Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Pseudo frequency? Related to phase shift

  1. Aug 20, 2013 #1
    I am reading a text about how MRI works and I came across a thing that I am totally confused.

    The book mentions about that few particles side by side with their nuclei spinning at the same frequency but they all have a phase difference. Since MRI cannot measure the phase differences directly, it will try to encode the phase differences in term of so called pseudo-frequency. With each unique pseudo frequency the MRI will know where that particle coming from.

    The thing I am confused is how can each nuclei share a common frequency yet they have a different frequency due to their phase differences?

    Am I misunderstanding something????
     
  2. jcsd
  3. Aug 21, 2013 #2

    Baluncore

    User Avatar
    Science Advisor

    I think the phase difference you are referring to is determined by the differences in distance from the nuclei to the antenna.
     
  4. Aug 21, 2013 #3

    marcusl

    User Avatar
    Science Advisor
    Gold Member

    They precess at the same frequency in a uniform magnetic field. Once a field gradient is applied, their frequencies differ slightly depending on position. The gradient means that the applied field changes a little bit, linearly with position. This results in the basic frequency being shifted, typically, by parts per million.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Pseudo frequency? Related to phase shift
  1. Phase Shift (Replies: 1)

  2. Frequency Shifting (Replies: 5)

  3. QPSK phase shift (Replies: 2)

Loading...