To achieve T2* weighting in a GRE sequence, which parameters are recommended?

T2* weighting in a Gradient Echo (GRE) sequence is influenced significantly by the choice of timing parameters, mainly echo time (TE) and repetition time (TR), as well as the flip angle. When aiming for T2* weighting, it is essential to maximize the time for T2* decay to have a significant effect on the image contrast.

Selecting a small flip angle is beneficial because it reduces the amount of transverse magnetization that is created and maintained before the TE, allowing a greater proportion of the signal decay due to T2* effects to influence the final image.

The use of a long TE allows sufficient time for T2* decay to occur before the signal is readout. This is crucial since T2* weighting is primarily affected by the decay of transverse relaxation, which happens over time. Short TR values are ideal in this context as they minimize the influence of T1 relaxation, allowing the imaging sequence to focus on T2* characteristics without being overly influenced by T1 recovery processes.

Thus, employing a small flip angle combined with a long TE and a short TR successfully achieves T2* weighting, as it enhances the impact of T2* decay while maintaining efficient imaging within the available timeframes.