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

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering
• Radiology

Background:

• Ultrashort echo time (UTE) techniques are crucial for imaging tissues with very short T2 relaxation times, such as bone.
• Conventional UTE methods are often lengthy and lack flexibility in defining the imaging volume.
• There is a need for accelerated and adaptable UTE sequences to improve clinical utility.

Purpose of the Study:

• To develop and evaluate novel UTE sequences, differential single-block presaturated UTE (δSB-UTE) and differential multi-block presaturated UTE (δMB-UTE).
• To enable simultaneous multi-slice UTE acquisition with enhanced field-of-view (FOV) flexibility and reduced scan times.
• To improve the efficiency and applicability of UTE MRI for short-T2 signal detection.

Main Methods:

• Implementation of δSB-UTE and δMB-UTE sequences combining spatial presaturation and subtraction.
• Utilized prepulses to presaturate specific magnetization blocks.
• Shifted saturation blocks and subtracted subsequent acquisitions to achieve simultaneous slice imaging.
• Investigated sequence design trade-offs using phantoms and tested in healthy volunteers at 3T.

Main Results:

• Signal strength positively correlated with prepulse flip angle and saturation block shift.
• Slice thickness was influenced by prepulse flip angle, saturation block shift/thickness, and prepulse time-bandwidth product.
• δSB-UTE and δMB-UTE imaged a 210×210×80 mm³ volume with 1.0×1.0×4.0 mm³ resolution in 2.66 and 1.45 minutes, respectively.
• Achieved simultaneous acquisition of 2 slices (δSB-UTE) and 4 slices (δMB-UTE).

Conclusions:

• The developed δSB-UTE and δMB-UTE sequences effectively capture short-T2 signals from the skull simultaneously across multiple slices.
• These sequences allow for reduced through-plane FOV acquisition.
• Significant reduction in scan times for bone imaging using UTE MRI was demonstrated.
• Enabled UTE acquisition with an echo time as short as 0.18 ms.