Quantification of fat infiltration in the sacroiliac joints with ankylosing spondylitis using IDEAL sequence

To quantitatively assess fat infiltration in the sacroiliac joints (SIJs) of patients with ankylosing spondylitis (AS) by measuring the fat/water signal ratios of periarticular bone marrow with iterative decomposition of water and fat with echo asymmetry and least square estimation (IDEAL). Routine SIJ magnetic resonance imaging (MRI) and IDEAL were performed on 40 patients with AS and 30 healthy subjects. The fat infiltration regions (FIRs) and normal-appearing regions (NARs) of patients were measured based on the fat/water signal intensity on IDEAL. AS patients had higher fat/water signal ratios on FIRs and NARs (65.4–85.4%, p