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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_605_Библиотеки_им_академика_М_И_Перельмана.pdf
Diagnostic Procedures
Figure 5.59 Very high volume of high-quality visual information. The evaluation is
time-consuming and tedious for the physician. Decreasing attentiveness makes it
mistake-prone. From MITI.
191
(Fig. 5.59). Therefore, algorithms are being introduced to detect automatically anomalies, such as bleeding, during WCE examinations
[210]
(Fig. 5.60).
Research for improving pixel resolution, frame rate, and video capture
facility is also on the rise, and developments will significantly benefit from
further emerging microelectronics
carried out to improve application in colon cancer detection
[189]. Ongoing research is also being
[205].
Furthermore, it has been shown to be possible to apply chromoendoscopic imaging to magnetically steered capsule endoscopy, which could
have great impact on enhancing the visibility of mucosa irregularities
[211].
Capsule endoscopy has great potential for the future. Patients’ preference for this procedure over conventional endoscopy and technological
opportunities support the rising relevance of capsule endoscopy in the
future
[212].
Last but not least, one additional weak point of the capsule has to be
eliminated. They still lack the ability to provide insufflation. The colon,
in particular, is very difficult to explore if the lumen is not distended for a
192
Biomedical Engineering in Gastrointestinal Surgery
Figure 5.60 Future colon cancer screening? A scenario like this one is very improbable. It is assumed that the diagnostic workup will soon be carried out by advanced
image processing and interpretation. Courtesy: PD Dr. M. Kranzfelder, Klinikum rechts
der Isar.
clear view of the internal wall. First approaches were published to use
biocompatible effervescent chemical reactions to convert liquids and powders carried on board a capsule to gas
[213].
5.7.9 Conclusion
Endoscopy is a field that has undergone a high level of technological
development in recent years, and innovations promise to even improve
the capabilities of endoscopy significantly in the near future. These technological improvements are very multifaceted. Advances in semiconductor technology have allowed detectors to become miniaturized, and have
led to the development of video endoscopes and wireless capsules. The
addition of US technology to endoscopy has allowed structural information to be collected beyond the tissue surface to depths of several millimeters and even into adjacent tissue structures. New methods are being
developed to elicit even more diagnostic information from tissue. OCT
and confocal endomicroscopy provide morphologic information with
subcellular resolution for real-time histopathology. Autofluorescence
endoscopy reveals biochemical and molecular information below the tissue surf ace. WCE provides images from previously unattainable regions
such as the small bowel. Finally, virtual chomoendoscopy enhances the
images of videoendoscopy and brings the visualization to a higher level.
193Diagnostic Procedures
5.8 HYBRID SYSTEMS
Various medical imaging technologies can be integrated with other units
and principles. In medical visualization, a hybrid system combines two or
more technological principles to operate jointly
come problems and limitations from individual systems
ple has already been presented in form of EUS (see
[214] in order to over-
[215]. One exam-
Section 5.7.7:
Endoscopic Ultrasound). For instance, US has been proven highly effective in medical applications. The information detected by the acoustic
sensor is transmitted by optical fiber, which makes US flexible and easily
combinable with several endoscopic instruments. It has a high penetration
depth and already provides high resolutions for internal examinations, but
its resolution is inferior to other fiber optic-based imaging systems
[216].
SPECT/MRI and PET/MRI scanners are similar examples. In the
following section, hybrid systems of interest, their characteristics, and
performance data will be presented. The systems mainly offer a high
application potential and research opportunities, and are being examined
for this reason (
Table 5.23).
5.8.1 Real-Time Virtual Sonography
Real-time virtual sonography (RVS) is a new fusion technique that combines the use of an US B-mode image with MRI or CT images in realtime by using a magnetic positioning system in order to achieve identical
cross-sectional images
The RVS system includes a magnetic positioning sensor that is fixed
on the probe of the US scanner in order to create images with identical
cross-sections in real-time. The achieved images are compared to the previously acquired CT or MRI volume data with due regard to the position
and the angle of the probe. It is necessary to transfer the CT or MRI
[217] (Fig. 5.61).
Table 5.23 Overview of hybrid diagnostic systems
Hybrid OCT-US Assessed
RVS Not assessed
SPECT/MRI Assessed
PET/MRI Assessed
SPECT/CT Assessed
X-ray/MRI Assessed
Microscope Integrated OCT and OCM Not assessed
Integrated OCT and Positron Detection Not assessed
194
Biomedical Engineering in Gastrointestinal Surgery
Figure 5.61 CT-navigated US: The actual US slice (right) is correlated with the respective CT image by electromagnetic tracking (see
Courtesy: PD Dr. M. Kranzfelder, Klinikum rechts der Isar.
Section 5.4: Diagnostic Ultrasound).
volume data to the US system to display virtual images, either wirelessly
or with a cable connected to the computer system. The magnetic sensor
detects the changes in location, direction, and rotation of the probe during normal US scanning of the patient. The workstation monitor displays
two images: the US real-time image and the virtually reconstr ucted CT/
MR image. Currently, there are only a few systems available on the market, such as Hitachi’s RVS.
