MRI Studio Forum » DTI Studio

Repeated measurements and regid body registration

(6 posts)
  • Started 7 years ago by yongzhangdti
  • Latest reply from yongzhangdti
  1. yongzhangdti
    Member

    Dear everyone,

    Repeated measurements are usually performed in DTI to improve SNR. Just wonder how DTIStuodio deals with the repeated measurements. My first guess is FA will be calculated based on each measurement and then the arithmetic mean of FA will be calculated across the multiple measurements or raw diffusion weighted images will be averaged first and the average images will be used to calculate FA.

    Also we would like to perform rigid body registration with Automatic Image Registration (AIR) to correct any potential motion artifact. Raw diffusion weighted images with different gradient directions applied are registered to B0 image. It seems that calculated FA values decrease for about 10-20% as compared to those without AIR registration. Just wonder if the difference is expectable and reasonable.

    Thank you very much for your help!

    Yong

    Posted 7 years ago #
  2. yongzhangdti
    Member

    Is there any additional smoothing step involved in rigid body registration which may decrease FA?

    Yong

    Posted 7 years ago #
  3. JHMI_Hangyi
    Member

    for multiple repetition dataset, the program will use each image individually, without averaging. for AIR, no smoothing performed internally. the FA dropping is not expected after AIR.

    Posted 7 years ago #
  4. yongzhangdti
    Member

    Hi Hangyi,

    Many thanks for your reply! Say we have four repeated measurements. If the program uses each measurement individually, we should have four FA maps from the different measurements. However, DTIStudio provides only one FA map even if a user specifies multiple repeated measurements. Just wonder how the program combines the FA map from each measurement. Thanks again!

    Yong

    Posted 7 years ago #
  5. JHMI_Hangyi
    Member

    the program will use "each image", not "each measurement" (I suppose that you mean "each repetition") individually.

    if a repetition has one B0+6DWIs, for 2 repetition, the program will use them just as a dataset with 2B0s+12DWIs. mathematically, one repetition results in a 6-equations system, two repetitions result in a 12-equations system. as long as the system has at least 6 uncorrelated equations, we can find out the 6 unknowns of the tensor elements and then one FA, not 2FAs. the more equations you have, the better SNR you get.

    for details of tensor calculation, please refer to: DtiStudio: resource program for diffusion tensor computation and fiber bundle tracking. Comput. Methods Programs Biomed. 2006 Feb;81(2):106-16.

    Posted 7 years ago #
  6. yongzhangdti
    Member

    Got your paper. Thank you very much, Hangyi!

    Yong

    Posted 7 years ago #

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