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Fig. 1. Laser Speckle Contrast Analysis Device (Moor Instruments). The laser is emitted
through the rectangular window on the
left
. The lens on the
right
is part of the CCD cam-
era. The two wheels on the
top side
allow manual adjustment of zoom and focus.
The penetration depth of the infrared laser depends on the optical
properties of (a) the laser light and (b) the sampled tissue and is
reported in the range of 500
2.1.2. Tissue Penetration
Depth
m to 1 mm (
6, 9
). In general, tissue
perfusion and fl ow velocity in large vessels can be measured in
exposed tissue such as the human brain, where the vasculature
courses close to the surface (
7
). In the mouse, after retraction of
the scalp cortical perfusion can be easily assessed through the intact
scull without the need for drilling a cranial window (
1
).
μ
The spatial and temporal resolution is inversely related and its
selection is a compromise of acquiring sharp and detailed images
with a suffi ciently high sampling rate for dynamic real-time live
imaging. For continuous high-resolution transcranial assesment of
the cerebrovascular reactivity by acetazolamide challenge in mice
(see chapter 2.1.4 and Fig.
2
), we recommend a sampling rate
between 1 and 0.25 Hz, depending on the duration of the entire
measurement.
2.1.3. Spatial
and Temporal Resolution
Laser speckle imaging delivers an immediate, noninvasive functional
readout of relative cortical blood fl ow with direct assessment of tis-
sue perfusion. In order to plot fl ux values over time in a graph or
chart, regions of interest (ROI) ROIs with variable size and location
can be positioned over the speckle images and the CBF-fl ux within
that ROI is recorded for each image at the same sampling rate as the
live image measurement. The fl ux value within this user-defi ned
ROI is a calculated mean of the individual fl ux values within the
region. The values are plotted and the resultant trace can be ana-
lyzed to compare fl ow changes before, during, and after an interven-
tion. Figure
2a
, b gives an example of in vivo LASCA images during
cerebraovascular reactivity testing (Fig.
2a
) and plotted CBF-fl ux
(Fig.
2b
) 6 h after experimental SAH in a C57/BL6 mouse.
2.1.4. Real-Time Recording
of CBF Flux
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