capsule experience - MG Lorenzatto

10
Chapter 1
THE OPTICAL DOME
The optical dome and its relationship to the other optical
components create two important advantages in capsule
endoscopy:
a. Improved illumination efficiency.
b. Favorable imaging geometry within the field of view.
Another minor factor which may be contributing to image
quality is the presence of a fluid interface between the optical
dome and tissue at the time of examination improving the
resolution of different anatomical structures such as villi.
Finally, another advantage of the optical dome is that it lends
itself to cleaning by the GI tract mucosa.
Geometric and optical differences between image acquisition
in wired and wireless endoscopy are compared in Figure 2A
and Figure 2B. Figure 2A depicts the geometrical relationship
for a push enteroscope inserted into the intestine. Geometrical
relationship for the M2A ® capsule endoscope is depicted in
Figure 2B. The standard endoscope (Figure 2A) includes an
illumination source (2), and a lens (3), producing the field of
illumination (4), and the field of view (5) shown in Figure 2A.
Collapse of the intestinal wall (6) may obscure either the field
of view or field of illumination. This technical problem is
resolved in standard endoscopy by insufflating the intestine
with air (7), resulting in the distancing of the intestinal muco
from the tip of the endoscope, clearing both the field of view
and the field of illumination. Air insufflation also enables the
operator to orient the tip of the endoscope in the proper
luminal direction, and to advance the endoscope tip accordingly.
Figure 2B shows the wireless capsule endoscope (1) in the
intestine. The capsule includes its illumination sources (2),
and the lens (3), comprising a field of illumination (4), and a
field of view (5) respectively. In order to prevent collapse of
Physiological Endoscopy
the intestinal wall (6), and resultant obscuring of either the
field of illumination or the field of view, a specially designed
optical dome (8) covers both the source of illumination and
the lens. The space remaining between the dome and the
intestinal wall may at times be occupied by fluid.
Figure 2. Geometrical and optical interrelationships for
the enteroscope and capsule endoscope in the
intestine.
A - Push enteroscope
2 - Illumination source
1 - Endoscope inside
intestine
6 - Intestinal wall
B - Capsule endoscope
6 - Intestinal wall
3 - Lens
4 - Field of illumination 5 - Field of view
3 - Lens
1 - Wireless capsule
endoscope inside
intestine
7 - Air filling, due to insufflation
8 - Optical dome
The field of view of most commercially available endoscopes
is within the range of 120˚-140˚, similar to the M2A ® capsule
endoscope. Depth of field of the standard endoscope starts
from 3-5mm from the endoscope tip and extends to a distance
of 100 mm. Unlike in the push endoscope, depth of view of
the capsule endoscope starts on the optical dome itself.
b
2 - Illumination source
4 - Field of illumination
5 - Field of view
a
7 - Liquid filling,
intestinal
liquids