Biomedical Engineering Reference
In-Depth Information
tomographic technique is measured to be approximately 0.5
μ
m in the transverse ( x
y )
directions and 0.75
μ
m in the longitudinal ( z ) direction.
A tomogram is measured for a single HeLa cell in culture medium. Cells were dissociated
from culture dishes and allowed to partially attach to the coverslip substrate. A 3D index
tomogram for a single cell ( Figure 12.3A and B ) and x
y tomographic slices of the same
cell at heights of z 5 12, 9.5, 8.5, 7.5, 6.5, and 5.5 microns above the substrate
( Figure 12.3C
H ) show that the index of refraction is highly inhomogeneous, varying from
1.36 to 1.40. Brightfield images for objective focus corresponding to Figure 12.3E and F
are shown in Figure 12.3I and J , respectively. There is a clear correspondence between the
tomographic and brightfield images in terms of cell boundary, nuclear boundary, and size
and shape of the nucleoli.
It is noteworthy that the refractive index of the nucleus ( n
1.36), apart from the nucleolus,
is smaller than some parts of the cytoplasm ( n
1.36
1.39) and that the refractive index
(C)
(D)
1.38
c
(A)
1.36
(E)
(F)
h
1.34
(G)
(H)
(B)
(I)
(J)
Figure 12.3
Refractive index tomogram of a HeLa cell. (A) 3D rendered image of a HeLa cell. The outermost
layer of the upper hemisphere of the cell is omitted to visualize the inner structure. Nucleoli are
colored green and parts of cytoplasm with refractive index higher than 1.36 are colored red. The
dotted box is a cube of side 20
μ
m. (B) Top view of (A). (C
H) Slices of the tomogram at heights
indicated in (A). Scale bar, 10
633 nm.
(I and J) Brightfield images for objective focus corresponding to (E and F), respectively [13] .
(For interpretation of the references to color in this figure legend, the reader is referred to the
web version of this topic.)
μ
m. The color bar indicates the refractive index at
λ 5
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