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Cone Heads was a major hit movie in 1993 |
Cone-beam CT (CBCT) is making silent inroads into several
practices by replacing certain technologies and providing better functionality
as well as opening up new applications. The initial application was for
dentistry, but it has spread its wings beyond that application. This article
explains the basics of CBCT and lists a couple of integration issues you might need
to be aware of.
How does it work? Well, as it name already reveals, the
system uses a cone or pyramid shaped X-ray beam. As the name implies, it uses a
cone shaped X-ray beam that goes through the object to be imaged and hits a
digital detector producing an image. Except for differences in beam geometry,
it operates very much like a conventional CT scanner. In contrast, the
conventional CT has a fan-beam that results in a thin axial slice while the
cone beam CT creates a 3-D object. A
CBCT might produce several hundred views while rotating 360 degrees in a single
scan which might take 10 to 30 seconds to acquire.
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Typical dental conebeam system |
Compared with conventional radiography, such as a panoramic
X-ray, the resulting images have less distortion, and compared with a
conventional CT scan, they have a much higher spatial resolution, i.e. less
than .01 mm, which allows for much higher precision that is especially
important when creating dental implants. This higher resolution is mainly due
to the smaller Field of View (FOV), ranging from 5 cm to 15 cm. The contrast
resolution however, is much worse than for a conventional CT, due to several
factors but mostly because of the high impact of the scatter radiation. The
scatter radiation is typically characterized by the scatter to primary
radiation ratio, which is typically .15 for a conventional CT scanner, but can
be as high as 2.09 for a CBCT scanner.
The dose for a CBCT scan could be 5 to 100 times higher than
for a conventional panoramic X-ray, but is at least 5 to 100 times lower than a
conventional CT scan. This wide range is due to a wide range of dose delivery
based on the field of view, collimation, and design differences among manufacturers.
The cost is also definitely higher than for a conventional X-ray unit, as these
devices cost at least $100,000, which might be a little bit hard to justify for
a regular dental practice, which in many cases is barely able to afford a
digital system to replace conventional byte wings.
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O-Arm: cone beam CT for spine imaging |
However, many years ago people would not have imagined that
CT would now be the standard of care. In many ER’s, trauma patients are by
default getting a CT scan, especially when there is any suspicion of head
trauma. This is despite its higher cost and much higher dose delivery compared
with a conventional X-ray. The same could happen with dentistry, where the
panoramic X-ray units might start to be replaced with these CBCT systems, which
is a scary thought. The scary part is that dentists are not really trained
(yet) to interpret these types of images and do not have experience with
radiation safety measures for their patients and staff. This is especially true
if these systems are installed in a non-dedicated room, but, rather in a hall
way or closet.
Dentistry is not the only application for CBCT systems, the
high precision and portability also allows for ENT specialists to better image
the inner-ear with its intricate structures. There is a also a dedicated CBCT
system which allows for spine imaging, especially for spine surgery
applications, which is referred to commonly as a “O-arm,” in comparison with
the popular C-arms. There is a CBCT developed for extremity imaging as well.
The latter allows one to stand up and therefore to image joints while carrying
its person’s weight.
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Extremity Imaging |
With regard to integration, all these systems have a DICOM
output for storing the images in a PACS or enterprise imaging and information
system, and a worklist allowing these procedures to be scheduled in an
information system or CPOE (Computerized Physician Order Entry) system.
Scheduling might be a little bit tricky as the scheduled procedures have to be
mapped by the modality worklist provider or broker to a specific station AE title.
The dose reporting for these systems also is lacking as most CT scanners are
starting to create the so-called DICOM structured reports to register this
information because there are still changes that have to be incorporated in the
DICOM standard to facilitate this specific geometry for dose reporting.
In conclusion, there are a few challenges with regard to
implementing and integrating these systems, and the standard still needs to
catch up with regard to dose reporting, but there is no question that these
devices are here to stay and will increasingly be implemented in your
enterprise systems. Therefore, it is time for support professionals to get
ready and learn as much as they can about this new technology and be prepared to
implement them. I myself learned a lot about this technology from my fellow
DICOM expert Dr. Allan Farman who co-authored an excellent tutorial about this
technology (see link).