Moor Instruments moorLDI2-VR - The Laser Doppler Processing Algorithm

MOOR INSTRUMENTS moorLDI2 RESEARCH USER MANUAL
35
4.5 THE LASER DOPPLER PROCESSING ALGORITHM
After detection and amplification the signals are digitised and processed to yield flux (proportional to
blood flow) and conc (proportional to the concentration of moving blood cells).
The algorithms used to compute these parameters are:
ω
2
flux = k
1
∫ ω . P( ω ) d ω - noise
ω
1
dc
ω
2
conc = k
2
∫ P( ω ) d ω - noise
ω
1
dc
ω is the frequency of Doppler shift
P( ω ) is the power of signal at frequency ω
dc is the intensity of all detected light
ω
1
is the high pass filter frequency
ω
2
is the low pass filter frequency
k
1
and k
2
are scaling constants
noise is the shot and dark noise of the detector
Speed of blood can be deduced from flux/conc.
The bandwidth settings for the moorLDI2 are:-
ω
1
ω
2
scan rate
250Hz 15KHz 4ms/pixel*
100Hz 15KHz 10ms/pixel
20Hz 15KHz 50ms/pixel
*This is the default setting.
Other bandwidth combinations are available but these should be used with care and are protected by
password. They are ω
2
= 3KHz and 22KHz and should be used in very low and high perfusion
conditions, respectively. For low perfusion states a reduction in scan rate is also recommended to
improve signal to noise.