Multidetector
CT and the Future of CT Imaging: Workflow and E-Training
Elliot
K. Fishman M.D.
Professor of Radiology and Oncology
Johns Hopkins University School of Medicine
Baltimore, Maryland
As
we approach the 30th anniversary of the introduction of Computed
Tomography (CT) into clinical practice, CT technology continues
to evolve. In the early years of CT, technical advancements were
typically measured by decreasing scan times and increasing speed
of data reconstruction. Although this increased speed definitely
represented progress, the first truly innovative concept change
in CT occurred in the late 1980's with the introduction of helical
or spiral CT. This technology along with significant advancements
in image post-processing software revitalized CT and allowed the
development of new CT applications such as CT angiography and
virtual imaging. The era of true volume imaging had begun.
Next,
the transition from single detector to multidetector row CT represented
another pivotal event in the evolution of CT imaging. Initially
4 then 8-detector scanners were developed. But, it was the introduction
of 16 detector scanners which has really revolutionized CT scanning.
16-slice MDCT represents what Andrew Grove, Ph.D. (cofounder of
Intel and former CEO) called a strategic inflection point. It
is a change, which is not a 5-10% improvement over previous capabilities
but one that strategically changes the whole landscape of CT.
That is, MDCT 16 with true isotropic datasets promises to further
advance volume imaging. Volume imaging will no longer be considered
as a supplement to traditional axial imaging, but instead, may
now be utilized for primary display and analysis. This paradigm
shift will require a rethinking of many of the core processes
in CT ranging from image transfer and data storage to redefining
the role of CT across a wide spectrum of clinical applications.
For instance, imaging the coronary arteries or peripheral runoff
studies were once considered possible but impractical with 4-slice
technology will soon be a reality. Workstations like the 3DVirtuoso,
which worked so well with single slice or even 4 slice MDCT, find
the volumes of data to be beyond system capability. Workstations
that can handle this larger volume of data and provide real-time
interactivity with these new datasets are needed. Workstations
are no longer a simple accessory but rather, the central core
of processing and display.
VOLUME VISUALIZATION
The
solution to the problem of large volume visualization with 4-
and now 16-slice MDCT is not simply a modification of standard
techniques such as faster scrolling with a computer mouse or roller
ball or novel filming protocols (i.e. film every 5th
or 10th image). Rather, it focuses on the data volume
itself with the understanding that volume acquisition requires
true volume visualization. The introduction of InSpace on the
Siemens Sensation 16 scanners and on the Multi-modality
Workplace
addresses this paradigm shift from axial images to volume images.
These volumes can be represented in a range of formats including
volume rendering, maximum intensity projection, minimum intensity
projection and multiplanar visualization (coronal, sagittal, axial).
InSpace
allows primary analysis of the data volume which is a necessity
given the large datasets as it is no longer practical to review
CT slices on film or even using a film surrogate, the PAC's workstation
or review station. For instance, with a 4-slice MDCT a dual phase
dataset using 1.25 mm thick sections of the liver or pancreas
was composed of 400-500 sections. At that point, it was still
possible, although cumbersome to scroll through these images on
standard workstations. Yet, in fact, most centers reviewed images
at 5mm thickness and 5 mm intervals and at best looked at the
1 mm sections as part of the 3D examination. Regardless, the strategy
of image review is not possible with 16- slice MDCT scanners.
With the use of the Sensation 16 scanner we are performing detailed
CT angiographic work with .75 mm thick sections reconstructed
at .5 mm intervals. The optimal reconstruction interval overlaps
is .25 mm which provides a dataset which is ideal for 3D reconstruction
and multiplanar imaging. If we scan an area like the pancreas
we are typically doing arterial phase images followed by venous
phase imaging. This results in 400-500 individual slices per acquisition.
If you view this dataset on a workstation or film it is likely
that you only reconstructed data at 3 or 5 mm intervals which
means you are looking at between 10 and 16% of the available information.
Although I would agree that in many cases the additional slices
do not change the specific diagnosis, they will often change the
staging of disease especially in regards to vascular invasion.
The concept then that must be understood is the ability to use
a 16-slice scanner in the optimum mode requires changes in how
images are reviewed and analyzed.
IMAGE
STORAGE AND TRANSFER
This
paradigm shift to volume visualization has some challenges to
overcome. Although a solution for volume image viewing has been
addressed with InSpace, the ability to move images through the
radiology department as well as the hospital or health care enterprise
remains a challenge. Similarly, the amount of data generated provides
perplexing problems for data storage and retrieval. Studies that
range in size from 600 megabytes to 1 gigabyte are truly a challenge
that must be addressed. New solutions must be identified and implemented.
The size of the datasets per case make it no longer possible to
use 2.3 or 5.2 Sony storage devices as these hold but a handful
of cases. A new workflow with massive storage is necessary either
as part of the hospital or clinic master plan (institutional PAC's
system) or as a free standing enterprise solution within the CT
environment. These cases typically approach 1 gigabyte when multiphase
imaging is used, so a solution for rapid data retrieval is critical.
Slow network transfer times with limited bandwidth can paralyze
the entire operation. Although this is commonly felt to be a problem
for the Radiology department it is, in truth, a problem for the
scanner vendors. Simply supplying "data acquisition devices"
is no longer enough. Scanner manufacturers also need to address
workflow and process solutions. Siemens seems to have recognized
the future in its name change to Siemens Medical Solutions but
now comes the hard part. Name changes are easy but providing those
solutions that live up to your name is the challenge.
Another
issue that relates to workstations like the Multi-modality
Workplace
is the amount of storage available. These systems typically have
hard drives in the 60 gigabytes range (55 G to be exact). This
is insufficient in an environment where 20-30 cases per day are
in need of analysis whether it be CT angiography, 3D imaging,
virtual colonoscopy or whole body screening. I recently purchased
from Apple Computer a 400-gigabyte hard drive for 700 dollars.
