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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_605_Библиотеки_им_академика_М_И_Перельмана.pdf
201Diagnostic Procedures
5.8.6 X-Ray/MRI
The X-ray/MRI system (XMR) is a fusion of X-ray fluoroscopy and
MRI. It enables the simultaneous acquisition of informat ion on anatomic structures and functional processes within the body. XMR is still
unde r research and not commercially available. However, it will have a
medium-high impact on preclinical settings in the next 4 years
In the future, it could be helpful for navigated medical interventions
like catheter-based procedures in cardiology or brain biopsy in
neurology.
The system basically consists of the same components as the individual
technologies. An X-ray tube and detector, which are compatible with
MRI systems, are arranged in a bore of a magnet. The detector used in
XMR is a digital flat panel detector (
Table 5.29).
Strengths and Weaknesses
The main advantage of this hybrid system is the combination of
the strengths of MRI, such as the flexible selection of planes, the
excellent soft-tissue contrast and functional information, with those of
X-ray fluoroscopy, such as the excellent display of anatomic structures,
and the creation of high-resolution projection images. The integration
of both systems into one enables a rapid switch between imaging
modalities without moving the patient. This reduces examination
times.
The weaknesses of XMR arise from its novelty. Current X-ray components like image intensifiers or rotating anode X-ray tubes are not yet
compatible with magnetic fields.
[219].
Table 5.29 Key facts of XMR
Typical
applications
Potential
applications are
catheter-based
procedures in
cardiology and
GI surgery
Strengths and
weaknesses
Combination of
strengths of both
technologies
Shorter
examination
time
Recent
developments
n/a High research
Research
potential and
future trends
potential
in the
development
of more
devices, which
are compatible
with magnetic
fields
202 Biomedical Engineering in Gastrointestinal Surgery
Recent Developments and Current Research
Because of the novelty of XMR, any potential impact on diagnostic
and interventional procedures requires further research. To adopt XMR
into routine care, it is necessary to develop a wider range of devices and
monitoring equipment that is compatible with magnetic fields. T his is
the fundamental requirement for accessing the true impact of XMR
systems.
XMR is currently under research and only applied in preclinical
settings. It is expected to be of greater relevance in the future, especially
in neurology and oncology.
5.8.7 Integrated Optical Coherence Tomography Ultrasound Imaging System
OCT-US is an integrated dual modality that combines optical components with an US transducer, enabling OCT and US imaging at the same
time. This hybrid modification has recently successfully been tested under
experimental conditions (animals).
Characteristics of the Modification
The consequences of atherosclerosis are one of the major causes for
morbidity in developed countries. In contrast to common imaging methods for diagnostic purposes like MRI and CT, OCT-US not only reveals
the shape of arterial lumen—which can remain unaffected until the final
stages of the disease—but provides direct tomographic cross-sectional
images of the vessel wall
Strengths and Weaknesses
The two imaging modalities, US and OCT, provide complementary
information. OCT adds highly detailed resolution to the high penetration
depth of US, allowing real-time 3D imaging (
[220].
Table 5.30).
Table 5.30 Key facts of OCT-US
Typical
applications
Cardiovascular
medicine
Strengths and
weaknesses
Fine resolution
High penetration
rate
Cross-sectional
images of
vessel walls
Recent
developments
USCT/warm
bath US
Research potential
and future trends
Optimization of 3D
reconstruction
algorithms
Increase of image
quality
203Diagnostic Procedures
Recent Developments and Current Research
Research on clinical applicability is currently being car ried out.
Current devices achieve axial and lateral resolutions of 1020 µm
with OCT and 38400 µm with OCT-US
[221] with a maximum
outer diameter of 1.18 mm. OCT-US improves diagnostics for intravascular diseases and has the potential to replace common technologies like MRI and CT in this particular field
[220]. In vitro 3D
imaging of human arter ies and in vivo imaging of atherosclerotic
microstructure in a rabbit abdominal aorta has been achieved using
this technology.
