Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_605_Библиотеки_им_академика_М_И_Перельмана.pdf
171Diagnostic Procedures
5.7.2.6.1 Colonoscopy
Lower GI endoscopy is mainly confined to the large bowel. However,
experienced endoscopists are able to intubate the last loops of the ileum.
Screening of cancer or preforms (polyps) is the most common cause.
Inflammatory bowel disease and bleeding are additional indications.
Colonoscopy is technically considerably more demanding than upper
GI endoscopy (
Fig. 5.47).
Prior to colonoscopy, the patient has to undergo full bowel preparation, which means that stool has to be removed completely. The list of
bowel preparation regimens is long, encompassing strong laxatives,
polyethylene-glycol balanced electrolyte solutions and others. A complete
washout of the colon has to be achieved to facilitate a comprehensive
exploration. For the patient, this is the most unpleasant par t of the procedure, but still unavoidable
5.7.2.6.2 Enteroscopy, “Deep Endoscopy”
[156].
The small intestine was, for many decades, something like a “white spot”
on the map of flexible endoscopy, since it could be reached through neither the mouth nor the anus.
The length and the mobility of the jejunum and the ileum did not
allow to introduce the endoscope by “push and retract” methods like in
gastroscopy and colonoscopy. The mobile segments are just stretched if
the endoscopist tries to push the endoscope forward. Hence, an active
forward moving element is required. Since it did not exist for a long
time, the assessment of small intestine disorders remained the domain of
the radiologists (see
Section 5.1.4: Real-Time Radiography).
With the advent of capsule endoscopy in the beginning of the new
millennium, the diagnostic gap concerning the small intestine could be
closed, at least to a limited degree.
However, locomotion of the capsule is passive only. The localization
of a lesion is less than precise and it does not offer any therapeutic option
(see
Section 5.7.8: Wireless Capsule Endoscopy).
Since a couple of years, even the small intestine is now endoscopically
accessible via the mouth using the so-called “balloon” technique
(so-called “device-assisted enteroscopes”)
[157].
The tip of the specially designed, long endoscope is advanced by pulling it stepwise forward according to the inchworm principle (see Chapter
10.1.3.2: Systems With Elements of Autonomous Locomotion).
Figure 5.47 A voyage through the colon. The insert in the left lower corner represents the actual configuration of the colonoscope: (A) The entrance of the colorectum: the rectal ampulla. (B) The curved sigma between rectum and descending
(Continued)
Diagnostic Procedures
173
Either one or two balloons are used. Fig. 5.48 illustrates the use of a
single-balloon system.
The most common indication for enteroscopy of the small bowel is
obscure gastrointestinal bleeding with a high rate of identification and
treatment of bleeding spots. Other indications are the staging of Crohn’s
disease, evaluation of findings on capsule endoscopy, and investigation of
small bowel tumors
[158,159].
Enteroscopy, with its rather short history, has still a slightly higher
complication rate than the upper GI endoscopy or colonoscopy.
Hopefully, further technical improvements will make it even safer and
easier to perform.
Figure 5.48 Balloon enteroscopy: Plain abdominal X-ray. The endoscope can be
easily recognized. Courtesy: Prof. S. v. Delius, Klinikum rechts der Isar.
colon. (C) The ascending colon. (D) Left (splenic) flexure which is often difficult to
L
pass. (E) As soon as the left flexure is overcome, the transverse colon with the characteristic triangular diameter of the transverse colon becomes visible. (F) In the middle of the transverse colon. (G) The tip of the colonoscope close to the right
(hepatic) flexure. (H) A few centimeters further on, a glimpse into the ascending
colon is offered (right upper corner). (I) After passing the right flexure, a full view of
the ascending colon. (J) In the middle of the ascending colon. Deep down, the end
of the colon (cecum) can already be recognized. (K) Bauhin ’s valve: The entrance
into the terminal ileum can be observed at the upper left corner. (L) A closer look
on the end of the colon (cecum). Note the entrance of the appendix (center). All
from MITI.
174
Biomedical Engineering in Gastrointestinal Surgery
5.7.3 Autofluorescence Imaging Endoscopy
Fluorescence imaging is mainly used in microscopy. With endogenously or
exogenously induced fluorescence, it is possible to visualize and quantify
fluorescent markers distributed in tissue and to identify pathological lesions.
