8 ms·

“ 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.” This has

“ 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.” 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.

rembal 8mo ago
Anecdotal evidence to confirm: I had two false alarms from an unrelated MRI scan, and beside wasting a lot of time on diagnosing them - it was also extremely stressful. 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.
- p0pularopinion 8mo ago
  > My father is a part of "full body PET scan every 3 years" program as part of post - cancer treatment, 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
  - mcbain 8mo ago
    I have multiple scans a year. "Scanxiety" is real.
    - lostlogin 8mo ago
      Multiple PETs?
      - mcbain 8mo ago
        Yes, with MRI brain too. I was on 4/year, but that number is reducing as time goes on without recurrence.
        lostlogin 8mo ago
        Sorry, I missed a key detail. What you are describing isn’t the ‘whole body mri’ I’m referencing by to. 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.
    - vasco 8mo ago
      I do once a year and have skipped 2 because of that. I've since resumed but for a while I convinced myself I'd rather not know.
    - robocat 8mo ago
      > Scanxiety 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
      - hbs18 8mo ago
        As a non-native English speaker, pronouncing it scan-xiety (sken-ZAHyetee) feels correct.
      - mcbain 8mo ago
        The former. It doesn't quite roll off the tongue, but with my (Australian) accent the difference is minor.
- ErroneousBosh 8mo ago
  > 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. 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.
  - codethief 8mo ago
    > in Scotland where we have (possibly as a result of the weirdly high levels of cancer) 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_rate https://en.wikipedia.org/wiki/List_of_countries_by_cancer_ra... . PS: Glad to hear your mom is doing well! [0]: https://pmc.ncbi.nlm.nih.gov/articles/PMC1939786/ https://pmc.ncbi.nlm.nih.gov/articles/PMC1939786/
    - ErroneousBosh 8mo ago
mcbain 8mo ago
Spot on. And dealing with false positives sucks. 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).
- deleted 8mo ago
  [deleted]
mgraczyk 8mo ago
And yes getting frequent full body MRIs is still overwhelming the right thing for the patient.
- tptacek 8mo ago
  No? The point of the article, and of the preceding comments, echoing a pretty common tenet of evidence-based medicine, is that frequent full-body MRIs are a bad idea for the patient.
  - deleted 8mo ago
    [deleted]
- mmaunder 8mo ago
  This guy has never heard the term 'scanxiety'. Go ask what it means on a cancer forum. The real OG's are the VHL folks. Bet we have a few here on this thread. Respect.
  - mgraczyk 8mo ago
    I have, it's the fault of how medicine is practiced to reduce cost. It's completely avoidable, you can just not tell people their scan results if they have no symptoms and the detection is less than 95% likely to be cancer. This is strictly better than the status quo because the only difference is some people who almost certainly have cancer learn that they have cancer and nothing else changes
    - tptacek 8mo ago
      Again, you're assuming the only downside of a routine scan is anxiety. No, the real downside is that you'll trigger needless invasive procedures.
      - mgraczyk 8mo ago
        How can you trigger an invasive procedure if nobody learns the result of the scan?
sharkweek 8mo ago
I had a CT scan last year for some stomach issues they wanted to look at. 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)
- OptionOfT 8mo ago
  > I do take slight offense to the following at the top of my results: 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.
  - jmcgough 8mo ago
    The bar is really low for patient behavior. Tbh I find anyone not screaming at me to be pleasant in comparison.
  - lostlogin 8mo ago
    Some RIS systems make semi form reports with ‘Dear <referrer> thank you for sending <patient> to see us for their <type of imaging> etc etc. Then you can just tab from field to field when doing the report.
  - JackFr 8mo ago
    I had a nurse chart “patient ‘feels like a million bucks’” while I was getting an immunotherapy infusion. She said “It’s just not often I hear that here.”
- gullywhumper 8mo ago
  2.5 years in of regular PET scans. At this point, I’m almost humored by what gets flagged as suspicious by the radiologist - usually mosquito bites and stomach bugs (kids in daycare means I’m almost always sick). I have a scan Monday and two weeks ago had a re-excision so there’s a two inch gash healing on my back. This week I got three vaccines. And then tonight my toddler bit me hard enough to draw blood. I had asked the oncologist if it made sense to delay the scan because of the re-excision and he said not to worry because he’d know why there’s inflammation in that area. I’m thinking the bite and the shots will probably get flagged too. I just hope I don’t forget any other maladies or mishaps that might get flagged that I can’t explain.
paulpauper 8mo ago
hmm that is still around 1.5% of ppl having cancer. not trivial. Even more if you include false negatives.
- bawolff 8mo ago
  I mean, i think you need to look more into it than that. If you make a test that always returns true, it would also meet that criteria.
  - kozzion 8mo ago
