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.
You'd have to be massively overexposed to CT or PET scanning to cause cancer, like in the region of spending months being scanned continuously with it at full beam current.
It comes down to the scan and the age.
3 scans for a 1 year old? Strongly associated with cancers later in life. 5 scans of a 50 year old? Less so.
The 1 year old has an 80 year run way to develop cancer, along with cells already set in a state of rapid division, and a less developed immune system.
But the association is quite strong.
https://www.sciencedirect.com/science/article/pii/S0720048X2...
There's excellent reason to think LNT is accurate: at low doses, almost every cell is exposed to at most one radiation event. The dose affects how many cells experience a (single) event, but does not affect the level of damage to those exposed cells. Linearity naturally falls out of this.
To abandon linearity you have to imagine some sort of signalling system (not observed) that kicks in at just the dose we're talking about (not lower, not higher) to allow exposure to one cell to affect other cells.
There's also no good evidence that LNT is wrong. The typical things that are pointed to by anti-LNT cranks are cherrypicked, often involving interim results from studies the full results from which do support LNT, which is evidence it was statistical noise.
Someone being born with no legs is strongly associated with them using a wheelchair in later life.
Why are you giving a one-year-old three CT scans? For shits and giggles? Or because you think they might have cancer?
Maybe a full body MRI once a decade is fine until your 30s, then once every 5 years until 50, then once ever 2 years beyond 50.
The test should scale with the probability of cancer.
The mean effective dose for all patients from a single PET/CT scan was 20.6 mSv. For males aged 40 y, a single PET/CT scan is associated with a LAR of cancer incidence of 0.169%. This risk increased to 0.85% if an annual surveillance protocol for 5 y was performed. For female patients aged 40 y, the LAR of cancer mortality increased from 0.126 to 0.63% if an annual surveillance protocol for 5 y was performed.
So, a just-about-measurable increase, if you pick and choose your values carefully?
You are not going to die from cancer caused by getting a PET scan. This will not happen.
You're going to die of heart disease or as a not-too-distant second in a car accident.
Continuous scanning for months would give a dose many orders of magnitude higher.
https://www.facs.org/for-medical-professionals/news-publicat...
How are they determining "this cancer was caused by the CT scan" versus "this cancer was caused by the cancer we were originally looking for that was there all along"?
Other than comparing population groups, what method do we have?
Why is "We think this person has cancer so we gave them a CT scan and look! Now they've got cancer! It must be because of the CT scan!" the conclusion to jump to?
Not a doctor - but maybe start with some quick & cheap tests of their blood & urine, polite questions about their sexual partners, and possibly an ultrasound peek at things?
At least in America, high-tech scans are treated as a cash cow. And cheap & reasonable tests, if done, are merely an afterthought - after the patient has been milked for all the scan-bucks that their insurance will pay out.
Source: Bitter personal experience.
Maybe it's a regional thing, but that hasn't been my experience. I've had one MRI and one CT scan in the 25+ years that I've been a full-time employed adult with insurance.
I'd have been happy to sign up for more so I could have proactive health information and the raw data to use for hobby projects.
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).
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.
Cute written word - even though two words pronounced completely differently at join (an versus añ).
Which do you pronounce correctly the scan or the anxiety? [scan]xiety or [sk]anxiety
My mum gets scanned a little more frequently than that, following treatment for an inoperable tumour in her lung around five years ago. During treatment she was getting scanned every three months or so, and it was remarkable watching this thing go from the size of a tangerine, to actually expanding a bit and looking "fuzzy" once the drugs kicked in, to being the size of a plum, then the size of a grape attached with a little thin thread of tissue, to being a thing the size of a pea. Now there's a tiny ripple of scar tissue that no-one wants to investigate further, because if it's not doing anything let's not poke at it.
There is a roughly pea-sized "thing" on her adrenal gland that was a bit worrying because anything like that is going to get intimately involved with your lymphatic system and then it's going to metastasise like hell. But it neither got bigger nor smaller in the nearly six years since the first scan, so it can't be that important.
This is one of the great things about the NHS, especially here in Scotland where we have (possibly as a result of the weirdly high levels of cancer) some of the best oncology services in the world.
If we'd lived in the US, the insurance companies would have taken one look at an 83-year-old about to become a grandmother and sent her home with a bottle of morphine to die. As it is, she's doing very well and got to see both her grandchildren start school.
Interesting, I had no idea and just looked this up[0]:
> Scotland had the highest overall incidence (446 for men and 379 for women per 100 000), and Wales had the second highest rate (450 and 366 per 100 000), compared with 394 and 338 per 100 000 in England and 394 and 345 per 100 000 in Northern Ireland.
This would make Scotland rank 3rd in the table on https://en.wikipedia.org/wiki/List_of_countries_by_cancer_ra... .