Strengths and Weaknesses
RVS combines the advantages of US imaging and CT/MR imaging.
In consequence, RVS has an increased diagnostic confidence and offers a
direct comparison of lesions using different imaging modalities, a more
precise monitoring of interventional procedures, and reduced radiation
exposure (
Table 5.24).
One disadvantage of RVS is the magnetic positioning sensor unit
itself. It provides steady state inter r uptions, a low scan efficiency and
signal saturation. Another limitation shows up because the software and
hardwa re integrations of these two modal ities are not yet fully
exploited.
Table 5.24 Key facts on RVS
Typical
applications
Strengths and
weaknesses
Recent
developments
195Diagnostic Procedures
Research potential
and future trends
Gastroenterology
Cardiovascular
medicine
Increased
diagnostic
precision
Low scanning
efficiency
Clinical
application
Training and
education
Motion correction
Guided biopsies
Recent Developments and Current Research
Currently, RVS is not yet common in medical use, but this technique
could potentially become relevant for examinations of the GI tract and to
provide more reliable abdominal sonographic images. Another possible
function for future development is using this hybrid system for motion
correction in different organs, fusing anatomic hemodynamic and perfusion images, and for image-guided biopsies.
5.8.2 Positron Emission Tomography/Computed Tomography
PET/CT offers additional information to correct attenuation, to precisely
localize lesions, and therefore to optimize medical procedures. PET/CT
is mainly applied for cardiologic and oncologic issues
[65] (Fig. 5.62).
Figure 5.62 Neuroendocrine tumor of the stomach (Ga-68)-DOTANOC PET-CT, pT4a,
pN0 (0/14), pL1, pV1, G2 (Ki67: 12%): 1, primary tumor, 2, lymph node metastases;
3, spleen, 4, ureters, 5, urinary bladder. Courtesy: Prof. R. Braren, Klinikum rechts der Isar.
196 Biomedical Engineering in Gastrointestinal Surgery
Table 5.25 Key facts on PET/CT
Typical
applications
Strengths and
weaknesses
Recent
developments
Research potential
and future trends
Oncology Attenuation
correction of PET
images
Short examination
times
Better localization of
lesions
n/a Improved
components
New radiotracers
PET/CT combines anatomic CT data with functional or metabolic
information given by the PET. In this case, CT images are helpful for
correcting the attenuation of the PET data. In conventional PET scanners, the attenuation is corrected by using data from a radioactive transmission source similar to CT tubes. However, the photon flux is lower
than in CT tubes. If the CT scan is only used as a support of the PET
findings, it is performed as a “low dose” CT. Self-evidently, diagnostic
PET/CT combinations are also available.
Strengths and Weaknesses
Using a combination PET/CT instead of performing both examinations separately not only offers anatomic and functional or metabolic information at the same time, but also results in shorter examination time and
provides additional information on the location of abnormalities, which
creates diagnoses that are more accurate. Shorter examination times also
help to use the fast-decaying PET radiotracer more efficiently (
Ta b l e 5 . 2 5).
Recent Developments and Current Research
Recent as well as future developments deal with improvements in
radiotracers and system components, such as different detector materials
and newer electronic designs. All this can improve the speed of image
acquisition and the spatial resolution. The discovery of new radiopharmaceuticals can help to expand the field of application for PET/CT into
areas like the diagnosis of infections.
5.8.3 Single-Photon Emission Computed Tomography/ Computed Tomography
SPECT/CT offers synergies of functional and anatomic information
(
Fig. 5.63). In addition, it allows precise anatomic localization of radioac-
tivity foci. SPECT/CT is mainly applied in oncology, cardiology, and for
the diagnosis of bone lesions and infections.
Diagnostic Procedures
Figure 5.63 Neuroendocrine tumor of the neck in the transverse (above) and coronary plane. Normal CT on the right, SPECT on the left. The active lump is clearly visible on SPECT (red bar, gray bar in print, marks the corresponding site). All: Courtesy:
Prof. K. Scheidhauer, Klinikum rechts der Isar.
197
Characteristics of the Modification
An integrated SPECT/CT system allows the sequential acquisition of
SPECT and CT data in a single examination. As in PET/CT, the CT
data are used for attenuation correction of the SPECT data.
Strengths and Weaknesses
The major advantage of SPECT/CT is the improved localization and
diagnostic certainty for a wide spectrum of applications. Further advantages for patients and physicians arise from the seamless acquisition of
anatomical and functional image data. As a result, SPECT/CT minimizes
the logistical delays and consequently improves the image attenuation correction. A benefit is the immediate availability of complementary image
information.
