Which type of electromagnetic waves are used to excite the protons in MRI?

Which type of electromagnetic waves are used to excite the protons in MRI?

• A. Radio waves
• B. Gamma rays
• C. Infrared rays
• D. Visible light

Answer: (A)

Radio waves are used to flip the spins of hydrogen nuclei in MRI. A strong static magnetic field creates distinct energy levels for the protons’ spins. An oscillating magnetic field in the radiofrequency range is applied at the Larmor frequency, which matches the energy difference between those spin states, causing protons to absorb energy and transition to a higher energy level. When the RF pulse ends, the protons relax back and emit signals that the scanner detects to form images. Higher-energy photons like gamma rays would ionize tissue and aren’t suitable for flipping nuclear spins, and infrared or visible light don’t interact with nuclear spins in the way needed for MRI. So the waves used are in the radiofrequency range.

Radio waves are used to flip the spins of hydrogen nuclei in MRI. A strong static magnetic field creates distinct energy levels for the protons’ spins. An oscillating magnetic field in the radiofrequency range is applied at the Larmor frequency, which matches the energy difference between those spin states, causing protons to absorb energy and transition to a higher energy level. When the RF pulse ends, the protons relax back and emit signals that the scanner detects to form images. Higher-energy photons like gamma rays would ionize tissue and aren’t suitable for flipping nuclear spins, and infrared or visible light don’t interact with nuclear spins in the way needed for MRI. So the waves used are in the radiofrequency range.