From a pure Bayesian PoV, you're better off with a noisy additional observation. At worst it doesn't get much weight.
At a pragmatic level, can't you say, hey here's something thats probably nothing, let's scan it again in 6 months? Why does an MRI necessarily lead to invasive follow ups?
I get that ideally we'd have a crystal ball with 0 type I / type II errors but short of that, why is a noisy predictor bad?
This has been my experience. And I’ve had oncologists echo exactly this. In the words of one: MRIs find too much.
The CT and the PET/CT are the gold standards for finding cancer, finding recurrences, and staging cancer. The trouble is the radiation dose.
MRI provides very inconclusive results. You’ll see something but it’ll be unclear what it is. And often what you see is not even visible on a CT. Or it’s visible on a PET/CT and is showing metabolic activity indicating its cancer.
MRIs are great for certain things like herniated disks in your back. They suck at cancer.
The problem is the specificity of the results and the prior.
A full body MRI by definition will provide detailed views of areas where the pretest probability for cancer is negligible. That means even a specific test would result in a high risk of false positives.
As a counter point, MRS means that you can now MRI someone's prostate and do NMR on lesions you find.
Lets say someone has lower urinary tract symptoms. And is 60 years old. An MRI could visualize as well as do a analysis that would otherwise require a biopsy. With the raised prior you can be quite sure suspicious lesions are cancerous.
Similarly for CNS tumours. Where fine detail. Subtle diffusion defects can mark csncers you couldn't even see if you cut the person open.
No sensible doctor would give you a whole body CT unless there was a very good reason. That very good reason is probably "we already think you have disseminated cancer". That pushes the prior up.
And less so for a PET/CT. Lets flood you with x-rays and add some beta radiation and gamma to boot!
The danger of an unnecessary CT/PET is causing cancer, the danger of an unnecessary MRI chasing non existent cancer.
One caveat is that regular PET isn't so good in the brain - there is so much metabolic activity that everything glows. So I get an MRI Brain to go with my regular full body PET/CT (cancer 5 years ago with recurrence 18 months later, currently NED).
Doctor warned me up front that the odds the images find something that looks weird is high but not to panic because of how many false positives there are when looking inside someone’s body.
While I am happy to report they didn’t find anything serious, I do take slight offense to the following at the top of my results:
Last name, First name: Unremarkable
(Kidding of course but still got a chuckle out of me)
When my brother was at the end of his run fighting cancer he felt a bit under the weather and managed to catch covid so everyone figured he was feeling bad due to that. The PET scan showed he had thousands of small masses converging into the large mass that eventually killed him by cutting off blood flow to his kidneys. His cancer was an aggressive blood cancer that had stood up to conventional and Trial Chemo drugs. There was no way to treat this but other cancers that are less aggressive can be treated at this point and would be treated differently than a single mass.
In a nutshell it’s that level of visibility that makes PET scans worth it.
No offense for me, just confusion. One of the status reports started as follows:
> OptionOfT is a very pleasant 36-year-old gentleman 6 weeks status post left anterior total hip arthroplasty done by Dr. _ on _.
I asked my wife whether I was particularly friendly (I sometimes fail to adjust my demeanor in certain situations).
She said: nah, they write that for everybody.
My father is a part of "full body PET scan every 3 years" program as part of post - cancer treatment, and it worked twice: early detected lung and prostate tumors, both removed.
These treatments are wonderful and it is great that they exist. But many people fail to understand the difference in terms of pretest probability, etc.
I can absolutely see the heavy psychological impact pending biopsy results may have. People are quick to discount these issues when you raise them as a concern, but only if they never went through this stress themselves
People in high risk situations like multiple myeloma, or various metastic diseases, or system conditions are a whole different category and there is clear benefit to screening them.
It sounds like you have had a tough time.
Wrong? I understand MRIs are the standard for certain types of cancer like brain and spinal tumors.
With respect to whole body MRI they can be less effective because it’s not optimized, accuracy can be traded for area.
But as a general statement MRIs do not suck at cancer.
In a full body situation, they are looking for mets, and the uptake of radioactive sugar by the tumors will let a PET scan find them.
If you make a test that always returns true, it would also meet that criteria.
https://www.ranzcr.com/college/document-library/2024-positio...
