ABSTRACT

68Optical radiation has unique properties which make it attractive for sensing certain physical biomedical parameters. It possesses a very short wavelength (typically in the range 0.4 to 1.0 μm), allowing accurate measurements of motion and displacements approaching this size. Interference is also minimized between the optical signal and lower frequency electrical noise usually present in the biological environment. The advent of the laser provides a means for generating narrow-frequency, spatially coherent light, and fiber optics may be used for conveniently guiding light to the sensor. Instruments capitalizing on these properties have been designed for the measurement of biological flow, force, displacement, and temperature.

Quantities such as blood flow and sperm motility can be measured by utilizing the optical Doppler shift from the moving scatterers, with high precision resulting when narrowband laser sources are used. Both air paths and fiber optic paths for in vivo measurements have been reported. For measuring small intralumen pressure changes, a thin reflecting membrane may be placed at the distal tip of a fiber-optic catheter, resulting in a varying reflected intensity as the membrane deflects in the pressure field.

Small displacements of bones and other body surfaces have been measured by interferometric techniques, either in real-time or recorded on film (holography). In a different technique, sarcomere length in excised skeletal muscle and cardiac muscle has been dynamically detected via changes in the diffraction pattern of laser light passed through the muscle.

Temperature probes using optical fibers connecting to the sensor have been reported for a variety of sensor types. The most successful employ either a liquid-crystal reflecting layer, a birefringent crystal, or a semiconductor band-edge absorber.