lesions that only show up on 3T MRI

[iambus]

I was wondering if anyone knows the science behind why some lesions will show up on a 3T but not 1.5T MRI.  (my best guess)=Is it because the lesions "are new" and not big enough to show up on a 1.5T, are they a different kind of lesion or is there another reason? Just curious.  I'm in limbo land and trying to justify spending more money getting an MRI done on a 3T.  My MRI on a 1.5T was completely clear.

[anon07072023]

Hearing Jen's experience with the 3T compared to the 1.5T is enough for me to want to get a 3T MRI.  I've asked for one at least twice, but my neuro has never ordered the 3T for me.  I do have lesions in my brain & spine on the 1.5T, but I know that they'll see more in my spine for sure on the 3T.

-Kelly

[iambus]

Yeah I had a c-spine and t-spine done on a 1.5T and it was clear (other then spinal cord compression from a herniated disc).  Not sure if I should try to get another MRI done on a 3T or not.  I feel like most likely it would come back clear but ya never know I suppose

[COBOB]

It is kind of strange, but once radiologists find the lesion on the 3T if they go back and look at the 1.5T they will see the lesions most of the time.  The lesions are there, but just don't seem to "jump out at them."  There are other sequences MT-MRI (Magnetic Transfer) and STIR (Short Tau Inversion Recovery) that seem to show lesions far better than T2 and FLAIR, but are rarely used outside research centers.

The odds are that if you have 5 brain lesions on a 1.5T you will have 6 on a 3T, so there is not a huge jump in detecting brain lesions.  Now, spinal lesions are a bit different.  It is not the volume of lesions, but the initial detection of lesions where 3T MRI helps out.  Have they done your c-spine and t-spine?

It really depends on your docs.  I have 5 lesions (and holding,) but two rounds of ON and one of TN.  The numbers for i case of ON with 2 or more lesions say that 51% of patients will go on to develop Clinically Definite MS (CDMS.)  Two cases of ON in the same eye with a negative NMO antibody are pretty rare outside of a demyelinating disease.  So my docs are kind of going where the statistics take them.

Bob

[iambus]

but how come some lesions need a higher MRI scanner to be seen?  What makes then not show up as easily as other lesions (maybe this is a stupid question.  But I'm just frustrated about having a lack of diagnosis due to every test being negative (well haven't had an LP or VEP or any of those kind of tests but negative MRI and negative blood work for everything imaginable)

[COBOB]

The toroidal magnet (the ring around the bore) is stationary.  The RF generator changes the spin of the water molecules and the hydrogen protons.  On a 1.5T, the T1W and T2W sequences are fine.  FLAIR is a version of  T2W sequence.  Many centers also do FSE (Fate Suppression Echo,) Fast Echo and Turbo Echo.  When you get to 3.0 T units T1W and T2W are too much exposure for people under about 200 lbs.  so most centers just do T1* and T2* (Gradient Echo studies.)

They work, but there is less spin to work with, so some of that additional signal gets lost.

Bob

[jensequitur]

Thanks, Bob!  That makes a lot of sense.  A lot of MRI technology seems to be about number crunching - different ways to spin the magnet, or how fast to spin it, or when to turn it off and turn it back on.

So is there any point to doing T1 and T2 sequences?  What about FLAIR?

[COBOB]

Well, the explanations so far are partially correct.  The magnetic field is twice as strong, but that doesn't mean much.  The main effect is that doubling the magnetic field strength doubles the Hydrogen Proton Larmor Frequency and improves the radio frequency (RF) signal to noise ratio when the MRI listens for the signal of the spinning Hydrogen Protons.  A 1.5T MRI has a Larmor Frequency of  63.87 MHz, a 3T is 127.74 MHz    Some sequences also use RF energy to change the "cross product" of the spin.

The magnet spins and relaxes the Hydorgen proton spin that is it.  It is a technique called Larmor precession.  See: http://en.wikipedia.org/wiki/Larmor_precession  The spin of hydrogen protons in a dipole molecule (thing H2O - Water) is louder than say a lipid molecule.  So the higher frequency increases the signal to noise  (S/N).  The magnet pulses on to spin the water then shuts off so the RF receiver can listed to the spin signal. and it pluses back on and off.  This increased S/N makes the higher resolution data set for the software to turn into a picture.  These 3.0T machines also have better software and more advanced techniques beyond T1*, T2* and FLAIR.  

So, the "twice the power" is true, but it is the double the Larmor Frequency that makes the imaging difference.  That and the improved software. Even for the improvements in S/N, the doubling of the Larmor Frequency only improves brain lesion detection by 20%.  In the spine, it may be better than that, because there is less water than in the brain, and the smaller number of Hydrogen Protons should improve the signal gradient.

So 1) Larger Larmor Frequency 2) Better software 3) improved sequences.
The downside is that You can not do T1W or T2W studies on most of the head, neck, and back with a 3.0T magnet. It would exceed the FDA SAR limits.  So manufactures cheat and do T1* and T2* sequences that use a measure of the gradient (not the full spin, but just a partial spin.)  While the images look better due to improved S/N, there is data lost by using gradient spins.  

Kind of a technical explanation from someone who repaired MRI, CT, SPECT, etc.,  but this "bigger" is better magnet thing is pretty misleading.   By the way, a 7.0 Tesla MRI has a Larmor Frequency of 298.06 MHZ.  

Bob

[jujuminx]

My neuro says 3T makes way more difference when imaging the spine than it does the brain.  Most 1.5T machines plenty good for imaging brain but b/c spine such a smaller condensed area, 3T may be needed.

Since my spinal lesions show on 1.5T I didn't have to decide whether to push for 3T. None on my brain but who knows maybe with 3T they will be seen. At this point since I have dx, it doesn't matter.

Don't think new or old matters as far as lesions being better able to see on 3T vs 1.5T.

Good luck!

Julie

[jensequitur]

A 3T MRI is like the difference between an old digital camera and one of the bad-a** newer cameras.  The photo quality isn't always better, just because it has a higher megapixel rate.  But consistently you're going to get more data with a newer digital camera than one of the old ones.

It's the same with the 3T vs. the 1.5T.  Yes, you can get some great scans from a 1.5T, and enough data to get a diagnosis.  But you're going to get more data from the 3T MRI, hands down.  This doesn't mean it'll show anything, though!

If you're going to ask for more tests, I would talk to the neurologist about an optical coherence tomography test.  This is a scan of the retinal nerve fiber layer of your eye.  It's one of the best ways to measure atrophy of your CNS, doesn't require gadolinium contrast, and costs much less.  

My 1.5T pre-diagnosis showed a lesion in the cerebellum, and a possible (unconfirmed by the radiologist) lesion in the brainstem.  It didn't show anything in my spine.  The 3T showed several lesions in the frontal, the temporal, two lesions in the brainstem, lesions in my cerebellum, and several lesions in the spine.  This scan was taken after I was already diagnosed, so it wasn't like I had to fight for it.

[Lulu54]

Hi and welcome.  The answer is very simple - the 3T (t stands for Tesla, a unit of measurement)  is a larger magnet than the 1.5T machines.  Bigger magnets are able to generate stronger signals from our bodies that are then constructed into images, thanks to the magic of wonderful software programs.

I hope that explains it well enough.

good luck,
Lulu