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Computer Aided Surgery, January 2006; 11(1): 43 – 49
Abstracts from ISRACAS 2005
Eighth Israeli Symposium on
Computer-Aided Surgery, Medical Robotics,
and Medical Imaging
Petach Tikva, Israel, May 19, 2005
ISSN 1092-9088 print=ISSN 1097-0150 online #2006 Taylor & Francis
DOI: 10.1080=10929080500496202
44
Abstracts from ISRACAS 2005
INVITED LECTURES
VALIDATION OF MEDICAL IMAGE PROCESSING FOR
COMPUTER AIDED SURGERY: METHODOLOGY AND
TERMINOLOGY
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Pierre Jannin
IDM, Medical School, University of Rennes, France
Image processing is used extensively in computer-aided surgery
(CAS). The importance of validation of image-processing
methods in that context is now well established. It is required to
highlight the intrinsic characteristics of a method, as well as to
evaluate performance and limitations. Moreover, validation clarifies the potential clinical contexts or applications that a method
may serve. Validation may also demonstrate a method’s clinical
added value, as well as estimate social or economic impact.
The validation process in the context of CAS is diverse and
complex. Different evaluation levels can be studied from technical
feasibility to societal impact. CAS systems involve many imageprocessing components, e.g., segmentation, registration, visualization, and calibration. Each component is a potential source of
errors. Therefore, validation should involve the study of the
performance and validity of the overall system, the performance
and validity of the individual components, and error-propagation
along the overall workflow. Clinical validation of CAS systems
(in terms of large-scale multi-site randomized clinical trials) is
difficult, since CAS is a recent technology and the required
randomization is an ethical problem.
Validation is usually performed by comparing the results of a
method or system with a reference that is assumed to be very
close or equal to the exact solution. The main stages of reference-based validation are as follows. The first step is to clearly
identify the clinical context and specify the validation objective.
Then, the validation criteria to be studied and corresponding to
the validation objective should be chosen, along with the associated
validation metrics that quantify validation criteria. Validation data
sets are chosen to provide an access to the reference. The method
of computing the reference should be specified, as well as the
format of the input and output of comparison between the reference and the results of the method applied to the validation data
sets. The validation metric used for comparison is chosen according to its suitability for assessing the clinical validation objective.
Quality indices are computed on the comparison output to characterize the properties of the error distribution. Finally, statistical
test(s) are used to assess the validation objective. During this
process, attention must be paid to the accuracy of the reference,
to the clinical realism of the validation data sets, and to the coherence between the validation data sets and the validation objective.
Issues concerning validation are numerous. Comparison of
method performances requires the use of standardized, or at least rigorous, terminology and common methodology for the validation
process. Validation data sets with available reference are needed.
Mathematical and statistical tools are required for quantitative evaluation. Validation differs from performance evaluation in the fact that
validation studies concern performance evaluation of a method in a
precise clinical context and for a precise objective. Consequently,
comprehension of clinical issues is also of importance.
Improving validation methodology for medical image processing components for CAS could help improve understanding and
interpretation of CAS system performance, increase the clinical
acceptance of CAS systems, and facilitate technology transfer
from the lab to the bedside.
THE INCREASING ROLE OF COMPUTATIONAL
ANATOMY AND PHYSIOLOGY IN MEDICAL IMAGE
ANALYSIS
Nicholas Ayache
Epidaure/Asclépios Laboratory, INRIA, Sophia-Antipolis, France
Medical image analysis brings about a revolution to the medicine of
the 21st century, introducing a collection of powerful new tools
designed to better assist the clinical diagnosis and to model, simulate, and guide more efficiently the patient’s therapy. A new discipline has emerged in computer science, closely related to others
like computer vision, computer graphics, artificial intelligence
and robotics.
In this talk, I describe the increasing role of statistical and functional modeling to guide the interpretation of complex series of
medical images, and illustrate my presentation with three applications: the modeling and analysis of 1) brain variability from a
large database of cerebral images, 2) tumor growth in the brain,
and 3) heart function from a combined exploitation of cardiac
images and electrophysiology.
I conclude with a presentation of some promising trends,
including the analysis of in vivo microscopic images.
SESSION 1: SURGICAL NAVIGATION AND
MEDICAL ROBOTICS
COMPUTER-AIDED SURGERY IN
OTOLARYNGOLOGY/HEAD & NECK SURGERY – THE
HADASSAH EXPERIENCE
Ron Eliashar, M.D.
Department of Otolaryngology/Head & Neck Surgery, Hebrew
University School of Medicine, Hadassah Medical Center,
Jerusalem, Israel
Endoscopic endonasal surgery (EES) has become the standard
practice in sinonasal and anterior skull-base surgery. A total of
265 endoscopic endonasal procedures have been performed since
the platform arrived in April 2001. Computer-aided surgery
(CAS) using the LandmarX System (LXS) was used in 63 patients
(23.7%) in whom it was assumed that the ability to identify surgical
sites accurately could be compromised by previous surgery,
massive recurrent polyposis, or abnormal anatomy, or when
biopsies had to be taken from specific anatomic locations (e.g.,
clivus, wall of sphenoid sinus, orbital apex). In addition, two
patients diagnosed with low-grade malignant tumors of the lower
jaw were operated on using both the Image-Guided Implantology
System (IGIS) and the LXS.
