Background: The volume enlargement of extraocular muscles is one of the most frequent reasons of exophthalmos in Graves' ophthalmopathy. Various diameters are widely used in clinical practice for estimating muscles' size. They are not sufficient for the precise and reliable determination of their real volume. Modern computing systems enable numerical analysis of medical images including Magnetic Resonance Imaging (MRI) in an almost automatic way. The aims of this study were: The analysis of different MRI sequences routinely used in the examination of intraorbital structures and their value for NSI application. Determination of clinical value of an NSI program in estimating extraocular muscle volume and comparing the obtained results with the degree of exophthalmos. Material/Methods: 45 patients were qualified to the study and underwent MR examinations in 1, 5 T scanner. The measurements of the degree of exophthalmos and quantity estimation of the total eye muscle volume using the NSI application were made. Results: The best sequence for the NSI application is SE T1. Correlation between muscle volume measurements obtained using the automatic method and after manual modification was the highest for this sequence. In all sequences the final values of volumes for each muscle after manual corrections were close what proves the repetitiveness of the NSI technique. Strong correlation between the total eye muscle volume determined by the NSI and the exophthalmos was found. Conclusions: T1 SE has the highest value for using NSI application for all sequences routinely used in MRI evaluation of orbital structures. The NSI technique is a clinically valuable application that provides objective volume data calculated individually for each orbit. The NSI technique allows more objective estimation of pathological processes leading to exophthalmos; it can be particularly helpful in monitoring discrete changes in muscle volume during the treatment
