How Cone-Beam CT is Superior
Computed
tomography imaging, also known as computed axial tomography scanning,
involves the use of rotating x-ray equipment, combined with a digital computer,
to acquire images of the body. Using CT imaging, cross sectional images of body
organs and tissue can be produced. Though there are many other imaging
techniques, CT imaging has the exceptional capability of offering clear images
of different types of tissue. CT imaging can provide views of soft tissue, bone,
muscle, and blood vessels, without giving up on precision and clarity. Other
imaging techniques are much more limited in the types of images they can
provide.
Cone-beam CT scanner is a compact,
quicker and safer version of the regular CT. Through the use of a cone-shaped
x-ray beam and a flat panel detector, the size of the scanner, radiation dosage
and time needed for scanning are all spectacularly reduced. A typical cone-beam
CT scanner can fit easily into any dental (or other medical) practice and is
easily accessible by patients. The time needed for a full scan is minimal and
the radiation dosage is up to a hundred times less than that of a standard CT
scanner.
What Does a Cone-Beam CT Scanner Produce?
Cone-Beam CT scanners
are continually generating x-ray images, while rotating around the patient. By
rotating the beam around the targeted region and creating an image every few
degrees, the region of interest can be studied from many angles. Then, with the
help of advanced image reconstruction software, the image can be viewed in 3-D
at high resolution.
Cone-Beam CT as Part of a Linear Accelerator
The Cone-Beam
CT system can be a part of the On-Board Imaging technology that is mounted
directly on some specific Linear Accelerators. Cone-Beam CT
produce a highly accurate image of the tumor for final patient positioning
and possible dose adjustments, immediately before the linear accelerator
delivers the radiation therapy. Since the pre-treatment CT imaging and the
radiotherapy treatment are both done on the same machine, the patient does not
need to be move from a CT room or department to a separate area for radiotherapy
treatment. Completing both steps on one machine improves the patient experience,
by reducing overall processing time and assuring treatment accuracy.
Cone-Beam CT in 3D Interventional Radiology
Cross-sectional imaging is a
frequently used tool in most interventional radiology departments, with
CT-guided biopsies and percutaneous drain placements being commonly performed
procedures. However, these procedures are usually performed outside the
interventional suite; in this manner limiting access to commonly used
interventional equipment, while at the same time significantly impacting the
diagnostic CT workflow. In busy radiology departments, this can decrease patient
throughput where procedural complications can lead to significant scheduling
conflicts. In certain types of interventions, there are situations in which both
cross-sectional imaging and real time fluoroscopy are required.
Efforts to develop a robust system for generating 3D data sets suitable for
use in interventional and surgical suites led to the development of several
novel technologies. Made possible by advances in post-processing algorithms,
computed rotational 3D became the first 3D in-suite interventional technique,
allowing 3D rendering of digitally subtracted contrast-enhanced vessels. With
this technology, multiple DSA images at various projection angles are generated
by rotating a conventional angiography unit around the patient.
Three-dimensional image sets are generated using a cone-beam CT backprojection
reconstruction algorithm.
Following shortly thereafter, 3D digital angiography was developed, allowing
3D visualization of high-contrast structure. Current C-arm allows volumetric
data acquisition in a single rotation of the source and detector. Such setup is
ideally suited for imaging in the interventional suite for several reasons. The
system is compact enough to allow mounting on a moving C-Arm, thereby allowing
the patient to remain stationary during the examination. In a single orbit about
the patient, a complete volumetric dataset covering a large anatomic region of
interest is generated, from which sub-millimeter isotropic reconstructions can
be created. The high-efficiency, two-dimensional detectors allow excellent
low-contrast delectability.
Cone-Beam CT Improves Clarity
The increased scatter generated by cone-beam CT
scanner systems, compared to conventional multi-detector CT, accounts for
the most significant differences in image artifacts, decreased contrast-to-noise
ratio and inaccuracies in CT number calculations. Differences in dynamic range
and temporal resolution between C-arm cone-beam CT scanner and multi-detector CT
and the resultant effect on image quality are also substantial.
Patient Dose in C-Arm Cone-Beam CT Scanner
The issue of patient dose in C-arm
cone-beam CT scanner is complex. First, comparisons with multi-detector CT
are complicated by lack of unanimously accepted common dose metric. CT dose
index and the dose length product do not correctly apply to cone beam CT
geometries secondary to the large z-coverage of a flat panel detector. Also, the
dose is non-linear with the central slice getting the highest dose. Secondly,
direct comparisons in the literature are limited by lack of equivalent image
quality in the resultant image sets. Through a 200 degree rotation of the
gantry, the C-arm cone-beam CT scanner generates homographic data sets that have
been shown experimentally to result in patient doses less than that from single
helical CT. However, it was noted in this experiment that spatial and contrast
resolution of the flat-panel detector system is inferior to that obtained with
multi-detector CT.
Cone-Beam CT in Dental Applications
Dental
cone-beam CT scanner is a recently introduced technology which provides 3-
dimensional radiographic imaging, typically as a series of cross-sectional
anatomic views of the area of interest. Two main types of dental cone-beam CT
scanner units are available. The first type of dental cone-beam CT system is
similar in appearance and construction to a dental panoramic tomography unit,
with the patient in an upright position. The second type, of which fewer systems
are available, has the appearance of a small, conventional CT scanner with the
patient lying completely flat on a couch.
Dental cone-beam CT scanning has a wide range of uses in oral and
maxillofacial surgery, orthodontic surgery, restorative work and implant
planning. It can also have applications in skull trauma and reconstruction
cases. An advantage of this technique is that it can provide a lower dose
alternative to conventional CT imaging. However, dental cone-beam CT cannot
replace conventional CT imaging in all cases, as it does not demonstrate soft
tissues adequately enough for all diagnoses.
Source: http://www.medwow.com/articles/
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