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One whole-body MRI could replace multiple cancer scans

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Re: One whole-body MRI could replace multiple cancer scans

#161

Post by MegaButts »

abecedarius wrote: post #138
mattkrause wrote: post #132

Earlier quoted context omitted.

I suppose you're right that the expected value of information, not including the acquisition costs, is never negative. That feels like cheating though--this information isn't free. My argument is that the expected value of this information, including acquisition costs, can very easily be negative, since you can't just "ignore" being dead. These costs are extremely large in my snarky autopsy suggestion, but dominate f…

Yup, agreed! In fact I wouldn't have done the test mentioned above if I'd been better informed (an MRI with gadolinium contrast; I was only told the latter bit the day I showed up for it. There seems to be a bit of controversy about possible low-level health effects of this contrast agent, and considering I was very probably fine a priori, I think it was a mistake to do this. But it's kind of another thing to decide…

My hunch from reading these comments is that the doctors tend to be experienced and pragmatic, and their experience teaches them what tests matter and when. The problem with this though is they start to believe those tests are useless when they might not be.

It becomes more complicated when you consider doctors have limited time and resources and cannot spend too much time with any single patient, at least the way the US healthcare system is designed. I believe this is a large contributing factor for why they behave the way they do - it's how the system is designed. And it's why I have all but given up on doctors even trying to help me with my bizarre symptoms, where I have been accused of lying multiple times.

Re: One whole-body MRI could replace multiple cancer scans

#162

Post by bsder »

arkades wrote: post #109
abecedarius wrote: post #101

Earlier quoted context omitted.

For a rational agent the expected value of information is never negative. (Of course it can be less than the cost of the test.) If a system is treating it as negative, that's a problem to fix. I'm reminded of a recent visit to a doctor who refused to say anything quantitative about a test. Sure, your average client knows little decision theory, but this doctor either didn't either or pretended not to follow. To make…

Cool, so your serum zorblaxian levels are 300 ng/L. The finding was incidental, so it’s jot tied to existing symptoms / clinical suspicion. It’s a molecule involved in the inflammatory cascade. We don’t know what diseases it’s associated with or not, nor what the change in probability of having the diseases it could be associated with are, not change in prognosis. But, you have a number which your local lab pegs at 1…

> Cool, so your serum zorblaxian levels are 300 ng/L. The finding was incidental, so it’s jot tied to existing symptoms / clinical suspicion. It’s a molecule involved in the inflammatory cascade.

This isn't that hard. You look at it again in 6 months. And you ask "Did it go up? Did it go down? Is this just your baseline?" And you keep your eyes open a little more strongly for issues that might correlate.

And, you know what, I, the patient, am FAR more invested in keeping tabs on whether things are going right or wrong in my own body than any doctor.

Re: One whole-body MRI could replace multiple cancer scans

#163

Post by Someone »

mattkrause wrote: post #112
rolleiflex wrote: post #67

Earlier quoted context omitted.

A decent portion of my family are MDs. This is accurate. However, this is also one of the places where it's quite disappointing to see human squishiness in action. When we opt to not receive data because we know there'll likely be non-malignant anomalies, we are also depriving ourselves of the raw data that allows us to discern non-malignant from malignant, data which would help very much in deciding on the cases we…

You're understating the costs. Determining whether something is (non) malignant isn't trivial. It often requires a more invasive test (e.g., biopsy, exploratory surgery). We try to avoid those procedures not just because we're cheap or afraid, but because they have a real risk of harming us 'squishy humans'. For example, detecting prostate cancer a few months earlier is often not a huge win on its own. It is even les…

”Determining whether something is (non) malignant isn't trivial. It often requires a more invasive test (e.g., biopsy, exploratory surgery)”

Not necessarily, waiting can in many cases tell you whether something is malignant. If we had, say, a century of monthly full-body MRIs of a million persons, together with their history and cause of death, the technology to align those scans across time, and the technology to analyze such a data set, a retrospective cohort study (https://en.wikipedia.org/wiki/Retrospective_cohort_study) probably could uncover quite some interesting and useful information.

