Download Aquilion ONE / ViSION Edition CT Scanner Realizing 3D Dynamic

TOSHIBA REVIEW GLOBAL EDITION Vol. 1, No. 1, 2015
Aquilion ONE / ViSION Edition CT Scanner
Realizing 3D Dynamic Observation with Low-Dose Scanning
• KAZAMA Masahiro • SAITO Yasuo
Computed tomography (CT) scanners have been continuously advancing as essential diagnostic imaging equipment for the diagnosis and treatment of a variety of diseases, including the
three major disease classes of cerebrovascular disease, cardiovascular disease, and cancer.
Through the development of helical CT scanners and multislice CT scanners, Toshiba Medical Systems Corporation (TMSC) has developed the Aquilion ONE, a CT scanner with a scanning
range of up to 160 mm per rotation that can obtain three-dimensional (3D) images of the brain,
heart, and other organs in a single rotation. We have now developed the Aquilion ONE / ViSION
Edition, a next-generation 320-row multislice CT scanner incorporating the latest technologies
that achieves a shorter scanning time and significant reduction in dose compared with conventional products. This product with its low-dose scanning technology will contribute to the practical realization of new diagnosis and treatment modalities employing four-dimensional (4D) data
based on 3D dynamic observations through continuous rotations.
1. Introduction
Computed tomography (CT) scanners were developed and applied in clinical practice in the first half of
the 1970s. Since its introduction over 40 years ago, CT
has evolved into an essential diagnostic imaging method supporting a variety of clinical applications, from
screening to detailed examinations. During the initial
stage of its introduction, improvements were made to
CT so that a single plane could be visualized with more
detail in a shorter time. By around 1990 when helical
CT scanners were developed and clinically employed,
permitting scanning to be performed continuously
while the patient is moved through the scanner, CT had
become an imaging method that permits the human
body to be visualized three-dimensionally (1). In the
second half of the 1990s, multislice CT was introduced,
enabling simultaneous acquisition of multiple slices.
This CT technique dramatically expanded the usefulness of helical scanning(2). In succeeding years, Toshiba
Medical Systems Corporation (TMSC) made efforts to
develop a new CT scanner that would enable the target
organ to be scanned in a single gantry rotation without
the necessity for helical scanning, and enable visualization of a moving organ with continuous scanning. After
initially developing a prototype 256-row multislice CT
scanner (3), TMSC eventually developed the 320-row
multislice CT scanner Aquilion ONE in 2007. This CT
scanner supports continuous scanning at 0.35 s/rotation and makes it possible to observe the dynamics of
the target organ three-dimensionally. Since the Aquilion
Figure 1. Aquilion ONE / ViSION Edition.
This is a CT scanner that permits dynamic 3D imaging to be performed for a 160-mm-wide area at a low exposure dose.
ONE realizes a new CT examination method, rather
than the conventional method that focused on the helical scan technique, it is referred to as “area detector CT”
(ADCT) or “dynamic volume CT.”
We have now developed the Aquilion ONE / ViSION
Edition, a next-generation CT scanner that evolved
from the Aquilion ONE. Since this scanner features a
shorter scan time, significant reduction in exposure
dose, improved operability, and energy-saving technology, it is both patient- and user-friendly (Figure 1). In
particular, realization of low-dose scanning has expanded the scope of dynamic 3D imaging by continuousrotation scanning, and target regions for functional
diagnosis based on dynamic scanning have expanded
accordingly(4).
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TOSHIBA REVIEW GLOBAL EDITION Vol. 1, No. 1, 2015
provided with single energy metal artifact reduction
(SEMAR) which accurately reduces artifacts generated
from such metals. This has made it possible to assess the
structures around such metal objects, which was previously difficult.
This report describes features of the Aquilion ONE /
ViSION Edition, the latest technologies available in this
system, and prospects for the future.
2. Features of the Aquilion ONE / ViSION Edition
A CT scanner is a diagnostic imaging device with an
X-ray tube and an X-ray detector located at diametrically opposite positions, with the scan target between
them. It continuously rotates around the scan target to
acquire 360° of projection data and images the 3D distribution of the X-ray attenuation coefficients inside the
scan target.