Autofluorescence imaging (AFI) is based on the detection of natural tissue
fluorescence emitted by fluorescent molecules (see
Fluorescence Imaging). The overall fluorescence emission differs among
various tissue types due to corresponding differences in fluorophore concentration, metabolic state, and/or spatial distribution
In endoscopy, the principle of autofluorescence is mainly used in gastrointestinal diagnostic workup to detect diseases such as Barrett’s esophagus,
gastric cancer, and polyps. It also finds application during bronchoscopy.
In autofluorescence endoscopy, the tissue is excited by a shortwavelength light source that emits ultraviolet, blue, or green light. After
the excitation, the fluorophores emit light of longer wavelengths.
Autofluorescence endoscopy is based on the acquisition exclusively of this
light, which is emitted by fluorescing molecules. Therefore, a CCD with
a barrier filter is incorporated to exclude the excitation light and capture
only the weak reflected autofluorescence.
There are autofluorescence imaging systems that postprocess the
images and enhance them in real-time with pseudocolors. In this case,
the image is composed of three parts: the total autofluorescence, exclusively the green reflectance, and exclusively the red reflectance light.
With AFI, it is possible to visualize and quantify fluorescent molecules
distributed in tissue and to identify malignant tissue more easily because
early cancer sites are better visualized (
Fig. 5.49). Tissues may contain
several fluorophores such as NADH, elastin, collagen, and flavin.
Section 5.6.3: Optical
[160].
Figure 5.49 Comparison of white-light (left) and autofluorescence endoscopy (right)
in depiction of cancerous tissue. From Aihara H, Tajiri H, Suzuki T. Application of auto-
fluorescence endoscopy for colorectal cancer screening: rationale and an update.
Gastroenterol Res Pract 2012;2012:971383.
Table 5.17 Key facts on AFI endoscopy
Typical applications Strengths and
weaknesses
Recent
developments
175Diagnostic Procedures
Research
potential and
future trends
Pulmonology
Gastroenterology
High contrast
without color
markers
High false
positive
detection rate
Improvement
of image
quality
Trimodal
imaging
Smaller devices
FLIM
Identification of
distinct
molecules and
their
concentration
Autofluorescence emission has been reported mainly with respect to
collagen, which is distributed in the submucosal layer. By spectrally measuring the fluorescence of tissue, it is possible to learn about the relative
concentrations and redox states of many molecules and the biochemical
state of the tissue, which is not yet fully applied in medicine
[162].
Strengths and Weaknesses
AFI provides a very high sensitivity in early-stage cancer detection. It
allows the identification of areas of abnormality in the GI tract that may
not be visible under white-light examination. Unfortunately, it has a high
false positive rate, which makes follow-up testing necessary (
Table 5.17).
Recent Developments and Current Research
The image quality of AFI still needs to be improved and the false
positive rate needs to be decreased further. Additional enhancements are
clearly desired in clinical applications, and may be achieved with computerized visualization
[163]. The measurement of distinct fluorescence
spectra and a resulting specialized analysis of the tissue and its diseases is a
field of current research. Currently, autofluorescence endoscopes have a
relatively thick outside diameter (up to 14.8 mm), which might limit
maneuverability
[161].
Recent developments cope with the introduction of fluorescence lifetime imaging (FLIM) in endoscopes. In 2013, a compact wide-field timegated FLIM flexible endoscope was presented. It is capable of continuous
lifetime imaging of up to three fluorescence emission bands simultaneously, but has not proven its clinical applicability until now
[164].In
2011, the first confocal FLIM endomicroscope for subcellular confocal
imaging was demonstrated
[165]. FLIM allows the characterization of the
biochemical composition of tissue. Fluorescence of organic molecules is
176
Biomedical Engineering in Gastrointestinal Surgery
Figure 5.50 Olympus “trimodal imaging” (autofluorescence): (A) overview; (B) detec-
tion; (C) differentiation. Courtesy: Prof. S. v. Delius, Klinikum rechts der Isar.
not only characterized by the emission spectrum, it has also a characteristic lifetime. The lifetime does not depend on the concentration of the
chromophore, and allows direct approach to all effects that involve energy
transfer.
