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I What is the unit of measurement in this X-Ray?

  1. Jun 14, 2018 #1
    Hi I hope I'm not posting under the wrong forum but I'm pretty sure this is physics related.

    If you go to have an X-ray, in the film there will be information detailing the dosage you just received. However I encountered a rather unusual one like this:

    70kV 100mAs 100mS -- dGycm2 El_s:300

    As far as dGycm2 goes, the figure following it should well below 1, most likely 0.2 or something, yet it has 300.

    What IS that? The X-Ray wasn't done in the US.

    My apologies again if it has been posted under the wrong subforum.
     
  2. jcsd
  3. Jun 14, 2018 #2

    davenn

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    I'm assuming that 100 mS should really be 100 mSv ?? as in 100 milliSieverts ?

    or maybe it really is 100mS = milli Seconds ?? as in dosage (exposure) time

    I don't know what 100 mAs is ???


    100 mSv = 1 dGy

    @ZapperZ help please :smile:


    Dave
     
  4. Jun 14, 2018 #3
    mA is current in milliamps applied for 100 milliseconds? At 70 kV, this is 700 joule (watt-seconds).
    decigray⋅cm2?

    Found this ... Understanding Radiology Exposure Indicators
     
  5. Jun 14, 2018 #4
    What is El_s then? If 300 is Gycm2 then it's nothing much better than a gass chamber.
     
  6. Jun 14, 2018 #5
    Most likely miliseconds. 100mSv is enough to cause someone symptoms.

    Then how do you really calculate the effective dosage?
     
  7. Jun 15, 2018 #6

    davenn

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    that's the easy part haha :wink: deciGrey per cm2
    1 dGy = 1 deciGrey is 1/10 of a Grey = 100 mSv = 10 Rad (10,000 milliRad)

    Yeah, I have no idea what "EL_s" is either haven't found a link

    hence why I called on ZapperZ for help in the thread


    Dave
     
  8. Jun 15, 2018 #7

    davenn

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    From
    https://www.translatorscafe.com/uni...n-absorbed-dose/18-25/milligray-millisievert/

     
  9. Jun 15, 2018 #8
    Also the 700 Joule makes it sound even scarier. I mean if we are talking about 700J per kilogram it's effectively death ray.
    700J per gram sounds like a neutron bomb.
     
  10. Jun 15, 2018 #9

    sophiecentaur

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    In general, I have found that Medics are a lot less fussy about their units than you might expect. They often rely on 'local rules' to specify doses in general - in the same way that they launch into acronyms and groups of capital letters for diseases and symptoms . I think the 'excuse' for this is the historical attitude that kept information away from their patients.
    It surprises me that there are relatively few disasters resulting from this habit of shorthand terminology.
     
  11. Jun 15, 2018 #10
    Ok then. Now, another question: how long after a large dose of exposure to gamma radiation should you able to observe abnormalities in white cell quantities?
     
  12. Jun 15, 2018 #11
    From the Understanding Radiology Exposure Indicators article,

    EI_s:300 would fit with it being such an exposure indicator.

    I'm wondering whether the '--' symbols preceding 'dGycm2' indicate this field wasn't enumerated.
     
  13. Jun 15, 2018 #12

    sophiecentaur

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    Surely you can find that from Google. Radiation effects on the human body are such a favourite topic.
    The total dose is not the only factor. Several years ago I was given Radiotherapy and the 50Gy total dose was given in less than 3Gy lots spread over many weeks on the grounds that the body can deal better with it than the cancer cells can, over a long period of time. I don't know how that relates to white cell population but I was not aware of any blood test for white cell levels.
     
  14. Jun 15, 2018 #13
    Well thanks! That's some major progress made! At least I know 300 isn't 300 dGy.

    Now, if only it can be figured out how much mSv of radiation were absorbed in taking that shot of digital X-ray...
     
  15. Jun 15, 2018 #14

    Wow. How did it go? Was the tumor eliminated?
     
