CBCT Imaging: Discussing the Field of View Concept
OsseoNews is pleased to present this interview about CBCT “field of view” with W. Bruce Howerton, DDS, MS.
OsseoNews (ON): Cone Beam 3-D or CBCT imaging is a very hot topic now, before we get into the topic of “field of view”, could you briefly describe how CBCT represents a major improvement over conventional 2-dimensional dental radiography?
Dr. Howerton: It is very difficult for two-dimensional intra-oral and extra-oral images to precisely replicate the anatomy captured on their receptors. Two-dimensional images inherently exhibit magnification, distortion, and overlap of anatomy. Therefore, measuring or determining anatomical relationships is not accurate. Cone Beam Computer Tomography (more correctly Cone Beam 3-D) captures a volume of data and through a reconstruction process delivers images that do not contain magnification, distortion, and overlap of anatomy. Measurements and anatomical relationships are therefore precise and provide practitioners clear insight into patient hard tissue relationships.
Cross-Sectional Slices – The Power of 3-D
ON: Once a practitioner decides to invest into 3-D imaging, he/she will need to choose a ‘field of view.’ Could you please describe what the ‘field of view’ refers to?
Dr. Howerton: Field of view refers to the area of the anatomy that is captured by the scan. A full field of view on a system like the i-CAT is nearly full skull. The standard, or medium, field of view on these machines and those specifically designed with this view, refer to capturing both arches including the TMJ area and finally, smaller fields of view captures an arch or quadrant of the maxilla and/or mandible. (ON: Please see Image A and Image B below.)
ON: What specialties are more likely to use a specific field of view?
Dr. Howerton: An endodontist may use a restricted field of view to a few teeth, but more commonly practitioners will use the standard or a full field of view that can be collimated, or ‘scaled down’ as needed. As an OMF Radiologist, I most commonly use a standard field of view and smaller fields of view depending on the region of interest. Many oral surgeons and orthodontists prefer the full field of view.
ON: What procedures does the full field of view support?
Dr. Howerton: Orthodontists require craniofacial anatomical landmarks in order to fully plan cases in addition to 3-D images. The patient data can also be used with specialized appliance software and hardware, such as SureSmile. For facial reconstructive and orthoganathic surgeries, full field is necessary to see complete facial structures and anatomical relationships. Third-party software is also available to accurately predict anatomical and occlusal results from orthographic surgery using Dolphin and SimPlant software.
ON: What about procedures served by other the views?
Dr. Howerton: Most practitioners (general dentists, periodontists, and prosthodontists) placing dental implants are interested in acquiring data from the maxilla and mandible. The standard fields of view can be used to capture the temporomandibular joint complex, the paranasal sinuses, as well as the maxilla and mandible. Smaller fields of view focus solely on sections of the maxilla and mandible. For endodontic procedures, a small field is adequate but in the maxillary arch should include a generous portion of the nasal cavity and maxillary sinuses. A field of view should be chosen that captures the regions of interest and prevents multiple scans at smaller fields of view.
ON: Are there any potential liability concerns for working with a full of view?
Dr. Howerton: There is a great deal of discussion about 3-D information liability. One has to remember that as dentists, our goal is to provide the best patient care, whether that’s for 3-D or 2-D radiographic diagnosis. It’s more an issue of ‘being responsible.’ If a dentist feels he or she is not qualified to read the entire scan, the issue is solved by having a qualified oral and maxillofacial radiologist review the data. It’s a nominal fee and one that very few patients will regret paying for.
ON: Does a medium or small field of view produce less radiation exposure to the patient than a full or extended field of view?
Dr. Howerton: Yes, but different machines yield varying amounts of radiation, even with the same scan area. Also, some smaller fields can yield nearly as much radiation as a standard field depending on the spatial resolution chosen. Dentists should take consider radiation exposure levels when selecting a system. And as with any radiographic examination, dentists must consider risk vs. benefit of the exposure and the information it provides.
ON: I hear about traditional and reconstructed pans that come from 3-D imaging machines. Can you explain the difference?
Dr. Howerton: A 3-D panoramic image is reconstructed by imaging software from the acquired patient data. It looks similar to a traditional pan but because of its 1:1 ratio, the 3-D panoramic image does not have the distortion of traditional 2-D panoramic images. An advantage of some machines is that a traditional panoramic image can be acquired without acquiring a full data set and without changing physical receptors on the machines. Therefore, these machines can be used to acquire a traditional panoramic image or a complete scan data set depending on the patient’s needs.
ON: Do you have any advice you would give to dentists who are considering 3-D Cone Beam technology for their practices?
Dr. Howerton: Investigate three-dimensional information thoroughly before making a large financial investment. If you’re going to invest in 3-D technology, make sure it’s true three-dimensional imaging processing, and not a machine that delivers reconstructed tomography that can’t grow with the practice.
Consider functionality of the system: low radiation, fast scan and reconstruction times, and compatibility with third-party software.
Use the fields of view and spatial resolutions that are appropriate for the task by taking advantage of quality continuing education about all that 3-D can offer you and your patients. Finally, wade through the hype and become involved with a manufacturer that has a trustworthy history and a current service history that will aid in updating software and maintaining image quality.
ON: Thank you Dr. Howerton for your time and for sharing your expertise.
About Dr. Howerton
Dr. Howerton received a DDS degree from the West Virginia University School of Dentistry in 1985. He completed a Certificate in Endodontics in 1987 from The University of North Carolina School of Dentistry. In 1999, he entered the UNC Oral and Maxillofacial Radiology graduate program and completed the Master of Science program. In addition to becoming an oral and maxillofacial radiologist, he became proficient in Web development and discovered novel forms of content delivery using authoring software. Dr. Howerton is a Diplomate of the American Academy of Oral and Maxillofacial Radiology. In 2003, Dr. Howerton opened Carolina OMF Imaging in 2004 in Raleigh, North Carolina. In 2006, he began co-heading the educational efforts at the i-CAT Imaging Institute, also in Raleigh.
