Contrast-to-noise ratio of multiple slice spin lock technique: prospects for liver imaging.

Abstract

Spin lock (SL) MRI technique has been demonstrated to provide similar lesion/liver contrast to conventional MR technique. Multiple slice SL technique allows a large number of slices to be collected within a given repetition time due to the short echo time. In addition, the short echo time reduces movement and susceptibility artefacts. In the present study, the potential of the multiple slice SL technique in liver imaging was evaluated by using tissue nuclear magnetic resonance (NMR) information and tissue NMR parameters obtained at 0.1 T. 10 healthy volunteers were imaged at 0.1 T for the measurement of tissue T1rho, T1, and T2 relaxation times. Tissue radiofrequency-attenuation information was obtained from the literature, and included in the contrast-to-noise ratio (CNR) calculations. Our results demonstrated that by increasing the number of slices the acquired liver-to-spleen CNR decreases with all locking field durations (locking time, TL). However, with small TLs, the difference is small which is important for liver MRI where a wide coverage, i.e. large number of slices, is important. Long locking pulse durations are more favourable than short TLs if large flip angles are used. With an optimal combination of a moderate amount of slices, reasonably large flip angle, and TL of the order of 20 ms, high CNR is achieved in SL MRI.