Development of a Respiration Monitor Based on Fibre Optics & CCD Camera for Small Animal Preclinical Imaging

Abstract

Current preclinical research in whole body imaging often involves the use of mice. Their respiration rate must be monitored during the imaging procedure while under anaesthetic. Current techniques used often require contact with animal, and use extra equipment, filters and amplifiers. One solution is to design a simple non-contact breathing detection device, that is cheap and easy to integrate. By placing a pair of transmitting and receiving fibre optic cables above the mouse, reflected light is captured continuously using a Charge Coupled Device (CCD) camera. These images are converted to an analogue average intensity value that are continuously plotted to display a waveform from which respiration rate can be measured. A series of experiments were carried out to find the optimal fibre positioning, and these were tested on a breathing simulation. This was carried out using a model mouse fitted with a balloon, that was pumped using a motor. The positions that gave the optimal response was a fibre position of 80° with a gap of 2mm, at 3mm away from the surface, for dark fur. For white fur it was a fibre pair position of 100° with a 12mm gap, 4mm away from the surface. By calculating the breathing rates from the recorded waves over a period of time, these values were found to be close to the correct breathing rate that was being simulated. This was true for low breathing rates, where the measured values where 0.2-1.8% higher than the simulated breathing rate (50bpm). The camera used in this device was unable to sample high frequencies, therefore failed to accurately measure very high breathing rates where values measured from recorded waves were up to 27% lower than the true simulated breathing rate.