Synopsis

Keywords: Contrast mechanisms: Fat, Body: Body

Water and fat are the dominating molecules in the human body. Water is involved in many structural and functional processes, as well as in pathology, and is key in many diagnostic MR contrasts. Fat has many other roles and is often seen as a confounding factor in MRI. Dixon-based water fat separation allows for robust and efficient fat suppression giving also access to fat including its quantitative assessment and biomarker use. Many clinical applications benefit, like liver, cardiac, MSK and whole-body imaging, but Dixon could also support angiography without contrast. The lecture will present selected clinical use cases for illustration.

Water and fat are the dominating molecules in the human body. Water is involved in many structural, functional, and physiological processes, and as well as in pathology. Therefore, water is key for many diagnostic MR contrasts. Fat has many other roles in the body and is often seen as a confounding factor impairing many MRI contrasts. Thus, the suppression of signal from fat in MRI procedures is a basic requirement in many MRI applications. This is often achieved during scanning, employing fat saturation, inversion recovery pre-pulses, or water excitation methods. Postponing the separation of water and fat signals until image reconstruction holds the promise of resolving some of the present problems. Chemical shift encoding-based techniques (often called Dixon (1-6)) allow robust and efficient water / fat separation and thus fat suppression, in presence of inhomogeneous main fields (B0) and also in inhomogeneous transmit fields (B1+). Furthermore, apart from fat signal suppression, Dixon is also giving access to fat information directly, including its quantitative assessment and its use as a biomarker (7). The basic concepts of modern Dixon-based water fat separation will be outlined in this lecture. They are also nicely given in a recent CME article (8). Many clinical applications will be discussed, which benefit already today from the Dixon technology and will be reviewed briefly in the lecture. Examples are liver, cardiac, MSK and whole-body imaging (including aspects of obesity assessment). In some more forward-looking applications, as MRI angiography without using contrast media (9), Dixon firms as an enabling technology, that can help to further reduce patients’ risks. This application will be discussed as an outlook.