In 62 of 63 ESS patients the surgical procedure was uneventful.
One patient with an atelectatic maxillary sinus developed a minor
complication of pre-septal orbital hematoma. In 94% of cases the
image-guided navigation system provided localization with less
than 2 mm of localization error (range: 1.1–2.0 mm; mean:
1.6 mm). In all cases the surgical team felt that the system
increased the intra-operative safety factor for the patient. The
overall operating room time at the end of the study was 10
minutes longer than when regular EES was used.
In the two mandibular patients the accuracy level of the
navigation provided by the IGIS was less than 0.5 mm, while
that of the LXS was in the range of 3–4 mm. Tumor resection
was done following the IGIS navigation. Pathologic examination
demonstrated resection with tumor-free margins.
Conclusion: CAS enables a new level of efficiency and safety in
EES. Nevertheless, it is not advised for surgeons who are not
familiar with regular EES. For the experienced endoscopist,
however, CAS is a valuable new tool in complex procedures. In
mandibular resections, unsynchronized mobility of the lower jaw
compromises the accuracy of the navigation, which is based on preoperatively acquired computed tomography. Specialized dental
computerized navigation systems employ teeth-supported tracking
appliances, which update the position of the mandible throughout
the surgery. This also enables more accurate registration since the
fiducial points are supported by the hard tissue of the teeth rather
than on the elastic soft tissue of the skin. Specialized dental computerized navigation systems (such as the IGIS) are therefore better
fitted to provide accurate navigation for surgery of the lower jaw.
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45
TABLE-MOUNTED VERSUS BONE-MOUNTED
REFERENCE FRAME ATTACHMENT IN
NAVIGATION-ASSISTED ORTHOPEDIC SURGERY
of the navigation process with the possible benefit of reducing
patient morbidity. This may have further application for
table-mounted devices and navigated surgical instruments.
I. Ilsar1, Y. Weil1, R. Mosheiff1, L. Joskowicz2, A. Peyser1, and
M. Liebergall1
1
Department of Orthopedic Surgery, Hadassah Hebrew University
Medical Center, Jerusalem; and 2School of Engineering and
Computer Science, The Hebrew University, Jerusalem, Israel.
MINIATURE ROBOT-BASED PRECISE TARGETING
SYSTEM FOR KEYHOLE NEUROSURGERY: CONCEPT
AND PRELIMINARY RESULTS
Introduction: Fluoroscopy-based navigation systems enable
surgeons to simultaneously correct parameters while placing
implants in multiple two-dimensional views. This facilitates
implant placement in all planes with less radiation exposure and
provides maximal accuracy. To enable a navigated procedure, a
rigid bony tracker named the reference frame is rigidly fixed to a
stable bony structure. This may create technical obstacles such
as interference with surgical instruments and the fluoroscope,
and create an additional – albeit small – operative site.
Subsequently, local wound complications may occur. As an
alternative, we propose to attach the reference frame to the fracture
table instead of the iliac crest, under the assumption that no relative
motion will occur between the table-mounted reference frame and
the target organ. We validate this assumption by comparing the
navigation accuracy while fixing the reference frame to the patient’s
bony anatomy and to the operating table.
Methods: The study population consisted of 10 patients with
femoral neck fracture (AO/OTA 31B1, 31B2.1) who underwent
fixation of the fracture with three cannulated 6.5-mm cancellous
screws using fluoroscopy-based navigation. To measure accuracy
during the navigated procedure, the following steps were
performed: Step 1–The patient was positioned on a fracture
table and the reference frame was attached to the iliac crest with
two 3-mm Shanz screws. Three guide wires used for cannulated
screw fixation were inserted under fluoroscopy-based navigation.
Step 2–New fluoroscopic images were acquired with the guide
wires in place. Step 3–The navigated drill guide was placed over
each guide wire to record the final navigated drill guide position.
The resulting images include the actual guide wire positions
(in lieu of the real implant) and the virtual trajectories of the navigated drill guide as computed by the navigation system. Ideally,
when no relative motion occurs, these two positions should completely match; in practice, a small error appears. Validation of the
navigation accuracy was performed by measuring the translational
and angular deviations of the virtual trajectory image from the real
image of the implant on the same fluoroscopic image in the anteroposterior and lateral views. Step 4 – The reference frame was
removed from the iliac crest and attached to the fracture table
with bars and clamps of an external fixator. Step 3 was then
repeated. Finally, the recorded images were downloaded and
analyzed, with all measurements reported in-plane. The twotailed T-test was used for statistical analysis.
