The peak of the gradient echo occurs when the net phase shift among spins is zero. Note that in our diagram the upward gradient has been left on twice as long as the dephase gradient. This is the optimal design
We introduce an accelerated gradient echo (GRE) sequence combining simultaneous multislice excitation (SMS) with echo-shifting technique for high spatial resolution blood oxygen level dependent (BOLD) functional MRI (fMRI). The simulation was conducted to optimize scan parameters. To validate the feasib...
(2) Gradient rise times describe the time interval needed for a magnetic gradient to go from zero to maximum strength, which in turn determines how quickly pulse sequences can be performed. The shorter the gradient rise time, the shorter TR and echo time (TE) can be made in 2D or 3D ...
The slew rate influences the minimum attainable TR and TE for conventional MR imaging and influences the echo spacing in fast spin echo and echo planar applications. In the current marketplace, high field superconducting scanners boast slew rates in the 150-200 T/m/s range; superconducting open...
fG R E1 T2 ’W I sequence,especially the enhanced T2 star weighted angiography (ESWAN1 double—echo sequence, mak es different iation of hem or hage and calciti cation po ssib le by detecting signals of m agnetic sensitiv e sub stances at the lesions .H ow ev er, mo st...
Fluctuations induced by gradient switching cause significant effects in MR images, especially in DWEPI (diffusion weighted echo-planar imaging), that uses MPG (motion probing gradient) pulses with a huge amplitude. However, we lack good tools for evaluation of the effe...
2 . Since this simple sequence is based on a Hahn spin-echo, the echo signal, S, is attenuated by both the effects of the spin spin relaxation and of diffusion. As shown in Part 1 Ž . 1 , the signal intensity is given by y 2 Ž . Ž . S 2 s S 0 exp ž / T 2...
Many gradient-echo pulse sequences use flip angles less than 90° so that only a small disturbance is made to the longitudinal magnetization component— preserving it for subsequent excitations. Clearly, if the B1 field is not homogeneous (because of imperfect coil design or sample interactions) ...
Gradient echo sequences are susceptible to local variations of the magnetic field (off-resonance). Common gradient echo image artefacts that are caused by off-resonances include geometric distortion, signal inhomogeneity (ripple or ringing-like structures) and signal voids. Signal voids occur in those...
FIG. 2 is a schematic diagram showing the timing of the spoiler current (bottom) with respect to a typical pulse sequence for gradient recalled echo (GRE) imaging. FIG. 3 is a schematic diagram of the coil for the spoiler gradient insert of FIG. 1. FIG. 4A is a contour plot of the...