FIGURE 3. The proposed ultra-short echo time-based approaches for MRI of cortical bone net, pore, and bound water content.
The CuTE sequence in A is sensitive to both bound and pore water, but their similar T2* present difficulties in quantitatively distinguishing bound from pore water if spectroscopic acquisition schemes are employed for BEuTE (see subplot). Incorporating a double-AFP T2 filter (DAFP) into the uTE sequence (B) drives the steady state bound water longitudinal magnetization to saturation at readout, thus creating a signal dominated by pore water. Conversely, the adiabatic inversion recovery (AIR) scheme in C drives pore water to saturation, creating a predominantly bound water signal. (TR=repetition time, TI=inversion time, GR= readout gradient, RF=slice or volume excitation).