Radiofrequency phase encoded half-pulses in simultaneous multislice ultrashort echo time imaging

Area of Science:

• Magnetic Resonance Imaging
• Medical Physics
• Radiology

Background:

• Ultrashort echo time (UTE) imaging is crucial for visualizing tissues with short T2* relaxation times, such as cortical bone.
• Simultaneous multislice (SMS) imaging accelerates data acquisition by exciting and acquiring multiple slices concurrently.
• Traditional 2D UTE methods are time-consuming, limiting their clinical applicability.

Purpose of the Study:

• To develop and validate a novel simultaneous multislice (SMS) ultrashort echo time (UTE) imaging technique.
• To achieve significant acceleration in UTE imaging, reducing scan times considerably.
• To generate high-quality, multi-slice UTE images with short T2* contrasts rapidly.

Main Methods:

• Implementation of radiofrequency phase-encoded half-pulses for SMS excitation (N SMS = 4).
• Integration of Power Independent of Number of Slices (PINS) inversion recovery (IR) pulses for contrast enhancement.
• Utilization of coil sensitivity encoding (SENSE) and controlled aliasing in parallel imaging (CAIPI) with a 2D spiral readout.
• Application of a model-based reconstruction method for image processing.

Main Results:

• Successful development of an SMS UTE sequence with an undersampling factor of 4.
• Acquisition of 8 slices with 0.86 mm² resolution in under 3 minutes.
• Demonstration of highlighted cortical bone signal in head UTE images.
• Comparable image quality and T2* contrast to single-slice acquisitions, with minor deviations.

Conclusions:

• The combined radiofrequency phase-encoded SMS half-pulses and PINS IR pulses offer a robust approach for SMS UTE imaging.
• The method achieves a scan time reduction factor close to 8 through coil sensitivity information and interleaved slice acquisitions.
• This technique presents a suitable and efficient method for rapid, multi-slice UTE imaging.