Download HyperSense Enables Shorter Scan Times Without Compromising

Issue Spotlight
HyperSense Enables
Shorter Scan Times Without
Compromising Image Quality
by Kevin King, Senior Scientist, GE Healthcare
All digital images are compressible, meaning that
after transforming the image into an appropriate
domain—for example using a wavelet transform
—some of the information can be discarded with
little loss of image quality. This is the basis of
image compression used to reduce the size of
digital images. MR images are no different. In fact,
studies have shown that MR images might be
as much as eight-fold compressible, with higher
compressibility for vascular images.1
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Across the MR community, there is a
keen interest in improving MR efficiency.
Compressed sensing (CS) is a technique
similar to image compression wherein
it accelerates scans by acquiring
less k-space data and uses a special
reconstruction algorithm to recover
the missing information without an
appreciable impact on image quality.2
While CS differs from parallel imaging
techniques, such as ARC or ASSET that
rely on multi-channel coil sensitivity, it
can be combined with parallel imaging.
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B
The improvement in scan efficiency
reducing the overall scan time without
been refined over the last few years,
from CS can be applied in three ways:
appreciably compromising spatial
and using ASSET and ARC we can
reduce scan time, increase spatial
resolution or image quality. HyperSense
obtain very good results. However,
resolution, or increase volume coverage.
is not dependent on coil geometry and
there is a limitation in how far you can
Compressed sensing techniques
is less sensitive to image artifacts or
push these conventional techniques.”
can also have a benefit of “denoising”
SNR loss at higher accelerations when
images, but it can introduce blurring if
compared to conventional parallel
too much acceleration is used or the
imaging techniques.
image is not sufficiently compressible.
While CS is a powerful technique, the
acceleration needs to be tailored
for specific applications. Intrinsically
sparse acquisitions such as MRCP, fat
saturation or MRA can utilize much
higher accelerations than complex
morphological imaging.
GE Healthcare has developed a
CS technology called HyperSense‡,
which obtains images with randomly
undersampled raw data, thereby
HyperSense opens up new opportunities
to further reduce scan time without a
substantial impact on image quality,
Martin J. Graves, PhD, Head of MR
Physics at Cambridge University
Hospitals NHS Foundation Trust,
and co-author of the award-winning
textbook: MRI: From Picture to Proton
has extensive experience in MR physics
and has evaluated HyperSense in a
number of research applications.
“Compressed sensing is the next
he adds.
Dr. Graves also acknowledges that
the benefit of CS varies by application.
For example, for morphological
evaluations such as proton density
weighted 3D imaging of the knee,
some image blurring may occur when
the acceleration is pushed too high.
An initial technical performance
dimension in image acceleration,”
evaluation in healthy volunteers
Dr. Graves says. “Parallel imaging has
demonstrates that a CS accelerated
3D MRCP acquisition can provide
similar diagnostic-quality information
to a standard 3D MRCP acquisition in
half the acquisition time. This has the
Martin J. Graves, PhD,
potential to reduce motion-related
Head of MR Physics at Cambridge
University Hospitals NHS Foundation Trust.
artifacts and improve efficiency.3
‡At the time of publication, HyperSense and HyperBand are 510(k) pending at FDA.
Not available for sale in the United States. Not yet commercially available in all regions.
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Issue Spotlight
A
Figure 1. 3.0T TOF images on
Discovery™ MR750w. Shown
are collapsed projection
images through the Axial slab
obtained with a 418 x 288
in-plane matrix and 2x ARC
acceleration. (A) Without
HyperSense and a scan time
of 4:25 min. (B) With the
addition of HyperSense factor
of 1.5 and a scan time of 2:59
min. Notice the equivalent
overall image quality, SNR,
and small vessel conspicuity.
A
Figure 2. MRCP images on
Discovery™ MR450w. Shown
are collapsed 3D frFSE images
obtained with respiratory
triggering and a 320 x 320
in-plane matrix and 2 x 1
ARC acceleration. Without
HyperSense and a scan time of
4:53 min (A). With HyperSense
factor of 1.2 and at least a 1:30
min reduction in scan time (B).
Note that the scans were
acquired 30 minutes apart.
B
There is also the possibility to use CS
is a high-performance computing
As CS is brought to market, it will be
to push image resolution higher while
software library toolbox that enables
important to educate users on where
maintaining existing scan times. Dr.
new possibilities for integration of
it can be best applied. Radiologists
Graves believes this application of CS
advanced reconstruction elements
will also need to be aware that the
may be most beneficial in neuro MR
such as HyperSense and HyperBand.
images may have a slightly different
imaging, where clinicians are interested
HyperBand enables the acquisition
appearance than conventional
in morphologic measurements and
of more slices or diffusion directions
acquisitions, Dr. Graves says.
segmentation of the brain. In addition,
within a typical scan. Delivering
Cambridge has also been utilizing
enhanced productivity gains by
CS to reduce the acquisition time
increased image reconstruction speed
for high-resolution quantitative T2
and minimizing workflow disruptions,
mapping of carotid atheroma using a
it is a powerful platform not only
blood-suppressed 3D Cube sequence.
built to support the most demanding
Since HyperSense—and all CS
techniques—is an iterative
reconstruction technique, the
reconstruction time is longer
applications, but also to provide
clinicians with easy access to these
reconstruction algorithms.
