H. Cai et al., LASER-DOPPLER FLOWMETRY - CHARACTERISTICS OF A MODIFIED SINGLE-FIBER TECHNIQUE, Medical & biological engineering & computing, 34(1), 1996, pp. 2-8
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.