Quantitative Measurements of Flow Acceleration by Means of Nuclear Magnetic Resonance Imaging

✍ Scribed by Tie-Qiang Li; Lars Ödberg; Robert L. Powell; Michael J. McCarthy

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 161 KB
• Volume: 109
• Category: Article
• ISSN: 1064-1866
• DOI: 10.1006/jmrb.1995.0013

✦ Synopsis

Bipolar gradients are widely used for velocity encoding

In Fig. , two alternative waveforms for the accelerationencoding gradient pulse are shown. The gradient waveform in nuclear magnetic resonance imaging. The idea to use the phase modulation of an NMR signal for measuring velocity shown in Fig. is essentially the same as that used by Dumoulin et al. (8). In order to encode acceleration, the was originally suggested by Hahn in 1960 (1). Various techniques for quantitative velocity measurements were devel-effective area and the first moment of the gradient waveforms must be nulled, and, thus, the gradient pulses do not oped in the 1980s (2-5) and much of the literature in this field was covered in recent reviews by Caprihan and Fukus-give rise to phase shifts among spins with different positions and velocities. If the acceleration is steady (time indepen-hima (6), and Callaghan (7). Phase velocity encoding can be readily extended to acceleration encoding by using two dent), the accumulated phase shift, Df, for a moving spin with acceleration, a, in the encoding direction is proportional bipolar gradients of reversed directions for flow acceleration. Dumoulin et al. (8, used a three-lobed magnetic field to the unnormalized second moment of the accelerationencoding gradient pulse, gradient pulse to measure the average acceleration in a pulsatile flow. They reported measurements of average accelerations up to 0.5 m/s 2 from the phase contrast of NMR images Df Å ga ͐ t 2 g(t)dt,