What is cone beam computed tomography?
Cone Beam Computed Tomography (CBCT) is an imaging technique that is widely utilized in human medicine.
Its unique characteristics make it especially suited to the fields of orthopedics, image-guided radiation therapy, interventional radiology, maxillofacial surgery, and dentistry.
Still, its benefits are only just starting to be realized within the veterinary world. CBCT is capable of producing detailed 3D images that are proving particularly suited to a range of veterinary applications such as maxillofacial surgery (especially trauma), dentistry, imaging of exotic species such as rabbits, and for orthopedics, in particular, imaging of joints and extremities.
CBCT is a specific form of Computed Tomography (CT). As with regular CT imaging, CBCT utilizes a moving beam of X-rays that are detected by a digital X-ray detector.
A series of images are obtained from various angles around the patient which can then be used to generate a 3D image using complex algorithms via specialist computer software.
The main difference between CBCT and regular CT, as its name suggests, is that CBCT utilizes a divergent beam of X-rays which form a cone shape. This allows the X-ray beam to cover a larger area in a single pass.
Regular CT machines in contrast take “slices” through the patient using a flat fan-shaped beam of X-rays that require several passes over the area of interest to acquire sufficient information.
What are its advantages and disadvantages?
The specific characteristics of the CBCT system mean that it has the advantage of being faster than a standard CT scan and exposes the patient to a lower radiation dose due to only a single pass being required to produce an image.
In addition, CBCT machines tend to be smaller and less expensive to purchase, making them more accessible. The images produced by CBCT can also show substantially superior spatial resolution compared with regular CT.
This means that images are clearer and more detailed, allowing better visualization of small structures and abnormalities, particularly within bony tissues.
There are however some disadvantages to the technique. Due to the shape of the beam and the lack of collimation, CBCT scans tend to produce more scatter radiation.
The consequence of this is inferior contrast resolution in soft tissues - meaning that subtle lesions of soft tissues, resulting in only slight differences in contrast, are more likely to be missed.
The scatter also increases the radiation exposure in the surrounding areas and potentially to operating staff. This scatter is amplified when CBCT is used for larger body parts such as the thorax or abdomen.
For these reasons, CBCT tends to be used for smaller body areas such as the head and bones, particularly the extremities. It is beneficial for imaging exotics and their dentistry.
Why is it important to use contrast in CBCT?
The use of contrast is common in many imaging modalities to further enhance and widen their application.
CT typically uses non-ionic contrast media (e.g. iohexol), commonly injected intravenously but can also be injected directly into a body cavity under investigation, such as a joint space.
Contrast is used to highlight specific areas of interest, especially those that may be usually hard to see. In CBCT, iodinated contrast media that are injected intravenously will highlight vessels and soft tissue structures supplied by these.
This has the potential to increase the diagnostic utility of CBCT massively.
The addition of contrast studies in addition to plain CBCT scans is crucial as it will both provide additional information and overcome some of the limitations of the technique.
In orthopedic examinations, the addition of contrast by direct injection into the joint provides high-resolution images of the articular surfaces aiding the assessment of lesions found in degenerative joint disease for example.
In dentistry and maxillofacial surgery, intravenous contrast techniques that highlight blood vessels allow the surgeon to assess vascular structures better and in particular any abnormalities of the vasculature that could be potentially affected by any planned procedures.
Contrast also improves the ability of CBCT to detect and assess soft tissue lesions, for example, neoplasms presenting at an early stage.
Cone beam CT is a relatively new diagnostic modality in the veterinary world.
However, its unique properties and affordability mean that it is likely to be more widely used in the future.
Contrast techniques can greatly increase the range and accuracy of diagnostic procedures possible with these systems and these techniques will likely continue to develop, offering new and exciting opportunities.
References:
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