Endomicroscopy - Biomedical Optical Imaging Technologies: Design and Applications - page 279

practical FOV and WD. It should be noted that except some unique applications, an
objective diameter of 2.5-4 mm is usually acceptable. This diameter range permits
passage through the standard accessory port of video endoscopic systems.

8.3 Applications

The design principles described in Sect. 8.1 and the core components described in
Sect. 8.2 have been applied and combined in many different configurations aimed at
translating endomicroscopy into animal and clinical studies. This section describes
how endomicroscopy systems have been applied in the laboratory, entered early
stage testing on biological specimens and in animal models, and are being currently
used in human subject clinical studies.

8.3.1 Endocytoscopy

Conventional endoscopes in current clinical use (including gastroscopes, colono-
scopes, bronchoscopes, etc.) are typically characterized as standard definition (SD)
or high-definition (HD) instruments, depending on the number of pixels used for
imaging [ 61 ]. Recent advances in the pixel size and density of CCD and CMOS
image sensors have led to instruments with up to 1.25 megapixel chips reaching
the commercial market. These HD scopes are used in the conventional fashion
to examine the mucosal surface for abnormalities under white light illumination.
While clinically relevant features such as the microvasculature can be seen in
exquisite detail, even HD scopes cannot resolve the individual cells of the mucosa.
A relatively recent development toward this goal is endocytoscopy, which is
essentially a very high-resolution/small FOV form of endoscopy [ 4 , 62 ]. Through
the use of probe-based systems which are passed within the accessory channel of a
standard endoscope, or integrated systems which are built into a standard endoscope,
endocytoscopy refers to the direct imaging of the tissue surface onto a digital image
sensor, with sufficient resolution and magnification to observe individual cells. The
technique requires the mucosa to be stained with a topical contrast agent, typically
0.5-1 % methylene blue or 0.25 % toluidine blue, immediately prior to imaging.
Images are acquired with a very short working distance, with the tip of the probe
(or a slightly protruding cap) placed in direct contact with the mucosal surface.
This results in a typical FOV of 400 400 m and lateral resolution around 4m.
Olympus (Tokyo, Japan) manufactures a selection of both probe- and endoscope-
based platforms with parameters in this range and also with higher resolution at the
expense of FOV. The depth of field for these systems is typically 30-50 m, but this
does not imply optical sectioning or rejection of out-of-focus light in as provided by
confocal and nonlinear endomicroscopy platforms.