    Basically half of all men have some early form of prostate cancer. Now that does not show up very well on an MRI, but there are quite a few diagnosis like that that are not necessary life saving.
NedF 8mo ago
[dead]
WhitneyLand 8mo ago
“MRIs…suck at cancer” 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.
- Spooky23 8mo ago
  MRIs are good if you know what you’re looking for, and usually with contrast, which in a situation like cancer where you need to do them often can result in allergic reactions. 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.
rustyhancock 8mo ago
It's not that MRIs suck at cancer. They provide fantastic structural and functional data. 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.
- ErroneousBosh 8mo ago
  > The danger of an unnecessary CT/PET is causing 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.
  - rustyhancock 8mo ago
    Even if you don't agree with linear no threshold models for cancers induced by radiation (I don't think LNT is accurate). 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/S0720048X25005571 https://www.sciencedirect.com/science/article/pii/S0720048X2...
    - 8mo ago
matwood 8mo ago
> MRIs are great for certain things like herniated disks in your back. 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.
- uf00lme 8mo ago
  Do you know which MRI you used? Not all are equal. Most MRI are 1.5T powered, and you can’t get fine details until you hit 3T. And there are differences even in the 3T power range. There are higher powered MRI which are mostly only used in research, whilst it is a bit scary thinking about the sheer power of them but a 7T machine doing a full scan of you, would be guaranteed nearly to find anything wrong with you. 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.
  - matwood 8mo ago
    My knee and back was years ago, so probably the 1.5T. No idea on my dogs who have had the more recent MRIs. Their scans are incredibly detailed though, so maybe the 3T?
tjpnz 8mo ago
>MRIs are great for certain things like herniated disks in your back. They suck at cancer. MRIs are fine for certain kinds of cancer like liver cancer.
azan_ 8mo ago
That’s completely and 100% false. It’s much easier to characterize things on MRI and MRI is indeed phenomenal for cancer! The problem is with screening, not actual staging or follow-up, and whole-body screening in ct and pet/ct is even worse than MRI screening even if you ignore radiation.
RobotToaster 8mo ago
>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. That can also be reframed as 1.71% of asymptomatic people having cancer, which is a really good argument for better screening.
- bonsai_spool 8mo ago
  That’s not the correct framing - your assertion first lacks evidence about why we should screen better. In fact, we aren’t improving longevity in many early diagnoses, and may be treating people whose immune system would resolve the cancers. 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.
  - M95D 8mo ago
    If the cancer is vizible in MRI or CT scans, the immune system already failed to "resolve" it and will not do so in the future, at least not without external help.
    - bonsai_spool 8mo ago
      > If the cancer is vizible in MRI or CT scans, the immune system already failed to "resolve" it and will not do so in the future, at least not without external help. This is false. A simple google search for spontaneous remission (or honestly anything similar) would show/have shown you this.
  - RobotToaster 8mo ago
    > we aren’t improving longevity in many early diagnoses, and may be treating people whose immune system would resolve the cancers. 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.
    - bonsai_spool 8mo ago
RataNova 8mo ago
But saying MRIs "suck at cancer" feels off. They're actually first-line or gold standard for certain cancers
- shevy-java 8mo ago
  I feel that label is actually deserved. Yes, some cancer types are easier to detect with MRI, in particular inside of a body, but at the same time MRI in and by itself isn't great at predicting all cancer types. How could it help with regards to leukemia, for instance? What exactly could MRI detect here better than other diagnostic tools? One has to keep in mind that diagnosis also takes time - plus the cost; and the overdiagnosis problem which means that some cancer that are not really relevant, are hyped up by MRI to be the end of the world for a patient. So there is a trade-off. IMO MRI needs to become cheaper; and more reliable too.
gcanyon 8mo ago
Not because of an MRI, but this happened to me: 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. N=1, but that biopsy should not have happened.
- ryan_n 8mo ago
  I don’t understand how you’re concluding that the biopsy shouldn’t have happened from that anecdote? Just because a test result is negative doesn’t mean that it shouldn’t have happened. That’s not how practicing medicine works.
  - gcanyon 8mo ago
    Hence the N=1 I started the statement with. If we had a thousand similar situations and it turned out that in, say, 1% of cases there was a lung tumor, then we could debate whether it's worth putting 990 people through a biopsy they don't need so 10 can find out they have a tumor. Maybe that gives us the opportunity to discuss waiting a month and taking another chest x-ray (which has its own negatives) vs. doing an immediate biopsy. 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.

