MOOR INSTRUMENTS moorLDI2 RESEARCH USER MANUAL
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Automatic Set is selected by default. The upper cutoff frequency will be 15KHz and the lower cutoff
will be automically selected to suit the scan speed. (20Hz for 50ms/pixel, 100Hz for 10 ms/pixel and
250Hz for 4ms/pixel.)
If the user wishes to change bandwidth, a password must be input in the Control menu.
Changing bandwidth will generally change the magnitude of the measured Flux so for consistency it
is advisable to use the Automatic bandwidth setting. For very low flows, signal to noise can be
improved by selecting the 3KHz upper Cutoff frequency and for very high flows the selection of the
22KHz upper cutoff frequency will result in more linear instrument response; however care must be
taken when comparing measurements done at different bandwidths.
6.3.4.2 Normalisation
DC normalisation (ie division of the scaled flux by a factor proportional to the detected light
intensity) is selected by default. If the user wishes to change normalisation to
DC
2
or no
normalisation. A
password must be input in the Control menu to enable the change to be made.
Note that changing the normalisation will change the magnitudes of the flux values.
Changes can be made to normaliastion in the image processing program if the user chooses to do so.
6.3.4.3 Background (BK) Threshold
This is set (either manually from the key board or by Auto BK) to blank out all perfusion values
where the detected light intensity is below the set threshold. If, for example a hand is placed on a dull
(ie not shiny) black cloth background the DC background level for this may be close to zero for an
imager using a visible red laser and 10 to 20 DC PU units for an infra-red laser imager.
As Flux measurements taken at very low DC levels are unreliable (eg close to the curved edge of a
finger), the background threshold should be set low enough to remove edge effects from the
recorded image but high enough to ensure the scanned tissue area is recorded. Note that the
background threshold for recorded images can be changed in the image processing program so that
the affect of different background threshold levels can be investigated to ensure that only those parts
(those with low associated DC levels) which the user wishes to blank out are blanked out.
6.3.4.4 Auto BK Set
The beam can be moved to any cursor position within the image window by right clicking the mouse
button. Moving the beam onto background cloth and clicking on Auto BK Set will set background to
the level at that point.
6.3.4.5 Hood Mirror Option
Select Mirror On only when the hood mirror is attached. (Only applicable to MK1 moorLDI
imagers.)
6.3.4.6 Gain Levels
This enables gain settings to be selected for DC, Flux and Conc.
The gain settings from low to high are 0, 2, 4. In general the shorter the distance between the scanner
and the skin surface being scanned, the lower the gain setting required. Too high a gain setting may
result in signal saturation (on a relative scale the flux or DC will have a value close to 4000 which is
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