This should be the bare minimum on a workstation with terabyte
probably a better number. Most sophisticated storage strategies
should also be made available for sites like our where we keep
months or years of CT angiographic and 3D online. I would guess
a system with 10-40 terabytes storage is not undoable and would
be cost-effective. This need for massive local storage should
come as no surprise to anyone. Even some of the lower priced consumer
computers by Dell or Hewlett Packard come with 200 gigabytes or
more of storage. A potential problem with some workstations also
is that they have not taken the clinical environment into their
planning process. The databases are not flexible enough to allow
particular particians such that case studies could be divided
by topic (i.e. pancreas, liver) as well as being limited in how
many absolute cases can be within the database. Although some
might be tempted to suggest that a workstation like the Multi-modality
Workplace
was never meant to store cases this is not a real world solution.
As a user I need a minimum of 4-6 weeks of 3D cases, and ideally
at least 3 months.
Another
issue is simply the ability to read a case. If a CT Workplace
or Multi-modality
Workplace
is used as the second console and is dedicated to physician review
then the shared database with the main scanner provides easy access
to current scan data. However, if it is not available than other
solutions like a second CT Workplace or Multi-modality
Workplace
can be use but there will be no shared database. Sufficient network
bandwidth is needed to prevent any bottlenecks in this scenario.
REFERRING
PHYSICIANS
An
area that is commonly overlooked with 4- and 16-slice MDCT is
the impact these changes in technology are having on our referring
physicians. The referring physician is not interested in stacks
of images be they are film or on a workstation. Clinicians demand
rapid access to critical information and images displayed in a
user-friendly environment. 100's or 1000's of images per patient
on film or computer screen on computer disc are not acceptable.
In contrast, an interactive volume display may be the answer.
The combination of a limited number of selected volume visualizations
coupled with the capability of real time 3D rendering should prove
ideal for a wide range of applications. If our personal experience
is any guide, the use of volume displays is immediate, and complete.
The
concept of InSpace or a similar system when available on multiple
workstations or PAC's systems across the enterprise moves us one
step closer to the "virtual" radiology department. That
is, it matters little where the information is acquired, as it
is available for a primary read or review anywhere throughout
the enterprise. This enterprise wide solution is critical to the
radiologist and the referring physicians who would also have access
to the volume datasets. The quality of a volume dataset is of
little value unless the information can be used.
DOCUMENTATION
Documentation
of 3D images or CT angiography can be done in several ways, which
may or may not work in your clinical environment. First of all
they can be filmed on a laser camera like routine CT scans for
example on a Kodak 2180 laser printer. What is perhaps better
in our experience is to film images directly to photographic film
is given directly to the physician or send them to him/her. In
the past we have done this using a Kodak 8650 dyesublimation printer
which makes good quality images at under $3.00 per page. We typically
might give the referring physician anywhere between 6 and 14 images
or 3 to 7 films. Recently a new lower cost camera from Olympus
has been introduced in the consumer market but has proven ideal.
The systems cost around $400 online and produces images of a quality
similar or better than the Kodak 8650, which might cost 20-50x
higher. Individual film cost only $1.60 each. As of this writing
it is our standard of communication in our PACS less environment.
Other
elegant methods of image transfer to the referring physician are
via the web as TIFF or PICT files or via CD's. CD's are especially
useful when studies that incorporate motion such as virtual colonoscopy
is done. An analysis of your own environment is critical in determining
the optimal delivery system.
TRAINING
Another
important aspects of this brave New World of volume visualization
is the challenge of training and continuously retraining staff
radiologists and radiologic technologists and perhaps ultimately
clinicians. Whether this training be on the CT scanner, a workstation,
or on a piece of software that runs on both systems, the process
needs revamping. The usual method of training is for a qualified
company trainer to spend 3-5 days at the site of a new scanner
installation. Additional training may be provided at a central
location where the training is typically didactic with some hands-on.
This scenario has worked reasonably well for nearly 20 years but
is showing its age. A simple mathematical calculation at an institution
like Hopkins is that even a week visit is inadequate. When you
consider our Body CT division has approximately 20 fulltime technologists,
11 physicians who read CT, and 10 fellows and 24 residents who
want to learn CT you can see the dilemma. Hands-on training typically
helps but a privileged few. The majority of users rely on second-hand
training. The same is true with the 3D workstations where much
of the training may be combined with the scanner training. Is
it any wonder that over 95% of radiologists and technologists
surveyed by this author over the past 3 years have been unsatisfied
with their training or workstation expertise.
The
problem then requires new solutions and new teaching paradigm
thinking. The introduction of www.InsideInspace.com in
March 2003 attempts to solve some of these problems. Developed
as a website dedicated exclusively to using the real-time 3D program
InSpace, the site combines technical information, "how to
do it" information, and case studies for use by the users
or potential users of InSpace. There is a question and answer
section for which answer to the most common questions are provided,
as well as an "ask the expert" section which puts the
user in direct contact with program developers, support staff
and radiologists knowledgeable in system performance and clinical
applications. The site will also provide lectures as well as allow
downloadable presets for 3D rendering developed at leading academic
and research centers for users to improve their practice. We believe
this represents the first attempt to create a true users community
within a medical imaging product. It will be interesting to see
how successful the site becomes and whether it becomes the prototype
for other products and applications. The site is free to the medical
community.
CONCLUSION
CT
continues make amazing technical advancements and is currently
enjoying unprecedented popularity based on its substantial capabilities.
These capabilities provide unique opportunities to improve patient
care while at the same time pose unique challenges. As part of
the Siemens Users Meeting, one should strive to achieve a common
understanding of the goals and challenges we all face.
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