What causes hydrogen atoms to line up during an MRI?

During an MRI, hydrogen atoms in the body are aligned using a strong magnetic field. This alignment occurs because hydrogen atoms have a magnetic moment due to the spinning of their protons. When placed in a magnetic field, these magnetic moments tend to align with the field, similar to how a compass needle aligns with the Earth's magnetic field.

The process of aligning hydrogen atoms in an MRI is called magnetization. It is achieved by applying a strong and uniform magnetic field, typically generated by a superconducting magnet. The strength of this magnetic field is measured in teslas (T). Higher magnetic field strengths result in better alignment of hydrogen atoms and, consequently, higher-quality MRI images.

Once the hydrogen atoms are aligned, they can be manipulated using radiofrequency (RF) pulses to produce the necessary signals for MRI. These RF pulses briefly disrupt the alignment of the hydrogen atoms, causing them to "flip" or change their spin orientation. When the RF pulses are turned off, the hydrogen atoms realign with the magnetic field, releasing energy in the form of radio waves. These radio waves are detected by the MRI scanner and used to create images.

By precisely controlling the timing and strength of the magnetic field and RF pulses, MRI can selectively excite and detect the signals from hydrogen atoms in different parts of the body. This information is then used to generate detailed cross-sectional images that provide valuable insights into anatomy and physiology, helping in the diagnosis and monitoring of various medical conditions.