With regard to MRI, the complicated signal we wish to decompose is the MR echo containing the frequency- and phase-encoded spatial information necessary to construct an image. Following the slice selection gradient for a typical spin-echo sequence, which isolates a particular imaging plane, all spin systems precess at the same frequency and phase as dictated by the main magnetic field (Bo). The application of superimposed, dynamically changing gradient fields introduces spatially dependent variations in frequency and phase across the ROI, effectively interrogating the anatomy for all different spatial frequencies. Strong gradients are necessary to seek out high spatial frequencies (detail), whereas less steep gradients bring out lower spatial frequencies (contrast). In addition, these smaller gradients generate much more collective signal than steep gradients because precessional frequencies and phase are overall more similar across the ROI (this will be evident when we compare the central portions of k-space with the periphery, discussed later). The amplitude of the returning echoes will vary with tissue composition, TR, and TE [3, 4].
New steeper new applied gradient, the greater amount of possible break up regarding twist possibilities is achievable
So it if not hopelessly tricky signal is digitized, dismantled of the Fourier transform, and you will joined on the k-room, an effective 2D Fourier place that organizes spatial volume and you will amplitude suggestions (Fig. 6A , 6B , 6C , 6D , 6E ). (more…)
