Spiral Pulse Sequences

Spiral scanning in MRI is unlike spiral scanning in CT where the x-ray tube is continuously rotating and data is continuously being acquired. In MRI the word "spiral" refers to the pattern of sampling k-space. In conventional imaging sequences including spin echo and gradient echo and in fast imaging sequences, a line or multiple lines of k-space in the frequency direction are acquired consecutively. In spiral scanning, k-space is acquired in a spiral trajectory. The entire k-space can be acquired during a single acquisition, or interleaved using more than one acquisition. This sequence allows faster image acquisition than the fast echo sequences but is slower than the echoplanar imaging. Spiral scanning tends to have fewer artifacts than echoplanar imaging since adjacent points in k-space are acquired in close temporal proximity. The figures below shows how the acquisition of data in k-space is done with conventional sequences and with spiral scanning.