5 ms·

You know, sometimes all you need is “do I have a baseball sized tumor or not”.

by TheJoeMan 5y ago

AnimalMuppet 5y ago
But if the answer is "yes", the next question is "do I also have pinhead-sized metastases, and if so, where?"
- littlestymaar 5y ago
  Isn't this question answered by a PET scan and not MRI ?
  - lostlogin 5y ago
    I am unsure of the exact state of play but believe that small mets (eg a few mm in size) are better seen with MRI. MR is probably easier to get than PET too. There are usually a few radiologists lurking here and they would have better knowledge than me (I’m an MR tech). https://appliedradiology.com/articles/diagnosing-brain-metastases-mri-still-better-than-pet-mri-in-nsclc-patients https://appliedradiology.com/articles/diagnosing-brain-metas...
  - doctoring 5y ago
    Usually not! PET scans are limited in resolution when you get down to the sub-5 mm or so range due to scanner technology and fundamental limits of the physics of positron/electron annihilation & photon emission. A typical MRI (i.e. alas, not what this article is describing) can usually resolve something at that size and identify characteristics like diffusion restriction or contrast enhancement which can confirm metastasis. Also, in the brain, PET scans (at least the most common, FDG, which is based on glucose) are extremely limited in utility because of the baseline high glucose metabolism of the brain, which makes it hard to distinguish from the metabolic activity of a tumor.
    - fluidcruft 5y ago
      The flip-side of that is that PET is vastly multiple orders of magnitude far more sensitive than MRI. So while PET may not be able to localize as well as MRI, it can detect smaller things if the targeting of the radioisotope is good.
      - lostlogin 5y ago
        Maybe the state of play has changed, as we scan for this indication in MR, not PET. Have you a link to something as my understanding is that small lesions are better found with MR? Or is this a rule that applies to high end research work and hasn’t hit clinical practice yet? Maybe a limitation of the isotopes used clinically?
        haldujai 5y ago
        I am a radiologist. FDG PET/CT is not used to stage intracranial metastases due to background brain activity significantly reducing sensitivity. You’re likely only detecting lesions 1cm or greater in the brain, or ones which demonstrate low metabolic activity and appear dark. MRI is much more sensitive and specific and is the standard of care for staging in my practice and as per the NCCN clinical guidelines. I haven’t been to any institution or heard of one where PET is used for staging of brain metastases. Not sure where this is coming from.
        lostlogin 5y ago
        Thanks, it’s reassuring that we aren’t way off piste.
        fluidcruft 5y ago
        I probably wasn't clear in context because different meanings of sensitivity seem to have crossed paths. I was referring to the physics of signal detection in MRI vs PET, not clinical disease detection. MRI only detects signal from an extremely small fraction of the protons in the sample. You have no chance of detecting individual protons. MRI makes up for that with brute force of proton numbers in tissue. Modalities like PET can detect events from a far greater fraction of the isotopes present. But they are limited in spatial resolution by the physics. This is why MRI is said to be a very insensitive modality. See for example the discussion about MRI vs other modalities here: https://wikipedia.org/wiki/Molecular_imaging https://wikipedia.org/wiki/Molecular_imaging which notes that MRI has a sensitivity around 10^−3 to 10^−5 mol/L whereas PET is many orders of magnitude more sensitive at 10^-11 to 10^-12 mol/L. So what I meant was if there's an analogy that you're looking at a skyscraper, MRI can "see" which which rooms have floodlights turned on. PET could detect whether there's a single candle burning somewhere in the building, but it can't tell you which room it's in.
- car 5y ago
  Those metastases get taken care of by chemo- or immunotherapy.
ska 5y ago
In that case, likely you found it before anyone asked for an MRI.
- deleted 5y ago
  [deleted]
mabbo 5y ago
This is precisely what saved my father's life last year. 16 years ago he had some kind of brain cyst. Totally benign. But as a follow up, the doctor ordered yearly MRIs, much to his annoyance. Last year those yearly routine MRIs spotted a brain tumor- before it had time to get dangerous or cause any damage to him. It was growing quickly though and was right near his eye. Quick surgery got it out. I want to live in a world where everyone has access to that.
- lostlogin 5y ago
  A tumour can be a lot smaller than 1cm and cause issues. A pituitary microadenoma is an example, and this machine would struggle to show it. That said, I’d like a go. I suspect that with more samples (more time) you could get the resolution up.
queuebert 5y ago
Or a massive brain hemorrhage.
- fluidcruft 5y ago
  That's generally been the challenge with these super low-field scanners--they can't get T2*/susceptibility that's anywhere close to useful (yet?).
  - mwint 5y ago
    Reading the terminology being thrown around here, where could I go to get a basic understanding of what you’ll are talking about? It sounds like different modes of taking (or interpreting/visualizing?) an MRI.
    - rasmus1610 5y ago
      These are different MRI sequences that are weighted differently to produce a specific contrast that show different characteristics of the tissue that is imaged. I really liked ‚MRI made easy‘ as an introduction to MRI physics. Just google it, it’s a free Book
      - lostlogin 5y ago
        How funny, you just beat my comment. A link to it. https://rads.web.unc.edu/wp-content/uploads/sites/12234/2018/05/Phy-MRI-Made-Easy.pdf https://rads.web.unc.edu/wp-content/uploads/sites/12234/2018...
    - fluidcruft 5y ago
      (vastly simplified) MRI basically functions on two fundamental mechanisms--"spin echo" and "gradient echo". Spin echo signal is described by T1 and T2. Gradient echo signal is described by T1 and T2*. The difference between T2 and T2* relate to local magnetic properties of the tissue which is called "susceptibility". Blood contains iron so its presence alters T2* and this is exploited clinically. A good example of T2* imaging used clinically is susceptibility-weighted imaging (SWI). T2* effects increase with higher MRI main field strength. From what I can tell so far these ultra low-field scanners have to rely on spin echoes.
innolitics 5y ago
That's absolutely true. We work with a lot of technical founders who are turning their research into a diagnostic medical devices. One of the first questions we always ask is: how will the information produced by your device help clinical decision making? More data is _nice_ but if it doesn't alter the course of treatment, it's pointless. Sometimes it's okay if the doctor doesn't know if the problem is A or B if the treatment for A and B is the same.

