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Homework Help: NMR Signal Physics Question! Please help!

  1. Jan 4, 2010 #1
    Suppose that you obtain a one dimension magnetic resonance image from two water-filled cubic shaped containers arranged as shown below. This diagram is a cross-section of the cubic containers in the x-y plane.

    figure description:
    -one of cube's is 2 cm wide, the other is 1 cm wide, and the 1cm cube is on top of the
    2cm cube
    -y direction, and x-direction are denoted as usual

    To obtain the one-dimensional image a gradient echo MRI signal is acquired while a magnetic
    field gradient of 10 mT/M in the x-direction is held on. Assume that signal (S(t)) has the form
    S(t) = Sa(t) exp(-i2pi*(f_a)(t) + Sb(t) exp(-i2pi*(f_b)(t) , where Sa(t) and Sb(t) are both sinc functions.

    Recall that the sinc (Fsinc(t)) defined as:

    F_sinc(t)= {A*sinc(pi*(delta of frequency)(t)]/ (pi*(delta of frequency)(t)

    which is the Fourier Transform of a rectangular function of frequency with width delta frequency, where A is the areaunder this rectangular function

    a) Determine the time between the zeros of Sa(t) and Sb(t).
    b) Determine the frequency difference |fa - fb|.
    c) Suppose that another one-dimensional image is acquired of the same water-filled
    cubes, but this time with the 10 mT/M gradient in the y-direction. For this gradient echo
    signal, determine the time between the zeros of Sa(t) and Sb(t) and determine the frequency
    difference |fa - fb|.

    Please help... need a lot of help here!

    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jan 4, 2010 #2


    User Avatar
    Science Advisor
    Gold Member

    The forum rules require that you show your work or your attempt at solving the problem. Hint: Beyond one MRI fact, this problem is about Fourier transform properties.
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