Results: The data for 29/30 screws is presented. For the anteroposterior view, when the reference frame was attached to the iliac crest,
the average translational deviation of the trajectory from the inserted
guide wire was 1.18 + 0.92 mm at the entry site and
1.25 + 1.53 mm at the trajectory tip. When the reference frame
was attached to the fracture table, the average deviation was
1.24 + 0.90 mm and 1.85 + 1.37 mm, respectively. The differences
were not statistically significant. The angular differences were
0.88 + 0.828 in the iliac-crest-mounted reference frame group and
1.07 + 0.828 in the table-mounted reference frame group, which is
also not statistically significant. For the lateral view, when the reference frame was attached to the iliac crest, the average translational
deviation of the trajectory from the inserted guide wire was
1.42 + 0.88 mm at the entry site and 1.63 + 1.25 mm at the trajectory tip. When the reference frame was attached to the fracture table,
the average deviation was 1.26 + 0.71 mm and 1.57 + 0.85 mm,
respectively. The differences were not statistically significant.
Angular differences were 1.05 + 0.848 in the iliac-crest-mounted
reference frame group and 1.20 + 0.808 in the table-mounted
reference frame group, again not statistically significant.
Conclusion: In navigation-assisted cannulated screw fixation for
femoral neck fractures, attaching the reference frame to the fracture table instead of to the iliac crest allows for similar accuracy
L. Joskowicz1, M. Shoham2,3, R. Shamir1, M. Freiman1,
E. Zehavi3, and Y. Shoshan4
1
School of Engineering and Computer Science, The Hebrew
University of Jerusalem, Israel; 2Department of Mechanical
Engineering, Technion, Haifa, Israel; 3Mazor Surgical
Technologies, Caesarea, Israel; and 4Department of Neurosurgery,
School of Medicine, Hadassah University Hospital, Jerusalem,
Israel.
This paper describes a novel system for precise automatic targeting
in minimally invasive neurosurgery. The system consists of a miniature robot fitted with a rigid mechanical guide for needle, catheter, or probe insertion. Intraoperatively, the robot is directly
affixed to the patient skull or to the head clamp. It automatically
positions itself with respect to predefined targets in a
preoperative CT/MRI image following a three-way anatomical
registration with an intraoperative 3D laser scan of the patient’s
anatomical features. We describe the system architecture, surgical
protocol, software modules, and implementation. Registration
results on 19 pairs of real MRI and 3D laser scan data show an
RMS error of 1.0 mm (std ¼ 0.95 mm) in 2 secs.
SESSIONS 2 & 3: MEDICAL IMAGE PROCESSING
EVALUATION OF PROXIMAL FEMUR BONE MINERAL
DENSITY USING DIGITALIZED PLAIN X-RAY
RADIOGRAPHY OF THE HIP
I. Ilsar1, A. Hareven1, I. Leichter2, L. Brocke1, O. Safran1,
A.J. Foldes3, Y. Mattan1, and M. Liebergall1
1
Department of Orthopedic Surgery, Hadassah Hebrew University
Medical Center, Jerusalem; 2Jerusalem College of Technology,
Department of Electro-Optics, Jerusalem; and 3Osteoporosis
Center, Hadassah Hebrew University Medical Center, Jerusalem,
Israel
Introduction: Many of the women affected by osteoporosis are
not diagnosed until fractures occur. This is largely due to the lack
of a convenient, reliable and inexpensive screening technique for
the diagnosis of osteoporosis. The most widely accepted method
for measuring bone mineral density (BMD) is Dual-energy X-ray
Absorptiometry (DXA). However, the need for relatively expensive
equipment and trained personnel reduce the accessibility of DXA
as a routine screening tool for osteoporosis in the general population. Plain pelvic X-ray radiography is a simple and inexpensive
examination. In principal, the gray level of the bone in the X-ray
radiograph is related to the BMD. Several factors render plain
X-ray radiographs of the hip unsuitable for BMD measurements,
mainly the variability in X-ray exposure levels and soft tissue
surrounding the bone. In this study, we aimed to develop new
modifications of plain X-ray radiography of the proximal femur.
These modifications were designed to compensate for some of
the interfering factors mentioned above.
Methods: The study population consisted of 99 women, divided
into three groups: Group 1 (28 patients, mean age 77.8 + 9.9
years) – elderly patients who were hospitalized due to a lowenergy fracture of the neck of the femur. Group 2 (38 women,
mean age 67.5 + 9.1 years) – the first control group - elderly
women without a fracture. Group 3 (33 women, mean age of
40.4 + 7.34 years) – the second control group – young women.
Each patient’s left hip (the contralateral, non-fractured, hip in
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Abstracts from ISRACAS 2005
group 1) was radiographed with a brass step-wedge positioned near
the hip as a standard reference, using a computerized radiography
system. A DXA examination of the same hip followed the plain
radiograph. On each radiograph, regions of interest (ROIs) of the
proximal femur were determined in concordance with the ROIs
of the DXA examination. The mean gray level was measured for
each ROI. Several geometric parameters of the proximal femur
were measured: the neck-shaft angle, femoral neck width and
length, and femoral head diameter. In addition, further regions
were determined: three soft tissue regions surrounding the proximal femur (on the medial and lateral aspect of the femoral neck),
and the various steps of the step wedge. The mean gray level was
measured for these regions as well. Statistical comparisons
between the 3 groups were done using one-way analysis of variance
with Sidak correction for multiple comparisons. Multiple linear
regression was applied to predict the DXA values.
