The use of combined T2-weighted and FLAIR synthetic magnetic resonance images to improve white matter region contrast: a feasibility study

Synthetic magnetic resonance imaging (MRI) allows the production of images with any contrast from a single scan after quantification. The combined T2-weighted image (T2WI) and fluid-attenuated inversion recovery (FLAIR) image is expected to have an improved contrast between the normal-appearing white matter (WM) and WM lesion (WML). The purpose of this study was to determine whether optimal T2 contrast-weighted images (SyFLAIR3) comprising the combined T2WI and FLAIR image generated using synthetic MRI could improve contrast in the WM region. Numerical simulations were performed to estimate the contrast-to-noise ratio (CNR) between the WM and WML and cerebrospinal fluid (CSF) ratio at any echo time (TE) using SyFLAIR3. The CNR and CSF ratio for SyFLAIR3 was compared with those for FLAIR and double inversion recovery (DIR) images in ten volunteers. In numerical simulations, the CNR for SyFLAIR3 was increased in the T2WI and FLAIR images with long TEs, and the CSF ratio was decreased on those with short TEs. An in vivo study indicated that the CNR for SyFLAIR3 using T2WI and FLAIR images with an optimized combination of TEs was significantly higher than those for FLAIR and DIR images; whereas, the CSF ratio for the optimized SyFLAIR3 was not significantly different from that for the FLAIR images. The use of SyFLAIR3 improves the contrast within the region of the WM without the need for additional scanning in synthetic MRI.