REPETITION TIME (TR)
Is the time between RF-excitations of MR acquisitions. It is also used for timing between 3D-volume sets of images as in volume imaging, although the investigated sample is globally excited more often (i.e. slice-specific). Within a TR, there could be one or more TEs, one or more phase encoding. TR directly affects the contrast, and in dependence of the T1 of tissue influences sensitivity (i.e. usually by setting the flip angle to the Ernst Angle). TA is proportional to TR.