Monday, December 31, 2012

Cone-beam CT’s, not just for Cone-heads.

Cone Heads was a major hit movie in 1993

Cone-beam CT (CBCT) is making silent inroads into several practices by replacing certain technologies and providing better functionality as well as opening up new applications. The initial application was for dentistry, but it has spread its wings beyond that application. This article explains the basics of CBCT and lists a couple of integration issues you might need to be aware of.

How does it work? Well, as it name already reveals, the system uses a cone or pyramid shaped X-ray beam. As the name implies, it uses a cone shaped X-ray beam that goes through the object to be imaged and hits a digital detector producing an image. Except for differences in beam geometry, it operates very much like a conventional CT scanner. In contrast, the conventional CT has a fan-beam that results in a thin axial slice while the cone beam CT creates a 3-D object.  A CBCT might produce several hundred views while rotating 360 degrees in a single scan which might take 10 to 30 seconds to acquire.

Typical dental conebeam system
Compared with conventional radiography, such as a panoramic X-ray, the resulting images have less distortion, and compared with a conventional CT scan, they have a much higher spatial resolution, i.e. less than .01 mm, which allows for much higher precision that is especially important when creating dental implants. This higher resolution is mainly due to the smaller Field of View (FOV), ranging from 5 cm to 15 cm. The contrast resolution however, is much worse than for a conventional CT, due to several factors but mostly because of the high impact of the scatter radiation. The scatter radiation is typically characterized by the scatter to primary radiation ratio, which is typically .15 for a conventional CT scanner, but can be as high as 2.09 for a CBCT scanner.

The dose for a CBCT scan could be 5 to 100 times higher than for a conventional panoramic X-ray, but is at least 5 to 100 times lower than a conventional CT scan. This wide range is due to a wide range of dose delivery based on the field of view, collimation, and design differences among manufacturers. The cost is also definitely higher than for a conventional X-ray unit, as these devices cost at least $100,000, which might be a little bit hard to justify for a regular dental practice, which in many cases is barely able to afford a digital system to replace conventional byte wings.

O-Arm: cone beam CT for spine imaging
However, many years ago people would not have imagined that CT would now be the standard of care. In many ER’s, trauma patients are by default getting a CT scan, especially when there is any suspicion of head trauma. This is despite its higher cost and much higher dose delivery compared with a conventional X-ray. The same could happen with dentistry, where the panoramic X-ray units might start to be replaced with these CBCT systems, which is a scary thought. The scary part is that dentists are not really trained (yet) to interpret these types of images and do not have experience with radiation safety measures for their patients and staff. This is especially true if these systems are installed in a non-dedicated room, but, rather in a hall way or closet.
Dentistry is not the only application for CBCT systems, the high precision and portability also allows for ENT specialists to better image the inner-ear with its intricate structures. There is a also a dedicated CBCT system which allows for spine imaging, especially for spine surgery applications, which is referred to commonly as a “O-arm,” in comparison with the popular C-arms. There is a CBCT developed for extremity imaging as well. The latter allows one to stand up and therefore to image joints while carrying its person’s weight.
Extremity Imaging

With regard to integration, all these systems have a DICOM output for storing the images in a PACS or enterprise imaging and information system, and a worklist allowing these procedures to be scheduled in an information system or CPOE (Computerized Physician Order Entry) system. Scheduling might be a little bit tricky as the scheduled procedures have to be mapped by the modality worklist provider or broker to a specific station AE title. The dose reporting for these systems also is lacking as most CT scanners are starting to create the so-called DICOM structured reports to register this information because there are still changes that have to be incorporated in the DICOM standard to facilitate this specific geometry for dose reporting.

In conclusion, there are a few challenges with regard to implementing and integrating these systems, and the standard still needs to catch up with regard to dose reporting, but there is no question that these devices are here to stay and will increasingly be implemented in your enterprise systems. Therefore, it is time for support professionals to get ready and learn as much as they can about this new technology and be prepared to implement them. I myself learned a lot about this technology from my fellow DICOM expert Dr. Allan Farman who co-authored an excellent tutorial about this technology (see link).