Limitations include the sequential acquisition of CT data and
then SPECT data. Because o f the patient’s movements, misregistrations
can occur, which leads to artifacts in the corrected images. There is
198 Biomedical Engineering in Gastrointestinal Surgery
Table 5.26 Key facts on SPECT/CT
Typical
applications
Strengths and
weaknesses
Recent
developments
Research
potential and
future trends
Oncology
Cardiovascular
medicine
Orthopedics
Combination of CT
and SPECT
information
Minimized logistical
delay
Movement-sensitive
n/a Dose reduction
Increased
resolution
Introduction to
further
applications
also the fact that a dditional radi ation exposure is caused by the CT
component.
Recent Developments and Current Research
Future developments for SPECT/CT include the possibility for
patients to undergo a full diagnostic procedure at a single location, as
well as continuously reduced radiation exposure. It is expected that
the use of SPECT/CT in clinical practice will continue to gain
importance as areas of clinical application increase in the future
(
Tab l e 5. 2 6 ).
Recent developments in detector technology offer the potential for a
better spatial resolution and energy resolution, while the stability is
greater and devices are more compact. But these new detectors have to
be implemented into newly designed systems.
5.8.4 Positron Emission Tomography/Magnetic Resonance Imaging
PET/MRI combines metabolic and molecular information of PET with
excellent anatomic details of MRI systems to enhance the image quality.
PET/MRI is applied for cancer in areas of the brain, neck, and pelvis,
which require a good distinction between diseased and healthy tissue due
to their complex anatomic structure
The usage of PET/MRI, especially in an integrated system,
depends on the development of components that avoid deleteriou s
interactions caused by high magnetic fields of the MRI scanner
and RF inter ference between the MRI and PET systems
(Ta b l e 5. 2 7 ).
[65].
[69]
Table 5.27 Key facts of PET/MRI
Typical
applications
Strengths and
weaknesses
Recent
developments
199Diagnostic Procedures
Research
potential and
future trends
Oncology Enhanced image quality
Revealing further
structural information
Shorter examination
time
Introduction
to clinical
practice
Improved
components
New radiotracers
Strengths and Weaknesses
A PET/MRI system can help to improve diagnoses and to monitor
treatments due to the combination of information and the resulting
image enhancement of both systems. It provides intricate str uctural
details compared to CT scans, especially in imaging soft tissues. If the
PET system is fully integrated in an MRI system, examination times can
be shorter because there is no need to move patients from one system to
the other. Compared to PET/CT, the radiation dose is lower in PET/
MRI
[65].
Disadvantages from the view of the operators are the relatively high
costs of PET/MRI systems
[69].
Recent Developments and Current Research
Recent developments have integrated PET/MRI into cli nical settings. In 2010, Philips introduced a system of a 3 T MRI system and a
high-resolution PET scanner with an integrated rotating table, which
allows sequential image acquisition by moving the patient from one
machine to the other. The first integrated PET/MRI scanner was introduced by Siemens in 2011, which is able to do simultaneous wholebody MRI and PET scans. This system combines a 3 T MRI system
with a PET scanner
[65].
5.8.5 Single-Photon Emission Computed Tomography/Magnetic Resonance Imaging
SPECT/MRI offers images that combine the high spatial resolution given
by MRI and the high sensitivity of SPECT. However, the implementation of an integrated SPECT/MRI scanner has not yet happened in
clinical practice due to the incompatibility of SPECT components with
magnetic fields.
200 Biomedical Engineering in Gastrointestinal Surgery
Due to the incompatibility of SPECT components like PMTs and
electronics with magnetic fields, SPECT/MRI is still under development.
However, semiconductor detectors have been used in preclinical settings
that show insensitivity to magnetic fields of up to 7 T, and could have
high application potential.
Strengths and Weaknesses
The main advantage lies in combining the strengths of both imaging
techniques. SPECT offers a high sensitivity and the ability to display
multiple biological processes through energy discrimination, while MRI
involves high contrast of soft tissue and sensitivity to tissue alterations.
Unlike the hybrid method of SPECT/CT, SPECT/MRI uses only the
ionizing radiation that appears in view of SPECT (
Table 5.28).
Limitations of SPECT/MRI are similar to those of PET/MRI, and
affect the compatibility of SPECT components inside higher magnetic
fields.
Recent Developments and Current Research
Recent developments include new findings in detector technologies
like semiconductor detectors to overcome the problem of incompatibility.
To make SPECT/MRI possible for clinical settings, further research into
magnetic field-insensitive SPECT devices has to be done. However,
researchers recently developed a stationary ring-type SPECT prototype in
a preclinical setting that is compatible with MRI. All the components
used in this prototype are made of nonferrous materials. The detector of
this system is a solid-state detector. However, todays developments are still
far away from the range of clinically usable SPECT/MRI systems,
although work is in progress to produce the first prototype
[218].
Table 5.28 Key facts on SPECT/MRI
Typical
applications
n/a Enhanced image
Strengths and
weaknesses
quality
Reveals structural
information
Technology not yet
mature
Recent
developments
MRI-
compatible
Introduction of
prototypes to
preclinical
setting
Research
potential and
future trends
Development
of improved
devices
Introduction to
clinical
practice