Prepulses are prior to the excitation. To optimize, this is usually as short as possible. The time from the prepulse to the center of K-space (K0) is the prepulse delay time, also known as the inversion time (TI). Prepulses are more effective if the flip angle is kept as short as possible to values such as 10 to 30 ms.
The Mx and My data (digital MR signal) sampled and stored during data acquisition as a function of time and phase from an MRI sequence are called raw data. The horizontal axis is the frequency code, the vertical axis the phase code (of the protons).
Every point in the raw data matrix contains part of the information for the complete image. A point in the raw data matrix does not correspond to a point in the image matrix. The outer rows of the raw data matrix provide information regarding the borders and contours of the image, detailed structures, and also determine the resolution.
This is also called k-space data.
The mathematical process by which the displayed image is produced from the raw k-space data obtained from the receiver circuitry, typically utilizing Fourier transformation and selective filtering.