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Dental Health Library Article

3 Dimensional Imaging - Cone Beam Scan Technology


Diagnostic Imaging Progression

Cone Beam Technology Video Demonstration - Galileos
Cone Beam Technology Video Demonstration - I-Cat

Preface

In May 2000, the American Academy of Oral and Maxillofacial Radiology released a position paper on selection criteria for dental implant site imaging. This article was published in the Oral Surgery, Oral Medicine and Oral Pathology Journal.

It clearly recommends “some form of cross sectional imaging be used for implant cases”

For review purposes, the article listed the various types of imaging available today including:
  1. Intraoral radiographs - Advantages “inexpensive, readily available, generally well tolerated by patients, and provide high resolution of the implant site. The disadvantages include nonreproducible imaging geometry, distortions that are inherit in intraoral radiography and lack of cross-sectional information”

  2. Cephalometric radiography - Advantages ”low cost, easy acquisition and ready availability. The disadvantage is that the cross-sectional anatomic information is limited to the midline of the maxilla and mandible.”

  3. Panoramic radiography - Advantages “visualization of many anatomic features, low cost, and availability. Disadvantages include the nonuniform horizontal magnification, the possibility of positioning artifacts, and the lack of cross-sectional information.

All of the previously mentioned radiographs only produce 2 Dimensional imaging.

3 Dimensional Imaging

Cross - sectional imaging is generated by conventional tomography, computer tomography, and magnetic resonance imaging (MRI).
  1. Conventional tomography: “the x-ray beam and film move with respect to each other, blurring out structures not in the desired thin imaging plane. “ “The advantages of conventional film tomography include moderate expense (compared with CT), uniform magnification, cross-sectional views available at any location, and reproducible imaging geometry when used with a cephalostat.” “The disadvantages of conventional tomography include limited availability, and more time needed to produce the images than with standard panoramic radiography. Significant experience and training is necessary to interpret the images.” Additionally they are film based and do not permit the use with CAD treatment planning software.

  2. Magnetic resonance imaging (MRI): “has shown definite potential as a future replacement for CT imaging, with the obvious advantage that it delivers no ionizing radiation. Presently, the cost of a low-field MRI scan is considerably higher than that of CT” (This article was written 7 years ago. MRI is rarely used in implant dentistry)

  3. Computed tomography - Advantages of CT - based systems:
    1. uniform magnification
    2. a high-contrast image with a well defined image layer free of blurring
    3. easier identification of bone grafts or hyroxyapatite materials used to augment maxillary bone in the maxillary sinus region than with conventional tomography
    4. multiplanar views
    5. 3-dimentional reconstruction
    6. simultaneous study of multiple implant sites
    7. the availability of software for image analysis.
  4. Computed tomography - Disadvantages of CT - based systems:
    1. limited availability of the reconstructive software
    2. expense
    3. higher dose of radiation compared with conventional tomography
    4. lack of understanding of the dentist’s imaging needs by the radiologic technologist and medical radiologists who acquire and interpret the CT images
    5. lack of usefulness for implant – interface follow-up because of metallic streak artifacts
In summary, the American Academy of Oral and Maxillofacial Radiology (AAOMR) recommends the use of conventional film tomography for the majority of dental implant cases with computerized tomography reserved for complex or trauma cases.

Currently the AAOMR is revising this position paper. The updated version should be available by the end of 2007.

Advance to 2007

Conventional Computerized axial tomography (CAT-scans) uses a highly collimated fan beam which rotates around the patient. The patient lays supine on a gantry which advances in millimeter increments after each rotation of the beam. There is a slight overlap of each “slice” to allow the image to be reconstructed into other views.

Spiral CT imaging continually advances the gantry which is compensated for by the computer.

Dosimetry

With both machines there is a substantial amount of radiation that the patient receives. A conventional panorex is approximately 6.7 microseverts. A conventional CT is closer to 3000 microseverts…per arch (top and bottom jaw)!

Cone Beam Volumetric Tomography

CBVT is a new technology that allows patients to have the accuracy of CT imaging without the high exposure to radiation and the high cost. The exposure varies from 20-150 microseverts ... a fraction of conventional CT scanning.

Instead of taking “axial-slices” of the patient, volumetric tomography takes multiple images for 14-20 seconds during a single partial rotation around the patients head. Click here to watch an animated Cone Beam scan process.

The x-ray beam is the shape of a cone instead of a fan. The CBVT is specifically designed for use on the maxillofacial area. The area exposed varies by manufacturer. All CBVT's allow the exposure of a single jaw. Most allow both jaws to be exposed simultaneously.

These units are compact and are designed to physically fit into a dental office. They cost several hundred thousand dollars plus the upgrades to allow the processing and storage of very large files. In addition, there is a steep learning curve for the doctor to become proficient with the application software programs.

Once mastered, Cone Beam Volumetric Tomography allows implant dentistry to be practiced at a whole new level. The diagnostic phase includes cross-sectional imaging as recommended by the American Academy of Oral and Maxillofacial Radiologists.

In addition, 3-dimentional reconstructions allow the virtual implant placement and fabrication of surgical guides prior to placing the implant. This increases predictability and virtually eliminates the likely hood of damaging vital structures.



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