It’s a great document, I’m an MR tech and we now have something to lean on when we say no to these scans. We can then scan people with problems rather than people with too much money.
> We can then scan people with problems rather than people with too much money.
Right, this is what it's really about. MRIs are a scare resource and providers need to manage cost. Fortunately I can afford to pay out of pocket, but I'm just annoyed that doctors are so irrational about this
To be clear, it's up to a doctor whether or not to do a "needless biopsy". That has nothing to do with a scan.
Avoiding a biopsy that wasn’t needed is a good thing.
You walk into a doctor's office and meet for the first time.
Case 1. You have 3 full body MRIs taken 6 months apart in hand and give them to your doctor. Nobody has opened or looked at the scans yet.
Case 2. You do not have a scan yet
You are claiming case 1 will lead to worse outcomes in expectation. I claim that's impossible because the doctor can simply do the following: Without opening the scans, email them to the world's best radiologist. Tell that radiologist "only reply if it is nearly certain the patient has an operable cancer with the information available"
Now there are 4 possibilities.
Case 1 without cancer: nothing happens
Case 2 without cancer: nothing happens
Case 1 with cancer: you maybe survive
Case 2 with cancer: you die
The only reasonable objection to this is "that's expensive"
Instead you could get thin slices at high resolution of a body site that has issues or is suspected to have them. Do that instead.
Whole body MR is 5-8mm thick slices at low in-plane resolution. A whole body scan has about 512 pixels over a 50-60cm field of view. Usually it’s even less pixels than this.
Something like a knee, or brain is 2-3mm slices, and high in-plane resolution. A knee is 512 or even 720 pixels over 14cm. It’s vastly better. The difference is stark.
A liver scan or other abdominal organ is lower resolution than a joint or brain, but unlike whole body MR is scanned in multiple planes with multiple image weighting (t1 in/out/fat sat, diffusion, t2, t2fs, gadolinium contrast). A liver scan has thin slices.
Whole body scans generally do two coronal images (stir and t1) then call it quits.
For clarity, I’m an MR tech and I can get scans of myself if I want to.
I generally don’t scan myself as it gets messy fast. If I had concerns and for some reason couldn’t get a proper imaging referral, I’d get a scan with small, good coils with high element counts (not body coils like whole body imaging uses) and scan individuals body regions.
The other bit is that no one follows your protocol, everyone looks at the scans, finds reasons to worry. Then you have the choice between unnecessary biopsies and psychological stress.
And I agree most doctors won't do this, but again I blame the doctors and their training
Scans are a tool, doctors are not allowed to use them rationally because it would be too expensive, so they don't use them. With an ideal doctor, patient outcomes would be better with a scan than without one, but my claim is that doctors are not ideal.
No doctor would order a full body MRI just to throw out the result in 99% of cases, because *it's too costly*
This is so obvious it's crazy, our entire world view is misshaped around saving money.
When you walk into a doctor's office, why do they take your blood pressure and temperature? Why do they look at the back of your throat and listen to you breath?
These are all diagnostic procedures with extremely high false positive rates. The reason doctors do these but do not do MRIs is because MRIs are expensive.
If MRIs were free you would get one automatically every time you go to the doctor.
The probability of finding something worth a biopsy is not low, it is high compared to the probability of the patient requiring intervention.
> One study in 2020 found that 95% of asymptomatic patients had some type of "abnormal" finding, but just 1.8% of these findings were indeed cancer.
So a bit less than 1.8% of the time in this study
> Prenuvo's recent Polaris Study followed 1,011 patients for at least one year following a whole-body MRI scan. Of these patients, 41 had biopsies. More than half of the 41 were diagnosed with cancer.
That's 2.0%
Note that this doesn't mean that 1.7~2.0% of people have cancer without knowing it. It could be more:
> A negative scan doesn’t mean you’re disease-free. Some cancers and conditions simply aren’t visible yet or aren’t reliably detected on a one-time full-body MRI."
But also perhaps less, in a way:
> "You're finding something that never would have caused you any problem in your life, and in cancer, we call that overdiagnosis," Vickers says.
It found a weird spot on me that turned out to a pancreatic rest.
