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

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

• A. At multiples of 2.1 milliseconds
• B. At multiples of 1.5 milliseconds
• C. At multiples of 4.2 milliseconds
• D. At multiples of 8.4 milliseconds

Answer: (A)

The point at which signals from fat and water become completely out of phase occurs at multiples of 2.1 milliseconds. This is based on the differences in resonance frequency between fat and water protons in a magnetic field, which leads to phase shifts due to their differing precession rates. Fat and water have a known chemical shift of approximately 3.5 parts per million (ppm), which corresponds to a period of 2.1 milliseconds at a typical clinical magnetic field strength of 1.5 Tesla. At this interval, the spins of fat and water have rotated around the magnetization vector enough so that they align oppositely, leading to destructive interference and resultant signal cancellation. Understanding this principle is important in MRI, especially in techniques such as fat saturation and in specific sequences where differentiation between fat and water is critical for image quality.

The point at which signals from fat and water become completely out of phase occurs at multiples of 2.1 milliseconds. This is based on the differences in resonance frequency between fat and water protons in a magnetic field, which leads to phase shifts due to their differing precession rates.

Fat and water have a known chemical shift of approximately 3.5 parts per million (ppm), which corresponds to a period of 2.1 milliseconds at a typical clinical magnetic field strength of 1.5 Tesla. At this interval, the spins of fat and water have rotated around the magnetization vector enough so that they align oppositely, leading to destructive interference and resultant signal cancellation.

Understanding this principle is important in MRI, especially in techniques such as fat saturation and in specific sequences where differentiation between fat and water is critical for image quality.