Partial volume effect

The partial volume effect , also known as the partial volume effect, is an image artifact in computer tomography . The effect arises when an object is only represented by part of the selected layer thickness; either because the object only partially protrudes into the layer or because the object is smaller than the layer thickness. The density of the object averaged over the layer thickness is then shown. This means that a bone with the density of soft tissue can be shown in the image. Partial volume effects often appear as stripes in the image; they are more frequent and more pronounced, the greater the layer thickness.

The problem was particularly pronounced in the early days of CT. At that time, the layer thickness was 10–15 mm and the first devices could only depict the head. However, the details of bone structures in the head are usually smaller than 10 mm.

The only really effective means of eliminating partial volume effects is to reduce the reconstructed slice thickness. The image noise increases the more the thinner the layer thickness is; For this reason, the sliding thin slab display has established itself for displaying thick layers with low image noise without partial volume effect .

Since today's CTs usually reconstruct much smaller slice thicknesses than in the past, the effect is now rarely encountered.

source

Willi A. Calendar: Computed Tomography . Basics, device technology, image quality, applications . Publicis MCD, Munich 2000, ISBN 3-89578-082-0 .