Results: The difference in the gray level of the different ROIs
within the proximal femur was not statistically significant
between any of the groups. However, correction of the bone gray
level to the exposure level, done by dividing the gray level of the
ROI to that of the step wedge, resulted in statistically significant
differences between group 1 and either group 2 or group 3, but
not between the two control groups. Similar results were obtained
by correction of the gray level of the ROIs to that of the soft tissue.
The DXA results were significantly lower in the fracture group in
comparison to the non-fractured elderly control group, and lower
still in this group as compared to the younger group.
Multiple R2 of 0.62 was found predicting the DXA value from
the gray level of each ROI (corrected for the gray level of the
step wedge), soft tissue gray levels (also corrected) and the
geometric measurements.
Discussion: This study shows that after correction for the
exposure level and the soft tissue surrounding the bone, a plain
digital radiograph of the pelvis can provide valuable information
concerning the bone mineral content of the proximal femur.
These preliminary results warrant further research aimed at
exploring the potential value of this fast, accessible and relatively
inexpensive technique for diagnosing osteoporosis and predicting
future fractures.
THE ACCURACY OF DIGITAL (FILMLESS)
TEMPLATING IN TOTAL HIP REPLACEMENT
William J. Murzic, M.D., Zeev Glozman, B.S., Paula Lowe R.N.,
and Priya Hirway, M.S.
Ortho-Crat, Ltd., Israel
Preoperative templating has been useful for determining the
correct size of prosthesis in cementless total hip replacement.
Typically, this has been accomplished with good success using
acetate overlays on plain radiographs. With the advent of digital
X-ray and PACS, software has been developed that incorporates
the templates of many different vendors into a program that
enables the surgeon to measure without radiographs the size of
the intended femoral and acetabular components. We compared
the two techniques to assess the relative accuracy of digital
templating.
A total of 40 cases were analyzed, comparing the preoperative
templated sizes with the actual size of the prostheses implanted
at surgery. Both acetabular and femoral component sizes were
reviewed. Magnification markers were used in all cases, and all
templating and surgery was performed by one surgeon. Twenty
hips that were templated using radiographs were compared to 20
hips that were done using digital templating software on a PACS
workstation (TraumaCad, Novapacs, Salt Lake City, UT) A
synergy femoral component and a reflection cup (Smith and
Nephew, Memphis, TN) were used in all cases. Preoperative templating data was compared to prosthesis size on operative notes.
Using standard templating, 30% of implanted stems were the
same size as templated, 65% were within one size, and 5%
within 2 sizes. With digital templating, 60% were the same size,
35% were within one size, and 5% within 2 sizes. For acetabular
components using acetate overlays, 50% of implanted cups were
the same size as templated, 45% were within 2 mm, and 5%
within 4 mm. Digitally, 45% were of identical size, 35% were
within 2 mm, and 20% within 4 mm. All postoperative films
show good fit of the components and there were no intraoperative
or postoperative fractures.
This preliminary study, using recently developed digital
templating software, showed no significant differences when
compared to the standard technique using magnified radiographic
overlays. Use of this templating software was safe and effective.
In total hip replacement, preoperative templating provides
valuable information about anatomy and appropriate implant
size. Having the information prior to surgery provides surgical
accuracy, reduces incidence of fractures, and decreases operative
time. With the increasing demand for digital imaging/PACS,
digital templating will become more prevalent.
DT-MRI PARTIAL VOLUME EFFECTS REDUCTION
USING THE MULTIPLE TENSOR VARIATIONAL
FRAMEWORK
Ofer Pasternak1, Nir Sochen2 and Yaniv Assaf 3,4
School of Computer Science; 2Department of Applied
Mathematics, Tel-Aviv University; 3Department of
Neurobiochemistry, Faculty of Life Sciences, Tel-Aviv University;
and 4Edersheim-Levi-Gitter Institute for Functional Human Brain
Imaging, Tel-Aviv Sourasky Medical Center and Tel Aviv
University, Tel Aviv, Israel.
1
Background: Diffusion Tensor Magnetic Resonance Imaging
(DT-MRI) has become a popular tool for analysis of Diffusion
Weighted Magnetic Resonance Images (DW-MRIs). It provides
quantitative measures for diffusion anisotropy of water molecules
and the ability to delineate and visualize major cerebral neuronal
pathways. It is often used as a pre-operative tool in brain surgery.
