Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

One whole-body MRI could replace multiple cancer scans

pharmatimes.com

Post reply on HN
Print view View original

91–100 of 236 posts

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

#91

Post by jmhmd »

rolleiflex wrote: post #67
nknealk wrote: post #13

Many doctors hate full body scans. Every individual has a handful of anomalies which are almost always benign. They show up on full body scans and chasing them down comes with cost and patient risk. I have a hard time with reporting like this that doesn't quantify cost of biopsy on false-positives as well as cost of complications from examining false-positives. Source: worked in clinical research for 2 years.

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…

The idea that lots of full body MRIs will necessarily lead to better discrimination of malignant vs benign anomalies assumes that the imaging is able to detect differences at all, which often is not true. Some benign and malignant abnormalities can look _exactly_ the same on imaging, particularly at an early stage, when you could make a difference, for example lung nodules. Nevermind the fact that many benign entities can undergo malignant transformation at some point in the future. Or that MRI is only a good test for a subset of cancers, CT is better for others. All these issues help explain why doctors are averse to full-body scanning everybody. It is neither cost-effective nor medically sensible.

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

#92

Post by stevesimmons »

chongli wrote: post #23
nknealk wrote: post #13

Many doctors hate full body scans. Every individual has a handful of anomalies which are almost always benign. They show up on full body scans and chasing them down comes with cost and patient risk. I have a hard time with reporting like this that doesn't quantify cost of biopsy on false-positives as well as cost of complications from examining false-positives. Source: worked in clinical research for 2 years.

This sounds to me like doing a full workup on blood chemistry. Individuals vary so much that you can get false positives. Wouldn't it be more useful as a baseline? Scan once and store it, then scan every few years and compare. If any of the "anomalies" has grown or new ones have appeared between scans, then they might be worth a second look?

Even if we can't reliably compare a time series of images today, wouldn't it be useful to start scanning now, for use as baselines in several years once the state of the art improves?

In the same way astronomers can make new discoveries by digitizing photographic plates from a century ago.

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

#93

Post by tejtm »

jcims wrote: post #56
arkades wrote: post #46

Earlier quoted context omitted.

We don’t advocate less frequent scans, we advocate targeted scans. Because the probability of a positive result being a false positive depends heavily on the population. In a population with a high baseline frequency, the probability of a positive being false is relatively low; in a population with a low baseline frequency, the likelihood of a positive being false is relatively high. So, you don’t mammogram every per…

Sitting in the oncology dept right now with my wife who’s gaving complications from a tumor. I’d just be happy with peer reviews of radiology reports so fuckups don’t cost us three months of potential treatment. I’m sitting bedside wading through pull requests for software installation scripts. How is it the opinions of folks on my team for a bullshit process get more scrutiny than a potentially life-altering assessm…

I've been there and recently, I hope you come through at least as well as we have. My understanding is at minimum several radiologists lay eyes on before you hear anything from any of them. P.S. My wife wife says she wishes you and your wife all the best.

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

#94

Post by DuskStar »

ChrisLomont wrote: post #81
DuskStar wrote: post #27

Earlier quoted context omitted.

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)

The link states "As a result, in our study the maximum hours per week on each scanner was limited to 35 h for the Vision (no hours on Tuesdays), 39 h for the Harmony, 32 h for the Sonata (no hours on Wednesdays) and 38 h for the Avanto." Why guess 67 when you can look at the answer?

Because from my reading that's not the number of hours they used the machines, but the number of hours in which the machines were available to be used. And since they also state that their utilization figures only include emergency cases (and exclude scheduled scans) I don't consider it a particularly relevant source in the first place.

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

#95

Post by concernedstats »

jmhmd wrote: post #91
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…

The idea that lots of full body MRIs will necessarily lead to better discrimination of malignant vs benign anomalies assumes that the imaging is able to detect differences at all, which often is not true. Some benign and malignant abnormalities can look _exactly_ the same on imaging, particularly at an early stage, when you could make a difference, for example lung nodules. Nevermind the fact that many benign entitie…

I think their statement is more general than what you're making it out to be. The goal of receiving better and more data puts pressure to have better imaging technology.

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

#97

Post by stevesimmons »

tptacek wrote: post #65
DuskStar wrote: post #28

Earlier quoted context omitted.

Are you saying that you wouldn't have your multi-million dollar imager running as much as possible?

I'm saying that it seems like a most optimistic, best-case scenario, and not the average case.

When my partner needed an outpatient MRI, we got it done the next day by accepting the 11pm time slot. This was at a private hospital in Australia in 2006. We were super impressed by everything that department did to maximise utilisation. It was like a production line!

