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Medical X-ray, CT scan, Ultrasound, MRI detecting blanks ?

  1. Jan 7, 2009 #1
    This is for a sci-fi novel I’m writing, and I actually posted this at another site but the answers given were a little vague.

    What would occur, either on a computer monitor (or other monitoring device, depending on the machine) or on a photo film, if an:
    a. X-ray
    b. CT scan
    c. ultrasound
    d. MRI scan
    did NOT pick up any information?

    To explain better, doctors are placing a person who is completely encased by a transparent, unknown material under an X-ray, CT scan, ultrasound, and MRI and yet all these detecting machines register as though the encased person is not there at all
    (the encased person is actually in another dimension yet is seen, heard, and felt by the doctors because of psychic stimulation of the doctors' brains, in the brain areas of sight, sound, and touch).
    Basically, I’m wondering if the X-ray film will appear just black...and if the CT scan picture will appear just black...and if the ultrasound will show blackness on the screen monitor...and if the MRI would show nothing on its monitor/picture...

    I suppose another way to ask this question is what would occur if any of the above radiological/medical devices were activated while nothing was present for the devices to pick up/register?

    Thank you very much for any help :-)
  2. jcsd
  3. Jan 7, 2009 #2


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    What has your research shown you so far? Are X-ray prints traditionally positives or negatives? What about the other imaging modalities that you are asking about?
  4. Jan 8, 2009 #3
    My research so far has revealed that x-rays would be black, ct scans would show a "table" only (whatever that means), ultrasound images would be black (I suppose a black screen on the monitor?), and MRI would show "noise" or k-space...

    x-rays being black I totally get, yeah so it's a black x-ray, with nothing there.

    ct scans showing a "table" needs more explanation...if someone knows, please mention, I need details...

    ultrasound images as black I suppose means on the monitor, as I mentioned above, but I'm not sure exactly...

    and I couldn't find any more info online about MRI scans showing just "noise" or k-space...I realize what is the mathematical explanation of k-space, more or less 3D x,y,z coordinates, gradients, etc. (just finished multi-variable and vector calc class this past semester, I'm a math major) but that doesn't tell me what it looks like on the viewing screen/monitor/whatever...

    So that's what I have so far...just need more details...anyone?? please?
  5. Jan 9, 2009 #4


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    Gold Member

    The CT scan image might look similar to this


    This is an image of a water phantom. Yours would look less dense because you are basically scanning a large tube of air since the body you see is not really there. Correct?
  6. Jan 10, 2009 #5
    An x-ray exam is essentially a shadow, made with light of shorter wavelengths that can penetrate more materials than visible light. They are rarely done on film anymore. But they still use the same convention as if you were viewing film. More dense areas (like bone or metal) appear lighter (less penetration) while less sense areas (muscle, fat, air) appear darker (more penetration. For more penetration, you increase the voltage (they would say kV) to as high as 150kV. A typical abdomen would be imaged between 60-81kV, and is equivalent to about 20cm of water for the same density. Modern xray detectors in the medical setting are usually no larger than 35cmx43cm, so a whole-body image would take several shots.

    A CT is essentially a series of X-ray exposures, so they are shadows as well. The difference is that they aquire many projections and then "C"ompute the "A"xial "T"omography. What you then get to look at is a "slice" of the body without the shadows of interfering anatomy you would see with a conventional exam. Again, what you would see would depend on what was penetrated. With large transitions in density (like a metal object) you might see a starburst effect around it.

    Ultrasound is sometimes called "Echo". You send ultrasonic pulses of varying frequencies through a hand-held transducer, through a puddle of goop to the body. The frequencies and amplitudes used are usually the same through human tissue. For your "cocoon, there might be a problem seeing anything at all if it can't make good contact, or doesn't transmit the ultrasonc vibes.

    MRI is very different. It is basically counting the density of hydrogen nucliei and isolating their location. Human tissue is mostly water, and water is mostly hydrogen. Depending on the material of your cocoon you might have different results. If it is ferromagnetic, you won't get it near the magnet or it might fly into it, causing damage and much time to remove it. If it is conductive, it could cause artefact in the image ranging from black areas surrounding it, to distortions of the image around it and it could cause heating of the body during the exam. If it is neither of those things, the scanner should be able to see inside, as long as there is no other "magic space material" that can block RF energy or magnetism. Remember, the MRI scanners pretty much only see hydrogen.

    Of course, as the author you can make the doc see whatever you want on the screen. Have fun with it!

    EDIT: If I would read a post twice, I could give shorter answers...
    a. you would see the density of the shell (provided it can be penetrated) without the usual anatomy.
    b. Same as xray. Axial slice of the shell show lighter than empty space (dark).
    c. Black, if anything. They wouldn't attempt echo if they can't get skin contact.
    d. Same as original answer. But they would know immediately, as the machine would not be able to "tune" if there was not a hydrogen mass in the bore. They wouldn'y get to start the actual scan.
    Last edited: Jan 10, 2009
  7. Jan 10, 2009 #6
    Tsu, thank you, good, helpful pic.

    And actually, I should have mentioned that it would be best if anyone can give me links to some illustrations/photos of what would appear if nothing was detected by any of these medical imaging devices.

    xykotik, thank you for your detailed response, very helpful. I especially appreciate what you mention about the MRI...if it cannot detect any hydrogen, the MRI machine will not start at all, this is very good to know. This is mostly what I am looking for, whether nothing or odd images will appear on the monitoring devices, or if something will malfunction or not work at all.
    I suppose anyone who uses these devices on a daily basis, such as those who work in a hospital radiology department might know what would occur if nothing was registered.

    Also xykotik, what you mentioned about ultrasound has me wondering if I need to work it into the story a little better...need to think about it some more...

    But thank you again!
  8. Jan 10, 2009 #7
    I'm studying x-ray physics and the application in medicine in school right now, so I think I can answer your question.

    Well, assuming your 'shell' is made of matter, it would attenuate the x-ray beam normally. So basically, assuming it's as dense or denser than bone, the x-ray & CT scan would appear as completely opaque, or on the film/monitor, solid white. MRI works on a very different principle; depending what the material is made out of, it would probably work like normal -- taking cross sections of the shell. If there was anything in there, I would believe the MRI would pick it up; but since the fellow is not currently occupying our dimension, they would probably see it as hollow.
  9. Jan 10, 2009 #8
    By the way, MRI can detect and image materials without hydrogen. So long as there's any ionic molecule/atom in the composition of the shell, the MRI will work. They just use hydrogen because it's so plentiful in the human body.
  10. Jan 13, 2009 #9

    Ivan Seeking

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    Hi! It's Tsu. Ivan is logged onto my computer and I don't feel like logging off and in. :biggrin:

    If it's images you want/need, I got this one with a single google (be sure to click on images on your google page).

    http://www.dochazenfield.com/images/CT_Maxillary_Sinusitis.jpg [Broken]

    This CT scan of the sinuses is a good demonstration of the visual difference between air and fluid. You can see one maxillary sinus is sick (opacified - full of guck) and the other is normal (full of air).
    Last edited by a moderator: May 3, 2017
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