Combining AFI with other imaging modalities in one device overcomes the problem of the high false positive rates of AFI and necessary
follow-up testing. Endoscopic trimodal imaging (ETMI) is a novel endoscopic technique that combines white-light endoscopy (WLE), magnification endoscopy, or high-resolution endoscopy (HRE) with AFI
and narrow band imaging (NBI)
have the ability to switch between these three modalities (
[166]. Trimodal imaging endoscopes
Fig. 5.50).
Currently, ETMI is mostly applied in academic settings, but is expected
to see use in the near future as a standard endoscopy technique in gastrointestinal pathology, with an emphasis on the diagnosis of early-stage gastrointestinal tract cancers
[115].
5.7.4 Computed Virtual Chromoendoscopy/Narrow Band Imaging (NBI)
Computed virtual chromoendoscopy (CVC) is a technique that digitally
enhances the contrast of images of the mucosal surface and highlights the
vascular pattern without the need for dye spraying as in conventional
chromoendoscopy.
CVC systems make use of the principle that different light spectra
have different tissue penetration depths
acquired by different light spectra allows early detection of small superficial mucosal lesions that are undetectable using conventional WLE.
It is mainly used in gastrointestinal endoscopy, bronchoscopy, for diagnosing bladder cancer during cystoscopy, and ENT medicine.
[167]. Thus, the analysis of images
Diagnostic Procedures
177
There are two approaches to CVC image acquisition. In NBI, light of
varying spectra is sequentially emitted. However, there are also CVC systems that use normal WLE and reconstruct the images with enhanced
contrast by estimating the different light spectra.
NBI endoscopes provide white-light examination and an NBI mode.
In NBI endoscopy, the emitted light is directed through bandpass filters,
which split the light into excitation wavelengths of blue light
(390445 nm) and green light (530550 nm) (
Fig. 5.51). The penetra-
tion depth before being scattered depends on the wavelength of the light.
The shorter the wavelength (e.g., blue), the earlier it is reflected. Longer
wavelengths (e.g., green) penetrate deeper
[168].
The low brightness of the reflected light requires special high-sensitive
dual-mode CCD chips. A video processor decomposes the light by its
wavelengths and creates a composite pseudocolor image that is displayed
directly on a monitor. In the resulting image, the superficial mucous
layers are displayed in blue, the capillary network of the deeper submucosal layer in green.
This blue light is particularly useful for detecting tumors, which are
often highly vascularized. The green light penetrates deeper than blue
light. It is absorbed by blood vessels located deeper within the mucosal
layer, and appears cyan on the NBI image. This wavelength allows a better understanding of the vasculature of suspect lesions (
Fig. 5.52).
Figure 5.51 Narrow band imaging. From Lukes P, Zabrodsky M, Plzak J, Chovanec M,
Betka J, Foltynova E, et al. Narrow band imaging (NBI)-endoscopic method for detection
of head and neck cancer. In: Amornyotin S, editor. Endoscopy. Rijeka: InTech; 2013.
178 Biomedical Engineering in Gastrointestinal Surgery
Figure 5.52 Mucosal blood vessels displayed in brown and submucosal vessels in cyan.
The different colors indicate the different height. Courtesy: Prof. S. v. Delius, Klinikum
rechts der Isar.
Table 5.18 Key facts on narrow band endoscopy
Typical applications Strengths and
weaknesses
Recent
developments
Research
potential and
future trends
Pulmonology
Gastroenterology
Otolaryngology
High contrast
images of
mucosal tissue
and lesions
Frequently false
positive
findings
Trimodal
imaging
Virtual image
enhancement
HD-CCD chips
Combination
with other
modalities
and virtual
image fusion
Narrow band imaging is applied in Olympus Narrow Band Imaging
Systems. There are two further CVC systems available: the Fujinon
Intelligent Color Enhancement (FICE) and the Pentax iScan. They
reconstruct the video images virtually with special algorithms to improve
the contrast.
