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Spectrum February 2009
Coned beam imaging – a new imaging modality
for cranio-facial imaging (non peer reviewed)
David Regan and Andrew Collins
Collins Street Radiography, Level 6, 15 Collins Street, Melbourne Victoria
Cone beam CT images and 3-D reconstructions
Imaging professionals who have been exposed to medical CT
imaging will most likely have encountered a third party software program called Dentascan. This package was specifically
designed for the use of dental specialists to further investigate
pathology demonstrated on OPG films and for implant therapy
placement as well as a number of surgical applications.
A new modality has been emerging – Cone Beam CT and
practicing radiographers may encounter this new modality in
their professional working lives.
The authors were fortunate enough to attend the first Coned
Beam Symposium on the Gold Coast in August 2008. The
Symposium featured presentations from a range of professionals
including Prof William Scarfe who is qualified in both the fields
of dentistry and radiology.
One of the key benefits of CBCT imaging is the reduction
in radiation dose when compared to CT scanning. In addition
to the reduction in radiation dose, the CBCT also benefits from
a reduction in artefactual image degradation because the use
of new “coned beam technology” and allows the radiologist to
report in real time using volumetric data.
What are coned beam CT scanners?
These scanners are designed specifically for examining faciomaxillary anatomy and can also be used to image sinus pathology, for the imaging of the mandible and maxilla and for the
planning of implant therapy placement.
Dentists have embraced this technology because it allows for
multiple 3D images of their patient with a dose slightly higher
than an OPG film.
These units generally employ a flat sensor panel – typically
20–30 cm with greyscale resolution of 14 bit yielding a voxel
size of 0.10–0.4 mm. Interestingly the effective dose is typically
30–90 microsieverts because of the pulsed exposure.
Vendors supplying these units include Hitachi, Kodak,
Imaging Sciences and Planmeca. They are expensive to
purchase and generally require the services of a regular
software engineer to keep them running well. The unit has
an acquisition computer which acquires the data during
the scan and a reconstruction unit which produces a three
dimensional image. CBCT units are extremely accurate and
provide point to point measurement in any plane within the
volumetric volume.
Common clinical applications
Dentists who provide implant services for patients will refer
patients for CBCT scans to evaluated the quality and quantity of
bone in the mandible and maxilla prior to the implant procedure.
Dental Implants are titanium screws that are bio-compatible
with human bone. They are placed in a site, left to heal and
finally a prosthetic crown is attached to the implant.
Spectrum February 2009
The Institute
Images from CBCT scans are printed out on paper rather
than laser film at a 1:1 ratio so that templates with implant
shapes can be placed over the prints. Dentists are also provided
with a radiology report to exclude any incidental pathology or
abnormal findings. Similar to medical CT patients, referring
practitioners may also be provided with the patient data set on a
CD as there are a number of dental software programs compatible with the data.
Other common applications of CBCT include the image
of the temporo-mandibular joint(s), which were historically
imaged using OPG, the tomogram and the transcranial projection. The data collected during a CBCT can be used to produce
a real time series of images of the joint that can be demonstrated
as an AVI movie file.
Conclusion
CBCT is a new and exciting technology, which produces
high-resolution 3D datasets of the mandible and maxilla
with reduced radiation exposure. As installation of CBCT
increases in Australia a new area of practice in dental
imaging will emerge requiring the radiographer to have a
thorough knowledge of cranio-facial anatomy, pathology and
3D imaging software. The authors have found this challenge
very rewarding and exciting, because increasing our knowledge is a wonderful thing.
References
1 Scarfe William C. Professor Towards Voxel Vision Clinical
Applications of Coned Beam imaging in Dental Practice. August
2007 Melbourne Seminar and first Australasian Dental Cone Beam
Symposium August 2008.
2 Farman Allan G. Comparative dosimetry of dental CBCT devices
and 64 slice CT for oral and maxillofacial radiology 2008. 106 (1).
Cone beam device
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