How many X-rays, CAT scans, MRI scans of the head is it safe to have?
June 7, 2020 6:57 PM   Subscribe

I have a small history of prior scans (CAT, MRI, X-ray - see below). Would having a routine health/check MRI scan of my brain pose any risk?

My local council has offered me a highly subsidised health-check brain MRI scan, to check for any risk of stroke etc. as I am about to turn 50. In the past I have had one CAT scan for sinus issues (3 years ago) and one head X-ray after an accident (15 years ago). I have also had two routine / health check x-rays of my lungs, one recently and one about 15 years ago.

I know that you're not my doctor, but would having an MRI scan with this history pose any risk? I have no family history of stroke etc. so I am not desperate for this check but it would be re-assuring to know everything is OK. Or is the procedure more risky than any potential threats? Are there any other factors to consider?

Any opinions gratefully received.

posted by mairuzu to Health & Fitness (18 answers total) 1 user marked this as a favorite
Because radiation is not used, there is no risk of exposure to radiation during an MRI procedure. However, due to the use of the strong magnet, MRI cannot be performed on patients with:

Implanted pacemakers
Intracranial aneurysm clips
Cochlear implants
Certain prosthetic devices
Implanted drug infusion pumps
Bone-growth stimulators
Certain intrauterine contraceptive devices; or
Any other type of iron-based metal implants.
MRI is also contraindicated in the presence of internal metallic objects such as bullets or shrapnel, as well as surgical clips, pins, plates, screws, metal sutures, or wire mesh.

posted by irisclara at 7:09 PM on June 7, 2020 [3 favorites]

Having an MRI causes no health risk, unlike X-rays/Cat scans which involve a risk of cell damage due to ionizing radiation. Go ahead and get the MRI!
posted by monotreme at 7:10 PM on June 7, 2020 [1 favorite]

The FDA says that MRIs do not use ionizing radiation and the main side effects are: 1) If you have some metal implants like a coclear implant or stent or something, it can yank them around in dangerous ways, 2) it makes noises which can be loud and can damage your hearing, and 3) it can make you warm. Also 4) if you have claustrophobia, you might find it extremely unpleasant to be in a noisy tube not allowed to move.

If you take any chemicals to increase the contrast in the imaging, those can have their own side effects, but I think the stuff they use is also considered to be quite safe.
posted by aubilenon at 7:13 PM on June 7, 2020 [2 favorites]

Also I encourage you to read that wikipedia article on how MRIs work that monotreme linked to, mostly because it's dang cool.
posted by aubilenon at 7:14 PM on June 7, 2020

Even if there is no direct harm, unnecessary tests can lead to harmful overtreatment.

The UK National Health Service says: Heart disease, stroke risk assessment and lifestyle advice
Screening is not currently recommended.

Choosing Wisely, an organization that works to reduce overtesting and overtreatment, has a page on Screening Tests for Brain Aneurysms: When you need them—and when you don’t. (Most people don't need them.)

So definitely check with your doctor before making a decision on whether to do this.
posted by Mr.Know-it-some at 8:42 PM on June 7, 2020 [8 favorites]

I'm a neuroscientist and I've studied MRI a fair amount and use it in my work. The resources others have linked and referenced are good sources: MRI is quite safe. Basically, for you it's a combination of sitting in a very powerful static magnetic field, which your body is essentially completely insensitive to, and having radio waves pass through your head, which affects your body mostly by warming it slightly. Clinical MRI scanners are equipped with safety systems that will automatically warn the MRI operator if they try to do anything that would cause enough tissue heating that you'd be able to notice it; this is far below the threshold where it would actually be dangerous.

There are a number of different MRI techniques, referred to as "pulse sequences," which differ only in the timing and frequency of the radio waves used. Some pulse sequences are actually capable of mildly stimulating the nerves outside your head, which is unpleasant but not dangerous, but to my knowledge these pulse sequences are only used in research settings and not for clinical diagnosis. (I've actually experienced this when volunteering as a subject for an MRI demonstration -- I requested an unusual pulse sequence be used because I was curious to see the images it would produce, and I experienced some muscle twitching in my back because of peripheral nerve stimulation. It was mildly unpleasant but not enough to make me ask them to stop, and when I told the technician about it at the end she said it was the first time she'd ever seen that. So this really isn't common at all.)

The contrast agents (drugs that are used to help visualize certain structures) that are sometimes used for MRI can pose a hazard if used repeatedly in a short time. The USFDA issued new guidelines on these contrast agents a couple of years ago, and I assume that similar guidelines exist in other countries, but really this only comes up if you're going to be getting multiple MRIs using contrast agents in relatively short time, which isn't a very common case.

On preview, I agree with Mr.Know-it-some that the biggest risk here is probably overdiagnosis. Discovering certain kinds of abnormalities in MRIs is actually quite common, and many (perhaps most?) people with these abnormalities are perfectly healthy and will never go on to develop any actual problems. Aggressive testing can lead doctors to treat diseases that aren't really there, which can do more harm than good due to side effects. Generally speaking, an MRI scan is really only warranted if there's good reason to think that there could be something wrong, so I'd concur this is something to discuss with your doctor before deciding on.
posted by biogeo at 9:02 PM on June 7, 2020 [7 favorites]

On the other hand, having a "baseline" scan of your head could be beneficial should you ever need a diagnostic MRI in the future -- again, something to discuss with your doctor.
posted by biogeo at 9:04 PM on June 7, 2020

The contrast agents (drugs that are used to help visualize certain structures) that are sometimes used for MRI can pose a hazard if used repeatedly in a short time

"Gadolinium-associated plaques" can be a sign of nephrogenic systemic fibrosis, a rare condition and one caused by tissue-specific accumulation of gadolinium, a contrast agent used for MRI imaging.
posted by They sucked his brains out! at 9:17 PM on June 7, 2020 [1 favorite]

The greatest risk is probably that this is an inappropriate and expensive tool to assess your risk of future stroke.
posted by chiquitita at 9:40 PM on June 7, 2020 [3 favorites]

I am a neurologist. An MRI of your brain will tell you/your doctor jack-diddly-squat about your future risk of anything. I agree very strongly with those above that its only utility, in an asymptomatic patient, is detecting incidentalomas -- apparently the most common of all is a pituitary incidentaloma (enlargement of your pituitary gland, seen in ~10% of healthy adults) which then leads to a lot of follow-up bloodwork, quite possibly for the rest of your natural life.