  16. Jun 16, 2018 #15

    sophiecentaur

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    Seems to be OK so far - thanks for asking. The surgery was about six years ago and no signs since all the treatment all ended. The Radiotherapy procedure and equipment was very interesting for me (the opportunistic Physicist). They use splines to form an aperture for the beam to fit the appropriate area and use three different radial directions for the beam to reduce damage to surrounding tissue. The beam uses a linear accelerator as an energy source for an electron beam which hits a target and produces the X rays (also interesting). It's very high precision stuff (they work to about a mm) and I lay totally motionless during the exposure to help the beam avoid nearby important bits. Nearly seven weeks of commuting up to London for it was far more knackering than the treatment itself, I think. So far so good!
     
  17. Jun 16, 2018 #16

    sophiecentaur

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    Looking at the units of that:
    A Gray is one J of Energy per kg. I'm not sure what the meaning of one Gy times 1cm2 could be indicating.
    Perhaps, if the density is in gm/cm3 then XGycm2 = X J cm/ρ
    If ρ is 1 (reasonable) then the thickness of the tissue that a 1cm2 beam passes through will dissipate X Joules of energy per cm as it passes through. I guess that's reasonable because the thicker the tissue being imaged, the less dose does the body get from a given beam power and area. Obvs, a good Xray image will use just enough radiation to register the most dense tissue of interest.
    It seems a funny approach to units though. What do you think?
     
  18. Jun 16, 2018 #17
    Hi,
    Gy.cm2 is a dose per fluence unit (D/phi)

    For example for k Gy.cm2 and for a parallel beam with a radius r the fluence rate is N/(pi.r.r) and the dose rate in Gray per second is k.N/(pi.r.r) (N the particles flux in s-1)
     
  19. Jun 16, 2018 #18

    sophiecentaur

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    That has confused me a bit, I'm afraid.
    The basic Definition of 1Gy is in terms of Energy per kg and that is how it seems to be defined everywhere I look. Using a derivative of the Gy is not an intuitive thing to do and it must be for a pretty subtle reason. The thing of interest if you want to assess potential damage must surely (once you have eliminated frequency variation etc.) still be the Gy. I can see how a source can be calibrated in terms of Power Flux or Flux density, which gives the Energy involved when the time is specified. That is independent of the mass of the receiving piece of body.
    Gy includes the mass of tissue.
    I have been looking at this link from the NPL which has helped a bit and it sort of suggests to me that the way doses are specified could usefully be looked at again. But I guess that it would all make perfectly reasonable sense to someone in the business.
     
  20. Jun 16, 2018 #19
    Since the dose which is specified by the energy deposited in tissue per unit mass does not really provide a risk estimate from a radiation exposure due to the fact that the amount to tissue receiving the dose must be taken into account it has become fashionable in the last decade or so to specify the dose area product (DAP) for a given film. This number is automatically calculated by the machine based on the collimator setting, the tube current, the time of exposure, and the KVP used. The larger the dose and or area exposed the greater the risk. The maximum area for a film is about 1000 cm2 . For 70 kVp (3 phase unit) the dose rate is about 0.06 mGy/mAs.. For 100mAs you get 6mGy or 0.06dGy. I am not familiar with the term EL_s (European?) in conjunction with DAP and for this exposure the 300 cannot be the DAP. If the DAP were cGycm2 then it would be reasonable.
     
  21. Jun 16, 2018 #20
    Hey no problem.

    So 6 years and you haven't developed anything malignant due to radio-therapy? That's really interesting, I am under the impression that one spine x-ray which blasts you with 2 mSv worth of X-ray dooms you for life. I'm really worried.

    Anyway, glad to know you are OK!
     
  22. Jun 16, 2018 #21

    I haven't the foggiest idea, that's why I'm here asking those who might have the technical side of the knowledge.
     
  23. Jun 16, 2018 #22
    0.06dGy equals 6 mSv. For a lumbar spine X-ray it is way too high. Heck for a CT that is way too high.
     
  24. Jun 16, 2018 #23
    In terms us laymen could understand, the radiation does for this 1 shot/view, in mSv, would be??
     
  25. Jun 16, 2018 #24
    Hi, thanks a lot for the information. Can you explain with a bit more detail how it is calculated? Technical documents are also appreciated :)
     
  26. Jun 16, 2018 #25
    Hello folks, thanks for the help so far but I am able to determine that "El_s" should actually be "EI_s", no idea what the "s" at the end stands for still but am pretty sure that "l" should infact, be "i", so it's most likely exposure index, as Asymptotic had suggested
     
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