What Is K – Space In MRI?
K – space is a imaginary space which represents a raw data matrix. It represents stage between reception of signals and image formation. After acquisition all the signal are stored in K- space In a particular fashion. This raw data from K- space is used to reconstruction image by Fourier transformation.
The k – space has two axis, one is Horizontal axis and other is frequency axis. The Horizontal axis represent the phase axis and is centered in the middle of several horizontal lines. The frequency axis of K – Space is vertical and is perpendicular to the phase axis. The receive single are filled in K- Space as horizontal lines. The number of lines of K- Space that are filled is determined by the number of different phase encoding. If 128 different phase encoding steps are selected then spin – echo imaging one line of K- space are filled to form an image. Array of signals as line in the K- Space does not correspond with rows or columns of pixel in the image. It is Complex transformation of this data into an image where center part of K – Space represent contrast of the image and the periphery corresponding with resolution and fine details.
Two halves of K – Space right and left or upper and lower are exact symmetric conjugate and represent same information. This fact is used to manipulate K- space sampling to get same image in less time. in fast imaging like single shot fast spin echo sequence such as HASTE just more than half of K – space is filled. In ultrafast Echo Planar imaging (EPI ) all the K- Space lines required to form an image are filled within a single TR , thus reducing the scanning time in second.