Canine Olfactory Thresholds to Amyl Acetate in a Biomedical Detection Scenario

Abstract

Dogs' abilities to respond to concentrations of odorant molecules are generally deemed superior to electronic sensors. This sensitivity has been used traditionally in many areas; but is a more recent innovation within the medical field. As a bio-detection sensor for human diseases such as cancer and infections, dogs often need to detect volatile organic compounds in bodily fluids such as urine and blood. Although the limits of olfactory sensitivity in dogs have been studied since the 1960s, there is a gap in our knowledge concerning these limits in relation to the concentration of odorants presented in a fluid phase. Therefore, the aim of this study was to estimate olfactory detection thresholds to an inert substance, amyl acetate presented in a liquid phase. Ten dogs were trained in a “Go/No go” single scent-detection task using an eight-choice carousel apparatus. They were trained to respond to the presence of solutions of amyl acetate diluted to varying degrees in mineral oil by sitting in front of the positive sample, and not responding to the 7 other control samples. Training and testing took place in an indoor room with the same handler throughout using a food reward. After 30 weeks of training, using a forward chaining technique, dogs were tested for their sensitivity. The handler did not assist the dog during the search and was blind to the concentration of amyl acetate tested and the position of the target in the carousel. The global olfactory threshold trend for each dog was estimated by fitting a least-squares logistic curve to the association between the proportion of true positives and amyl acetate concentration. Results show an olfactory detection threshold for fluid mixtures ranging from 40 parts per billion to 1.5 parts per trillion. There was considerable inter-dog difference in sensitivity, even though all dogs were trained in the same way and worked without the assistance of the handler. This variation highlights factors to be considered in future work assessing olfactory detection performance by dogs.

Methodological Considerations in Canine Olfactory Detection Research

“…This can be achieved by having the observer behind a screen or one way mirror, watching on a monitor connected to a video camera, or using a mobile device to communicate with the handler. Other systems have been used that do not require this type of relaying from one individual to another, such as custom-made software in which the handler presses a key to reveal the result (9). In all of these instances, a slight delay will be imposed between the dog's response and its reward, which can be introduced in training until the dog is accustomed to the delay.…”

“…This design is sufficient when dogs are trained to sample systematically and are quite accurate, however, adjustments are sometimes required. For example, it may be necessary to allow dogs to rerun the trial or search if an area is missed, the dog displays a COB, or shows interest but doesn't respond (9). Critically, the decision of whether the dog sufficiently searched the area or not should be made by a blind handler or evaluator before any feedback of the trial outcome is given.…”

“…Bloodhounds possess 300 million odor receptor cells, more than any other breed ( 4 ), and are considered to have the greatest olfactory acuity ( 5 ). However, studies on canine olfactory threshold have been limited to single breeds ( 6 – 8 ) or few dogs from several breeds ( 9 ), with few studies examining breed as a factor in olfactory detection performance. In one study, differences in olfactory threshold were examined by comparing different breeds in a natural detection task in which food was hidden in containers of varying levels of permeability ( 10 ).…”

Breast Cancer Detection From a Urine Sample by Dog Sniffing

“…An effective training protocol is essential for good performance [20]. Even though dogs can be subject to the same training manner by the same trainer, inter-dog difference or poor performance due to stress have been pointed out in similar studies [10,17].…”

“…Cancer detection by dog sni ng (hereinafter referred to as "canine cancer detection") is one of the candidates as a new method to detect breast cancer. Detection threshold has been shown to be as low as 1.5 parts per trillion (ppt) [10]. Trained dogs can successfully discriminate between patients with cancers of skin [11,12], bladder [13], lung [14][15][16][17][18], breast [14,19,20], prostate [20][21][22] ovary [23][24][25], colorectal [19,26], liver [27], uterine cervix [28] from controls on the basis of odors in breath, urine, blood or cell culture medium.…”