Magnetic Resonance Imaging (MRI) Board Practice Exam 2026 - Free MRI Practice Questions and Study Guide

MR imaging relies on three intentional magnetic fields: a strong static field that aligns the proton spins, gradient fields to encode spatial information, and an RF field that tips and excites the spins to produce a signal. The gravitational Earth field is not a magnetic field used in MRI at all. Gravity is a separate force and does not manipulate spin precession in a way that can be harnessed for imaging. The Earth does have a magnetic field, but it is extremely weak—much smaller than the main MRI field—and cannot be controlled to provide reliable spatial encoding. Its presence would just add unwanted inhomogeneities, not useful imaging information. So the gravitational Earth field isn’t a magnetic field associated with MR imaging, whereas the static, gradient, and RF fields are.