rembal 8mo ago

Anecdotal evidence to confirm: I had two false alarms from an unrelated MRI scan, and beside wasting a lot of time on diagnosing them - it was also extremely stressful. 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.

p0pularopinion 8mo ago
> My father is a part of "full body PET scan every 3 years" program as part of post - cancer treatment, 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
- mcbain 8mo ago
  I have multiple scans a year. "Scanxiety" is real.
  - lostlogin 8mo ago
    Multiple PETs?
    - mcbain 8mo ago
      Yes, with MRI brain too. I was on 4/year, but that number is reducing as time goes on without recurrence.
      - lostlogin 8mo ago
        Sorry, I missed a key detail. What you are describing isn’t the ‘whole body mri’ I’m referencing by to. 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.
  - vasco 8mo ago
    I do once a year and have skipped 2 because of that. I've since resumed but for a while I convinced myself I'd rather not know.
  - robocat 8mo ago
    > Scanxiety 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
    - hbs18 8mo ago
      As a non-native English speaker, pronouncing it scan-xiety (sken-ZAHyetee) feels correct.
    - mcbain 8mo ago
      The former. It doesn't quite roll off the tongue, but with my (Australian) accent the difference is minor.
ErroneousBosh 8mo ago
> 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. 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.
- codethief 8mo ago
  > in Scotland where we have (possibly as a result of the weirdly high levels of cancer) 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_rate https://en.wikipedia.org/wiki/List_of_countries_by_cancer_ra... . PS: Glad to hear your mom is doing well! [0]: https://pmc.ncbi.nlm.nih.gov/articles/PMC1939786/ https://pmc.ncbi.nlm.nih.gov/articles/PMC1939786/
  - ErroneousBosh 8mo ago

mcbain 8mo ago

Spot on. And dealing with false positives sucks. 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).

deleted 8mo ago
[deleted]

mgraczyk 8mo ago

And yes getting frequent full body MRIs is still overwhelming the right thing for the patient.

tptacek 8mo ago
No? The point of the article, and of the preceding comments, echoing a pretty common tenet of evidence-based medicine, is that frequent full-body MRIs are a bad idea for the patient.
- deleted 8mo ago
  [deleted]
mmaunder 8mo ago
This guy has never heard the term 'scanxiety'. Go ask what it means on a cancer forum. The real OG's are the VHL folks. Bet we have a few here on this thread. Respect.
- mgraczyk 8mo ago
  I have, it's the fault of how medicine is practiced to reduce cost. It's completely avoidable, you can just not tell people their scan results if they have no symptoms and the detection is less than 95% likely to be cancer. This is strictly better than the status quo because the only difference is some people who almost certainly have cancer learn that they have cancer and nothing else changes
  - tptacek 8mo ago
    Again, you're assuming the only downside of a routine scan is anxiety. No, the real downside is that you'll trigger needless invasive procedures.
    - mgraczyk 8mo ago
      How can you trigger an invasive procedure if nobody learns the result of the scan?

sharkweek 8mo ago

I had a CT scan last year for some stomach issues they wanted to look at. 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)

OptionOfT 8mo ago
> I do take slight offense to the following at the top of my results: 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.
- jmcgough 8mo ago
  The bar is really low for patient behavior. Tbh I find anyone not screaming at me to be pleasant in comparison.
- lostlogin 8mo ago
  Some RIS systems make semi form reports with ‘Dear <referrer> thank you for sending <patient> to see us for their <type of imaging> etc etc. Then you can just tab from field to field when doing the report.
- JackFr 8mo ago
  I had a nurse chart “patient ‘feels like a million bucks’” while I was getting an immunotherapy infusion. She said “It’s just not often I hear that here.”
gullywhumper 8mo ago
2.5 years in of regular PET scans. At this point, I’m almost humored by what gets flagged as suspicious by the radiologist - usually mosquito bites and stomach bugs (kids in daycare means I’m almost always sick). I have a scan Monday and two weeks ago had a re-excision so there’s a two inch gash healing on my back. This week I got three vaccines. And then tonight my toddler bit me hard enough to draw blood. I had asked the oncologist if it made sense to delay the scan because of the re-excision and he said not to worry because he’d know why there’s inflammation in that area. I’m thinking the bite and the shots will probably get flagged too. I just hope I don’t forget any other maladies or mishaps that might get flagged that I can’t explain.

paulpauper 8mo ago

hmm that is still around 1.5% of ppl having cancer. not trivial. Even more if you include false negatives.

bawolff 8mo ago
I mean, i think you need to look more into it than that. If you make a test that always returns true, it would also meet that criteria.
- kozzion 8mo ago
  Basically half of all men have some early form of prostate cancer. Now that does not show up very well on an MRI, but there are quite a few diagnosis like that that are not necessary life saving.

