What is the typical value of the flip angle in MRI?

In MRI, the flip angle refers to the angle at which the magnetization of hydrogen nuclei is rotated away from its alignment with the main magnetic field. A typical flip angle used in standard imaging techniques, particularly in T1-weighted sequences, is 90 degrees. This angle effectively rotates the net magnetization vector into the transverse plane where it can produce the strongest signal.

When the flip angle is set to 90 degrees, the maximum amount of signal is generated, which is crucial for producing high-quality images. This angle allows for optimal excitation of the protons in the tissue, enhancing the signal measurable by the MRI system.

While other flip angles may be used in specific applications, such as 45 degrees for certain fast imaging techniques or 180 degrees for inversion recovery sequences, the universal standard for general MRI imaging is indeed 90 degrees. This is why the correct answer reflects the typical value of the flip angle in standard MRI protocols.