In a pulse sequence diagram, Gz is used to represent?

In a pulse sequence diagram, Gz refers to the gradient field that is applied along the z-axis, which is responsible for slice encoding. This gradient is crucial in magnetic resonance imaging (MRI) as it allows for the selection of specific slices of the body to be imaged. By varying the Gz gradient, one can determine which slice of tissue is being excited and ultimately captured by the imaging process.

When Gz is applied, it alters the magnetic field strength along the z-direction, allowing only the spins within a specific slab or slice at a given position to be resonantly excited and subsequently detected. This is essential for constructing a detailed image of the body's internal structures, as MRI relies heavily on the ability to isolate and visualize thin slices of tissue.

Other choices involve different aspects of gradient encoding. Phase encoding typically uses a gradient applied in the y-direction to sample different frequencies represented in the Fourier transform of the MR signal, while frequency encoding, typically linked with the readout gradient which operates in the x-direction, focuses on spatial localization based on signal frequency. Temporal encoding pertains to time-related elements in imaging but is not relevant in the context of a single pulse sequence slice selection.