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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_605_Библиотеки_им_академика_М_И_Перельмана.pdf
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Biomedical Engineering in Gastrointestinal Surgery
Figure 7.14 The standard endoscope (above) and Hopkins telescope design (below).
The glass rods in the Hopkins telescope provides a larger image, better light
transmission, and improved clarity of vision. From Karl Storz GmbH.
Figure 7.15 Standard laparoscopes with various angles of view. From MITI.
His idea to fill the air space between the lenses with glass rod significantly
improved light transmittance and image quality (
Fig. 7.14).
Laparoscopes are currently available with diameters of 2, 3, 5, 7, 10, and
12 mm. The angle of view is 0, 12, 30, 45, 70, 90, or 120 degrees. Modern
laparoscopes can be steam sterilized at 134˚C (
7.1.5.1.1 Advanced Laparoscopes
Figs. 7.15 and 7.16).
Most innovative designs enable the surgeon to change the angle of view of
the laparoscope, e.g., the EndoCAMeleon, by STORZ. The viewing
angle can be adjusted continuously between 0 and 110 degrees (
Fig. 7.17).
Endoeye Flex is a comparable system provided by Olympus (Tokyo,
Japan) which is even capable of 3D visualization (
Fig. 7.18).
For different applications, special telescopes are available. Today, fluorescence imaging (see Chapter 5.6: Advanced Optical Systems) is being used
increasingly to visualize changes in the abdominal cavity or to visualize the
sentinel lymph nodes, for example, which are not visible with conventional
light. Therefore, special colorings like Fluorescein or Indocyanine green are
Operative (Surgical) Laparoscopy
283
Figure 7.16 Specially designed laparoscopes. (A) Laparoscope with zoom function.
(B) Needlescope with a diameter of 2 mm. (C) Working channel laparoscope. All
from MITI.
Figure 7.17 Karl Storz EndoCAMeleon with on-the-rod adjustable viewing angle.
From MITI.
Figure 7.18 Olympus Endoeye. Angulation is achieved by mechanical bending
on the tip. From Olympus Deutschland GmbH.
284
Biomedical Engineering in Gastrointestinal Surgery
applied over the vessel system. To make these colored fluids visible, special
light sources with adapted wavelengths are necessary and additional laparoscopes with filters to let only pass parts of the light spectrum to the video
chip (
Fig. 7.19).
7.1.5.1.2 Future Developments
In flexible endoscopy, glass fiber endoscopes with mounted cameras have
long been replaced by chip-on-the-tip endoscopes.
Similarly, it is expected that rod lens scopes will be substituted by
photochips which would be certainly advantageous in many regards (less
space, less weight, etc.). Up to now, however, the image quality of the
Hopkins optic is still unmet.
7.1.5.2 Laparoscopic Cameras
The camera system has tw o components: The head of the camera (
Fig. 7.20)
and the processor unit which is positioned apart on the trolley (see
Section 7.1.5.3: Lapar oscopic Image Processors (Camera Contr ol Unit)).
Figure 7.19 Laparoscope with filter for visualization of different fluorescence agents
(see Chapter 5.6: Advanced Optical Systems). From MITI.
Figure 7.20 Head of the camera. From MITI.
Operative (Surgical) Laparoscopy
285
The key elements of the head of the camera which is attached to the
ocular of the telescope are the objective lens and the charge coupled
device (CCD). The lens focuses the image of the object of the CCD
chip. The chips (usually three of them for red, green, and blue) convert
the optical image into electrical signals which are conducted to the
controller.
The camera has to be focused as soon as it is mounted to the telescope. This is achieved by rotating the ring switch at the front end. An
object should be selected with sufficient cues like a suture pack or a surgical instrument at an adequate distance (e.g., 10 cm for a 10-mm
telescope).
Modern cameras have, in addition, a second rotating ring to modify
the zoom.
White balancing is required prior to any use of the telescopecamera
combination to adjust the primary colors (red, green, blue) to make a
pure natural white color.
A white object (e.g., a white towel or a sterile sheet of paper) is kept
in front of the telescope and the respective button of the head of the
camera is pushed. A signal indicates that white balancing is successfully
achieved.
The head of the camera is not suitable for sterilization. Prior to use it
has to be covered by a sterile plastic hose including the camera cable
(
Fig. 7.21).