The only reason we did the scans were because we were making a significant life decision that we didn’t want to have to backtrack if either got diagnosed with cancer within a year . We knew nothing was guaranteed but we wanted to do some tests.
Is it though? Isn't it possible you could be early-detecting something serious that is much easier to treat now vs when symptoms appear?
There's some support for this view because agressive screening for thyroid and prostate cancers increases the number of surgeries a lot but doesn't seem affect the mortality rates.
Risks from a surgery are non-negligible, if you perform it to treat a low-risk condition it may be a net loss in the end.
So you're technically right about the "early-detecting" part, but the "much easier to treat" step is problematic because it's unclear what a net-positive treatment looks like for low-risk cases. Probably it comes down to yearly monitoring of whatever was detected, not the actual treatment.
Nothing in medicine comes for free—everything is a tradeoff.
It could be. It could also be the cade that you undergo invasive surgery for something that would have never caused you problems within your life. The problem is that cancer isn‘t cancer. Even if it originates from the same tissue, some tumors behave very different from others.
And the few that would kill you and would otherwise not be noticed are so rare that the risk of the procedures on the others is considered higher.
But scanning frequently is overwhelmingly good for the patient. The problem is the doctors. Imagine two possibilities. 1. You scan every six months and a doctor reviews your scans but never tells you anything no matter what 2. You scan every six months and a doctor reviews your scans and only tells you results if you have an obviously growing mass that has a probability greater than 95% of being cancerous
Obviously #2 is better for the patient than #1, but #1 is equivalent to never testing if you ignore cost.
So the actual reason we don't have effect frequent scans combined with effective diagnostic techniques is cost, and doctors cope with this reality by saying clearly wrong things about "over diagnosis". It's a local minimum of the payer/provider dynamic that has nothing to do with scans per se.
Here, you have a tool with a ~100% false positive rate, so if we start administering it to everyone, it will almost certainly cost lives. Botched biopsies, unnecessary treatments, other complications. Not to mention the huge cost that would divert money from other welfare programs. So you need to show that when it actually detects something, it saves at least as many lives. And I doubt that's the case.
Additionally for me, I have a scan that shows what my body currently has. I had something show up that I did get a scope to check out that was a pancreatic rest. No big deal. Now, if I ever have another MRI and somethings is somewhere else, we have a baseline to compare against. Everything is a risk calculation. When I did my MRI, I also had other procedures done like a heart calcium score.
I will get a little more personal. We didn't do it out of the blue. My wife and I decided we want to live on a sailboat. That was a big purchase for us and boats take a long time to sell. We didn't want to commit to such a purchase then 1 year later find out either of us had cancer then we have the stress of cancer and the stress of trying to sell a boat.
I would never suggest everyone do it, but I am happy we did.
You don't need to show that it's possible to avoid false positives. That's doctors being irrational.
You only need to show that it's possible to build a diagnostic system that's better than no testing, and I have shown that already
If you have an growing mass in your body, then if it's cancer, after a year, it might be too late for treatment. Or it may turn out to be nothing: a benign tumor / cyst / fat deposit in an unusual place. Or it may be slow-growing prostate cancer that you can live with for another 20 years, and maybe it's the chemotherapy that will do you in. It's really not that clear-cut in medicine.
To give you have another example: let's say that the risk of appendicitis in people who have an appendix is 1%. And the risk in people who had an appendix removed is 0%. Does this justify proactively removing the appendix? No, because the consequences of complications are much higher than the harm you're preventing. The same applies here: detection, even if 100% accurate, doesn't mean anything. You need to show that what you do with the result actually helps.
With my change: 95% of people who are shown scans have cancer and are treated earlier. 5% of people do not have cancer and get CT scans. 0.5% of people get useless biopsies Without my change: many of those 95% die, the 0.5% do not get useless biopsies
And the beauty of this is you can pick the percentage!
> If you have an growing mass in your body, then after a year, it may very well no longer make a difference whether you treat it or not. Or it may be that you would have lived another 20 years just fine
This is just wrong for many parts of the body. In your brain? Your lungs? Growing for a year between 3 scans 6 months apart? Extremely unlikely to be benign
> The same applies here: detection, even if 100% accurate, doesn't mean anything. You need to show that what you do with the result actually helps.
