Which gradient is typically applied for slice selection during an MRI?

The slice selection gradient is specifically designed for the purpose of selecting a particular slice of tissue during an MRI scan. This gradient is applied along the direction in which slice selection is desired and is critical for determining the spatial location of the imaging slice.

When the RF pulse is applied, the slice selection gradient modifies the resonant frequencies of the tissue within the selected slice. Only the tissues that resonate at the specific frequency corresponding to the chosen slice will be excited and produce a signal. This ability to isolate a specific slice is fundamental to volume imaging in MRI, allowing for detailed examination of different layers of the body without interference from adjacent structures.

In contrast, the frequency encoding gradient is used to map the signal in the direction of frequency changes, while the phase encoding gradient is involved in spatially encoding signals based on the phase differences. The intensity gradient is not a standard term used in MRI contexts. Hence, these gradients serve different functions and do not fulfill the specific requirement of slice selection that the slice selection gradient does.