MOOR INSTRUMENTS moorLDI2 RESEARCH USER MANUAL
36
Flow Units
It is generally agreed by researchers and manufacturers that because of the nature of the flow in
capillaries and connecting small blood vessels and the effect of varying skin colour and structure, it is
not generally appropriate to use absolute flow units such as ml/min/100gm. To justify the use of
these units it is necessary to calibrate for the particular tissue type and site of the measurement. This
is impractical except in very special circumstances and is not appropriate for normal day to day
measurements.
Arbitrary units are used for Flux and DC in the moorLDI2 in common with most other
manufacturers. To assign values to a measurement the imager is calibrated using flux standard: a
standard flux signal which is generated by the laser light scattered from polystyrene microspheres
undergoing thermal motion (i.e. Brownian motion). Ideally, calibration should always be at the same
temperature though a change of + 5
o
C will result in changes of the average speed of only + 5%. The
increase in average speed results from the increase in kinetic energy with temperature increase, and
from the decrease in the viscosity of water. Changes of a few
o
C are acceptable; however, it is
essential that temperature stability of the flux standard is achieved to avoid convection currents
within the suspension of microspheres.
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