In and out

Question 1

What is in-phase and out-of-phase imaging in MRI?

Answer 1

It’s a technique where MRI images are acquired at specific times when fat and water signals either add together (in-phase) or cancel each other out (out-of-phase).

Question 2

Why do fat and water signals go in and out of phase?

Answer 2

Because fat and water protons spin at slightly different frequencies, their signals periodically align (in-phase) or oppose (out-of-phase).

Question 3

What happens to tissue signal if it contains both fat and water on out-of-phase images?

Answer 3

The signal drops (gets darker) on out-of-phase images because the fat and water signals cancel each other out.

Question 4

What does a signal drop on out-of-phase images indicate?

Answer 4

It suggests the presence of microscopic fat within the tissue.

Question 5

What are common clinical uses of in-phase/out-of-phase MRI?

Answer 5

To detect and quantify fat in tissues, differentiate adrenal adenomas from metastases, and assess liver and other abdominal lesions.

Question 6

What artifact is associated with out-of-phase imaging?

Answer 6

The “India ink” or chemical shift artifact of the second kind, seen as a black line at fat-water interfaces.