Steady state of gradient echo sequences with radiofrequency phase cycling: Analytical solution, contrast enhancement with partial spoiling

✍ Scribed by Carl Ganter

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 422 KB
• Volume: 55
• Category: Article
• ISSN: 0740-3194
• DOI: 10.1002/mrm.20736

✦ Synopsis

Abstract

Spoiled gradient echo sequences can only reach a homogeneous steady state if sufficiently strong crusher gradients are used in combination with RF phase cycling (RF spoiling). However, the signal depends quite sensitively on the chosen phase increment ϕ and—lacking analytical solutions—numerical simulations must be used to study the transient and steady‐state magnetization. For the steady state an exact analytical solution is derived, which holds for arbitrary sequence and tissue parameters. Besides a considerably improved computation performance, the analytical approach enables a better understanding of the complicated dependence on ϕ. For short repetition times (TR) the regime of small ϕ turns out to be particularly interesting: It is shown that the typical ϕ~c~, where RF spoiling starts to become effective, is essentially inversely proportional to T~2~. This tissue dependence implies that contrasts can be considerably larger with partial spoiling (ϕ ≈ ϕ~c~) than with conventional RF spoiling (ϕ ≫ ϕ~c~). As an example, the uptake of contrast agents in tissues is investigated. For typical parameters a considerably improved contrast enhancement can be obtained, both theoretically and experimentally. Magn Reson Med, 2006. © 2005 Wiley‐Liss, Inc.