Tag Archives: MRI

Fat-Water Separation in MRI

A figure from Dixon's original paper on fat-water separation.

A figure from Dixon’s original paper on fat-water separation.

To anyone who is interested in fat-water separation within the field of MRI, I offer the following (click for PDF):

Fat-Water Separation

This is a chapter from my master’s thesis that explains the most common methods of fat-water separation and presents a very handy geometric interpretation of two-point Dixon imaging. I’ve been told that the interpretation is very helpful for newcomers to the field.

If you find it useful at all, please share it.

What is fat-water separation, you might ask?

Good question.

MRI detects hydrogen atoms; and there are two main places in your body where hydrogen atoms hang out: fat molecules and water molecules. So in the context of MRI, we can say that most tissue in your body is either fat or water. (Examples of “water” here include muscle, blood, skin, and pretty much anything except fat.) Fat-water separation is simply the process of distinguishing between the two tissue types in an MRI image.

Doctors often want either to remove the fat from an image so they can see things the fat might be hiding, or to create two separate images, one of fat only and one of water only. Doing so can help them give patients a more accurate diagnosis.

Fat-water separation techniques involve some interesting physics and math. For more info, click on the link provided above.

Introduction to MRI


(Before you complain, see note at end of post.)

Back in 1997, at the end of my tenth grade year, my chemistry teacher explained the principles underlying magnetic resonance imaging. I’m sure it wasn’t a very in-depth explanation, but I still remember thinking, “Wow, that’s complicated. I’ll never understand it.”

Well, a lot has happened since then. I got a bachelor’s degree in physics and math. I worked as a teacher for seven years, five of which were spent in China. Then I went back to graduate school to get a master’s degree in applied physics.

The topic of my research? Magnetic resonance imaging.

As I began studying MRI in graduate school, I still worried that I might not be able to understand it. But I once again rediscovered a truth that I keep finding myself rediscovering: namely, that if you invest enough time and hard work in studying a topic, you’ll eventually get it, no matter how daunting it may at first seem.

In the end, I didn’t just learn the basics of MRI, but I published a thesis on my own contribution to the field: an improved method for distinguishing between fat-based and water-based tissue in magnetic resonance images.

If you’re curious about how MRI works, I offer you this (click the link to download the PDF):

Foundations of MRI

It’s a chapter from my thesis that explains the basic physics of MRI — from how the tissue in your body is magnetized when you are placed in a magnetic field, to how images are obtained with the desired contrast between different tissue types.

I hope you’ll find it to be puddles of fun. Please splash around to your heart’s content.

NOTE: Anyone familiar with medical imaging will immediately notice that the Homer Simpson image at the top of this post is not an MRI. But hey, it’s already a fictional image of a fictional character, and it’s really funny, so please give me a break.