Rat lungs were imaged by 19F projection MRI of hexafluoroethane, mixed with 20% oxygen to form the inhaled gas. The 3D image had 700 microm resolution, and the data took 4.3 h to acquire. Free induction decays were collected in the presence of steady magnetic field gradients in 686 different directions. To take advantage of fast relaxation (T1 = 5.9 +/- 0.2… (More)
We describe an NMR method to make a quick determination of average fluid velocity by monitoring the change in phase of the magnetization during a transient signal. We give an example utilizing the second Carr-Purcell-Meiboom-Gill echo in which we measured the velocity of water up to 54 cm/s where each velocity was determined by data taken over 2.5 ms.
We measure the velocity distribution of slow fluid flow in model systems using stimulated echoes and velocity phase encoding. We show velocity images of slow coherent flow with velocities of the order of 0.1 mm/s which is slower than can be obtained by the bolus-tracking method. The eddy current errors were compensated by phase correction.
MRI systems often use magnetic field gradient and shim pulse-shaping networks (pre-emphasis) to correct for magnetic field distortions caused by eddy currents. A pre-emphasis system that uses up to 16 fixed resistor-capacitor (RC) time constants per channel with programmable amplitude coefficients is described. The magnetic fields induced by the… (More)
UNLABELLED The middle latency response (MLR) to an acoustic stimulus occurs between 10 and 80 ms. The waveform is characterized by a series of peaks and troughs labeled N0, P0, Na, Pa, Nb and Pb. Certain acoustic stimuli may excite specific cochlear areas in contrast with clicks, that activate the cochlea between 1000 and 4000 Hz. The logon stimulus… (More)
The middle latency response (MLR) to an acoustic stimulus occurs between 10 and 80 ms. The waveform is characterized by a series of peaks and troughs labeled N0, P0, Na, Pa, Nb and Pb. Certain acoustic stimuli may excite specific cochlear areas in contrast with clicks, that activate the cochlea between 1000 and 4000 Hz. The logon stimulus activates… (More)
We demonstrate a new rapid NMR method to measure the average velocity and the velocity distribution of a flowing fluid. We use a truncated Carr-Purcel-Meiboom-Gill pulse sequence, pi/2-T-pi-2T-pi-T-echo, in the presence of a static magnetic field gradient. The pi/2 pulse is selective and tags a narrow slice of nuclei. The second echo from the tagged nuclei… (More)