"T2* decay refers to an exponential decrease in Mxy (i.e. signal strength) following the initial excitation pulse as a function of time constant T2*. A picture of the signal or free induction decay (FID) is shown on the right, occurring immediately after a 90o RF excitation pulse in a liquid phantom."
"The relationship between T2 and T2* can be illustrated by the multiecho spin echo sequence shown in Figure 2. The 180 degree RF pulses used to generate the echo are rephasing the spins that have undergone T2* decay. The gradual decline in signal from subsequent echoes reflects T2 decay. T2* decay can be refocused by 180o pulses as in the simplified spin echo sequence in the figure but not be gradient refocusing seen in gradient echo sequences."
"The effects of T2* can therefore be seen and utilised in gradient echo imaging and in the FID signal following a 90o RF pulse."
"static field non-uniformity within each voxel: due to imperfections in the construction of the scanner magnet itself, as well as from magnetic susceptibility effects in the patient inside the field"
"spin-spin interactions (T2 relaxation)"
Expected headings
"Discussion"