This is wrong. If you had a 100% accurate cancer detector, fewer people would die of cancer with no downside
When there is low prevalence of a condition, but a non-zero false positive rate of a test, the false positives generated by universal testing can in fact be a net dis-benefit (worry, invasive further procedures, etc) to the patient population as a whole, regardless of cost. This is a well understood statistical phenomenon, and is carefully considered by healthcare systems when advising on testing.
* financial cost vs level of care. A full body MRI costs a huge sum but it is the most detailed non-invasive diagnosis we have for any disease that can lead to earlier therapy. Used as a screening method, does it worth to save one patient in tens/hundreds tests performed? You answer, but public health authorities, health insurances and medical societies are negative.
* MRI shows some minor findings that would never cause symptoms and better not be known to the patient due to the stress they bring and cost of ongoing follow up (eg in the brain small meningiomas or angiomas). This might bring more harm than good and limit their net value.
So that would be 1.71% of people getting a full body MRI catching cancer early.
That seems like an astoundingly good return to me. What does late cancer treatment and lost lives cost? Many times these MRI’s.
If everyone did this, would there be any significant number of late stage cancer discoveries anymore?
Obviously, reducing the cost of false positives is important. But if 1.7% of us have cancer - wow. My guess is that percentage can be tuned up and down by demographics. So maybe there is still an argument against everyone doing it.
Maybe I don't want to look for cancer right now but if I spend $1,000 every 5 years to take an image for later use... isn't that useful?
(for some people that question may not apply, of course, but at a population level it does, and we have population-level questions about effective use of MRI time.). And if there's something better, you should spend it on that and then ask the question _again_. So it could be that getting a whole-body MRI is something like $30k down the list of best ways to spend money for improved health.
I'm not sure what the best use of $1k is from a health standpoint is, just noting that it's good to have a comparator.
Spending 1k on a gym membership and more fresh vegetables would be a pretty high return on investment, if one isn't in shape and eating healthy already.
So if you have abnormal findings in 10% of patients that merit follow-up scans, you can trivially do a series of 3-4 scans without affecting the overall cost too much.
Doctors simply need to get out of the headspace where MRIs are extremely scarce tools of last resort and treat them like we treat blood tests.
A lot of this however is how it is discussed with the patient. Discussions about the likelihood of there being a real issue when something is seen need to be clear and informative without being alarming. 'We did a routine scan and these often show transient artifacts that turn out to be nothing, but in an abundance of caution we want to do a followup' is totally different than 'we saw something we are concerned about and need to do a followup'. How things are messaged really matters.
Treating MRIs the way we treat blood tests would almost certainly result in huge numbers of needless invasive procedures.
https://www.ranzcr.com/college/document-library/2024-positio...
Again, _all_ you need to do is to make a follow-up scan in 1-3 months to see if there are any changes. It's a preventative tool, so unless you have other indications, it's almost always safe to wait for a bit.
And yes, it requires educating patients that sometimes just waiting and doing a follow-up scan is right. And yes, I also have a personal experience with that (I had an "idiopathic lymphadenopathy", aka "we don't know WTF is going on").
But now you've found it you pretty much have to remove it, which has significant quality of life implications.
Age is a big factor in the with/of cancer factor. If someone is 80 years old then there's good chance it won't be cancer that kills them (assuming they aren't already in a late stage).
But if you are 40 and you have cancer, there's a good chance you'll die of that cancer if it's left untreated.
I'm personally of the opinion that cancer screening should happen earlier for younger people and less frequently for older people. Like, if you hit 80, there's really basically no reason to screen for cancer.
Rohin Francis does a good video on it, which you don't have to watch because it has references underneath you can click straight through to (the video is good though): https://youtu.be/yNzQ_sLGIuA
I am frustrated by this because it seems obvious to me that "more data == better" but I guess it makes sense if you think of the scans as having high amounts of noise, and us having a poor understanding of the system we're monitoring (this never happens in tech, of course :)).
Let everyone who wants to pay get their scans! But don’t make me pay for you
2. i can afford the money for the chance of early detection. Many cancers are symptomatic only in the latter stages. It does not hurt to check.
And anyway, you have to die of something so for me cancer would just be a sign that time's up.