis ISSN 2398-2977

Thermography

Contributor(s): Vetstream Ltd, Chris Whitton, Rachel Murray, Graham Munroe

Introduction

  • Infrared thermography involves the detection of infrared radiation (heat) emitted by the body surface by a special camera which produces an image where the colour gradient corresponds with the distribution of surface temperatures.
  • Heat is lost from the skin in a variety of ways and thermal cameras measure the infrared radiation part of this loss.
  • The radiation is optically focused, collected, and converted into an electrical signal which is then used to produce a video signal and image.
  • It has been used as a diagnostic imaging modality in veterinary medicine since the late 1960s.
  • Much of its use in the horse has been in the field of orthopedics.

Uses

  • Detection of the differences in the expected distribution patterns of surface temperature between and within limbs of the horse, and in the axial skeleton (neck, back or pelvis). The normal thermal patterns are related to the topography of blood vessels and the anatomical structures within the area, eg in the distal limb the third metacarpal/metatarsal bones, fetlocks and proximal interphalangeal joint typically have cool temperature patterns compared to the foot coronary band.
  • Identification of areas of inflammation (increased blood flow), such as seen in disease or injury, or vascular stenosis (decreased blood flow) in cases associated with lameness in the horse.
  • With experience and care in interpretation thermography may be useful in lameness diagnosis as part of a full approach using clinical examination and imaging techniques. In one case series it was found to correlate with ultrasonographic Ultrasonography: overview, scintigraphic Bone: scintigraphy Non-musculoskeletal: scintigraphy - overview and radiological Radiography: overview findings in 63% of 64 lameness cases. Unfortunately however, too often it appears to be used as an alternative to the conventional lameness workup with subsequent anecdotal and inaccurate claims for its effectiveness. 

Advantages

  • Non-invasive.
  • The equipment is easy to handle.
  • Results are rapidly obtained.
  • Minimal or no risk of injury to animal or humans gaining the images.
  • Whole body can be imaged quickly.

Disadvantages

  • The use of thermography, particularly in the field of equine orthopedics, is still controversial and it is not universally accepted as providing useful and accurate results.
  • Ambient temperature and other immediate environmental conditions, such as sunshine and airflow, can influence surface temperatures in the horse and confuse the interpretation of acquired images.
  • In addition, there is considerable doubt as to whether all orthopedic conditions in the horse will affect the surface temperature pattern and be detected. Furthermore changes in skin temperature may occur for other pathological and non pathological reasons creating considerable variability in results and a high incidence of artefacts.
  • The camera equipment can be expensive.

Requirements

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Preparation

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Procedure

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Rekant S I et al (2016) Veterinary applications of infrared thermography. Am J Vet Res 77 (1), 98-107 PubMed.
  • Rushton J O, Tichy A & Nell B (2015) Introduction of the use of thermography and thermometry in the diagnosis of uveitis in horses: a pilot project. Vet Rec Open 2 (1), e000089 PubMed.
  • Yarnell K et al (2014) Monitoring changes in skin temperature associated with exercise in horses on a water treadmill by use of infrared thermography. J Therm Biol 45, 110-116 PubMed.
  • Westermann S et al (2013) The effect of airflow on thermographically determined temperature of the distal forelimb of the horse. Equine Vet J 45 (5), 637-641 PubMed.
  • Westermann S et al (2013) Effects of infrared camera angle and distance on measurement and reproducibility of thermographically determined temperatures of the distolateral aspects of the forelimbs in horses. J Am Vet Med Assoc. 242 (3):388–395.
  • Bowers S et al (2009) Assessment of pregnancy in the late-gestation mare using digital infrared thermography. Theriogenology 72 (3), 372-377 PubMed.
  • Levet T et al (2009) Distal limb cast sores in horses: risk factors and early detection using thermography. Equine Vet J 41 (1), 18-23 PubMed.
  • Verna  M, Turner T A & Anderson K L (2005) Scintigraphic, radiographic, and thermographic appearance of the metacarpal and metatarsal regions of adult healthy horses treated with nonfocused extracorporeal shock wave therapy--a pilot study. Vet Ther 6 (3), 268-276 PubMed.
  • Tunley B V & Henson M D (2004) Reliability and repeatability of thermographic examination and the normal thermographic image of the thoracolumbar region in the horse. Equine Vet J 36 (4), 306-312 PubMed.
  • Holmes L C et al (2003) The effect of perineural anesthesia on infrared thermographic images of the forelimb digits of normal horses. Can Vet J 44 (5), 392-396 PubMed.
  • Turner T A (2001) Diagnostic thermography. Vet Clin North Am Equine Pract 17 (1), 95-113 PubMed.
  • Van Hoogmoed L et al (2000) Use of infrared thermography to detect performance-enhancing techniques in horses. Equine Vet Educ 12 (2), 102-107 VetMedResource.


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