Spiral CT: Medical use and potential industrial applications

Demands on image quality in general and on low-contrast resolution in particular are very high for medical uses of x-ray computed tomography (CT). Therefore, in conventional single-slice CT, perfect planar geometry was strictly adhered to where consistent data over 360 degrees can be acquired. This implied scanning the object slice by slice. Fast volume imaging had been a request in medical imaging for a long time, but results of various approaches like cone-beam CT remained unsatisfactory. Spiral CT, the first non-planar scan mode which gained general acceptance, was first introduced in 1989. 3D volume imaging of 3 to 100 cm body sections within 10 to 60 s by spiral CT is now routine in medical imaging. We will review the spiral scan principle and the different approaches to image reconstruction which are presently implemented. In particular, the type of z-interpolation algorithm can be used to influence noise, z-axis resolution and artifact behavior. Aspects of image quality are discussed in detail. There are only subtle differences between conventional single slice CT and spiral volume scanning. Thereby the old paradigm that high quality CT scanning demands perfect planar geometry has become obsolete. The medical use of spiral CT is meanwhile undisputed; but a review of typical applications indicates the need for further improvements in the speed of volume data acquisition, in particular the need for more efficient use of the available x-ray power. This shall lead to new approaches like the combined use of spiral CT and multi-row detectors and cone angle CT based on area detectors. We review respective efforts and their implications for potential industrial applications.