Showing papers on "Steady-state free precession imaging published in 1989"
TL;DR: It is shown theoretically and confirmed by experiments on phantoms that diffusion coefficients can be directly measured from SSFP images when large enough diffusion gradient pulses are used.
Abstract: A theoretical analysis of the effects of diffusion and perfusion in steady-state free precession (SSFP) imaging sequences sensitized to intravoxel incoherent motions by magnetic field gradients is presented and supported by phantom studies. The capability of such sequences to image diffusion and perfusion quickly was recently demonstrated. The possible residual effects of T1 and T2 in diffusion measurements are evaluated, as are the effects of the sequence design and the acquisition parameters (repetition time, flip angle, gradient pulses). It is shown theoretically and confirmed by experiments on phantoms that diffusion coefficients can be directly measured from SSFP images when large enough diffusion gradient pulses are used.
209 citations
TL;DR: In this article, a simple mathematical description of the SSFP NMR signals is presented, which can be used to accurately model SSFP experiments on a 40 cm bore 2.35 T Bruker Medspec system.
90 citations
TL;DR: In this paper, a fast scan technique for magnetic resonance imaging of molecular self-diffusion is described, based on a modified CE-FAST nuclear magnetic resonance sequence acquiring echo coherences of the steady-state free precession (SSFP) signal.
49 citations
TL;DR: A fast imaging technique, missing pulse steady‐state free precession (MP‐SSFP), is described and it is shown that θ1 and θ2 provide two degrees of freedom to optimize the signal‐to‐noise ratio and improve tissue contrast.
Abstract: A fast imaging technique, missing pulse steady-state free precession (MP-SSFP), is described. MP-SSFP is one of a class of steady-state free precession techniques in which every nth RF pulse is missing. MP-SSFP has been implemented for the case where every third RF pulse is omitted: [-theta 1-r-theta 2-r-echo-r-]. A RF-refocused echo forms at the time of the missing pulse. This echo is less sensitive to field inhomogeneities than the gradient-recalled echoes used in most fast imaging methods. An analytical expression is obtained for the signal strength as a function of the flip angles theta 1 and theta 2, the interpulse interval tau, and the amount of interpulse dephase. The expression shows that theta 1 and theta 2 provide two degrees of freedom to optimize the signal-to-noise ratio and improve tissue contrast. Two different cases, theta 1 = theta 2 and theta 1 = -theta 2, are described to demonstrate the difference in contrast. The first case gives a strong signal from spins with short T1 and short T2 while the second case has contrast very similar to a conventional SSFP technique. The theoretical expression predicts that the signal consists of multiple components which may be observed experimentally by adjusting the gradient pulses.
35 citations
Patent•
13 Jul 1989
TL;DR: In this article, a series of 90° RF pulses are applied, each in the presence of a slab or slice select gradient (52), to excite nuclear magnetic spins in the selected slab.
Abstract: A series of 90° RF pulses (50) are applied, each in the presence of a slab or slice select gradient (52) to excite nuclear magnetic spins in the selected slab. The spins are phase encoded (56). A preliminary read gradient (60) of one polarity and a primary read gradient (62) of the opposite polarity are applied to induce a gradient echo (64) during the primary read gradient. After the primary read gradient, a residual magnetization dephasing gradient pulse (66, 66') is applied, with an alternating polarity from cycle to cycle. The residual magnetization dephasing pulse has an area defined by the product of its duration and amplitude which is selected relative to the area of the preliminary and primary read gradient pulses such that the residual magnetization does not refocus during collection of the gradient echo data in later cycles.
16 citations