This is frankly a waste of resources, and would be well outside the standard of care in the "gimme gimme" US healthcare system. I assume you are in the UK because of your spelling of "subsidized/subsidised" -- I am amazed that the NHS would sanction something like this.
posted by basalganglia at 3:12 AM on June 8, 2020 [6 favorites]

Thanks for all the responses. The comments about over-diagnosis and over-treatment are food for thought and making me question the necessity of the procedure. I'm in Japan, where this kind of testing seems to be commonplace. As one post correctly mentions, the NHS in the UK would not fund the like.
posted by mairuzu at 6:34 AM on June 8, 2020

Now that I've had my coffee and am less of a grump, this table of radiation safety may be useful to answer the broader question of how much ionizing radiation is safe. The "natural background radiation" column refers to living at sea level (I think) -- background radiation is higher at elevation. This US-based calculator will give you an approximate annual radiation exposure; the advised limit is up to 100 mrem per year from non-background sources.
posted by basalganglia at 9:17 AM on June 8, 2020 [1 favorite]

basalganglia, thanks for weighing in. If I can add a follow-up question that might also help the OP and others looking at this, as well as satisfying my own curiosity: is there ever any clinical value in having a baseline scan of a patient's brain? (Recognizing that the high cost and risks of overtreatment probably outweigh whatever benefit there may be; I'm just curious if that's something a clinician can make use of if it's available, or if in practice you only really need to look for lesions when they present symptoms.)
posted by biogeo at 12:33 PM on June 8, 2020

Fun fact, Japan has more MRI machines per capita than any other country (by a lot - like 25% more than the second-place USA). So there’s basically a ton of excess capacity that they want to use on SOMETHING. In fact as soon as I read this question, I thought, oh, OP must be in Japan.

biogeo, there can be benefit to having a baseline image of the brain - if/when someone develops something like brain cancer or MS, or suffers stroke or traumatic brain injury it can be useful to see what the brain hooked like before. Also in the case of something progressive like MS or cancer it can be useful to say, “oh, you definitely didn’t have any disease five years ago,“ or “this sub clinical dark spot on your scan from 10 years ago might be the beginning of your slow-growing tumor.” But generally speaking it doesn’t seem to be worth the risk of overdiagnosis.
posted by mskyle at 4:05 AM on June 9, 2020 [1 favorite]

I'm going to disagree with mskyle; if someone has a clinical event (new diagnosis of MS, stroke, seizure, etc), I'm most interested in what the brain looks like now as opposed to 5 years ago. An MRI does show evidence of past events through hyper/hypointensities and encephalomalacia, and sometimes patterns of atrophy can be useful (there are some degenerative processes that have a predilection for particular regions of the brain), but knowing what someone's brain looked like last year, or five years ago, or at birth, doesn't change anything about management. Not to mention that people can have clinical events without imaging correlate, and frequently have imaging findings without clinical correlate. And don't get me started on failed localization, where the source of the problem isn't even in the brain, but somewhere else on the neuraxis.

Interpreting an MRI is all about putting radiographic evidence in a clinical context. If you don't have a clinical context to go along with the imaging, and the diagnostic acumen to actually connect the two, all you have is an extremely expensive black-and-white photo.

As one of my mentors used to say: treat the person, not the scan.
posted by basalganglia at 5:28 AM on June 9, 2020 [3 favorites]

Yeah I guess I was thinking about a highly specific situation where an old MRI might inform prognosis more than treatment - when my husband was diagnosed with brain cancer his oncologist was interested in seeing any older scans, if available, because it would be interesting to know whether the tumor had been growing slowly for years or if it had just come out of nowhere in the last three months. But he didn’t have any old MRIs, and it wouldn’t have changed his treatment regardless.
posted by mskyle at 3:12 PM on June 9, 2020

Yup, looking at an old scan could satisfy curiosity (to continue the photo metaphor, like looking at senior yearbook photos from the 1980s), but I would think the appearance of the tumor on the current/initial diagnosis scan/biopsy would give a better indication of the type of tumor and thus prognosis. The slow-growing benign ones look really different from the more aggressive/malignant ones.

Of course, that presumes certain tumor-specific sequences were done, which in turn implies that the radiologist had some reasonable clinical information to be able to choose the most appropriate MR settings. (At one place I worked, everyone's MRI was for "Altered Mental Status" because that was the first/default choice on the stupid alphabetical drop-down list.) I guess what I'm saying is that one MRI really isn't much like another.

Hope your husband is doing ok!
posted by basalganglia at 5:40 PM on June 9, 2020

To add to what basalganglia is saying (and agree 100%), there are a few conditions where someone might have no significant symptoms but a plaque on the MRI that mimics that of MS or something similar.

You're not going to get treated for that plaque medically if you don't have symptoms and you may never develop clinical MS, but your life insurance premiums will sure as hell treat you like you have MS.

It could end up a very expensive scan even if "free".
posted by chiquitita at 5:35 AM on June 10, 2020 [1 favorite]

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