Designing long‐T₂ suppression pulses for ultrashort echo time imaging

Abstract

Ultrashort echo time (UTE) imaging has shown promise as a technique for imaging tissues with T 2 values of a few milliseconds or less. These tissues, such as tendons, menisci, and cortical bone, are normally invisible in conventional magnetic resonance imaging techniques but have signal in UTE imaging. They are difficult to visualize because they are often obscured by tissues with longer T 2 values. In this article, new long-T 2 suppression RF pulses that improve the contrast of short-T 2 species are introduced. These pulses are improvements over previous long-T 2 suppression pulses that suffered from poor off-resonance characteristics or T 1 sensitivity. Short-T 2 tissue contrast can also be improved by suppressing fat in some applications. Dual-band long-T 2 suppression pulses that additionally suppress fat are also introduced. Simulations, along with phantom and in vivo experiments using 2D and 3D UTE imaging, demonstrate the feasibility, improved contrast, and improved sensitivity of these new long-T 2 suppression pulses. The resulting images show predominantly short-T 2 species, while most long-T 2 species are suppressed. Magn Reson Med 56:94 -103, 2006.

Zero Echo Time Magnetic Resonance Imaging of Contrast-Agent-Enhanced Calcium Phosphate Bone Defect Fillers

“…13,14 More recently, a no-echo-time method called sweep imaging with Fourier transformation (SWIFT) was introduced, which acquires data quasi-simultaneously with the excitation pulse, using adiabatic pulses. It already has been applied in imaging of bone samples and thermoplastic objects.…”

Optimization of RF excitation to maximize signal and T2 contrast of tissues with rapid transverse relaxation

“…Typical minimum TE values for clinical scanners, which depend on the RF transmit-receive switching and settling times, are 40-200 ms (12), while the shortest TE reported is 8 ms (13). In order to achieve a better delineation of the morphology within short T 2 tissues, several long T 2 suppression techniques have been developed, including dual echo subtraction techniques (1,5,14), and long T 2 preparation clusters using either long-duration hard pulses (15)(16)(17) or adiabatic pulses (12,18) to saturate or invert long T 2 tissues.…”

Ultrashort TE (UTE) Imaging of the Knee Cartilage at 3T

“…These techniques include fat suppression, long T2 water signal saturation [39,40], and inversion recovery techniques [38]. Clinical fat saturation techniques employ a non-selective saturation pulse to selectively suppress fat signals.…”

“…An alternative approach is to use linear combination filtering [41], where the addition of properly weighted multiple TE images results in good suppression of long T2 signals with less noise enhancement. Another approach for direct imaging of the short T2 tissues is to use long duration 90° pulse followed by gradient dephasing and UTE acquisition [39,40]. Recently a dual-band long-T2 suppression pulse was reported to suppress fat and long T2 water signals simultaneously, providing good contrast for short T2 tissues such as ligaments, tendon and meniscus [40].…”

“…Another approach for direct imaging of the short T2 tissues is to use long duration 90° pulse followed by gradient dephasing and UTE acquisition [39,40]. Recently a dual-band long-T2 suppression pulse was reported to suppress fat and long T2 water signals simultaneously, providing good contrast for short T2 tissues such as ligaments, tendon and meniscus [40]. The limitation of this approach is that long duration pulses typically have limited bandwidth coverage, and are sensitive to off-resonance and B1 inhomogeneity.…”