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Two discoveries - part one: Juha

Colin Campbell
by Colin Campbell on 31/10/18 18:00
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This week I (we) made two quite startling discoveries related to my work. The first one of these relates to Juha Koivisto who is a post-PhD physicist and research scientist based at the University of Helsinki (also working for Planmeca)

Juha came to my practice to do some stuff, and it was cool stuff.

This week we installed our third CBCT machine having first had a Carestream 9000 in 2009, then a Sirona 3D XG in 2014. On Thursday we installed a Planmeca ProMax Classic into the practice, removing the Sirona machine and selling it on.

Juha came to test things and to measure the dose of the Sirona machine before it was removed. We also made arrangements for him to test two other machines (both Carestream) and obviously the Planmeca.

The reason for this is that I have found it increasingly difficult, in fact near on impossible, to get any reasonable dose data from the companies themselves that I am able to use to compare the machines before I buy. This is a huge problem because it really feels to me now like the companies are actually being evasive in the way they present their dose data.

In 2006 Ludlow provided a study of comparative data of CBCTs and it’s still about the best bit of work out there but it is, of course, now considerably out of date because of the advancements in CBCT and the change in models.

Juha worked with Ludlow.

So, we decided to try to collect information from several different machines in order to provide a comparison and may take this even further from here.

What I found out though, was that one of the most important measurements and figures you can derive is called factor of merit.

The factor of merit is the contrast versus the noise ratio (squared) divided by the effective dose.

This figure gives you a quality of image against the dose required to provide that image and might be the most important figure for anyone looking to purchase a CBCT machine. I had never seen this figure before, in fact I’d never heard of it, never ever from the manufacturers.

If you had a table of these figures for each machine it would allow you to see how much dose it was taking to get a decent quality image (if a decent quality image was possible at all) So you see the point… no point in having a low dose if the image is terrible, no point in having a good dose if the image is massive.

The numbers for this little study, which we hope to get published, aren’t out yet. But here’s the spoiler…

There were two Carestream machines measured: the CS 8100, one Sirona 3D XG and Planmeca (we tried to measure a Gendex machine but couldn’t fit the equipment into it)

By a long way (50% over its nearest rival) the Carestream provides the highest effective dose to the patient, in the region of about 170 microsieverts but I know from experience that the image quality of the Carestream is extremely good.

The Sirona sits at about 130 microsieverts if you place it in the HD mode (about 1/3 of that if you place it in normal mode) but the image quality is much poorer. And so, it looks quite likely that the factor of merit for both these machines will be about the same.

The ultra-low dose  8 x 8cm scan for Planmeca is now at 9 microsieverts.

I will be taking a considerable amount of these and will be reporting back on the image quality but, if the image quality is anywhere near the Carestream quality (and I believe it will be at least that) the factor of merit for the Planmeca machine will be tiny.

If you add into this the ability that the Planmeca software has to reorganise the image to reduce any artefacts from patient movement (the Calm mode) and the artificial intelligence of scan learning that’s coming next, it makes it quite a powerful tool indeed.

Please don’t misunderstand this.

I am not selling Planmeca machines, I’m telling you why I bought one.

I asked Sirona on four separate occasions for the dose data for the 3D XG so that I could present it in my CBCT course and they never ever answered.

I asked Carestream too and the same thing happened.

I asked Planmeca and they sent their head physicist to show me.

That’s quite a different way to do business and perhaps an easy way to do business when you know your product is good. First make your product good and then sell it in the right way.

Watch this space because I will be honest and open about how this goes but I don’t expect to hear from Sirona any time soon.

 

Blog Post Number: 1811

 

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Colin Campbell
Written by Colin Campbell
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