Single-image water/fat separation

Introduction In MRI, fat can be hard to distinguish visually from pathology or contrast agent, due to its high signal intensity in many imaging sequences. Water and fat separation techniques provide an alternative to conventional fat suppression, and are also of interest in body composition applications. Dixon techniques [1] utilize the property of chemical shift to separate water and fat with the use of two or more source images acquired at different echo times. If field heterogeneity is negligible, water and fat can be separated with only one source image [2]. Yu et al. [3] studied water-fat separation from one source image in a heterogeneous field, with the aid of an additional reference scan, in the context of dynamic imaging. Ma [4] showed that water and fat can be separated from a single image in a heterogeneous field even without reference scans. This work describes a straightforward single-image water-fat separation technique, that utilizes the belief propagation (BP) algorithm [5] to find the field inhomogeneity phase map. The image can be acquired at any echo time where water and fat are not in-phase or opposed-phase. However, the best SNR performance is achieved if the relative water and fat phase is an odd multiple of π/2 [3].