The mathematical model of DT-MRI was found to be inappropriate in cases of partial volume, where more than one type of diffusion compartment resides in the same voxel. Among the artifacts
related to partial volume are fiber orientation ambiguity and
cerebro-spinal fluid (CSF) contamination, both of which damage
the credibility and effectiveness of in-vivo neuronal fiber delineation. MRI voxel dimensions are much larger than those of neuronal
cells, resulting in partial volume effects. In addition, the borders
between different tissues are not aligned with the grid determined
by the voxels. Therefore, partial volume effects reduction requires
diffusion models that permit higher tissue complexity. However,
when a model allows more geometric freedom it demands more
free parameters, and the fitting process becomes ill-posed.
Methods: In this work we delineate neuronal fibers using the Multiple Tensor Variational (MTV) framework. The framework encapsulates a multiple tensor model into a functional and adds
biologically driven constraints in the form of regularization
terms. The multiple tensor model assumes that each voxel contains
a number of separated diffusion compartments. The regularization
terms added by the MTV framework constrain the shape of the
compartments, thus stabilizes the fitting process. The minimization of the MTV functional results in a set of diffusion tensors
and their relative weights which best describes the MR signal
attenuation. Euler-Lagrange equations are solved via the gradient
descent method that produces a set of diffusion-reaction Partial
Differential Equations (PDEs). The PDEs flow leads to the minimization of the functional while preserving the tensor’s attributes.
The regularized fitting results in separated compartments and also
reduces noise by smoothing neighborhood variations.
By adjusting the constraints enforced by the MTV framework,
we were able to use the same framework for reducing either fiber
ambiguity or CSF contamination. When resolving fiber ambiguity,
the compartments were constrained as anisotropic, cylindrically
shaped ellipsoids, each resembling a single fiber orientation. To
resolve CSF contamination, we constrain one of the compartments
as an isotropic, spherically shaped ellipsoid, with radii similar to
those found for free water diffusion. We assume that the remaining
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Abstracts from ISRACAS 2005
compartment is free of CSF contamination, thus reflecting the
diffusion of tissue water and not CSF. We use this uncontaminated
compartment for the fiber delineation.
Results: The MTV framework was tested in resolving fiber ambiguity on synthetic data resembling crossing neuronal fibers, and on
a phantom with known fiber orientations. The phantom was built
to have areas of homogenous neuronal fibers matter and areas with
partial volume due to multiple fiber orientations. We show how
MTV resolves the fiber ambiguity in the synthetic data, and
results in more accurate fiber orientations for the phantom compared with common DT-MRI analysis. Using the resulting fiber
orientations, we were able to successfully trace fibers through
fiber crossings.
The ability of MTV to reduce CSF contamination is demonstrated in cases of patients with hydrocephalus, where DT-MRI
encounters high CSF contamination. We show that MTV
found larger anisotropic areas, especially in proximity to the
CSF-filled ventricles, while maintaining the contrast between
fibrous anisotropic areas and isotropic tissue. A large portion of
neuronal fiber pathways are obscured by CSF contamination in
hydrocephalus patients. Therefore, the addition of anisotropic
voxels identified by MTV proved helpful for appropriate analysis
in these patients.
47
calculated in the produced anisotropic metric. Finally, the isosurface mesh is extracted using one of the common grid-based
contouring techniques. This approach has the following important
advantages:
The geometric adaptation of the grid is shape-driven and not
axis-aligned as with octrees. Therefore, complex geometric
features can be recovered with a lower number of voxels.
The geometric adaptation only perturbs the grid’s geometry,
while keeping the structured topology. That is, this adaptation
can be used as a preprocessor for any existing grid-based contouring method.
The meshes extracted from the adapted grids exhibit much
higher quality than those extracted from the original grids with
the same number of voxels. Moreover, dual contouring of the
adapted grids produces all-quad, anisotropic meshes.
INDUSTRIAL SESSION
CAPSULE ENDOSCOPY
Rafi Rabinovitz, Ph.D.
Given Imaging Ltd.
A NEW WARPING GRID-BASED METHOD FOR
SURFACE RECONSTRUCTION OF MEDICAL MODELS
Sergei Azernikov and Anath Fischer
Technion - Israel Institute of Technology, Haifa, Israel
Volumetric implicit models of 3D objects have recently been
introduced into the reconstruction processes from scanned data.
The grid-based methods are considered to be the major technique
for reconstructing surfaces from volumetric models, mainly due to
their efficiency and simplicity. However, these methods suffer from
a number of inherent drawbacks, resulting from the fact that the
imposed Cartesian grid in general is not well adapted to the
surface. Therefore, a novel grid-based iso-surface extraction
method is proposed. With this method, the imposed volumetric
grid is deformed adaptively according to the object’s shape. This
adaptation improves the quality of surfaces reconstructed from
the volumetric models.
The typical reconstruction process that applies on scanned data
consists of four main phases: a) scanning a 3D object; b) registration of the data into a single point cloud; c) meshing the point
cloud; and d) high-level CAD model creation. This approach is
suitable for objects with simple topology. However, meshing a
cloud scanned from a complex object is difficult. Moreover, the
point clouds are often incomplete and noisy, making the meshing
process very unstable. To deal with these obstacles, volumetric
approaches were introduced. With these approaches, the implicit
volumetric model is first reconstructed from the scanned points.
