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

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 300ms and a series of TI values ranging from 10 to 240ms. Five healthy volunteers were also imaged with the same sequence. Single- and bi-component models were utilized to calculate the T-2* and relative fractions of short and long T-2* components. Bi-component behavior of the signal from cortical bone was seen with the IR-UTE sequence, except with a TI of around 80ms, where the short T-2* 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 T-2 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. Copyright (c) 2014 John Wiley & Sons, Ltd.