Introduction
Sequential acquisition was the first mode for CT acquisition: one slice was acquired and then the table was moved before another was initiated. The scanning process was long and therefore respiratory and movement artefacts were frequent. In the early 1990s, a big step forward in CT technology came from spiral (or helical) acquisition, in which image acquisition was continuous while the table moved. Since this reduced scanning time, breath-hold acquisition became possible and image quality improved substantially in three axes. The fast, volumetric acquisition of spiral mode increased the diagnostic capabilities of CT with respect to the sequential acquisition mode. For example, this permitted the CT diagnosis of pulmonary embolus. Furthermore, multiple, fast acquisitions during different imaging phases made the diagnosis of lesions in solid organs, such as liver, more accurate.