Contrary to the piecewise-linear triangular mesh, this model is a
piecewise-smooth and mesh-independent representation of the
unknown surface. For downstream applications, however, i.e.,
visualization and analysis, explicit mesh representation may be
required. Therefore, an implicit representation is converted into
an explicit one by iso-surface extraction or contouring.
We have improved the performance of the grid-based implicit
surface contouring methods by adapting the imposed volumetric
grid with the anisotropic metric field induced by the surface
shape. With the proposed approach, the process begins by reconstructing an implicit model from the scanned points cloud. In the
current work, the multi-level partition of unity method is used.
With this method, a set of overlapping quadric patches is fitted
to the cloud. Then, these patched are blended to produce a piecewise-smooth implicit representation of the surface. In the next
phase, the background octree is constructed in order to represent
the geometric tensor field. Then, the field is evaluated and propagated on this octree. As a result, a metric tensor is set for each point
in the problem domain. Afterwards, the uniform grid is adapted
geometrically by relaxing the vertex position, while edge length is
Traditional methods aiming for direct visualization of the digestive
tract do not provide information on the small bowel, which is
approximately 6 m in length. Furthermore, visualization of other
parts of the digestive tract, i.e., the esophagus, stomach and
colon, requires inconvenient procedures with long endoscopes
(flexible tubes) that are advanced into the digestive tract through
the throat or rectum.
Given Imaging Ltd. is developing patient-friendly products
for visualizing gastrointestinal disorders. The company’s technology platform is the Given Diagnostic System, featuring a
single-use miniature video camera placed in a capsule (PillCamw), 11 26 mm, which the patient swallows. The
PillCam acquires several color video images per second as
natural peristalsis propels it through the digestive tract, and
sends them to a data recorder worn on the patient’s waist. A
typical capsule endoscopy of the small bowel provides 50,000
images for up to 7 hours, which are stored at the data recorder.
After the capsule is ingested, the patient is not restricted to the
medical environment. At the end of the procedure, the stored
data is loaded into a dedicated PC workstation which is
equipped with special application software (Rapidw) for processing, presenting and storing images and for generating medical
reports.
Currently, Given Imaging is selling video capsules for the small
bowel (PillCamw-SB) and the esophagus (PillCamw-ESO).
PillCam capsules are a naturally ingested method for direct visualization of the entire small bowel and esophagus. PillCams are
currently marketed in more than 60 countries, and have benefited
more than 150,000 patients.
CARDIOP-B SYSTEM FOR 3D CORONARY ARTERY
RECONSTRUCTION FROM FEW 2D X-RAY
ANGIOGRAPHIC PROJECTIONS
Michael Zarkh and Moshe Klaiman
Paieon Medical Ltd., Israel
As opposed to the computer tomography approach, which
provides 3D volume images, the standard coronary angiography
procedure nowadays uses 2D X-ray angiographic projections.
CardiOp-B is a system for 3D reconstruction of coronary vessel
segments based on single-plane angiography. The system is
intended for use in real time in the context of the standard angiography procedure, and overcomes the limitations that are inherent
in 2D analysis of 3D vessel anatomy.
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Abstracts from ISRACAS 2005
The system reconstructs a 3D coronary vessel segment, unfolding its true morphology and providing accurate dimensions, in
particular an accurate quantitative lesion analysis. The 3D vessel
segment is represented as a tree of generalized tubular organs
given by a tree of 3D centerlines and local radii at every centerline
point. To obtain the 3D reconstruction, the following algorithm
steps are performed.
A 2D analysis for two or three ECG-gated images from different
perspectives is carried out. At this stage, the 2D centerlines and
edges of an artery are extracted and corresponding radii are
calculated. In addition, a densitometry measurement attaches a
cross-section area value to every 2D centerline point. The densitometry is based on gray-value analysis around the vessel of interest
within each single image. The stage of 2D analysis requires a
minimal user interaction to define a vessel of interest using 3
marking points per image.
The next algorithmic step is a point-by-point matching of 2D
centerlines. After the point-by-point matching is done, the 3D
centerline point calculation is simply the intersection (in the
generalized sense) of the projection lines of matched 2D points.
The matching of 2D centerlines is a nontrivial task for the following
reason: The coronary artery is a moving organ depending on heartbeat phase and breathing. Because the video sequence rate is
limited and breathing is usually not under control, there exist
local distortions not covered by the geometry model, even if the
imaging system is well calibrated and the imaging geometry
model is known exactly. We proposed an approach of using a
simple geometry model (orthographic projection) and a technique
to overcome local distortions and provide a precise match.
After the 3D centerline has been reconstructed, the 3D radius for
every 3D centerline point is calculated. The 3D radius value
aggregates densitometry and radius values coming from every 2D
source that participated in 3D reconstruction. The quantitative
information optimally combines 2D measurements, taking into consideration the local 3D skeleton orientation and viewing geometry.