7.1.5.3 Laparoscopic Image Processors (Camera Control Unit)
The image processor is the link between the telescope and the monitor
(
Fig. 7.22).
Figure 7.21 Telescopecamera combination. Camera and cable covered by a sterile
plastic hose. From MITI.
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Biomedical Engineering in Gastrointestinal Surgery
Figure 7.22 Front panel of an image processor (CCU): a, power switch; b, white
balancing button; c, USB connectors for mobile storage devices; d, connector for
the camera head. From MITI.
Figure 7.23 Rear panel of the CCU: a, link connectors to other CCUs for image
switching; b, SCB (STORZ Communication Bus) connector, bus system to transfer
data between other peripheral devices; c, network connector for storage; d, USB
connector for portable storage media; e, DVI and composite video outputs; f, link out
for video connection to other CCUs; g, electrical ground connector; h, mains plug.
From MITI.
Most camera control units (CCUs) are equipped with an automatic
gain with a link to the light source control to compensate inadequate
illumination (too weak or too high) in a certain range (
Fig. 7.23).
7.1.5.4 Monitors
Surgical monitors should offer a higher quality level than standard
consumer products.
Especially the color reproduction must be as natural as possible, since
diagnostic decisions are made based upon the color tone of tissues.
The image has to be completely flicker-free to ensure a nontiring work,
Operative (Surgical) Laparoscopy
287
as well as distortion-free and with high contrast to maintain a sufficient
image representation even in not well dimmed rooms, higher dynamic
ranges (minimum to maximum contrast) offer improved visualization
of details.
Surgical Monitors are available in sizes from 15 to 46 inches. Large
monitors are impressive but they have to be watched from a certain distance. The closer the screen is located to the surgeon the smaller it has to
be to obtain a good image (
Fig. 7.24). Today, typically 24-inch liquid
crystal display (LCD) or thin film transistor (TFT) displays with Full-HD
resolution with 1920 3 1080 pixels are widespread in operating rooms.
Technically it is the same technique, LCD stands for the use of liquid
crystals in the individual pixels of the screen and TFT for smallest transistor elements which control the orientation of the liquid crystals and thus
their light transmittance.
These displays use the optical characteristics of small crystals to deflect
light at a certain angle. An LCD cell consists of two 90 degrees rotated polarizing films which are per se opaque. However, there is a layer of liquid crystals between these two polarizing films, which is dimensioned such that it
rotates the light waves exactly 90 degrees back to the original position. The
viewer sees the backlight of the display as “full lighting.” By applying a voltage to the liquid crystals, the angle of radiation can be changed, which results
in a reduced light transmission, up to completely opaque. This voltage is
controlled by the TFT element, a film with thousands of small transistors.
In the TFT element not only the overall brightness, but also the color
rendition of the image is controlled. The light for each pixel passes
Figure 7.24 Monitors for laparoscopic surgery. Boom-mounted video screens can
easily be positioned to provide “optical correctness.” The position of the surgeon,
the working field, and the monitor have to be arranged in one line. From MITI.
288 Biomedical Engineering in Gastrointestinal Surgery
through a color cell that consists of three adjacent RGB (red, green, blue)
color filters. Each filter is equipped with a separately controllable transistor—a TFT with 1920 3 1080 pixels consists therefore exactly 3 3
1920 3 1080 transistors, controlling the light transmission for each color
cell. By additive mixing, one of the necessary color pixels is then
produced.
The most important quality factors which affect the represented image
on the monitor are:
• luminance,
• contrast ratio,
• viewing angle,
• color representation,
• constancy of color and luminance.
The screen luminance describes the emitted brightness of the screen
in candela/square meter (cd/m
A surgical screen should have a luminance of at least 300 cd/m
2
) and must be higher in brighter rooms.
2
.
The contrast ratio describes the relative brightness difference
between black and white on the screen and is a measure of the screen’s
capability for generation of a well contrasted image. Current surgical
displays offer a contrast ratio of 1:1000, wherever possible more is
preferable.
Since in a common OR setting typically more persons are looking at
the same screen, which results in not all being able to view at a right
angle. Depending on the surgical scenar io quite large viewing angles are
necessary, therefore a display should have a large viewing angle. The
viewing angle is defined as the maximum angle where the contrast ratio
is reduced to 1/10.