The Aquilion ONE is provided with an X-ray tube
and an X-ray detector that cover a wide 160-mm range
in the axial direction and permits a 3D image of entire
organs such as the brain or the heart to be acquired in
a single rotation. By performing continuous-rotation
scanning, dynamic scanning of the target organ is possible.
The new-generation CT scanner Aquilion ONE /
ViSION Edition has the following features.
2.1
2.5
Standby power consumption accounts for a large part
of total system power consumption. We have therefore
employed an optimized image reconstruction unit and
introduced sleep mode as an energy-saving measure for
the gantry, achieving an approximately 40% reduction in
power consumption.
In addition, shorter scan times and low-dose scan
conditions using AIDR 3D have led to reduced power
consumption during scanning, which makes the Aquilion ONE / ViSION Edition a CT scanner that benefits
both hospital management and the global environment.
3. Dose reduction technologies that support
dynamic 3D imaging
Because dynamic 3D imaging, which was a concept
for development of the Aquilion ONE, is based on
continuous-rotation scanning of the same region, it was
essential to reduce the exposure dose. Although dynamic 3D imaging was made available when the Aquilion
ONE was developed and released in 2007, subjects were
limited because the use of the technique increases the
total exposure dose in a study. In order to expand the
field of dynamic 3D imaging and promote wider acceptance of this technique as a new functional study method, it was necessary to reduce the exposure dose to the
same level as for a conventional CT study, even though
continuous-rotation scanning is required.
In order to significantly reduce the exposure dose in
dynamic 3D imaging, it was necessary to make major
improvements to fundamental items such as X-ray
detector sensitivity and image reconstruction technologies to reduce noise.
The high-sensitivity large-area X-ray detector and
the AIDR 3D function employed in the Aquilion
ONE / ViSION Edition are described below.
Shorter scan time
By improving the ability of the CT scanner main
unit to withstand centrifugal forces, the shortest scan
time has been improved from 0.35 s/rotation to 0.275
s/ rotation (more than 20%). This has made it possible
to obtain images with less blurring, even for patients
with high heart rates, facilitating low-dose scanning in a
single cardiac cycle.
2.2
Significant reduction of exposure dose
The scanner incorporates a new X-ray detector with
1.4 times higher sensitivity than a conventional detector, and the adaptive iterative dose reduction 3D (AIDR
3D) function, an image reconstruction technology that
reduces image noise by up to 50% (corresponding to
reduction of up to 75% for dose conversion). These
features have made it possible to significantly reduce
exposure dose in dynamic 3D imaging (which requires
continuous-rotation scanning), which has contributed
to an acceleration of clinical research into dynamic
assessment.
3.1
2.3
Improved operability
High-sensitivity large-area X-ray detector
In order to acquire 160-mm-wide high-definition projection data with a slice thickness of 0.5 mm in a single
gantry rotation, the Aquilion ONE requires a large-area
X-ray detector with detector elements of approximately
300 000 precisely arranged pixels. For the Aquilion
ONE / ViSION Edition, we have developed a new X-ray
detector with significantly improved sensitivity in order
to ensure high image quality, even at low-dose scanning
(Figure 2).
Image noise significantly depends on the signal-tonoise (SN) ratio of the X-ray detector, and in order to
A large gantry bore (opening) of 780 mm has been
achieved by using compact units inside the scanner
main unit. This has made it possible to improve access
to the patient during examination and easier for the
patient to positively move joints etc. during examination, thus facilitating dynamic scanning.
2.4
Reduced power consumption
Reduction of metal artifacts
At clinical sites, various types of metals are used in
treatment etc. The Aquilion ONE / ViSION Edition is
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TOSHIBA REVIEW GLOBAL EDITION Vol. 1, No. 1, 2015
Acquired
projection data
Scanner
model
Anatomical
model-based
noise reduction
Image
update
AIDR 3D
image
Projection
data noise
reduction
Statistical
model
Figure 2. High-sensitivity large-area X-ray detector.
Figure 3. Outline of AIDR 3D technology.
This is a new X-ray detector with a sensitivity 1.4 times higher than
the conventional detector, ensuring high image quality even in lowdose scanning.