NedF 8mo ago

[dead]

WhitneyLand 8mo ago

“MRIs…suck at cancer” 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.

Spooky23 8mo ago
MRIs are good if you know what you’re looking for, and usually with contrast, which in a situation like cancer where you need to do them often can result in allergic reactions. 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.

rustyhancock 8mo ago

It's not that MRIs suck at cancer. They provide fantastic structural and functional data. 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.

ErroneousBosh 8mo ago
> The danger of an unnecessary CT/PET is causing 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.
- rustyhancock 8mo ago
  Even if you don't agree with linear no threshold models for cancers induced by radiation (I don't think LNT is accurate). 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/S0720048X25005571 https://www.sciencedirect.com/science/article/pii/S0720048X2...
  - 8mo ago

matwood 8mo ago

> MRIs are great for certain things like herniated disks in your back. 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.

uf00lme 8mo ago
Do you know which MRI you used? Not all are equal. Most MRI are 1.5T powered, and you can’t get fine details until you hit 3T. And there are differences even in the 3T power range. There are higher powered MRI which are mostly only used in research, whilst it is a bit scary thinking about the sheer power of them but a 7T machine doing a full scan of you, would be guaranteed nearly to find anything wrong with you. 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.
- matwood 8mo ago
  My knee and back was years ago, so probably the 1.5T. No idea on my dogs who have had the more recent MRIs. Their scans are incredibly detailed though, so maybe the 3T?

tjpnz 8mo ago

>MRIs are great for certain things like herniated disks in your back. They suck at cancer. MRIs are fine for certain kinds of cancer like liver cancer.

azan_ 8mo ago

That’s completely and 100% false. It’s much easier to characterize things on MRI and MRI is indeed phenomenal for cancer! The problem is with screening, not actual staging or follow-up, and whole-body screening in ct and pet/ct is even worse than MRI screening even if you ignore radiation.

RobotToaster 8mo ago

>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. That can also be reframed as 1.71% of asymptomatic people having cancer, which is a really good argument for better screening.

bonsai_spool 8mo ago
That’s not the correct framing - your assertion first lacks evidence about why we should screen better. In fact, we aren’t improving longevity in many early diagnoses, and may be treating people whose immune system would resolve the cancers. 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.
- M95D 8mo ago
  If the cancer is vizible in MRI or CT scans, the immune system already failed to "resolve" it and will not do so in the future, at least not without external help.
  - bonsai_spool 8mo ago
    > If the cancer is vizible in MRI or CT scans, the immune system already failed to "resolve" it and will not do so in the future, at least not without external help. This is false. A simple google search for spontaneous remission (or honestly anything similar) would show/have shown you this.
- RobotToaster 8mo ago
  > we aren’t improving longevity in many early diagnoses, and may be treating people whose immune system would resolve the cancers. 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.
  - bonsai_spool 8mo ago

RataNova 8mo ago

But saying MRIs "suck at cancer" feels off. They're actually first-line or gold standard for certain cancers

shevy-java 8mo ago
I feel that label is actually deserved. Yes, some cancer types are easier to detect with MRI, in particular inside of a body, but at the same time MRI in and by itself isn't great at predicting all cancer types. How could it help with regards to leukemia, for instance? What exactly could MRI detect here better than other diagnostic tools? One has to keep in mind that diagnosis also takes time - plus the cost; and the overdiagnosis problem which means that some cancer that are not really relevant, are hyped up by MRI to be the end of the world for a patient. So there is a trade-off. IMO MRI needs to become cheaper; and more reliable too.

gcanyon 8mo ago

Not because of an MRI, but this happened to me: 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. N=1, but that biopsy should not have happened.

ryan_n 8mo ago
I don’t understand how you’re concluding that the biopsy shouldn’t have happened from that anecdote? Just because a test result is negative doesn’t mean that it shouldn’t have happened. That’s not how practicing medicine works.
- gcanyon 8mo ago
  Hence the N=1 I started the statement with. If we had a thousand similar situations and it turned out that in, say, 1% of cases there was a lung tumor, then we could debate whether it's worth putting 990 people through a biopsy they don't need so 10 can find out they have a tumor. Maybe that gives us the opportunity to discuss waiting a month and taking another chest x-ray (which has its own negatives) vs. doing an immediate biopsy. 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.