CBCT vs Everything Else


CBCT versus Dental X-ray



Cone beam images provide an undistorted or accurate dimensional views of the jaws. Panoramic images, by contrast, are both magnified and distorted. Magnification by itself is not a problem, as long as one knows or can calculate the magnification factor. Distortion, on the other hand, is the unequal magnification of different parts of the same image. (see Figure below). Due to distortion panoramic images are notoriously unreliable to use for making measurements. 1


In addition, while CT images can provide cross-sectional (bucco-lingual), axial, coronal, sagittal, and panoramic views, a panoramic film provides an image of only one dimension, namely a mesio-distal or antero-posterior perspective. Further, in a panoramic image all the structures between the x-ray tube and the image detector are superimposed on one another. With CT it is possible to separate out the various structures, for example, the left condyle from the right one.


CBCT compared to Tomography

Unlike panoramic radiography, plain-film tomography, if performed with the appropriate equipment, does not result in distortion. Like panoramic radiography, however, it does result in magnification, the degree of which differs from manufacturer to manufacturer. Plain-film tomography provides direct (as opposed to reconstructed) cross-sectional, sagittal and coronal views. The disadvantage of plain-film tomography is that it requires much more chair time than CT. It can thus be especially difficult to do on patients who are unable to sit or hold still for a period of time. Cone beam CT, on the other hand, can be performed within a 10-40 second range, depending on the region being imaged and on the desired quality of the image. Cone beam CT also provides stronger indication of bone quality.


1 (Serman NJ. Pitfalls of panoramic radiology in implant surgery. Ann Dent 1989;48:13–16.)


CBCT versus MDCT



  • Cost of equipment is approximately 3-5 times less than traditional Medical CT
  • The equipment is substantially lighter and smaller.
  • Cone beam CTs have better spatial resolution (i.e. smaller pixels)
  • No special electrical requirements needed
  • No floor strengthening required
  • The room does not need to be cooled
  • Very easy to operate and to maintain; little technician training is required
  • Some cone beam manufacturers and vendors are dedicated to the dental market. This makes for a greater appreciation of the dentist ’s needs
  • In the majority of cone beam CTs the patient is seated, as compared with lying down in a medical CT unit. This, together with the open design of the cone beam CTs virtually eliminates claustrophobia and greatly enhances patient comfort and acceptance. The upright position is also thought by many to provide a more realistic picture of condylar positions during a TMJ examination
  • The lower cost of the machine may be passed on to the patient in the form of lower fees
  • Both jaws can be imaged at the same time (depending on the specific cone beam machine)
  • Radiation dose is considerably less than with a medical CT.





Limitation of CBCT compared to regular MDCT

Lower contrast resolution which means less discrimination between different tissue types (i.e. bone, teeth and soft tissue)



Sample MDCT axial image to compare with Conebeam for contrast resolution Sample Conebeam axial image to compare with MDCT for contrast resolution





3D Color Plot Comparison

Images show a color plot comparing two maxilla 3D reconstructions of the same patient rendered from a conebeam CT and a regular MDCT scanner.




Parameter/scanner

Newtom 3G

GE light speed ultra

Slice Thickness

0.5 mm

1.0 mm

Pixel size

0.25 mm

0.293 mm

Total number of image

60

28

3D processing time

60 min

25 min




*The same experienced imaging processor used best 3D outcome judgments on both models.





Both models were registered together using 4 distinct anatomical structures. A color plot of the deviation between both models is then calculated using the MDCT 3D as the reference model and the CBCT 3D as the test model. Shortest distance was used as the deviation measurement algorithm. Units in Millimeters.