Noise can be reduced efficiently while maintaining image resolution
by applying a scanner model, a statistical noise model, and an anatomical model.
effectively while maintaining the required level of 3D
spatial resolution (Figure 3).
AIDR 3D reduces image noise by up to 50%. This
corresponds to 75% dose reduction when converted to
the exposure dose required to acquire an image with the
same level of noise (the exposure dose can be reduced to
1/4 that of the conventional method).
The reconstruction time is almost the same as that for
the conventional method. In-scan dose setting is also
possible, which is another feature of this function. Specifically, AIDR 3D is a noise reduction processing technology that can be used while maintaining throughput
comparable to that for conventional methods(5).
improve the SN ratio, it is necessary to improve the
efficiencies of the X-ray detector (geometric efficiency,
absorption efficiency, emission efficiency, and condensing efficiency), thus enhancing its sensitivity.
By employing an inter-element separator that optimizes the reflection factor while minimizing the dead
space for the incident X-rays, and improving the scintillator manufacturing process to produce a scintillator
that can efficiently convert X-rays into light and direct
it to the optical sensor, the geometric efficiency and
condensing efficiency have been increased in a wellbalanced manner. In addition, emission efficiency has
been increased by improving the raw materials used in
the scintillator. With these improvements, we have succeeded in developing a high-sensitivity X-ray detector
with 1.4 times higher sensitivity than that of a conventional X-ray detector.
This corresponds to exposure dose reduction of up to
30% when low-dose scanning is performed.
3.2
Blending %
4. 4D applications to realize dynamic 3D
imaging
Diagnosis using dynamic 3D data acquired by the
Aquilion ONE / ViSION Edition, which permits continuous-rotation scanning to be performed at lower
exposure dose, is being accelerated in clinical practice.
To support this, we have been supplying a range of 4D
application software packages. Typical recent applications are described below.
AIDR 3D
Noise reduction processing in image reconstruction
has been a challenge since the beginning of CT scanner
development, and various methods have been applied.
However, the conventional noise reduction processing
methods basically involve a tradeoff with resolution.
Specifically, if noise reduction is given priority, image
resolution is significantly reduced, and vice versa.
AIDR 3D is an image reconstruction technology that
employs an iterative method to reduce image noise, taking into account the characteristics of the scan target
(the human body). With this technology, it is possible
to significantly reduce noise in the target region where
uniformity is required while maintaining the required
level of resolution.
Noise elements are extracted from the acquired projection data based on the scanner model and statistical
model. Noise elements are also extracted from the image
data based on a 3D anatomical model (target region and
tissue structure). By repeating extraction and elimination of noise elements, image noise can be reduced
4.1
4D cerebral artery morphological analysis
application for the cerebral blood vessels
To support assessment of the risk of rupture of a cerebral aneurysm, it is necessary to visualize the aneurysm
and measure it with high precision.
The 4D cerebral artery morphological analysis application is provided with functions for automatically
extracting a cerebral aneurysm and measuring the longaxis diameter, volume, aspect ratio, and volume-to-ostium ratio (Figure 4).
Currently, clinical research is in progress. It is expected that a change in the wall of the aneurysm during
pulsation can be visualized by performing electrocardiogram (ECG)-gated analysis of the image data acquired
by continuous-rotation scanning and varies over time,
thus making it possible to identify a portion with a high
risk of rupture.
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(a) A series of images showing chronological change in the cerebral aneurysm
(a) 3D image and several cross-sectional images
that allow dynamic observation
(b) Graph showing the relationship between the cardiac phase and the VOR
(change in the dome-to-neck ratio of the aneurysm over time)
Data courtesy of Fujita Health University Hospital
Figure 4. Example of temporal changes of cerebral aneurysm obtained by 4D cerebral artery morphological analysis.
By visualizing and measuring the change in a cerebral aneurysm over
time, it is possible to identify a portion with a high risk of rupture.
4.2
(b) Graph showing changes in the
specified measurement data
during the respiratory cycle
4D airways analysis application for the
chest (bronchi)
Data courtesy of Ohara General Hospital
For the diagnosis of tracheobronchomalacia and
chronic obstructive pulmonary disease (COPD), it is
useful to observe the 3D image of the bronchi in multiple phases during the respiratory cycle.
