# Data Space and *K*-Space

Just the axes. Asymmetry in the data space is possible, because the axes of data space are *time*. This is obvious, because acquiring one phase encoding step (filling a line in the frequency encoding direction) takes milliseconds, whereas filling *k*-space to have a full dataset in the phase encoding direction can take minutes. *K*-space axes are *spatial frequency* and so this matrix is symmetric. Getting from data space to *k*-space is a simple mathematical manipulation. You can Fourier transform either to get the image. We work with *k*-space and not data space because it is more instructive about *what* the data is and thus aids understanding.

So they're equivalent, for all intents and purposes!

What the data in *k*-space really is, is explored more fully in the What Is K-Space? tutorial.

Further reading on this topic:

Books: MRI The Basics p163