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The Advantages of Cone-Beam CT Scanners

8 August, 2011 | Cone-Beam CT Scanners

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.

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