3t signa twinspeed scanner

In our study, the 3D UTE-Cones AFI and conventional UTE-Cones sequences (see Figure 1) were implemented on a 3T Signa TwinSpeed scanner (GE Healthcare Technologies, Milwaukee, WI). An 8-channel transmit/receive knee coil was used for both RF transmission and signal reception. The sequences used unique k-space trajectories that sampled data along evenly spaced twisted paths in the form of multiple cones (27 (link)–29 (link)). Data sampling began from the center of k-space and continued outwards. It began as soon as practical after the RF excitation with a minimal nominal delay time of 32 μs. Both RF and gradient spoiling were used to crush the remaining transverse magnetizations. In 3D UTE-Cones AFI, the areas of gradient crushers in TR₁ and TR₂ were 180 and 900 mT·ms/m respectively, and the RF phase increment was
$39°$ (17 (link)). In 3D VTR or VFA UTE-Cones, the area of the gradient crushers was 180 mT·ms/m and the RF phase increment was
$169°$ (17 (link)). The 3D UTE-Cones sequence allowed anisotropic resolution (e.g., high in-plane resolution and thicker slices) to provide an improved SNR and a reduced scan time relative to isotropic imaging (28 (link), 29 (link)).

3D UTE sequences (Figure 1) were implemented on a 3T Signa TwinSpeed scanner (GE Healthcare Technologies, Milwaukee, WI). The basic 3D UTE sequence employed a short radio frequency (RF) rectangular pulse (duration = 26-52 μs) for signal excitation ^{21 (link)}. The z-gradient could be turned off to allow non-selective 2D UTE imaging for fast imaging of cortical bone. Both collagen-bound and pore water are detectable with the basic UTE sequences (Figure 1B). Furthermore, adiabatic inversion recovery prepared UTE (IR-UTE) sequences were developed for selective imaging of collagen bound water (Figure 1C). In the IR-UTE sequence, a Silver-Hoult adiabatic inversion pulse (duration = 8.64 ms, bandwidth = 1.5 kHz) was used to invert the longitudinal magnetization of pore water ^{18 (link),22 (link)}. The longitudinal magnetization of collagen-bound water which has a very short T₂* was not inverted but largely saturated by the adiabatic IR pulse ^{22 (link)}. After an inversion time (TI) during which the inverted pore water magnetization approached the null point, the UTE acquisition was initiated to selectively detect signal from collagen-bound water (Figure 1D). 2D UTE and IR-UTE sequences were used for fast T1 and T2* quantification, while 3D UTE and IR-UTE sequences were used for bound and pore water concentration quantification (details below).