Design of Differential Single-Block and Multi-Block Presaturated Ultrashort Echo Time Pulse Sequences for Fast and...

Ultrashort echo time (UTE) techniques are essential for the magnetic resonance imaging of short-T₂ signals. Current UTE techniques are time-consuming and often require the acquisition of an inflexible volume. In this work, we implement new UTE sequences-differential single-block presaturated UTE (δSB-UTE) and differential multi-block presaturated UTE (δMB-UTE)-that combine spatial presaturation and subtraction to enable simultaneous multi-slice UTE acquisition with increased flexibility in field-of-view (FOV) and reduced scan times.

The sequences use a prepulse to presaturate blocks of magnetization and a whole-volume excitation to enable UTE acquisition. By shifting the saturation blocks and subtracting subsequent acquisitions, two and four simultaneous slices can be imaged with the δSB-UTE and δMB-UTE sequences, respectively. Design trade-offs were investigated in a phantom, and the sequences were used to image healthy volunteers at 3 T.

The received signal strength increased as prepulse flip angle and saturation block shift increased. Slice thickness increased as prepulse flip angle, saturation block shift, and saturation block thickness decreased, and prepulse time·bandwidth product increased. The δSB-UTE and δMB-UTE sequences were used to image a 210 × 210 × 80 mm³ in vivo volume with 1.0 × 1.0 × 4.0 mm³ resolution in 2.66 and 1.45 min, respectively.

The δSB-UTE and δMB-UTE sequences can be used to capture short-T₂ signal from the skull in multiple slices at the same time with an echo time of 0.18 ms. The δSB-UTE and δMB-UTE sequences enable the acquisition of a reduced through-plane FOV and reduce scan times for imaging bone.