Fat suppression for ultrashort echo time imaging using a single-point Dixon method

Purpose: In ultrashort echo time (UTE) imaging, fat suppression can improve short T ₂ * contrast but can also reduce short T ₂ * signals. The conventional two-point Dixon (2p-Dixon) method does not perform well due to short T ₂ * decay. In this study, we propose a new method to suppress fat for high contrast UTE imaging of short T ₂ tissues, utilizing a single-point Dixon (1p-Dixon) method. Methods: The proposed method utilizes dual-echo UTE imaging, where UTE is followed by the second TE, chosen flexibly. Fat is estimated by applying a 1p-Dixon method to the non-UTE image after correction of phase errors, which is used to suppress fat in the UTE image. In vivo ankle and knee imaging were performed at 3 T to evaluate the proposed method. Result: It was observed that fat and water signals in tendons were misestimated by the 2p-Dixon method due to signal decay, while the 1p-Dixon method showed reliable fat and water separation not affected by the short T ₂ * signal decay. Compared with the conventional chemical shift based fat saturation technique, the 1p-Dixon based approach showed much stronger signal intensities in the Achilles, quadriceps, and patellar tendons, with significantly improved contrast to noise ratios (CNRs) of 11.8 ± 2.2, 16.0 ± 1.6, and 26.8 ± 1.3 with the 1p-Dixon method and 0.6 ± 0.2, 4.6 ± 1.0, and 17.5 ± 1.4 with regular fat saturation, respectively. Conclusion: The proposed 1p-Dixon based fat suppression allows more flexible selection of imaging parameters and more accurate fat and water separation over the conventional 2p-Dixon in UTE imaging. Moreover, the proposed method provides much improved CNR for short T ₂ tissues over the conventional fat saturation method.