Assessment of intraorbital structure volume using a numerical segmentation image technique (NSI): the fatty tissue...

Measurement of the degree of exophthalmos is one of the main methods used in the assessment of pathological processes that occur in the orbital space and is widely used. However, this only provides initial information about the volume relations between the intraorbital structures. The aims of our work were as follows: to draw up a new computer application, namely the numerical segmentation image (NSI) technique, for the automatic calculation of the volume of the intraorbital structures on the basis of magnetic resonance imaging (MRI) images, to determine its usefulness in the segmentation of fatty tissue and the eyeball and to estimate their volume in relation to the degree of exophthalmos.

A total of 45 patients (90 orbits) were included in the study. All the patients underwent MRI examination of the orbits by a 1.5 T scanner using a head coil. The degree of exophthalmos was determined clinically and radiologically in relation to the interzygomatic line. Quantitative assessment of the eyeball and fatty tissue was made using an NSI application.

The influence of fatty tissue volume on the degree of exophthalmos was determined as being statistically significant (r = 0.367, p = 0.000374) but was smaller in comparison with the relationship between total eye muscle volume and degree of exophthalmos; eyeball volume was found to have the least influence (r = 0.344, p = 0.000374). Two eyeballs of significantly smaller volume were found in the group of 90 orbits analysed.

The NSI technique is a clinically useful application, providing objective data calculated individually for each orbit. A credible protocol for estimating the degree of exophthalmos on the basis of the NSI technique should include the eye muscle volume, fatty tissue volume and, in cases where eyeball pathologies coexist, the eyeball volume as well.