If, at every step, you pick the option with the highest expected QALYs (https://en.wikipedia.org/wiki/Quality-adjusted_life_year), and you manage to make doing the MRI very efficient, I think doing that experiment even might pass an ethics committee (at the cost of making the analysis harder)

(might because one could argue that the patient would be better of if the money spent doing those MRIs were spent on something else)

Unfortunately, doing such an experiment isn’t practical (¿yet?).

Re: One whole-body MRI could replace multiple cancer scans

#164

Post by skwb »

tellak wrote: post #134
rolleiflex wrote: post #67

Earlier quoted context omitted.

A decent portion of my family are MDs. This is accurate. However, this is also one of the places where it's quite disappointing to see human squishiness in action. When we opt to not receive data because we know there'll likely be non-malignant anomalies, we are also depriving ourselves of the raw data that allows us to discern non-malignant from malignant, data which would help very much in deciding on the cases we…

I am actually an MD. > Had we enforced a full-body MRI for every patient, we would quickly amass enough imaging data to know which anomalies are malignant and which are not to a very high degree How, pray tell, are we actually determining which are malignant and which are not?? I’ll give you a hint: the charitable explanation is you are completely ignorant, the less charitable one is that you consider Mengele and Ish…

I don't even think it's about the ethics that necessarily make this statement wrong (though, you are correct in that HN needs to consider basic ethics on a much more frequent basis).

In the case of these detections, the ground truth can be very subjective and is certainly not a simple explanation. Is the ground truth read by a radiologist? A radiologist with fellowship training? Multiple radiologists? Biopsied? Followed for 5 years to see if the patient actually died of their tumor?

The complexity is a lot more than the underlying algorithms and computer science (though they are important!).

Re: One whole-body MRI could replace multiple cancer scans

#165

Post by Brakenshire »

louden wrote: post #145
Brakenshire wrote: post #126

Earlier quoted context omitted.

> The collection process itself can be dangerous or unpleasant for the patient. That’s asinine, obviously he doesn’t mean more data is always better even if the test is invasive or dangerous. > Biopsies caused by benign findings from a full body scan are not without pain, emotional distress, risk or cost to the patient. Period. It must be weighed against the benefit that the patient would recieve (all in the aggregat…

In medicine, there are physically harmless tests that can still cause harm. Full body scans are one of them. If something is found, it will likely have an emotional impact on the patient. Not all people are equally rational. Not all people have a good grasp of the statistical nature of the findings. That applies to educated people and medical professionals who deal with this stuff everyday. My point was not that eith…

It’s perfectly reasonable not to use such a test if medical science doesn’t have strong evidence what the data means. Likely that sort of statistical evidence would require institutions with teams of researchers managing and adjusting screening campaigns rather than the judgement of an individual doctor anyway. I really can’t accept the idea though that any test which is safe, cost and time effective, and produces actionable data shouldn’t be undertaken on the basis of some other judgment of emotional state. Doctors are in no way competent to make such judgements about individuals, and even accepting the premise on the scale of population, it means pandering to ignorance and in so doing damaging people’s health. You might as well limit vaccination programmes because of anti-vaccination PR campaigns.

Re: One whole-body MRI could replace multiple cancer scans

#166

Post by mattkrause »

koboll wrote: post #140
mattkrause wrote: post #112

Earlier quoted context omitted.

You're understating the costs. Determining whether something is (non) malignant isn't trivial. It often requires a more invasive test (e.g., biopsy, exploratory surgery). We try to avoid those procedures not just because we're cheap or afraid, but because they have a real risk of harming us 'squishy humans'. For example, detecting prostate cancer a few months earlier is often not a huge win on its own. It is even les…

It's nice that you think those are costs worth remaining ignorant over. However, when the ignorance is about things that literally might kill me, my personal opinion is that it's worth it.

The word 'cost' seems to be confusing things.

Both options have risks and both options can kill you. Namely:

A) Doing nothing may allow a problem to fester until it either kills you or becomes detectable with standard treatments. However, you have no exposure whatsoever to side effects, infections, or medical errors for the things that are missed.

B) Doing whole-body MRI 'fishing expeditions' decreases the risk of missing something, but increases the likelihood of possible false positives. Each thing flagged by the scan now needs to be ruled out (otherwise, why bother?) and this usually requires invasive procedures with their own risks.

With our current imaging and understanding of biology, Option A may be less likely to kill people. Opinion doesn't even have to enter into this--you can literally run the numbers.