PS: Glad to hear your mom is doing well!
Thanks, she had little to no side effects from the experimental immunotherapy drug. She'd said at the outset she didn't want to be a "chemo zombie" having been through all that about 20 years ago (she's had four different cancers throughout my lifetime, treatment getting better every time).
It's fucking expensive, but immunotherapy is really a miracle cancer treatment. We're not quite at "Oh you've just got a wee bit of cancer, we can give you something for that if you see the pharmacist on your way out" but we're not far off.
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.
Getting regular scans to track cancer progression is a different matter altogether, since most of the blips can be eliminated over time and there’s a history to compare against.
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.
Then you can just tab from field to field when doing the report.
She said “It’s just not often I hear that here.”
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.
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.
This article is about services like Prenuvo, where the entire point of the service is to get the results of elective scan not related to any symptoms.
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
You're thinking of this as there being an objective positive utility for not dying of cancer and a objective negative utility for biopsies, and there being an objective optimal "rational" tradeoff that the best radiologist can optimize for to get their "nearly certain" detection threshold.
But frankly - the tradeoff for the value of a human life is perhaps the most uncertain thing one could choose. It lies in the eyes of the patient if the worry and time associated with a false detection is worth their reduced chance of death. The ethical uncertainty expressed in the OP - are these unnecessary biopsies worth it - is warranted.
Case 1 without cancer: you're a guy that knows more than doctors because you're the "I have 3 scans on hand guy", so as soon as you open the scans and the doctor says there's a mass, you will say 'OK what can we do???' And then you had a worthless biopsy.
Case 1 with cancer: you saved the 1 week it would take to schedule the new scan and get results and you're basically in the same situation except one week earlier.
And for the first part that doesn't happen in my scenario before the doctor doesn't look at the scans
I have had a lot of experience with MRIs on both myself (back and knee [1]) and my dogs with herniated discs. The doctors always make it sound like MRIs are great to confirm what's suspected because of other symptoms like pain, but a point in time MRI alone is not that valuable. Everyone's bodies (including animals!) are surprisingly different inside making normal be somewhat unique. I think what would be interesting is if scanning technology like MRIs could be made so inexpensive and easy that everyone had one done 4x/year. That way it's the differential being checked and I'm guessing it would be way more valuable. Normalization such as this could also lower anxiety around findings.
[1] Even when I tore my ACL the MRI came back only as probable.
When I last looked the full body scans for sale seemed to used 1.5T setup, which seems like a waste. The 3T advanced scans looks much more detailed, but it just depends on where you live - I couldn’t find any around.
MRIs are fine for certain kinds of cancer like liver cancer.
IMO MRI needs to become cheaper; and more reliable too.
That can also be reframed as 1.71% of asymptomatic people having cancer, which is a really good argument for better screening.
* The cancer is aggressive and resistant to treatment. Chemo/radiation only pause the growth for a bit, but ultimately the cancer keeps growing and the total survival time is the same (only that the patient spent more time knowing they had cancer).
* The cancer is susceptible enough to treatment that it's still curable when it becomes symptomatic and found through other means.
* The cancer is slow enough that the patient dies from other causes before.
Early screening brings benefits only when the cancer ends up causing issues and responds differently to treatment between the "early screening detection" time and the "normal detection" time.
It's impossible to know beforehand which of the scenarios have more weight, specially because we have very little data on what happens way before cancer is detected via the usual methods. We need better studies on this, and for now the evidence doesn't really point out to these large, indiscriminate screenings being actually helpful.
Further, the denominator is asymptomatic people who were able to get MRI’s they didn’t need. That doesn’t tell us anything about the normal world.
This is false. A simple google search for spontaneous remission (or honestly anything similar) would show/have shown you this.
Even assuming your statement is true, if what is detected is small enough for that there's no reason "treatment" can't just be monitoring it's size with follow-up scans.
It is true. You need only trouble yourself to search. Here's a recent paper, for example: https://jamanetwork.com/journals/jamainternalmedicine/articl...
> if what is detected is small enough for that there's no reason "treatment" can't just be monitoring it's size with follow-up scans.
This is false—it is exactly what the article is trying to convey. There is a risk to any test, and one of the major risks for imaging is getting treatment for things that would never cause symptoms or require intervention.
1. I had a chest x-ray
2. It showed a small dark patch, and my lungs over-inflate.
3. Erring on the side of caution, doctor ordered a lung biopsy.
4. Lung biopsy is painful, annoying, expensive, and non-zero-risk.
5. Lung biopsy turns up nothing. "Maybe you aspirated some food?" We learn nothing.
But we don't have 1000 similar cases. As I said, we have 1: mine. And it turned out negative. So 1 person was put through a biopsy they didn't need, and 0 people found out they have a tumor.
Hopefully that makes my point clearer.
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.