A study for a portable IR sensor to detect the blood temperature during coronary bypass implantation

The objective of this research was to investigate the possibility of using an infrared prototype device for the detection of the blood temperature during a surgical operation for coronary bypass implantation. The correlation between the fluid temperature profile and the fluid flow rate was demonstrated. Currently, an expensive infrared (IR) camera placed in a corner of the operating room is used for the qualitative detection of these data, but a lot of problems arise regarding noise generated by external heat sources (medical staff, instrumentation...). The idea was to design a low cost portable device to be placed near the region of interest. Each blood vessel acts like a thermal wave emitter, so the amount of heat is proportional to the blood flow detected by the IR sensor. The first step in our research was the implementation of a coronary system model for predicting its operation and carrying out punctual and profile measurements. We chose a pyroelectric sensor for its high quality-cost ratio. Because this kind of sensor detects only a variable infrared source, we used an electromechanical chopper for modulating the radiation. It consists of an electronic shutter whose opening speed is controlled by an astable multivibrator. The output signal was analysed using a dedicated electronic circuit including a bandpass filter and an amplifier; then an acquisition board is employed for capturing and displaying the signal using a PC. The prototype assessment was made using a laboratory equipment. Further steps will concern in vivo measurements during surgical operation for coronary bypass implantation.