Digitisation of a MRI signal. Digitised numbers are represented as greyscale values in this diagram.
CORRECT. Each MRI signal is sampled into a list of numbers, which are recorded in one line of k-space. This must be repeated many times (with different phase encoding) to produce just one image.
Although the MRI signal is an analogue emission (it varies continuously), we record a digital representation of that signal (a list of numbers). Thus digitisation is an approximation of an analogue signal. When we have filled k-space, we can perform calculations on this matrix of (complex) numbers to produce the MRI image.
INCORRECT. This is not digitisation. The fast Fourier transform processes MRI signals to produce an image, and then only after many MRI signals have been digitised and recorded.
Further reading on this topic:
Books: MRI From Picture to Proton p48