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techniques (
68, 72, 78
). In general, it is necessary that animals are
injected intravenously with a fl uorescent dye which labels the
plasma within the vasculature. Dextran-conjugated dyes are used
for this purpose: Tetramethylrhodamine isothiocyanate-dextran
(T1162, Sigma Aldrich), rhodamine B isothiocyanate-dextran
(R9379, Sigma Aldrich), or fl uorescein isothiocyanate-
dextran (FD70S Sigma Aldrich). The anesthetized and instru-
mented animals are injected i.v. with 5% (
w
/
v
) solution of dextran
dissolved in saline (mice: 75-100
l) directly
before the start of the rCBF imaging. Directly after injection, the
objective is changed to higher magnifi cation and a 40× or 63×
objective is used to acquire line scans along the axis of capillaries
(Fig.
6
). These single-line scans are repeated for 1 s with lowest
possible laser power. Parameters of red blood cell (RBC) velocity
and fl ow are calculated off-line from the obtained images (
20, 68,
70, 72
). Software programs for data acquisition and analysis have
been published (
79
). By use of line scans along the axis of arteri-
oles, it is also possible to calculate blood fl ow in larger vessels than
capillaries (
20, 72, 73
). In this case, the stripe pattern is not gener-
ated by passage of one single erythrocyte at a time. Nevertheless, it
is possible to use automated algorithms for fi nding the slope of the
stripes formed by moving RBCs in larger vessels and calculate the
direction and speed of RBC fl ux from these data (
66, 72
).
μ
l and rats: 300-500
μ
Acknowledgment
Supported by grants of the Deutsche Forschungsgemeinschaft
(DFG DR 323/3-1), the Bundesministerium für Bildung und
Forschung (Center for Stroke Research Berlin, 01 EO 0801), and
the Kompetenznetz Schlaganfall to Dr. Dreier.
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