Comparison of long-T₂ Suppression Techniques for 3D Ultrashort Echo-Time Imaging

Abstract

In this study two different approaches for long-T₂ component suppression in ultrashort TE (UTE) imaging haven been investigated. The aim was to improve depiction of short-T₂ components by means of the UTE technique.

A “dual-echo” and a magnetization-preparation technique were implemented on clinical scanners operating at 1.5T and 3.0T field strength. 3D images obtained in healthy volunteer examinations using both approaches were compared with respect to short-T₂ SNR, long-T₂ suppression quality as well as scan efficiency. A quantitative SNR evaluation was performed using ankle scans of six volunteers. T₂ suppression profiles were simulated for both approaches to facilitate interpretation of the observations.

Both techniques provide comparable results at 1.5T regarding the suppression of long-T₂ species and fat. At 3T however the magnetization preparation suffers from stronger off-resonance effects. The magnetization preparation approach is more sensitive to magnetic field inhomogeneities due to the application of narrow band RF pulses and requires more shimming effort. The “dual echo” approach needs an additional post-processing step to calculate the subtraction image of two data sets acquired with different echo times. The signal-to-noise ratio in image areas with short-T₂ components is superior in the “dual-echo” approach.

In conclusion, both techniques provide good suppression of long-T₂ species with comparable short-T₂ SNR. The “dual-echo” approach offers better scan efficiency and is less sensitive to field inhomogeneity.