SPOILING OF TRANSVERSE MAGNETIZATION IN GRADIENT-ECHO (GRE) IMAGING DURING THE APPROACH TO STEADY-STATE

The signal evolution behaviors and corresponding image appearances for different methods of spoiling or refocusing the transverse magnetizat ion in short TR gradient-echo imaging during the approach to steady st ate were investigated experimentally and using computer simulations ba sed on the Bloch equations. Specifically, ideally spoiled, gradient-sp oiled, gradient-refocused, and RF-spoiled pulse sequence configuration s were studied. This study showed that, for the gradient-spoiled confi guration, the signal evolution is position and phase-encoding order-de pendent and, under typical imaging conditions, can deviate substantial ly from the ideally spoiled signal evolution at some spatial positions , resulting in intensity banding image artifacts. For the gradient-ref ocused configuration, the signal evolution oscillates toward the stead y state and, generally, does not closely approximate that of ideal spo iling, resulting in different image contrast or image blurring. Using RF spoiling, the signal evolution closely approximates the ideally spo iled case for flip angles less than approximately 20 degrees and T-2 v alues of less than approximately 200 ms and results in relatively arti fact-free images. Also, this study showed that, for RF spoiling, an RF -pulse phase-difference increment other than 117 degrees, such as 84 d egrees, may be optimal for gradient-echo imaging during the approach t o steady state.