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

#98

Post by arkades »

MegaButts wrote: post #89
arkades wrote: post #76

Earlier quoted context omitted.

Well, that’s part of why there’s constant research into what risk factors / predictive factors are. These aren’t mutually exclusive activities. “Data” implies something neutral. Nothing about lab tests is neutral. Without contextual information and studies on how to -interpret- a finding, it’s just potentially terrifying noise. And terror usually results in action. Poorly informed action is often harmful. So... we ar…

I understand it is not a black-and-white situation, and that data is obviously not perfect. And I certainly am not advocating that doctors should order a gamut of tests unnecessarily. But if there is any doubt, how likely is the added data to harm more than help? And I firmly believe the doctor should not fight the patient on a test unless there is a strong reason not to (apart from an obvious medical disorder such a…

You can’t ignore the noise because we don’t know it’s noise. I know I’m failing to get that idea across, but I honestly don’t know how to articulate it better than I have been. I can tell you’re honestly trying to understand, and I feel the blame is likely on me as a communicator.

Possibly what I’ve failed to communicate is this:

MRI, CXR, etc are not images of the body. It’s not like getting a photograph of a liver and saying, at least we know this is or isn’t going on in the liver. They’re indirect measures of certain attributes of the body, such as tissue density, which we use - coupled with their medical information, and the mechanisms of likely diseases - to infer what’s happening. That’s why reading radiology is a medical specialty, and not something anyone with an anatomy background can do. (There’s a radiologist currently browsing the thread - he’s very welcome to correct me if I’m wrong about what radiology “is”.)

Because of this, every such finding has to be interpreted in a context, and studies tell us how.

Completely out of context findings aren’t a big problem if they’re completely unambiguous: hey, that bone is in two pieces and it should be in one.

What about the finding that isn’t, though? This is equivalent to not having any information on a test’s false positive / false negative rate, only now it’s open-ended to “every condition that could look like that thing” because the defining characteristic of an incidental finding is that it’s -incidental-. It’s not related to any symptoms. So what do I do with “every disease or non-disease process that could potentially look like a spot on the lung, without any accompanying symptoms of that disease”?

What I believe is the responsible answer is: “if I think the pre-test probability isn’t borderline zero, AND the post-test probability would change my course of treatment or diagnosis, order the test. If the pre-test probability is so low that any positive test result would be very likely to be a false positive and thus force me to act in a manner harmful to the patient, don’t order it - it shouldn’t be allowed to change the course of treatment. If the pre-test probability is already so high that any negative result is likely a false negative, don’t order it - it shouldn’t be allowed to change the course of treatment. Only order tests whose results should impact the course of diagnostics or treatment.” What do I do with findings that haven’t been studied in a given context, so I have no clue what their impact on the post-test probability of a diagnosis is? I don’t know. But “test just in case” isn’t the zero-risk option. There aren’t any zero consequence options.

Not every test is an RCT because grant funding agencies don’t provide the budget, plus or minus, many RCTs we’d like to do are unethical (if you have good reason to believe one course of therapy is superior to another, you don’t have the clinical uncertainty to ethically allow randomizing people into an inferior therapy), plus or minus many sub-populations are just too uncommon to build an RCT on without a gigantic budget that facilitates long collection periods across multiple institutions.

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

#99

Post by mparlane »

wolfi1 wrote: post #96

There is no mentioning of exposure during MRIs. Is there none? I would have thought, CTs as well as MRIs are a problem because of exposure.

Because CT scans and MRI scans are very different technologies....

CT = xray

MRI = Magnetic resonance imaging

There is no exposure in an MRI to radiation. The only danger would be having bits of metal on you or inside you.

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

#100

Post by pgeorgi »

duxup wrote: post #69
petschge wrote: post #55

Earlier quoted context omitted.

Getting a baseline is harder than it sounds. In the case of blood chemistry that is caused by fluctuations due to time of day, time of month, season, what you recently ate and so one. In the case of MRI the problem is that internal organs shift to the point that it is impossible to automatically compare. And a experienced doctor comparing the scan millimeter for millimeter takes hours and would be very expensive. Eve…

> internal organs shift to the point that it is impossible to automatically compare I didn't even know that is a thing, I just sorta assumed they stayed put.

When undergoing abdominal radiation treatment, patients are asked to stop breathing to keep organs at their place (and not radiate healthy tissue), but apparently that still isn't good enough: https://www.ncbi.nlm.nih.gov/pubmed/27773445
Post reply on HN