When do signals from fat and water become completely out of phase?

Signals from fat and water become completely out of phase at intervals of 4.2 milliseconds. This occurs due to the frequency difference between fat and water protons when measured in a magnetic resonance imaging (MRI) system.

In an MRI, fat protons resonate at a slightly different frequency compared to water protons because of the differing magnetic environments. The specific time, 4.2 milliseconds, represents the timing when the phase difference between these two signals reaches 180 degrees, resulting in them being completely out of phase. This behavior can create distinctive imaging contrasts and is crucial for understanding how different tissues respond in MR sequences.

This timing is significant in practical applications like Fat Saturation techniques, where differentiating between fat and water is essential for achieving clear and accurate MR images. By knowing that 4.2 milliseconds is the point where these signals are fully out of phase, technologists can optimize sequences to enhance image quality and provide better diagnostic information.