Effects of inversion time on inversion recovery prepared ultrashort echo time (IR‐UTE) imaging of bound and pore water in cortical bone

Abstract

Water is present in cortical bone in different binding states. In this study we aimed to investigate the effects of inversion time (TI) on the signal from bound and pore water in cortical bone using an adiabatic inversion recovery prepared ultrashort echo time (IR-UTE) sequence on a clinical 3T scanner. In total ten bovine midshaft samples and four human tibial midshaft samples were harvested for this study. Each cortical sample was imaged with the UTE and IR-UTE sequences with a TR of 300 ms and a series of TIs ranging from 10 to 240 ms. Five healthy volunteers were also imaged with the same sequence. Single- and bi-component models were utilized to calculate the T2* and relative fractions of short and long T2* components. Bi-component behavior of the signal from cortical bone was seen with the IR-UTE sequence except with a TI of around 80 ms where the short T2* component alone were seen and a mono-exponential decay pattern was observed. In vivo imaging with the IR-UTE sequence provided high contrast-to-noise images with direct visualization of bound water and reduced signal from long T2 muscle and fat. Our preliminary results demonstrate that selective nulling of the pore water component can be achieved with the IR-UTE sequence with an appropriate TI, allowing selective imaging of the bound water component in cortical bone in vivo using clinical MR scanners.

Measurement of bound and pore water T1 relaxation times in cortical bone using three-dimensional ultrashort echo time cones sequences

“…The 2D nonselective IR‐UTE sequence employed similar imaging parameters except the reduced reconstruction matrix size of 128 × 128, five TR/TI combinations (representative TR/TI values = 50/24; 100/48; 200/90; 300/130, and 400/160 ms, in which TI was adjusted based on the measured and was further verified by measuring the decay of IR‐UTE signals, and a total scan time of 6 min). A single‐component signal decay would suggest the nulling of pore water and selective detection of bound water . The 3D IR‐Cones UTE sequence employed similar imaging parameters except reconstruction matrix size = 128 × 128 × 10, a slice thickness of 7 mm, the same five TR/TI combinations, and a total scan time of 10 min.…”

“…Furthermore, bound and pore water images and relative fractions can be accessed using bi‐exponential fitting of UTE signal decay . Bound water images can be measured selectively with adiabatic inversion recovery prepared UTE (IR‐UTE) techniques in which pore water with a longer can be selectively suppressed . However, T 1 of bound water ( ) and pore water ( ) have not been well investigated using clinical MR scanners, although and have been reported using high‐performance NMR spectrometers .…”

Continuous MR bone density measurement using water- and fat-suppressed projection imaging (WASPI) for PET attenuation correction in PET-MR

“…Similar techniques capable of short T2* imaging have previously been used in studying tendon microstructure (Han et al , 2014), bone water content (Li et al , 2015), and detection of iron oxide nanoparticles (Wang et al , 2014), etc.…”

Three-dimensional adiabatic inversion recovery prepared ultrashort echo time cones (3D IR-UTE-Cones) imaging of cortical bone in the hip

“…Previous studies employing the UTE sequence have shown that both bound water (short T 2 ⁎ component) and pore water (long T 2 ⁎ component) in cortical bone can be quantified using a bi-component T 2 ⁎ analysis technique [18,[25][26][27][28]. Moreover, T 2 ⁎ decay time for bound water in cortical bone can be measured with the IR-UTE technique by suppressing the signal from the pore water and then using a single component analysis of the remaining signal [27,29,38]. A single component decay pattern of the cortical bone in the hip suggests that the 3D IR-UTE-Cones signal is likely from bound water.…”

“…This is done by inverting the longitudinal magnetization of the long T 2 signal components (i.e., muscle and bone marrow fat) while saturating the signal from cortical bone [27][28][29][30][31]. The Cones acquisition starts after an inversion time (TI) delay, which is used to null the long T 2 ⁎ components while permitting detection of recovered cortical bone signal (Fig.…”