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DLP projector inside an MRI room

Vicente Parot
Prodigy 20 points

I'm working on a design which contemplates a DLP projector inside an MRI examination room.  This ambient has special conditions concerning high magnetic fields, high frequency variations in magnetic field and an electromagnetic shielding to isolate MR signal readings from outside RF signals among others.

Does anybody know the interactions between a DLP projector system and magnetic / electromagnetic fields? Is the DLP system going to work in high magnetic fields? does it emit RF signals? etc.

Thank you in advance.

  • 0
    TI__Mastermind 49905 points

    Hello Vincente, 

    First welcome to the DLP section of the TI E2E community! 

    I am consulting with others here at DLP to get their input regarding your question.  Your application sounds very interesting.  I will post back in the next day or two with what I find out with respect to your questions.

    Fizix.

  • 0 in reply to Fizix
    TI__Mastermind 49905 points

    Hello again Vincente,

    A magnetic field should not impact the mirrors although a strong EMF could interfere electrically.  The DMD itself does not emit RF signals but the drive circuitry, in particular the reset waveform, does have significant pulses.  Where they would show up and whether they are significant to the system is very system dependent.

    The only way to know this would be to test the system for EMC/EMI and EMF compatibility.  We have not performed any evaluations at levels such as those in an MRI.

    Fizix

  • 0 in reply to Fizix
    Prodigy 20 points

    Thank you very much.  I'll do my tests and let you know if anything surprising comes along.

  • 0 in reply to Vicente Parot
    Prodigy 60 points

    Hello,

    I'm very interested in this question as well. We are operating a number of projectors very close to the MRI. We have been using LCD projectors without significant problems, but the only DLP we ever tried a few years ago did not fare well. Hence I have two questions, A) Is it really true that DLP technology in itself is not affected by strong magnetic fields and B) Does anyone have a working setup ? We do have EMI shielding and filtered power for the projector setups.

    Thomas

  • 0 in reply to Thomas Witzel
    TI__Mastermind 49905 points

    Hello Thomas,

    I believe that the DMD itself is not particularly affected by strong static magnetic fields, but I do not know about the supporting electronics.  Further, I do not know the result of quickly changing fields.

    I would like to hear a little more about the DLP projector that did not fare well.  Could you describe what happened when operated near the MRI.

    Fizix

  • 0 in reply to Fizix
    Prodigy 60 points

    This was many years ago, and not necessary related to the DLP technology, but it smoked. I'm in the process of evaluating new DLP projectors in the fringe field of the magnet ( 100 gauss region). I'll report back if there is issues.

    Thomas

  • 0 in reply to Thomas Witzel
    TI__Mastermind 49905 points

    Thomas,

    Thank you for the reply back on this.  I would be very interested to know the results of your investigation.

    Fizix

  • 0 in reply to Fizix
    Prodigy 20 points

    Hi Fizix,

    I am also interested in a related question. So essentially I want to reach a refresh rate of 120 Hz in MRI (3D is less important for me but good to have for future use). If I use a DLP projector and drive the display with, say, a normal movie (In fact I will use some program usually used to run psychology experiment to draw each frame for display on the fly). And the person inside the MRI scanner does not wear the glasses. Will this achieve the effect of a normal movie displayed in 120 Hz? And can this type of projector be driven by normal graphic cards easily as if a normal 120 Hz display is connected? Do I need any specific configuration?

    Related to this, which brands would you recommend that have the least rainbow effect? 

    If in future I want to have 3D effect, do you think the glass can function within high frequency RF field and 3 T static magnetic field (with the projector itself outside strong magnetic field)?


    Thanks!


    Mingbo

  • 0 in reply to Mingbo Cai
    TI__Mastermind 49905 points

    Hello Mingbo,

    Welcome to the DLP section of the TI E2E Community.

    Some of the newer projectors employ a 6x color wheel  - usually higher end projectors.  Do a search for "DLP projectors 6x color wheel".

    I knowBenQ and Optoma make 6X color wheel projectors - some of them are 3D. 

    You are correct that if you were to make a "3D" that did not have alternating viewpoints (i.e. left and right eye) and played the movie without glasses you would effectivily have a move that plays at 2X the refresh rate (i.e. a full 60 Hz 3D would effectively give a120 Hz regular movie.  You would have to build the movie. 

    I do not know of any editors that will do this for you.

    Fizix

  • 0 in reply to Fizix
    Prodigy 20 points

    Hi Fizix,

    Thanks very much for pointing to the 6x color wheel projectors! From my understanding of your reply about using the projector as a 120 Hz non-3D projector, I still have several questions:

    1) It sounds like special program or driver is needed for playing 3D movie (since you mentioned about editor to build movie). I will be using a Matlab toolbox called Psychtoolbox to draw the display in real time instead of playing some pre-made video. This toolbox is already capable of driving traditional reg/green or polarized stereo display, stereo goggles etc. through operation of GPU wtih OpenGL. Given this description of capacity, do you think a DLP projector can be operated similarly as those traditional stereo display?

    2) According to the documentation of Psychtoolbox, the way the toolbox manage timing of drawing display in real-time is to draw image to an invisible backbuffer (VRAM), and wait for the vertical blank/ retrace (they call it VBL) of the display (traditionally, e.g., from CRT monitor) and then graphic hardware switch the buffer for the LUT and DAC to draw image on the display. It is said that LCD projector has a long and variable delay between the VBL signal and the time each pixel actually change color. I am still learning the mechanism of DLP projector. Do you have idea of this delay from VBL to actual change of color on a DLP projector? If you happen to know such delay for some brands it is also great.

    3) Following the last question, if a DLP projector is running in 120 Hz (60 Hz on each eye), does the VBR signal goes in 60 Hz or 120 Hz? Actually, is there such a similar VBL signal in DLP projector?

    Thanks very much!

    Mingbo