OCT-US is expected to gain further relevance as a superior and
highly specific imaging modality. As it matures and is adapted, its
relevance can be expected to rise.
5.8.8 Integrated Optical Coherence Tomography and Positron Detection
Integrated OCT and positron detection is a means of combining OCT
with a common imaging modality. These probes allow simultaneous
OCT and scintillator proton detection.
Regular PET, such as for the purposes of ovarian cancer diagnosis or
detection of intravascular plaque or cancer, usually provides low resolution and often does not offer detailed information about malignant tissue. This novel hybrid imaging modality consists of multiple scintillating
fibers and an OCT probe, allowing simultaneous OCT scann ing and
positron detection
and can be used in intravascular as well as dur ing inter ventional
procedures.
Strengths and Weaknesses
This hybr id imaging modality provides a combination of 3D
volumetric OCT imaging and infor mation gathered from positron
detection, which helps to overcome problems in distinguishing
between signals from early-stage cancer and healthy tissue as well
as in localizing lesions. Prototypes offer both structural and functional infor mation in surroundings with high radiotracer uptake
[223].
Recent Developments and Current Research
Recently, initial ex vivo studies have been obtained after a variety of
animal testing. The feasibility of detecting ovarian cancer at an early state
using this technique has been proven
[222]. It can be designed in the form of a catheter
[222]. Positron detectors with
204 Biomedical Engineering in Gastrointestinal Surgery
optical coupling between optical and scintillating fiber have been developed in order to reduce the SNR. There is a potential role for this hybrid
imaging modality in intraoperative application, as well as in early-stage
cancer detection. Current research is also focusing on designs for application fields other than detection of ovarian cancer, such as endoscopic
diagnosis in laparoscopy
[224].
5.8.9 Microscope Integrated Optical Coherence Tomography and Optical Coherence Microscope
Integrated OCT and microscopy (MIOCT) combines different microscopes
with interferometry-based coherence tomography, providing microscopic
resolutions with OCT depth scan information. There is also the possible
integration of interferometry directly into microscopic devices, creating a
so-called optical coherence microscope, or OCM
Characteristics of the Modification
This hybrid modification finds use in both intraoperative and general
pathologic applications, such as tumor excision and ophthalmologic
operations, as well as in other tissue imaging, such as endoscopy for
gastrointestinal investigations
[226].Asmentionedearlier,the
fiber optic-based OCT can be placed i n the optical path of a microscope, a technique referred to as OCT mounted microscopy that allows
simultaneous image acqui sition
[227]. The principle of interferometry,
employed in OCT, is also brought directly into microscopic imaging
[226].
Strengths and Weaknesses
MIOCT and OCM can provide complementar y infor mation. It
combines cellular sensitive imaging with depth resolution to generate
real-time 3D information. The images obtained can have resolutions
greater than 1 µmaxiallyand0.5µm transversally
devices reach acquisition rates of 210,000 A-scans per second with an
axial resolution of 4.2 µm and a transversal sensitivity of 2.9 µm
[225].
Recent Developments and Current Research
MIOCT has passed testing on clinical applicability and has found its
way to a wide range of applications such as intrasurgical use, which
expandsasthisquicklydevelopingtechnologyisbeingimproved
[228230]. Cur rent devices have not been able to leverage advances in
molecular-targeted cont rast agents. MIOCT is undergoing research and
[225].
[92], yet current
205Diagnostic Procedures
might reach molecular sensitivity, providing structural information
about the tissues examined as well as their pathological state
Two sample market and technology assessments are being conducted.
It is intended to underline the differences and similarities between the
original modification and the hybrid systems, as well as drawing the
attention to their potential and possible specificity.
[231].
5.9 INTRAOPERATIVE DIAGNOSTIC PROCEDURES
Intraoperative decision making is based upon the knowledge of preoperative findings (e.g., CT, US, MRI) and the actual findings and conditions
while doing the surgery.
In some cases, however, it would be helpful to perform diagnostic
imaging in the acute surgical situation either to “refresh” th e preoperative findings or to get new information upon the actual conditions
[232].
