What is the primary purpose of gradients in MRI?

The primary purpose of gradients in MRI is indeed related to slice selection. Gradients are necessary for spatial encoding of the MR signal. They vary the magnetic field strength across different spatial locations within the imaging volume, which allows the system to distinguish between signals coming from different slices of tissue.

When the gradient is applied, it alters the frequency and phase of the magnetic resonance signals depending on their position. By adjusting the gradient strength and direction, the MRI machine can selectively excite a specific slice of tissue while suppressing signals from other slices. This is essential for constructing a two-dimensional image from the three-dimensional data set acquired during the scan.

While gradients also play a role in other aspects of MRI, such as influencing tissue contrast through the control of timing and echo sequences, their primary function is slice selection. This capability allows radiologists and clinicians to obtain images of targeted areas within the body, making it crucial for diagnostic purposes.