Spiral pulse sequences

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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 echo-planar imaging. Spiral scanning tends to have fewer artifacts than echo-planar imaging since adjacent points in k-space are acquired in close temporal proximity. The figures to the right show how the acquisition of data in k-space is done with conventional sequences and with spiral scanning.

Imaging technology