Magnetic Resonance Imaging (MRI) Practice Test

Which MRI sequence is least affected by magnetic field inhomogeneity?

1. Gradient echo

2. Spin echo

3. Inversion recovery

4. Fast spin echo

The correct answer is: Spin echo

The spin echo sequence is least affected by magnetic field inhomogeneity due to its specific mechanism of data acquisition, which incorporates a 180-degree refocusing pulse. This refocusing pulse corrects for the dephasing of spins caused by field inhomogeneities during the time between the excitation pulse and the signal readout. As a result, the spin echo sequence produces cleaner and more uniform signals, making it more robust in inhomogeneous magnetic fields compared to other sequences. In contrast, sequences such as gradient echo are more sensitive to field variations because they do not utilize a refocusing pulse, resulting in increased susceptibility effects that can distort the MRI images. Inversion recovery and fast spin echo sequences also face challenges from magnetic inhomogeneities, though to varying degrees, but they still do not offer the same level of compensation as the spin echo sequence. The ability of the spin echo to regain coherence among spins effectively mitigates the adverse impacts of magnetic field inconsistencies.