Ultra‐short echo time images quantify high liver iron
MRI‐based iron quantitation at 1.5T is now standard of care 7. However, it is estimated that 50% of new magnet installations are 3T and some imaging centers use exclusively 3T magnets; this necessitates development of robust imaging techniques for high‐field systems. Previous studies have validated quantitation over lower iron burdens at 3T 8. However, liver iron quantitation with high‐field scanners (3T and above) remains limited by rapid signal decay. When increasing the field strength from 1.5T to 3T, field‐dependent enhancement causes JOURNAL/mrim/04.02/01445475-201803000-00037/math_37MM1/v/2018-01-24T161827Z/r/image-png (1/ JOURNAL/mrim/04.02/01445475-201803000-00037/math_37MM2/v/2018-01-24T161827Z/r/image-png ) decay to approximately double, leading to transverse decay times below 0.5 ms in the liver, well below the range standard gradient‐echo techniques can reliably capture 11. Inadequate sampling of rapidly decaying signal components leads to an underestimate of liver iron concentration (LIC). The development of ultra‐short echo time (UTE) sequences has dramatically decreased the minimum achievable echo time (TE), enabling acquisition of ultra‐fast decay species 12. UTE has shown promise to perform structural imaging of cartilage and bone. The reduced TE could potentially lead to significantly increased dynamic range in quantitative imaging approaches used to non‐invasively estimate LIC at 3T and above. Proof of concept in this regard was published quite recently 13.
In this work, we measured liver JOURNAL/mrim/04.02/01445475-201803000-00037/math_37MM3/v/2018-01-24T161827Z/r/image-png in human volunteers receiving treatment for transfusional iron overload using Cartesian gradient echo (GRE) and UTE sequences. We obtained 3T LIC estimates in milligrams of iron per gram of dry liver (mg/g) for comparison with clinical LIC estimates obtained at 1.5T using a previously derived relationship between liver JOURNAL/mrim/04.02/01445475-201803000-00037/math_37MM4/v/2018-01-24T161827Z/r/image-png at 1.5T and 3T 11. We demonstrate that 3D radial UTE imaging increased the achievable dynamic range of LIC estimates to match, and possibly exceed, estimates from Cartesian gradient echo images obtained at 1.5T, providing a reliable means to quantify high liver iron at 3T.