When the target is close to one interface, the target echo is hidden in the reverberation resulting in a low signal-to-reverberation ratio (SRR).
Sixty-one percent of echoes resulted in a change of management (5% of which were to continue with increased confidence).
The AEC aims at reducing the echo resulting from the acoustic feedback in loudspeaker-enclosure-microphone (LEM) systems such as teleconferencing and hands-free systems.
This appears to echo results in other sensory areas showing that tuning of inhibition is broader than for excitation (reviewed by Isaacson and Scanziani, Neuron 2011).
The two-dimensional, multi-slice gradient-echo sequence used a four-interleave spiral readout (Glover and Lee, 1995; Kim et al., 2003), 30° flip angle, 750 ms TR, and 12 ms echo time, resulting in 23 coronal slices (128 × 128 matrix size).
This sequence, which was introduced by Ying and Schmalbrock [ 5], and further developed by Song and Wehrli [ 4] and recently by Deligianni et al. [ 14], utilises varying phase-encoding gradients to manipulate the effective echo time, resulting in sub-millisecond TE that enables the visualisation of fast-relaxing tissues.
Then the supra-aortic arteries were imaged from the aortic arch to the circle of Willis with a breath-hold three-dimensional (3D) gradient echo sequence, resulting in 72 adjacent coronal slices (FLASH 3D, TR 3.54 ms, TE 1.39 ms, flip angle 25°, FOV 320 × 208 pixels, isotropic voxel size 1.1 × 1.1 × 1.1 mm, acquisition time 21 s).
This state-space representation for the wave equation gives additional prior physical knowledge and incorporates perturbations and distortion like echoes, thereby resulting in improved estimation accuracy.
Larger clusters would cause a stronger signal loss in gradient-echo images resulting in higher R2* values compared to a diffuse distribution of the same amount of iron within all cells of the tissue.
Another important advantage – mandatory for evaluation of small lesions – is that the technique is able to provide a substantially shortened echo-time resulting in a high signal-to-noise ratio (SNR).