You know, sometimes all you need is “do I have a baseball sized tumor or not”.

AnimalMuppet 5y ago

But if the answer is "yes", the next question is "do I also have pinhead-sized metastases, and if so, where?"

littlestymaar 5y ago
Isn't this question answered by a PET scan and not MRI ?
- lostlogin 5y ago
  I am unsure of the exact state of play but believe that small mets (eg a few mm in size) are better seen with MRI. MR is probably easier to get than PET too. There are usually a few radiologists lurking here and they would have better knowledge than me (I’m an MR tech). https://appliedradiology.com/articles/diagnosing-brain-metastases-mri-still-better-than-pet-mri-in-nsclc-patients https://appliedradiology.com/articles/diagnosing-brain-metas...
- doctoring 5y ago
  Usually not! PET scans are limited in resolution when you get down to the sub-5 mm or so range due to scanner technology and fundamental limits of the physics of positron/electron annihilation & photon emission. A typical MRI (i.e. alas, not what this article is describing) can usually resolve something at that size and identify characteristics like diffusion restriction or contrast enhancement which can confirm metastasis. Also, in the brain, PET scans (at least the most common, FDG, which is based on glucose) are extremely limited in utility because of the baseline high glucose metabolism of the brain, which makes it hard to distinguish from the metabolic activity of a tumor.
  - fluidcruft 5y ago
    The flip-side of that is that PET is vastly multiple orders of magnitude far more sensitive than MRI. So while PET may not be able to localize as well as MRI, it can detect smaller things if the targeting of the radioisotope is good.
    - lostlogin 5y ago
      Maybe the state of play has changed, as we scan for this indication in MR, not PET. Have you a link to something as my understanding is that small lesions are better found with MR? Or is this a rule that applies to high end research work and hasn’t hit clinical practice yet? Maybe a limitation of the isotopes used clinically?
      - haldujai 5y ago
        I am a radiologist. FDG PET/CT is not used to stage intracranial metastases due to background brain activity significantly reducing sensitivity. You’re likely only detecting lesions 1cm or greater in the brain, or ones which demonstrate low metabolic activity and appear dark. MRI is much more sensitive and specific and is the standard of care for staging in my practice and as per the NCCN clinical guidelines. I haven’t been to any institution or heard of one where PET is used for staging of brain metastases. Not sure where this is coming from.
        lostlogin 5y ago
        Thanks, it’s reassuring that we aren’t way off piste.
        fluidcruft 5y ago
        I probably wasn't clear in context because different meanings of sensitivity seem to have crossed paths. I was referring to the physics of signal detection in MRI vs PET, not clinical disease detection. MRI only detects signal from an extremely small fraction of the protons in the sample. You have no chance of detecting individual protons. MRI makes up for that with brute force of proton numbers in tissue. Modalities like PET can detect events from a far greater fraction of the isotopes present. But they are limited in spatial resolution by the physics. This is why MRI is said to be a very insensitive modality. See for example the discussion about MRI vs other modalities here: https://wikipedia.org/wiki/Molecular_imaging https://wikipedia.org/wiki/Molecular_imaging which notes that MRI has a sensitivity around 10^−3 to 10^−5 mol/L whereas PET is many orders of magnitude more sensitive at 10^-11 to 10^-12 mol/L. So what I meant was if there's an analogy that you're looking at a skyscraper, MRI can "see" which which rooms have floodlights turned on. PET could detect whether there's a single candle burning somewhere in the building, but it can't tell you which room it's in.
car 5y ago
Those metastases get taken care of by chemo- or immunotherapy.

