What’s the best CBCT for my practice? Part 1 – Field of View (FOV)
I often get asked this question by so many doctors during CE, seminars or presentations that I thought it would be best to write about the different things a doctor needs to consider before purchasing a CBCT for their practice.
To make it easier, this subject will be divided into smaller parts (posts) for easier reading and to also makes it easier for me as shorter multiple posts are more manageable than a lengthy post.
So let’s get started!
Part 1 – Field of View (FOV)
Rightfully so, a Cone Beam CT (CBCT) is a significant investment for a dental practice. The cost of CBCT machines have come down quite a bit since early 2000. This is driven by technology improvements, lower manufacturing costs, and more competition from CBCT vendors all competing in the market. That’s great news for us doctors!
Yet, those machines still cost tens of thousands of dollars —anywhere between $70,000 and $250,000.
The CBCT buyer doctor needs to make sure to cover different things and learn as much as he/she can about CBCT before taking the leap and making the switch to 3D imaging. It’s better to spend more time learning different aspects of CBCT imaging and what your practice needs are than feeling sorry later.
The main cost of a CBCT is the imaging sensor which is what captures the X-ray photons to generate the image. It’s the heart of a CBCT, if we may say. Similar to a DSLR camera, full frame sensors are more expensive than smaller sensors (APS-C) or Point and Shoot cameras. Larger sensors can capture more light photons and greatly improve signal to noise ratio for night shooting.
In CBCT, the story is a bit different. Sensor size dictates how big your image volume will be. In other words, how much of the patient’s head can be captured at a time.
The larger the CBCT sensor the larger the final FOV is going to be and the higher the cost of the machine will be. That’s why choosing the right sensor size is crucial and should be at the top of your list.
FOVs in CBCT can be divided into small, medium, large and extended fields of views.
For endodontics, a small FOV is quite sufficient as we’re concerned with a single tooth or few teeth. Small is around 5 x 5 x 5 cm (width, depth, and height)
For single site implant, small is usually enough, but if you’re thinking you’ll be doing multiple implants then medium FOV makes more sense. More on that later.
Medium / large FOV CBCT machines can collimate the X-ray beam to different smaller FOV volumes via the CBCT software. So even if you want to scan a tooth you don’t have to scan the entire head. This reduces the radiation dose to patients and improves the image quality as smaller FOV generates less scattered radiation which increases noise in the final image volume and reduces image quality.
Medium FOV can capture both jaws at a time excluding the temporomandibular joint (TMJ). However, TMJs can be scanned each separately if needed.
Medium FOV is perfect for most general dentistry work. The image volume is around 8 x 8 x 8 cm.
Large FOV is usually preferred by oral surgeons. It’s used for pathology evaluation, surgical evaluation and planning, sleep apnea studies, and TMJ evaluation. We’re looking at around 15 x 15 x 15 cm image volume.
The extended or extra large FOV is reserved mainly for orthodontics as it can capture areas outside the maxillofacial region including sella turcica and base of the skull.
The image volume is around 20 x 20 x 20 cm.
These numbers are average and some orthodontists can still use large FOV for their work but in general these are the main categories, so to speak, for different uses of fields of views.
Final thoughts, some small FOV machines allow the practitioner to stitch multiple image volumes together to get a single large volume. However, these can increase radiation dose to patients, use extra time to capture and stitch and sometimes the volume doesn’t get stitched properly. So it’s a good option to have, but if you think you’re going to do a lot of stitching then you’re better off going with a larger field of view machine.
Keep in mind that smaller volumes usually have better image quality due to less scattered radiation and smaller voxel size. Smaller volumes have less file size so they’re easier to work with in a computer, less liability for the image volume reading since it’s smaller, less radiation does to patients, and in case you forgot, they’re cheaper!
Lastly, even though some large FOV machines can generate small FOVs by collimating the X-ray beam a lot, the resulting image quality for the smaller FOV is inferior to a volume generated by a dedicated smaller FOV CBCT, for reasons we don’t have the time to explain here.
Comments? Feel free to write below and we’ll be happy to help. If you need a professional consultation to help you choose which CBCT machine is good for your practice needs, drop us a line in the contact us form on http://www.marcilan.com and one of our radiologists will be happy to assist you with that.