It is self-evident that the surgical display must be able to represent the
complete color spectrum. Current CCUs deliver an 8 bit signal per pixel
and color channel, which means 2
resulting in (2
8)3
5 16.7 Mio different colors for a typical color model
8
5 256 different shades per color
[i.e. RGB (red-green-blue)]. The same must be possible for the monitor
to visualize the video signal with true color.
An important quality cr iterion of medical monitors is the constancy
of color and luminance which should not differ over the size of the
display.
Picture-in-Picture modes are available on most displays and offer
the possibility to display more than one video signal simultaneously.
This could be very helpful for combined procedures to visualize the
Operative (Surgical) Laparoscopy
289
intraluminal and the extraluminal view or for the parallel display of
preoperative imaging on the same screen.
Optimal positioning of the screen during the operation is crucial: The
rules of “optical correctness” have to be observed. The manual activities
of the surgeon have always to be in line with the view. Eyes, hands, and
the screen have always to be on one axis. Otherwise, the manual skills
of the surgeon will be drastically diminished. Accordingly, the positioning
of the monitor must be flexible enough to enable a proper placement
anytime.
7.1.5.5 3D Endoscopy
As endoscopy attracts increasing attention in fields like minimally invasive,
computer-assisted, and telesurgery, 3D enhanced imaging and better
image analysis can be advantageous and improve endoscopic technology.
3D endoscopy can help to reveal meaningful information about
anatomical structures, shapes, and conditions. Further, spatial imaging
allows improved distinguishing of deformations appearances and general
tissue conditions, with great impact on especially surgical applications
(
Fig. 7.25).
There are different ways to obtain 3D information from endoscopic
images. On the one hand, the use of principles like optical coherence
tomography can add a third dimension to acquired images (see
Chapter 5.6.2: Optical Coherence Tomography). On the other hand, in
what is also referred to as a 3D endoscope a pair of two optical channels
is used to generate two images of the same site, but from a slightly different angle. This is similar to physiologic conditions, since human beings
Figure 7.25 Full-HD stereo telescope with fixed camera head and four light
emersion points with the possibility to switch to 2D by using only one imaging
channel. From MITI.
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Biomedical Engineering in Gastrointestinal Surgery
Figure 7.26 Stereopsis: The human FOV is confined to a forward angle of about
140 degrees which is achieved by the two eyes. Stereopsis is possible in the overlapping area of both eyes. From MITI.
are able to perceive spatial depth since both eyes produce images at a
slightly different angle (
Figs. 7.26 and 7.27).
This can be initiated by presenting to the human brain alternately
images from the right (right eye) and the left side (left eye) in a rapid
sequence. As long as the right image is presented to the right eye, no
visual information is given to the left one (and vice versa) (see below).
The images obtained in stereoscopic imaging can be displayed using
either two different 2D displays, viewed separately by each of the surgeon’s eyes (e.g., in head-mounted displays) or a 3D display (
Table 7.4).
A 3D monitor presents, in a frequency of at least 25 Hz, the leftright
images in a sequence. If the right image is shown, the left eye has to be
shuttered and vice versa. Thus, the 3D display requires the use of special
3D glasses, much like in a 3D film screening. Another, even more widespread method to present 3D images is the use of polarization glasses: two
images are projected onto the same display through different polarization
filters. The glasses with corresponding polarization filters let only pass the
light in the same polarization mode, resulting in a separation of the image
for the left and the right eye (
Fig. 7.28).
In the past, one of the most limiting factors to stereoscopic technology
in surgical application was the surgeon‘s reluctance to employ the necessary 3D glasses. The use of such glasses can be experienced to come with
Operative (Surgical) Laparoscopy
Figure 7.27 3D visualization: The brain is able to synthesize 3D information out of
two images of the same objects from different angles. From MITI.
291
Table 7.4 3D viewers
Head-mounted
One display for each eye
displays
Shutter systems The image of one eye is blocked while it is presented to
the other one
Passive systems (a) Polarization systems
(b) Interference systems
(c) Color anaglyph systems
(d) Chromadepth systems
Figure 7.28 Selective left/right visibility is achieved either by shuttering (A), red/cyan
splitting (B), or by polarization (C). Shuttering needs to be synchronized with the
screen, which is achieved by wireless or wired connections, and must be powered
electrically. From MITI.