Which statement correctly describes energy state for imaging: protons in lower energy state contribute to net magnetization used for imaging?

• A. High energy protons
• B. Protons with mixed energy
• C. Low energy protons
• D. Neutral energy protons

Answer: (C)

In MRI, spins in a static magnetic fieldSplit into two energy states: lower energy (aligned with the field) and higher energy (opposite alignment). Because of the Boltzmann distribution, more protons sit in the lower energy state than in the higher one, creating a net magnetization along the field direction. This excess longitudinal magnetization is what the imaging system uses; when an RF pulse tips this magnetization into the transverse plane, it precesses and induces the detectable signal. So protons in the lower energy state are the ones that contribute to the net magnetization used for imaging.