The CardiOp-B system underwent comprehensive validation
and has received FDA and CE approval. The clinical studies
have demonstrated that our system is precise, robust and easy to
operate.
POLESTAR N20 - MR IMAGE GUIDANCE SYSTEM,
R. Ben-Kish
Odin Medical Technologies, Yoqneam, Israel
PoleStar N20 is an image guidance system featuring both
intraoperative MRI and optical navigation capabilities. Its main
application today is neurosurgical, but since it is easily integrated
into any general operating room it has a lot of potential for other
applications as well.
The MRI scanner is based on a mobile open 0.15T permanent
magnet. It supports a wide range of different MRI sequences in a
field of view that covers the whole head. The images are easily
acquired at any stage of the surgery, providing the surgeon with
powerful means to plan the surgical procedure and perform
accurate resection as the surgery progresses. MRI images taken
in the OR help the surgeon distinguish between benign and malignant tissue, even in cases where they are visually undistinguishable.
The navigation employs an IR camera that tracks pointing
devices and other surgical instruments. It also constantly follows
the movement of the magnet and the patient on the operating
table, providing accurate and reliable navigation throughout the
surgery, despite the changing anatomic environment. Imaging
performed during the progress of the surgery allows the surgeon
to navigate on the basis of up-to-date information, thereby
overcoming the brain-shift problem.
The PoleStar N20 is the second generation of the PoleStar
family. The first generation, PoleStar N-10, was installed in
22 sites in 2000–2004. The new generation offers a larger field
of view, improved image quality and navigation options. More
than 2000 surgeries have already been performed in more
than 30 PoleStar N-10 and PoleStar N20 sites throughout the
US, Europe and Israel. The PoleStar N20 system supports many
neurosurgical procedures, including resection of low- and highgrade gliomas, transphenoidal pituitary surgery, posterior fossa
surgery, biopsies, shunt placement and more.
VRI: NEW IMAGING MODALITY FOR THE LUNGS
Igal Kushnir, Meir Botbol and Alon Kushnir
Deep Breeze 2, Hailan St. Industrial Park, Or-Akiva, Israel
We present a new imaging technology for the human body that is
radiation-free and organ-oriented. It is called Vibration Response
Imaging (VRI). Unlike magnetic resonance imaging (MRI),
X-ray or ultrasound, VRI uses passive vibration energy that is naturally created in organs to produce a dynamic image of the organ.
The development of the first VRI for the lungs was based on
the finding that the lung vibration energy directly correlates to
the lung airflow. As VRI constructs an image from the amplitude,
frequency, intensity and timing of lung vibrations caused by
airflow, any change in these parameters should be reflected in the
image. Moreover, structural and functional alterations, such as
bronchial obstruction or space-occupying lesions such as lung
cancers, are reflected by a corresponding modification of the
vibration response. VRI employs this vibration response to
record lung vibrations, and displays an image of the vibration
characteristics of the lungs. The method of accumulating the
VRI energy of the lungs requires full coverage of the lungs by
attaching 40 specially designed piezo-electric pressure sensors
over the back. VRI sensors are attached by a low-vacuum computer-controlled method. The VRI device uses several stages of filtering to select the frequency band that typically represents the lung.
The filtering is also used to reduce distortion (e.g., background
noise and undesirable signals coming from the heart and muscle)
and to enhance the signal by reducing all other frequency
components. The filtering process includes band-pass filtering
(100–250 Hz) that allows through only a desirable range of
frequencies; median filtering that suppresses impulse noise; and
truncation of samples above a given threshold. Finally, singular
value decomposition (SVD) is used to identify only meaningful
underlying variables. At each time interval, the output of the
time domain filtering reflects the vibration energy by integrating
the previously filtered signals over a certain time interval.
These new samples are then processed to produce a spatial,
2-dimensional image, which is assumed to be ruled by the solution
of the diffusion equation. For data acquisition, we have developed a
special 64-multi-channel A-to-D converter, which enables filtering, amplification and conversion of the analog signal into digital
data. The system includes a 16-bit acquisition level and a variable
sampling rate (4 –20 KHz) that acquires the analog signals and
converts them to digital data. The VRI graphic representation
generates a gray-level-coded spatial representation of the lung
vibrations. High data values, in which lung vibration energy is
greatest, are depicted as dark colors (black) and low data values
are shown as light colors (light gray); the minimum is defined as
“white”. This representation enables the viewer to follow the
course of the dynamic development of the lung in the image. An
additional advantage of VRI is that it also detects and records
lung sounds; each channel can be examined by the VRI algorithm
for crackles (i.e., discontinuous abnormal lung sounds), wheezes
(i.e., continuous abnormal lung sounds), and automatic breathing
cycle selection. Crackles and wheezes that are identified by the
algorithm are presented in the display as colored dots on the
lung image.