ska 5y ago

In that case, likely you found it before anyone asked for an MRI.

deleted 5y ago
[deleted]

mabbo 5y ago

This is precisely what saved my father's life last year. 16 years ago he had some kind of brain cyst. Totally benign. But as a follow up, the doctor ordered yearly MRIs, much to his annoyance. Last year those yearly routine MRIs spotted a brain tumor- before it had time to get dangerous or cause any damage to him. It was growing quickly though and was right near his eye. Quick surgery got it out. I want to live in a world where everyone has access to that.

lostlogin 5y ago
A tumour can be a lot smaller than 1cm and cause issues. A pituitary microadenoma is an example, and this machine would struggle to show it. That said, I’d like a go. I suspect that with more samples (more time) you could get the resolution up.

queuebert 5y ago

Or a massive brain hemorrhage.

fluidcruft 5y ago
That's generally been the challenge with these super low-field scanners--they can't get T2*/susceptibility that's anywhere close to useful (yet?).
- mwint 5y ago
  Reading the terminology being thrown around here, where could I go to get a basic understanding of what you’ll are talking about? It sounds like different modes of taking (or interpreting/visualizing?) an MRI.
  - rasmus1610 5y ago
    These are different MRI sequences that are weighted differently to produce a specific contrast that show different characteristics of the tissue that is imaged. I really liked ‚MRI made easy‘ as an introduction to MRI physics. Just google it, it’s a free Book
    - lostlogin 5y ago
      How funny, you just beat my comment. A link to it. https://rads.web.unc.edu/wp-content/uploads/sites/12234/2018/05/Phy-MRI-Made-Easy.pdf https://rads.web.unc.edu/wp-content/uploads/sites/12234/2018...
  - fluidcruft 5y ago
    (vastly simplified) MRI basically functions on two fundamental mechanisms--"spin echo" and "gradient echo". Spin echo signal is described by T1 and T2. Gradient echo signal is described by T1 and T2*. The difference between T2 and T2* relate to local magnetic properties of the tissue which is called "susceptibility". Blood contains iron so its presence alters T2* and this is exploited clinically. A good example of T2* imaging used clinically is susceptibility-weighted imaging (SWI). T2* effects increase with higher MRI main field strength. From what I can tell so far these ultra low-field scanners have to rely on spin echoes.

innolitics 5y ago

That's absolutely true. We work with a lot of technical founders who are turning their research into a diagnostic medical devices. One of the first questions we always ask is: how will the information produced by your device help clinical decision making? More data is _nice_ but if it doesn't alter the course of treatment, it's pointless. Sometimes it's okay if the doctor doesn't know if the problem is A or B if the treatment for A and B is the same.