Thermographic Imaging of the Normal Canine
Thermography is a non-invasive diagnostic imaging technique involving the recording of cutaneous thermal patterns. This imaging modality provided information about normal and abnormal function of the sensory and sympathetic nervous systems and has been used to detect vascular dysfunction, myofascial trauma, and local inflammatory processes.
Thermography has recently been used in human medicine for breast cancer assessment, cutaneous evaluation of burn patients, rheumatologic assessments, and for lameness evaluations in veterinary equine patients.
Because of the recent advances in technology and the lack of sedation needed to image patients, thermography has potential use as a screening test for a variety of conditions in veterinary patients, however, no information could be found regarding the limitations of imaging with an intact hair coat or what impact clipping would have on thermographic patterns. Additionally, normal thermographic patterns in canine patients have not been determined. The purpose of this study is to establish a thermographic imaging protocol and identify thermal imaging patterns for various regions of interest (ROI) in the normal canine, and to determine what impact, if any, clipping of the hair coat has on the thermographic pattern.
Ten Labrador retrievers were evaluated with CBC, chemistry profile, radiography of all limbs, orthopaedic examination by a board certified surgeon and found to be normal. All dogs were intact females, and the median age was 13 months (range 11- 15 months). The thermal images were generated with a Meditherm Med20000 IRIS* infrared camera. Each dog was imaged, with views determined by the authors, in the same room, with an ambient temperature of 70 -71 F. The protocol included anterior and posterior views of the body, followed by full limb views. Additionally, each joint was imaged with four views of the ROI.
Once all the dogs with full hair coats were imaged, the hair coat was clipped over the fore limbs and rear limbs with a number 40 clipper blade. Each dog was then imaged at 15 minutes, 60 minutes, and 24 hours after clipping using the same imaging protocol. The temperature averages of each ROI were compared. The thermal patterns of the full limb views were reviewed by the authors.
Results indicate similar thermographic patterns and average temperatures between dogs in each ROI when comparing regions of dogs in similar groups and between left versus right. There was a significant difference (p< 0.05) in average temperature between the regions with full hair coats and the regions with clipped hair at all times, but the patterns remained similar. When comparing average temperatures in the various ROI between 15 minutes after clipping, and 60 minutes and 24 hours, there was a significant statistical difference between the average temperatures in most regions at both 60 minutes and 24 hours. When comparing average temperatures in the various ROI between 60 minutes and 24 hours the difference between average temperatures was not statistically different in most cases; however, differences were noted based on anatomic region.
With normal patterns and average temperatures of canine limbs established, further studies will be necessary to document different patterns and temperatures for disease processes and to establish if clipping the hair is necessary.
Based on these findings, thermography is a viable imaging modality that generates consistent images with reproducible thermal patterns in the ROI examined in normal dogs. Although hair coat did have a predictable influence on average temperature readings, thermal patterns remained consistent.
Future studies evaluating clinical patients with known pathologic conditions are underway to compare the ability of thermography to detect cutaneous temperature alterations indicative of the known pathologic condition and whether hair coat will interfere with the generation of a diagnostic image.
Custom image recognition software is currently being developed to objectively assess thermal patterns and compare them with known normal patterns.
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