1.5T vs 3T MRI of the brain. What's the difference?

August 8, 2013 12:18 PM

What are the pros/cons of using a 1.5 Tesla MRI machine vs. 3.0 Tesla MRI machine for imaging the brain, from both the patient's perspective and imaging perspective?

So... My Dr is having me go for an MRI of my brain & inner ear. It's being used to rule out a possible tumor which might be causing unilateral LOUD tinnitus in my right ear. Onset of this was very rapid and uncharacteristic of someone my age.

I spent quite a bit of time volunteering in a hospital whilst in undergrad and spent some time around the radiology suite there. At the time, 3T machines were just starting to be produced. From the glossy sales lit from the girls in skirts (a.k.a. sales reps) the images were amazing.

So, I'm wondering, for what I'm getting looked at, what's the difference (if any) from what I, as a patient, would experience and what imaging quality differences would there be (if any) between a 1.5T and 3.0T machine. I remember hearing that some places were getting crappier images from the 3.0T machines than they were with the 1.5T and that the ultra-slick images we were given by the salesholes were indeed taken with their 3.0T machines, but the settings used to make those images with those machines weren't practical for normal outpatient imagining use.

posted by OTA to Health & Fitness (8 answers total)

3T is stronger than the 1.5T, that's pretty much it. The 3T is pretty standard now, especially in research, if they are getting crappier images from the 3T is is a software issue that I would be surprised if they weren't fixed. I do research and use a 3T scanner for brain imaging and have been for the past 9 years.
posted by katers890 at 12:32 PM on August 8, 2013 [1 favorite]

You will almost certainly not feel the static field (the 1.5T versus the 3T) by itself. With some scan sequences, a few people will experience tingling or twitching. For example, I get a very regular mild twitch going up the side of my trunk with an anatomical MPRAGE aimed at my head. I suspect this is more common with 3T magnets and their more powerful gradient coils, but I've never worked with 1.5T magnets. In research, at least, 3T magnets are now standard, and I think the same holds in medical imaging. Imaging sequences need to be optimized for specific magnets and image acquisition components (receiver coils). There are literally hundreds of factors that can be potentially adjusted to optimize the resulting images, although 3T generally affords better signal-to-noise ratios and faster acquisition times.

From your perspective as a patient, I think it's a matter of choosing the current standard and relying on the expertise of the technicians and radiologists who are used to the output of that standard equipment. It's not really a matter of "when should I choose 1.5T over 3T."
posted by Nomyte at 12:42 PM on August 8, 2013

The power is directly related to the resolving power - it's analogous to asking, "Should I pic the doctor with the 100x microscope or the 200x microscope?" If the symptom is visible at 100x, it's something of a moot question; if not, clearly only the 200x will do.

And, as has been pointed out, humans really don't get much sensory feedback from the magnetism (assuming all ferrous metal bits have been removed!!! - there have been horrifying accidents when they were not).
posted by IAmBroom at 12:58 PM on August 8, 2013 [1 favorite]

Best answer: We do a lot of MRI's here and have 3 machines, both 1.5 and 3T. There are a lot of variables besides the magnetic field that affect the quality of the scan. What type of coil they use, the scanning protocol, the experience of the technician all enter into it. Furthermore, if you have any sort of implant, there are a few situations where a 3T MRI is not safe, but a 1.5T is (or more commonly, 1.5T has been more thouroughly tested than 3T). And different machines are made with different capabilities, such as the ability to do FMRI or spectroscopy. So while in general, a newer, more powerful machine should be better, that is not always the case. This is especially true of scans of the head, since that was the first widespread use of MRI; any machine should give good images. If I were having an MRI I would be inclined to go with whichever one the technician and/or radiologist recommend. The scan you descibe is very common and they should get good results easily. Hope it all goes well.
posted by TedW at 12:58 PM on August 8, 2013 [5 favorites]

I would want to use whatever machine the radiologist (or magnetologist?) prefers.
posted by gjc at 3:33 PM on August 8, 2013

I wouldn't go so far as saying that it's analogous to a 100x vs 200x microscope -- there are tradeoffs when you go to higher field strengths. We have scans that look great on our 3 T but look like crap on the 7 T (and vice versa). Personally I'd trust my neurologist/radiologist to know whether in my particular case the field strength would make a big difference -- sometimes it will, but often it won't.

I have all kinds of 3 T scans done on me pretty often and I've never noticed any kind of sensation, though the techs recommend that you don't cross your arms in the scanner to prevent tingling. I've never been in a 1.5 T so I don't know how they compare.
posted by no regrets, coyote at 3:56 PM on August 8, 2013

Thanks, TedW and no regrets, coyote. I was generalizing, of course, but the differences no regrets, coyote is seeing are probably due to differences within the machine types, unrelated to the power. I'll stand by my statement that magnetic field strength (Teslas, or T) is analogous to microscope resolving power, because it is precisely so: the least theoretically resolvable distance in an MRI is linearly proportional to the magnetic power.

A 400-hp engine is twice as powerful as a 200-hp engine, but that doesn't necessarily mean a car with a 400-hp engine is faster or better to drive (for every situation) than a 200-hp engine car.
posted by IAmBroom at 10:50 AM on August 9, 2013

Response by poster: Thanks to all who answered! The biggest take-away point I got from this thread, as well as a few radiologists, is the newer the machine, the better.

Apparently 3T machines can be run in such a way (read:quicker/more patients per day) that can make the images inferior to 1.5T machines. Likewise, software almost makes more of a difference than the magnet strength. It's all in how they choose to run/maintain them.

Similarly, not all 1.5T machines are the same, and again newer is better due to the improvements in software.
posted by OTA at 2:14 PM on September 16, 2013