Intraoperative US is the most popular intraoperative diagnostic tool
for the surgeon at the time being.
Intraoperative radiography is older than US, but it certainly lost
importance over the past decades. Modern variants of X-ray application,
however, seem to have gained a new role in intraoperative imaging in
vascular surgery.
5.9.1 Ultrasound
Intraoperative ultrasonography (IOUS) has been established for almost
30 years. Primarily, it was introduced to detect pathological findings
which had not been revealed during preoperative imaging (metastases,
lymph nodes, general tumor staging). IOUS had a significant impact
upon intraoperative changes in surgical strategy
considerable advances in preoperative diagnostic imaging, IOUS still plays
a major role
A large variety of specially designed intraoperative US probes is available both for open and laparoscopic surgery (
[234,235].
[233]. Even today, after
Fig. 5.64).
5.9.2 Conventional Radiography (C-Arm)
Intraoperative radiography is the oldest imaging modality in surgery.
In the beginning, radiographic cassettes were placed beneath the patient
to produce an image. Later on, dynamic fluoroscopy using a C-arm was
206
Biomedical Engineering in Gastrointestinal Surgery
Figure 5.64 (A) IOUS probes in laparoscopic use; (B) IOUS in open liver surgery;
(C) laparoscopic IOUS. All from MITI.
Figure 5.65 C-arm positioned for intraoperative cholangiography. From MITI.
introduced. The key domain of intraoperative radiography is orthopedic
surgery. However, it is also still in use in visceral surgery. The most common application is intraoperative cholangiography, i.e., the examination
of the bile duct (
Highly informative images are provided in real time (
Fig. 5.65).
Fig. 5.66).
If intraoperative fluoroscopy has to be considered, special care should
be taken to select the right OR table. It has to be translucent at the area
where the X-rays have to be taken.
This spot should be accessible for the C-arm.
5.9.3 Isocentric Radiography
A normal C-arm can be rotated manually to provide X-ray images of the
object in two planes. Due to the construction, the arm does not move in
a perfect semicircle but the orbit resembles an egg shape.
Diagnostic Procedures
Figure 5.66 Intraoperative cholangiography during laparoscopic cholecystectomy:
a catheter is inserted via the cystic duct stump into the common bile duct.
Though the common bile duct is not dilated, a small biliary stone can be seen in the
distal duct. From MITI.
207
If the device is designed as an “isocentric” C-arm, the central X-ray
remains in the isocenter of the object independent of the actual position
of the arm. The distance of the X-ray tube and the image intensifier is
always constant. Thus, by continuous (automatic) rotation around the
object a series of images can be produced which serve as a basis to create
a real 3D data set, similar to CT.
5.9.4 Intraoperative Volume Data Acquisition
The SIEMENS ARTIS pheno is an isocentric C-arm which is moved by a
KUKA robot into the appropriate position. The multiaxis robotic arm is
floor mounted. The Syngo DynaCT is a special imaging procedure which
creates a 3D data set from a series of images and projections acquired as the
X-ray tube and the detector rotate around the patient (
Fig. 5.67).
Currently, the system is mainly used in vascular surgery (hybrid ORs)
and spinal surgery
visceral surgery
[236]. However, its usability has already been proven in
[237239].
5.9.5 Intraoperative Computed Tomography/Magnetic Resonance Imaging
Prior to the era of 3D arms, CT machines or MRI were established in
the OR to gain intraoperative information. Despite some technical
improvements (e.g., open MRI), intraoperative examinations remained
208
Biomedical Engineering in Gastrointestinal Surgery
Figure 5.67 Robotically positioned isocentric C-arm. From r Siemens Healthcare
GmbH.
difficult, interrupting the normal workflow significantly. Nonetheless,
some groups found it valuable enough to do intraoperative CTs or MRI
regularly, mainly in neurosurgery
[240]. In visceral surgery, intraoperative
CT/MRI did never play a role.
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