It's worth noting that we limit testing FOR EVERYTHING. When you get a blood test, you could be screened for everything from ADH to Zika. You aren't though, because you're almost certainly a perfectly healthy outlier on a few tests; that's just how statistics work (someone has to be 3 sigma above the mean). Instead, tests are picked and interpreted based on your symptoms and circumstances.

Re: One whole-body MRI could replace multiple cancer scans

#167

Post by louden »

Brakenshire wrote: post #165
louden wrote: post #145

Earlier quoted context omitted.

In medicine, there are physically harmless tests that can still cause harm. Full body scans are one of them. If something is found, it will likely have an emotional impact on the patient. Not all people are equally rational. Not all people have a good grasp of the statistical nature of the findings. That applies to educated people and medical professionals who deal with this stuff everyday. My point was not that eith…

It’s perfectly reasonable not to use such a test if medical science doesn’t have strong evidence what the data means. Likely that sort of statistical evidence would require institutions with teams of researchers managing and adjusting screening campaigns rather than the judgement of an individual doctor anyway. I really can’t accept the idea though that any test which is safe, cost and time effective, and produces ac…

You are comparing a program where the benefits vastly outweigh the cost to a program where the benefit is mostly speculative and the cost known.

The cost of full body imaging is not just in the scan itself but in the procedures that follow it that require anasthesia (non-zero chance of killing the patient), cause pain and may cause secondary infection. In fact, just being in the hospital or doctors office to get the procedure has a non-zero risk to due to the concentration of sick people there.

Re: One whole-body MRI could replace multiple cancer scans

#168

Post by mattkrause »

DuskStar wrote: post #27
ChrisLomont wrote: post #25

Earlier quoted context omitted.

Because scans are not booked wall to wall every hour of every day. Needs more likely follow a poisson distribution with ample waits in between uses. To try and pack it that densely, with the large variation in how people show up at the hospital, would cause bottlenecks and loss of service. 20 a week is a more common number for most places. Here's actual data [1] measured on site. The usage is indeed around 50%, so th…

40% utilization means that it was in use for 67 hours per week. I don't think an MRI takes three hours. (In the case of the study listed, the utilization figures might be out of ~35 hours, which would make things different - but they also exclude scans scheduled in advance)

MRIs take as long as you can afford.

I have actually run ~3 hour MRIs for experiments, but we're being very fussy and trying to get the best possible image with the smallest possible voxel, which you do by acquiring tons of volumes and averaging them. Obviously, you can be in and out of there much quicker if you're just looking for a gaping hole.

Re: One whole-body MRI could replace multiple cancer scans

#169

Post by mattkrause »

nradov wrote: post #8
eutropia wrote: post #2

With sufficient software and computational horsepower, a single whole-body MRI could replace most diagnostic imaging systems, I'd wager. Computer models regularly outperform radiologists in diagnosing several conditions involving structural abnormalities.

CT scans still have higher resolution than MRI for certain vascular and cardiac imaging studies. The down side is radiation exposure.

The new digital CTs are crazy.

We have one that goes down to 90 µm resolution for the whole head.

Re: One whole-body MRI could replace multiple cancer scans

#170

Post by MegaButts »

bsder wrote: post #162
arkades wrote: post #109

Earlier quoted context omitted.

Cool, so your serum zorblaxian levels are 300 ng/L. The finding was incidental, so it’s jot tied to existing symptoms / clinical suspicion. It’s a molecule involved in the inflammatory cascade. We don’t know what diseases it’s associated with or not, nor what the change in probability of having the diseases it could be associated with are, not change in prognosis. But, you have a number which your local lab pegs at 1…

> Cool, so your serum zorblaxian levels are 300 ng/L. The finding was incidental, so it’s jot tied to existing symptoms / clinical suspicion. It’s a molecule involved in the inflammatory cascade. This isn't that hard. You look at it again in 6 months. And you ask "Did it go up? Did it go down? Is this just your baseline?" And you keep your eyes open a little more strongly for issues that might correlate. And, you kno…

> And, you know what, I, the patient, am FAR more invested in keeping tabs on whether things are going right or wrong in my own body than any doctor.

As someone who has had to figure out his health on his own after multiple doctors have failed or many never even attempted to help, I cannot agree with this more.

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