“There is a range of potential
than conventional reconstruction.
applications, from the patient who
However, Dr. Graves says the
needs to be scanned as quickly as
benefits far outweigh the additional
possible to generating images with
reconstruction time. GE’s latest
higher resolution,” he adds.
reconstruction platform, Orchestra,
Dr. Graves has seen continued
improvements in GE Healthcare’s CS
technology—from an early research
stage to the US 510(k)-pending
HyperSense. “CS is in its infancy, and
while we see academic researchers
demonstrating the use of CS, the
commitment from GE Healthcare to
extend this technology into product—in
a relatively short period of time—is
admirable,”Dr. Graves adds.
Initial clinical experience
Richard Kijowski, MD, Professor of
Radiology and a MSK radiologist at
the University of Wisconsin School
of Medicine and Public Health, has
Richard Kijowski, MD,
collaborated with GE Healthcare for the
Professor of Radiology and a MSK
radiologist at University of Wisconsin
School of Medicine and Public Health.
evaluation of HyperSense in a clinical
setting. His initial findings, presented
at ISMRM 2016, found that Cube with
compressed sensing (Cube-CS) can
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Cube
Cube-CS
B
Images courtesy of University of Wisconsin School of Medicine and Public Health.
provide a 30% reduction in scan time
partial-thickness cartilage lesions and
images for comprehensive knee joint
for imaging the knee joint without a
subtle meniscus tears. While additional
assessment and allow advanced
decrease in SNR.4
larger clinical studies are needed
cartilage thickness analysis using 3D
to compare Cube and Cube-CS for
segmentation software,” he adds.
“We did a preliminary study on 50
patients with knee pain and found no
difference in diagnostic performance
between Cube and Cube-CS—that
was encouraging. In most cases, there
was no appreciable difference in the
appearance of knee joint pathology
between the accelerated and nonaccelerated images,” Dr. Kijowski says.
“While ARC parallel imaging decreases
SNR, Cube-CS did not.”
However, Dr. Kijowski and colleagues
reported increased blurring on CubeCS images, especially when visualizing
low-contrast structures, which could
potentially decrease the conspicuity of
detecting knee joint pathology, he
sees the potential to utilize CS to
reduce the scan time of current Cube
protocols or to acquire better quality
Cube images by allowing the use
of higher isotropic resolutions and
decreased echo train lengths without
an increase in scan time.
“We acquired 0.5 mm isotropic
resolution Cube-CS images with a 35
echo train length in a 5-6 minute scan,
which is something that could not be
done without the use of HyperSense,”
Dr. Kijowski says. “A single Cube-CS
acquisition could provide high-quality,
high-resolution multi-planar reformat
The full results of Dr. Kijowski’s Cube-CS
study on the knee have been recently
published in the Journal of Magnetic
Resonance Imaging.5
References
1. Maldjian et. al., “Wavelet transform-based image compression
for transmission of MR data.” AJR Am J Roentgenol 1997.
169:23-26.
2. L ustig et. al. “Sparse MRI: The Application of Compressed
Sensing for Rapid MR Imaging.” Mag Reson Med 2007.
58:1182-1195.
3. Reid SA, King KF, van der Wolf-de Lijster F, Graves MJ ,
Estkowski L, and Lomas DJ. Proc. Intl. Soc. Mag. Reson. Med
Navigated 3D MRCP with Compressed Sensing 23 (2015)
1533.
4. Liu F, Rosas H, Holmes J, King K, Peters R, Kijowski R. Rapid
Three-Dimensional Fast Spin-Echo Knee Imaging Using
Compressed Sensing. Proc. Intl. Soc. Mag. Reson. Med.
24 (2016). 1061.
5. L iu F, Rosas H, Samsonov A, King K, Peters R, Kijowski R.
Knee Imaging: Rapid Three-Dimensional Fast Spin-Echo
Using Compressed Sensing. J. Mag. Reson. Imaging.
Published online October, 2016.
Martin J. Graves, PhD, is Head of MR Physics and Radiology IT at Cambridge University Hospitals NHS Foundation Trust. He obtained his PhD from the
University of Cambridge and is a Fellow of the Institute of Physics and Engineering in Medicine and an Honorary Member of the Royal College of Radiologists.
The University of Cambridge is a collegiate public research university in Cambridge, England. Founded in 1209, Cambridge is the second-oldest university
in the English-speaking world and the world’s fourth-oldest surviving university.
Richard Kijowski, MD, is a Professor of Radiology and MSK radiologist at University of Wisconsin School of Medicine and Public Health. He received his MD
from Loyola University, Stritch School of Medicine; completed his residency at Oakwood Hospital and Medical Center in Dearborn, MI; and completed his
fellowship at Indiana University Hospital.
Founded in 1907, the University of Wisconsin School of Medicine and Public Health located in Madison, Wisconsin, is recognized as an international,
national and statewide leader in education, research and service. In 2005, the school transformed into the nation’s first School of Medicine and Public Health,
integrating traditional medical school principles with public health policies and approaches.
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Issue Spotlight
A
Figure 3. Cube (A) and
Cube-CS (B) images show
identical appearance of
a posterior horn medial
meniscus tear (small arrows)
and diffuse full-thickness
cartilage loss on the medial
femoral condyle (large arrow).