Strengths and Weaknesses
NBI offers a significantly increased diagnostic accuracy compared to
WLE and autofluorescence endoscopy. Blue light has less penetration and
less scattering, thus enhancing image resolution. Image processing allows
high contrast images without the usage of dyes, as would be the case in
chromoendoscopy. Dye-sprays like methylene blue, used for polyp characterization, have the risk of possible DNA damage, which is avoided
using NBI. Nevertheless, NBI can lead to false positive findings in some
cases (
Table 5.18).
Recent Developments and Current Research
Advances in CCD technology have resulted in smaller CCDs with an
increased number of pixels and increased resolution.
179Diagnostic Procedures
As explained in the discussion of AFI endoscopy, NBI has high potential in combination with other imaging modalities. ETMI is a novel
endoscopic technique that combines WLE, magnification endoscopy, or
HRE with AFI and NBI
[166]. Trimodal imaging endoscopes have the
ability to switch between these three modalities. The combination of
NBI with autofluorescence endoscopy overcomes the main disadvantages
of each technique
[115]. Using magnifying HDTV endoscopy in combi-
nation with NBI dramatically improves the sensitivity and specificity of
endoscopic examination
[167].
5.7.5 Confocal Endomicroscopy
Confocal endomicroscopy is a novel technology that enables real-time
imaging at the cellular level by using miniature optical systems integrated
into the tip of a small imaging probe or endoscope
“optical biopsy” is sometimes used to underline that the resulting images
previously could have only been acquirable using histological or cytological analysis; in contrast, no tissue is removed in confocal endomicroscopy.
The most common endomicroscopy application is confocal laser imaging,
which is described in more detail in
Section 5.6.6: Confocal Laser
Scanning.
Confocal endomicroscopy provides instantaneous histopathology during upper and lower endoscopy. The main applications currently lie in
imaging of the gastrointestinal tract, particularly for the diagnosis and
characterization of Barrett’s esophagus, pancreatic cysts, and colorectal
lesions. It also has high potential in the screening and surveillance of
ulcerative colitis and gastric cancer
[170].
In confoca l endomicroscopy, a special confocal optical unit detects
backscattered light alone at a precisel y defined h orizontal level (see
Section 5.6.6: Confocal Laser Scanning). This produces high-resolution
microscopic images, making it possible to assess structures up to the size
of a cell nucleus. A resolution of 0.53.0 µm, an axial resolution of
310 µm, and a s ubsur face de pth of 250500 µm are possible in this
manner
[171]. In most cases, the fluorescein sodium is intravenously
administered as fluorophore for subsequent excitation by a laser light,
allowing cell structures to be easily identified. Either scan can be performed at the proximal end of a fiber bundle or the distal tip using a
piezoelectric fiber scanner, a MEMS scanning device, or a technique
called spectral encoding
[172] (Table 5.19).
[169]. The term
180
Biomedical Engineering in Gastrointestinal Surgery
Table 5.19 Key facts on confocal endomicroscopy
Typical
applications
Strengths and
weaknesses
Recent
developments
Research
potential and
future trends
Gastroenterology
Oncology
Figure 5.53 (A) Nonneoplastic Barrett mucosa of the esophagus; (B) normal, healthy
mucosa of the colon. Courtesy: Prof. A. Meining, University of Ulm.
High resolution
High contrast at
certain depths
Low penetration
Dual-axis confocal
endomicroscopy
New specialized
molecular
markers
Telepathology
Introduction
to new
applications
Strengths and Weaknesses
The confocal images have a very high resolution on the order of his-
tology and can be acquired in vivo (
Fig. 5.53). Therefore, it can guide
excisional biopsies for a better diagnostic yield.
Although the depth resolution is very high, confocal endomicroscopy
has, like most optical technologies, a very limited penetration depth
[173].
Confocal endomicroscopy does not provide information about biological
behavior either above or below the achieved depth, but cancer may nonetheless occur in deeper tissues. Moreover, horizontal cross-sections are an
atypical view of the tissue when compared to traditional biopsy specimens
that pathologists are accustomed to view. Hence, a specialist must be
trained to interpret confocal endomicroscopy images
[171].
Recent Developments and Current Research
There are various applications of confocal endomicroscopy that are
still not used in the field of human medicine. In animal models of human
diseases, confocal endoscopy has provided molecular imaging of cancer,
functional imaging of altered perfusion in malignant and inflammatory