LASER-DOPPLER FLOWMETRY - CHARACTERISTICS OF A MODIFIED SINGLE-FIBER TECHNIQUE

The single-fibre percutaneous laser Doppler technique has been used in previous studies of intramuscular blood flow. This method facilitates studies of blood flow in deep tissue volumes and minimises the tissue trauma. The technique has been further developed with the aim of impr oving the signal quality. This has been accomplished by modifying the geometry of the fibre tip. By melting the fibre core material, lenses of different shapes are formed. Flat, spherical and 'pear'-type tips h ave been manufactured and are evaluated theoretically and experimental ly. The paraxial theory cannot accurately predict the position of zone s of highest irradiance. Therefore, a ray-tracing program has been dev eloped in the C language, by means of which some of the optical proper ties of the modified fibre tips can be simulated, Isoirradiance graphs and beam profiles are calculated for the three different fibre tips, Measured and calculated irradiance curves are used for evaluation of t he properties of the ray-tracing model. The three types of fibre tips are also evaluated and compared in flow models. The sphere and pear-ty pe probes show a higher flow sensitivity than the flat-end type, These improvements in flow sensitivity are interpreted as being related to the larger, strongly irradiated tissue volumes in front of the fibres. Intramuscular measurements with the pear-type probe show high sensiti vities to induced blood flow changes.