With ethical committee approval, the VRI was studied on more
than 200 human subjects, both healthy and with various lung pathologies. Dynamic lung images from the VRI were compared to
existing gold-standard imaging technologies. It has been possible
to discern specific VRI signs for the different lung abnormalities.
A test of 20 healthy subjects found a significant, direct correlation
between the lung vibration energy and the actual airflow, providing
evidence that the VRI also has the ability to produce quantitative
measurements of the lung. VRI is tested for imaging other organs
Abstracts from ISRACAS 2005
in the human body, such as the heart, by using their own intrinsic
vibrations.
PEDICLE SCREW INSERTION BY SPINEASSIST
MINIATURE ROBOTIC SYSTEM
Computer Aided Surgery Downloaded from informahealthcare.com by Hebrew University on 08/04/15
For personal use only.
Ori Hadomi, Avi Posen and Moshe Shoham
Mazor Surgical Technologies, Caesarea, Israel
This presentation describes a new approach to medical robotics
using a miniature robot that is directly mounted on the patient
anatomy. It is currently indicated and FDA-approved for spinal
applications. Attaching the robot to a vertebra renders the system
and spine a unified rigid body, hence patient movement and
breathing do not change the location of the robot relative to the
vertebra, thus providing significantly higher accuracy in the insertion of implants, e.g., pedicle screws. In addition, the proposed
system is a semi-autonomic one designed to accurately guide and
assist the surgeon; the actual surgical procedure is still performed
by the surgeon, who remains in full control at all times.
Cadaver and clinical cases performed by the system in the last
several months, during which tens of screws were inserted, show
high accuracy of implant location with respect to the planned
location, in the range of 1 mm. The system’s potential to enable
minimally invasive percutaneous procedures is also addressed.
3D ULTRASOUND: VISUALIZATION TECHNOLOGY
AND MEDICAL ADDED VALUE
Ziv Soferman
BIOMEDICOM, Creative Biomedical Computing Ltd., Israel
Three-dimensional ultrasound provides nice pictures of anatomical structures which may be understood by non-ultrasound
experts, by practitioners of other disciplines, or even by the patients
themselves. However, it is still questioned whether 3D ultrasound
has added clinical value for the ultrasound expert compared to
classical 2D ultrasound.
BIOMEDICOM’s product is an add-on to any 2D ultrasound
system (connecting to the standard video-output port) that
upgrades it to 3D imaging capabilities. This upgrade is achieved
as follows: 1) The user acquires a series of 2D images in a typical
49
fan acquisition protocol, using a gyroscopic orientation sensor
attached to the ultrasound probe; 2) Reconstruction of the 2D
set of images using the respective geometric information obtained
with the gyroscopic sensor results in a 3D image of the scanned
region; 3) Optionally, the user may perform an almost automatic
segmentation of the organ of interest; 4) The user may invoke
ordinary means like a bounding box and other navigation/
orientation utilities; 5) Three visualization modes are available,
namely “smooth” surface-volume rendering, volume rendering
with transparency, and multi-planar representation (MPR).
The segmentation algorithm is unique in its ability to isolate
organs or other anatomies in difficult cases, such as fetus from
the placenta (as compared to the rather easy separation of fetus
from fluid). The algorithm is successful in doing so even when
the ultrasound images are corrupted by speckles and shadows.
Two clinical examples are shown which demonstrate the added
value of 3D ultrasound. The first example is a follow-up imaging of
a patient who had undergone an ablation procedure for a tumor in
the liver. In the follow-up session, the 2D ultrasound wrongly
showed that the “hole” at the location of the ablated tumor
appeared fine and no traces of the tumor could be observed.
Eventually, therefore, the patient would have been discharged.
However, 3D ultrasound was then performed after injecting a
contrast agent, and in the 3D image formed by grouping the
series of 2D images, it was found that the boundary of the “hole”
had a layer or “shell” which had an excess of blood vessels. This
“shell” provided evidence that the tumor had not, in fact, been
fully ablated. Therefore, a follow-up procedure was invoked on
the spot to complete the ablation. This “shell” was too weak to
be identified in any of the 2D slices, and was visible only in the
grouping of slices into a combined 3D image. Ultrasound contrast
agents were also used in the second example. Here, the dense
vascular structure obscured the malignant part. In 2D it was very
difficult to determine the 3D vascular structure. In an ordinary
3D volume rendering, the vascular structure would have appeared
too dense, obviating the ability of observing its malignant center. In
transparency mode, however, the brighter center could be
enhanced by making the less-bright parts more transparent.
Therefore, the malignant bright center became visible and
distinguishable from all the other parts. This transparency mode
is found very valuable when the object of interest is vascular and
contrast agents are applied to emphasize the brightness of the
desired object or structure.
Three-dimensional ultrasound, together with the suitable
visualization method, proves to be of added value when the
desired object has a complex 3D structure, as in a complex 3D
vascular structure, or when the phenomena to be observed can
be identified in 3D but not in any one 2D slice.