Fast acceleration-encoded magnetic resonance imaging

Direct acceleration imaging with high spatial resolution was implemented an d tested. The well-known principle of phase encoding motion components was applied. Suitable gradient switching provides a signal phase shift proporti onal to the acceleration perpendicular to the slice in the first scan of th e sequences. An additional scan serving as a reference was recorded for com pensation of phase effects due to magnetic field inhomogeneities. The first scan compensated for phase shifts from undesired first- and second-order m otions; the second scan was completely insensitive to velocity and accelera tion in all directions. Advantages of the proposed two-step technique compa red to former approaches with Fourier acceleration encoding (with several p hase encoding steps) are relatively short echo times and short total measur ing times. On the other hand, the new approach does not allow us to assess the velocity or acceleration spectrum simultaneously. The capabilities of t he sequences were tested on a modern 1.5 T whole body MR unit providing rel atively high gradient amplitudes (25 mT/m) and short rise times (600 mus to maximum amplitude). The results from a mechanical acceleration phantom sho wed a standard deviation of 0.3 m/s(2) in sequences with an acceleration ra nge between -12 and 12 m/s(2). This range covers the expected maximum accel eration in the human aorta of 10 m/s(2). Further tests were performed on a stenosis phantom with a variable volume flow rate to assess the how charact eristics and possible displacement artifacts of the sequences. Preliminary examinations of volunteers demonstrate the potential applicability of the t echnique in vivo. (C) 2001 American Association of Physicists in Medicine.