Shin-ichi Urayama, Presenter: Nothing to Disclose

Leon Axel MD, Abstract Co-Author: Nothing to Disclose

Jun Okamoto, Abstract Co-Author: Nothing to Disclose

Takashi Azuma, Abstract Co-Author: Nothing to Disclose

Sugimoto Naozo PhD, Abstract Co-Author: Nothing to Disclose

Hanakawa Takashi MD, Abstract Co-Author: Nothing to Disclose

Sadami Tsutsumi, Abstract Co-Author: Nothing to Disclose

Hidenao Fukuyama, Abstract Co-Author: Nothing to Disclose

While steady state free precession (SSFP) imaging can provide improved SNR, it is subject to transient artifacts whenever the steady state is interrupted. The use of intravoxel phase dispersion is proposed as a new method to reduce the transient artifact in coherent SSFP imaging.

Theory: Transient response of the magnetization from the initial to the steady state is known to evolve along a spiral orbit in (Mx, My, Mz) coordinates [MRM 46:149–158, 2001]. The axis of the orbit is almost parallel to the magnetization vector of the steady state and the rotation angle (determined by the flip-angle and the free precession angle during TR) is constant. Therefore, if the initial magnetization is distant from the axis, the successive signal changes, which are proportional to the distance, will be large and will produce a large artifact. Intravoxel phase dispersion, which can be induced by slightly reducing the dephase- and the rephase-gradients associated with slice selection, causes precession angle variation and, as a result, signal dispersion around the spiral orbit. Since the dispersion increases with successive RF iterations, the net dispersed signal approaches the axis rapidly and the difference between successive signals is smaller, reducing the associated artifact.Experiment: Magnetization-tagged imaging of the myocardium with coherent SSFP was developed using the proposed method, Transient Artifact Reduction with Dispersion of phase (TARD), implemented on a conventional 1.5T MRI system (Sonata, Siemens Medical Solutions). The amount of the reduction of the dephase- and rephase-gradient was adjusted to produce a 90 degree dispersion along the slice thickness direction during TR. Adjustment of RF phase angle was done with prescans taken during successive breath holds. Five normal volunteers were examined. Imaging parameters were: TR, 3.15 ms; TE, 1.58 ms; FOV, 350-394 mm; acquisition matrix, 256 x 128-192; dummy RF pulses, 1-2.

In all cases, the transient artifact associated with tagging was significantly reduced without reducing signal intensity.

TARD is a simple and promising method for the reduction of transient artifacts in coherent SSFP imaging.

Urayama, S, Axel, L, Okamoto, J, Azuma, T, Naozo, S, Takashi, H, Tsutsumi, S, Fukuyama, H, Transient Artifact Reduction with Dispersion of Phase (TARD) in Coherent SSFP Imaging.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4405948.html