Biomedical Engineering Reference
In-Depth Information
t
= 0
t
= 31.5 h
t
= 31.5 h
(A)
(B)
(C)
t
= 0
t
= 31.5 h
t
= 31.5 h
(D)
(E)
(F)
10
1.0
0.02
0.8
0.6
0.4
0.2
0.0
-10 -8 -6 -4 -2 0
Δ
z
(cm)
0.00
-0.02
-0.04
-0.06
-0.08
0
-10
t
= 0.0 h
t
= 31.5 h
t
= 41.0 h
-20
246810
0
10
2030405060
t
(h)
(G)
(H)
Figure 6.5
Subsequent numerical refocusing during time-lapse investigations. (A)(C) Reconstructed
amplitude and (D)(F) unwrapped phase distributions obtained from long-term investigations on
living HBMECs; (A), (D): t
0; (B), (E): t
31.5 h with fixed mechanical focus; (C), (F):
5
5
31.5 h with holographic autofocusing; (G): exemplary focus values in dependence of the
propagation distance
t
5
0, 31.5,
and 41 h; (H): temporal dependency of autofocus position z
AF
and corresponding change of the
axial object position
Δ
z, calculated by
Eq. (6.5)
for digital holograms recorded at t
5
Δ
g
AF
. Source: Modified from Ref.
[65]
.
from digital holograms recorded at
t
5
0, 31.5, and 41 h. The global minima of the curves
indicate the propagation distances for which the amplitude images of the phase specimen
appear sharply in focus with minimized contrast in the amplitude distributions. Finally,
Figure 6.5H
shows the temporal dependency of the focal position that was detected by
numerical autofocusing for the whole measurement period (
t
max
5
52 h). The nonlinear drift
also illustrates the need for a permanent focus control during long-term investigations.
Furthermore, quantitative measurement data for the axial object position are provided (see
also
Section 6.7
) that may be used to improve the stability of the experimental setup or to
identify the sources of instability.
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