Magnetic Resonance Imaging (MRI) Practice Test

What is the name of a gradient echo sequence that removes all remaining residual transverse magnetization before the next excitation pulse?

1. Coherent Sequence

2. Incoherent or Spoiled Sequence

3. Continuous Wave Sequence

4. Static Sequence

The correct answer is: Incoherent or Spoiled Sequence

In gradient echo sequences, the primary goal is to manipulate the transverse magnetization for image formation. The term "Incoherent or Spoiled Sequence" refers to a specific technique used to eliminate residual transverse magnetization from previous excitations. This is critical because any leftover magnetization can lead to image artifacts or unwanted signals that interfere with the clarity of the image. In a spoiled gradient echo sequence, specific techniques, such as using a series of RF (radiofrequency) pulses or a frequency-selective saturation pulse, are employed to "spoil" any residual transverse magnetization. This ensures that only the transverse magnetization created during the current excitation pulse is available for echo formation, resulting in clearer images that are less distorted by prior signals. In contrast, a coherent sequence retains the transverse magnetization, which can enhance certain imaging characteristics but may introduce artifacts. Continuous wave sequences and static sequences do not fundamentally relate to the preservation or elimination of transverse magnetization in the same manner as the spoiled sequence does. Hence, the design and purpose of an Incoherent or Spoiled Sequence directly address the need to manage residual magnetization efficiently.