Spiral echo planar imaging using segmented trajectory

Abstract

Ultra fast MR imaging is recently focused because of the necessity of dynamic imaging and Cine imaging in medical implementation. Also the artifacts due to long imaging time can be reduced by fast imaging. Spiral echo planar imaging is newly refocused among these fast sequences. Since 1986 when the spiral-scan has been proposed by Z.H. Cho et al., many similar spiral scan techniques were proposed such as square spiral scan, trapezoidal spiral scan, interlaced spiral scan, segmented spiral scan, etc. The interlaced spiral scan and segmented spiral scan is recently proposed and used since they have many advantages as dynamic imaging or motion imaging sequences. In this paper, two techniques are compared in many ways such as effects of $T_2$-decay, phase error and motion artifact. $T_2$-decay is an important phenomenon of MR imaging. The effect is shown as reduction of FID signal in time. We simulated the artifact of $T_2$-decay and proposed some signal processing algorithm to reduce $T_2$-decay. The phase error was also simulated with two spiral scan techniques, so that the images were compared with each other. The phase error distorts k-space trajectory since the off-resonance affects the spin which is excited and encoded. The motion artifact is simulated using objects which move in different velocity. For the motion artifact, the segmented spiral scan worked successfully. The theories and results of spiral simulation will described, and interlaced spiral scan and segmented spiral scan will compared in the respect of the artifacts described above.