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How often do full-body MRIs find cancer?

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Re: How often do full-body MRIs find cancer?

#91

Post by Snoozus »

mgraczyk wrote: post #86
lostlogin wrote: post #85

Earlier quoted context omitted.

… they do it based on the scan result. Avoiding a biopsy that wasn’t needed is a good thing.

You're imagining that the doctor is required to act irrationally or against the patient's interest. I understand that they do act this way, but I'm pointing out that they don't have to! 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…

It is not only money, machines and doctors are also a limited resource.

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.

Re: How often do full-body MRIs find cancer?

#92

Post by mgraczyk »

lostlogin wrote: post #90
mgraczyk wrote: post #86

Earlier quoted context omitted.

You're imagining that the doctor is required to act irrationally or against the patient's interest. I understand that they do act this way, but I'm pointing out that they don't have to! 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…

A whole body MRI is low resolution and thick slices, they are crap. 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…

Yes the machines should definitely get better, but I recommend you do get it if the cost it truly zero. Based on the data in the article it is still worth it despite the low resolution!

Re: How often do full-body MRIs find cancer?

#93

Post by mgraczyk »

Snoozus wrote: post #91
mgraczyk wrote: post #86

Earlier quoted context omitted.

You're imagining that the doctor is required to act irrationally or against the patient's interest. I understand that they do act this way, but I'm pointing out that they don't have to! 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…

It is not only money, machines and doctors are also a limited resource. 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.

I agree, and I think rationing is the correct thing to do. I just don't like being gaslit by doctors (or would prefer doctors who know better).

And I agree most doctors won't do this, but again I blame the doctors and their training

Re: How often do full-body MRIs find cancer?

#94

Post by Snoozus »

mgraczyk wrote: post #67
tptacek wrote: post #65

Earlier quoted context omitted.

Doctors are not ordering biopsies to salvage the value of a scan they just ordered.

I agree, but they are failing to order scans when the probability of finding anything worth biopsying is low because of cost. 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 extr…

No, you still wouldn't, because doctors are neither free nor perfectly rational.

The probability of finding something worth a biopsy is not low, it is high compared to the probability of the patient requiring intervention.

Re: How often do full-body MRIs find cancer?

#95

Post by mgraczyk »

Snoozus wrote: post #94
mgraczyk wrote: post #67

Earlier quoted context omitted.

I agree, but they are failing to order scans when the probability of finding anything worth biopsying is low because of cost. 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 extr…

No, you still wouldn't, because doctors are neither free nor perfectly rational. The probability of finding something worth a biopsy is not low, it is high compared to the probability of the patient requiring intervention.

Yes that is my point. It's about cost

Re: How often do full-body MRIs find cancer?

#96

Post by Snoozus »

paulpauper wrote: post #33
lucb1e wrote: post #2

Answering the question in the title... > 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 diag…

Yeah a 2% risk of having something which can easily kill you and is very expensive to treat, especially if you're not elderly and still have lots of life ahead of your, is not exactly trivial. I would want to know about this

That's not the case. Most of these wouldn't kill you. Many of those that would kill you would be spotted in time anyways.

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.

Re: How often do full-body MRIs find cancer?

#97

Post by lostlogin »

mgraczyk wrote: post #92
lostlogin wrote: post #90

Earlier quoted context omitted.

A whole body MRI is low resolution and thick slices, they are crap. 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…

Yes the machines should definitely get better, but I recommend you do get it if the cost it truly zero. Based on the data in the article it is still worth it despite the low resolution!

Sorry, I edited my above comment to remove references to myself.

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.

Re: How often do full-body MRIs find cancer?

#98

Post by rich_sasha »

Can someone ELI5 why false positives on a MRI are so bad?

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?

Re: How often do full-body MRIs find cancer?

#99

Post by lostlogin »

mcbain wrote: post #83
lostlogin wrote: post #73

Earlier quoted context omitted.

Multiple PETs?

Yes, with MRI brain too. I was on 4/year, but that number is reducing as time goes on without recurrence.

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.

Re: How often do full-body MRIs find cancer?

#100

Post by Moto7451 »

_heimdall wrote: post #89
gullywhumper wrote: post #68

Earlier quoted context omitted.

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 ask…

How often are they finding actual positive hits on the PET? If its so unreliably with regards to false positives why do you continue to have PET scans done?

PET Scans feature areas with blood flow so tumors show up as hot spots for follow up. People who are maybe only feeling off or had one confirmed tumor can have a lot of small tumors spread across their body which will show up clearly on a PET scan.

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.

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