Vlog: When it comes to MRI magnets, bigger may be better

On this week's episode of the NeuroOp Guru, Andy Lee, MD, and Elizabeth Fortin, MD, compare the 1.5 Tesla magnet and the 3.0 Tesla magnet for MRI.

Andy Lee, MD:

Hello and welcome to another edition of the neuron guru. I'm here with my good friend Dr. Elizabeth Fortin.

Elizabeth Fortin, MD:

Hi.

Andy Lee, MD:

And today we're going to be talking about comparing the 1.5 Tesla magnet and the 3.0 Tesla magnet for MRI of acute demyelinating optic neuritis. So Elizabeth, maybe you could just tell us the difference between a 1.5 and a 3.0. Tesla. And of course, we're not talking about the car here, we're talking about magnets.

Elizabeth Fortin, MD:

Exactly. So the Tesla is a unit of measurement of the strength of your magnetic field in your MRI. The higher the Tesla number is the highest the signal-to-ratio will be which translates into better image quality and definition. So that's basically what the Tesla is.

Andy Lee, MD:

So with magnets bigger is better.

Elizabeth Fortin, MD:

Bigger is normally better.

Andy Lee, MD:

And what were the results here that we have on this little slide here?

Elizabeth Fortin, MD:

Yeah, so that's actually showing the results of this study, which was a retrospective review of patients diagnosed with the optic neuritis in 2020 in one university academic center. And this slide specifically shows that you have an increased sensitivity of diagnosis, radiographically, diagnosing optic neuritis, with a 3 Tesla as opposed to a 1 Tesla. So if you look at the three columns, the first one is globally the overall radiologic diagnosis of optic neuritis and you see that the difference is statistically significant. If you look at the P up top, there's a higher proportion of patients who had gadolinium enhancement of their optic nerve and also hyper T to a hyperintensity of the optic nerve, which are two signs on MRI of optic neuritis. And so that slide basically shows basically the main results of this study, which shows that you have a higher performance if you use the 3 Tesla, MRI.

Andy Lee, MD:

So what's the downside here? Why not just do the 3 Tesla on everybody?

Elizabeth Fortin, MD:

So that's a good question. Well, first, I think the main issue is access to the 3 Tesla MRI. So I think not all the centers have access to them. Personally, it's harder to get access here to the 3 Tesla. So 1.5 Tesla's are normally what we have around. So I don't know about you what you've been using recently. But it's normally easier for us to get the 1.5.

Andy Lee, MD:

Yeah, so for us, we get what they give us. So whichever machine comes open, first, I don't really get to choose the 1.5 or 3 Tesla magnet. However, I have a patient who had an MRI already, and I know it was a 1 Tesla or a 1.5 Tesla, and it didn't show enhancement, and for some reason I'm repeating it because they didn't do the orbit or they didn't do that suppression, then I will try and do a better magnet 3 Tesla magnet. We actually have a 7 Tesla magnet here at Methodist as well. But we haven't been using it for routine care. Although I think in the future bigger magnets are going to become the standard. Right now. It's just for research purposes.

Elizabeth Fortin, MD:

No, exactly. And I think one other finding that was interesting in that study is that if you do your MRI very early after the onset of clinical symptoms, you might miss the enhancement or the findings on MRI and they showed in there that up to four days new so if you do it within four days, as opposed to after four days, you might miss radiologically your findings. And so sometimes like you're saying it might be worth repeating even just for the time, purpose, the MRI later to see if there's enhancement that appears on your optic nerve.

Andy Lee, MD:

What difference does it make? Who cares if it's clinically acute demyelinating optic neuritis? Would it matter to you if it was a short segment or a long segment of enhancement?

Elizabeth Fortin, MD:

Yeah, well, we've been using it a lot more recently for diagnosing idiopathic versus antibody associated optic neuritis. So I think that's a very good point, that you want to look at how it looks on MRI to base your decision on early treatment of your optic neuritis. So if you have a long segment enhancement, or if you have bilateral involvement or hierarchize involvement, then you might be more aggressive because that these are signs that points toward an antibody associated optic neuritis. So you might want to treat those patients more aggressively. And definitely want to start them on steroids as opposed to if you have just a sort of short segment then this points towards an idiopathic optic neuritis and then you might want to be more conservative. So yes, there's a very you know, it's very important to look at the radiologic appearance of your optic neuritis because this might guide management in the early phases.

Andy Lee, MD:

And what would you think about having a negative No, no enhancement in terms of changing your differential diagnosis, for example, in a young male with a central scotoma. If I don't see the enhancement, I start getting worried about labor. But how much weight are you going to put to it's not optic neuritis if you don't see the enhancement?

Elizabeth Fortin, MD:

So it really depends on how high your clinical suspicion is. First, I rely on clinics more than, you know, radiology. But as this the sensitivity of the MRI is increasing over time like we're seeing that study, almost 98% of optic neuritis were caused by the 3 Tesla machine as opposed to 76 with the 1.5 Tesla. So, it used to be true that you will miss some of your optic neuritis. So there will be no enhancement on your MRI because the imaging has some limitations. But I think over time, this will become less and less true, and you can rely more and more on your MRIs as they get more performance. But you always have to keep in mind your clinic because I think optic neuritis from the get go is a clinical diagnosis and you use the imaging to help you with management.

Andy Lee, MD:

What do you think about this T-2 hyperintensity? Without enhancement? How do you use that? Or do you think that nonspecific?

Elizabeth Fortin, MD:

Well, T-2 hyperintensity you can find in any type of optic neuropathy, I think so if you have even you know, at any one you might find in any type of you know, in the chronic phase of your optic neuropathy is with a lot of different causes of optic neuropathy, you might find T-2 hyperintensity. So I don't use it a lot without enhancement. I always keep my cards up. And I want to consider all the differential diagnosis. What about you?

Andy Lee, MD:

So we have gotten a lot more reports lately with this T two hyperintensity. And now that we have the 3 Tesla, the 3 Tesla is detecting a lot more T-2 hyperintensity from people who don't have anything that's neurotic they had old NAI when a million years ago or they even had glaucoma or some other optic neuropathy. So I don't think it's specific at all, but they certainly are finding it more.

Elizabeth Fortin, MD:

Yeah, absolutely. And I think if you do your MRI later after you know the onset of symptoms, and you might be stuck with only hyperintensity. And then you have to decide if you know the clinic's was really consistent with optic neuritis or not.

Andy Lee, MD:

So Elizabeth, what do you think the take home message is for our audience in terms of 1.5 versus the 3 Tesla?

Elizabeth Fortin, MD:

Well, I think this study demonstrates that there's a higher sensitivity of the 3 Tesla, which isn't surprising at all, but then you need to be lucky enough to have access to it if you want to use it. So I think you still need to rely on your clinical, you know, impression and if you have a negative 1.5. Then like you were saying I think it's a good idea to see if you can have access to a 3 Tesla to confirm your diagnosis.

Andy Lee, MD:

Well, I want to thank you again and thank our audience for joining us for another edition of the NeuroOp Guru.

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