Which of the following best describes an EPI sequence?

An EPI (Echo Planar Imaging) sequence is characterized by the acquisition of multiple image echoes during a single excitation. This is achieved through a train of gradient echoes, which allows for rapid imaging. In EPI, after an initial RF pulse, the sequence rapidly switches gradients to capture quick successive echoes. This makes it possible to collect a large amount of data in a very short time frame, leading to reduced overall scan times compared to traditional imaging techniques.

The design of EPI is particularly advantageous for functional MRI (fMRI) and other applications requiring quick imaging because it enhances temporal resolution and allows for real-time observation of dynamic processes in the body. So, describing an EPI sequence as involving a train of gradient echoes accurately encapsulates its unique method of data collection and imaging efficiency.