Which of the following is NOT one of the four parts of an MRI pulse sequence?

The aspect of signal calibration does not belong to the fundamental components that make up an MRI pulse sequence. MRI pulse sequences are designed to manipulate the magnetic properties of hydrogen atoms in the body to create high-quality images. The essential parts of a pulse sequence include:

• Phase encoding, which involves varying the phase of the spins to produce spatial localization along one direction; this is critical in determining how the data is organized to create images.

• Slice excitation, which refers to the use of radiofrequency pulses to selectively excite a specific slice of tissue within the magnetic field, enabling imaging of a particular cross-section of the anatomy.

• Echo generation, which involves capturing the signal produced after the initial radiofrequency pulse and relaxation of the spins; this process is crucial for forming the image since the echoes carry the data needed for reconstruction.

In contrast, signal calibration relates to the process of ensuring that the acquired signal intensity is accurately represented and can be related to actual tissue properties. While important in the overall performance of the MRI system, it does not constitute a direct part of the MRI pulse sequence itself, which is focused more on the specific manipulations of the magnetic field and radiofrequency energy used to capture the data for imaging.