The 4D airways analysis application is provided with
a function for tracking movement of the bronchi during
the respiratory cycle with high precision and automatically measuring the luminal diameter and cross-sectional area of the bronchi (Figure 5).
It is expected to improve the diagnostic accuracy for
tracheobronchomalacia and COPD by quantitatively
visualizing the change in shape of the bronchi during
respiration, and clinical research using this function is
under way.
4.3
(c) List of the positions (ROI) and
types (distance, area, volume,
etc.) of measurement data
Figure 5. Example of trachea data for one breathing cycle
obtained by 4D airways analysis.
It is possible to measure the change in the luminal diameter and
cross-sectional area of the bronchi during the respiratory cycle.
Because all bones move, it is difficult to recognize an abnormality.
4D orthopedic analysis application
(a) Conventional display method
Among patients who feel pain when they move joints
etc. during daily activities, there are many who do not
show clear morphological abnormalities. In this case, it
may be possible to identify complex mechanical abnormalities causing symptoms in each patient by visualizing
continuous movement. The 4D orthopedic analysis
application is provided with visualization and measurement functions to precisely view an abnormality in a
joint.
In order to intuitively understand an abnormality in
the complicated movement of multiple bones such as a
joint, a display method in which a specific bone is fixed
is more useful than a display method in which all bones
move.
It is easier to view the movements of the surrounding bones.
(b) Display method in which the specified bone is fixed in one space
Data courtesy of CHU Central Hospital (Nancy, France)
Figure 6. Example of 4D data of joint obtained by 4D orthopedic analysis.
An abnormality in movement can be detected more easily by fixing
and displaying the bone specified in advance.
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References
The 4D orthopedic analysis application is provided
with a function in which, rather than fixing the viewpoint and direction in space for 3D display of 4D joint
movement data, the coordinate axes are dynamically
adjusted in advance. They are set to a specified target
bone so that it remains stationary during observation.
This function makes it easier to intuitively identify an
abnormality in complex movement of several bones
(Figure 6).
The 4D orthopedic analysis application is also provided with a function that automatically measures distance
and angle for 4D data of several bones to quantitatively
display changes over time, allowing abnormalities in
movement to be assessed using a quantitative index.
(1) Kimura, K. et al., eds. 1993. “Basic Principles and Clinical
Applications of Helical Scan: Applications of ContinuousRotation CT.” Iryokagakusha (in Japanese).
(2) Saito, Y. 1998. “Multislice X-ray CT Scanner.” Medical Review
66: 1–8.
(3) Endo, M. et al. 2003. “Development and performance evaluation of the first model of 4-D CT-scanner.” IEEE Trans.
Nuclear Science 50 (5): 1667–1671.
(4) Katada, K. 2012. “Evolution of Area-Detector CT.” INNERVISION 27 (6): 62–63 (in Japanese).
(5) Sugihara, N. 2011. “Aquilion ONE and AIDR 3D Technologies.” New Medicine in Japan 38 (12): 92 (in Japanese).
5. Conclusion
The Aquilion ONE development project started more
than 20 years ago with the goal of freely visualizing
motion in the human body. The newly developed Aquilion ONE / ViSION Edition has made it possible to perform dynamic 3D imaging at a lower exposure dose, and
the future vision established at the beginning of Aquilion ONE development is becoming reality.
At TMSC, we have been making efforts to develop CT
scanners that provide faster, more detailed, and widerrange scanning at lower exposure dose.
We will continue to bring innovation to the basic
performance of CT scanners in order to further shorten
scan times, improve resolution, expand the scan range,
dramatically reduce noise, and reduce the exposure
dose. Through such advances, we aim to contribute
widely to healthcare.
KAZAMA Masahiro
Senior Specialist, CT Systems Development
Department, CT Systems Division, Toshiba
Medical Systems Corporation. He is engaged in
the development of X-ray CT systems.
SAITO Yasuo
Senior Specialist, CT Systems Development
Department, CT Systems Division, Toshiba
Medical Systems Corporation. He is engaged in
the development of X-ray CT systems.
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