Image manipulation and error estimation for MRI analysis

Manipulation of MRI images prior to volumetric analysis is a common practice that may unwittingly lead to errors in measurement. In this study, we examine the effects of two types of image manipulation: changes in the total number of slices used to obtain volume estimates (slice sampling rate) and image rotation. A phantom containing two regularly-shaped and two irregularly-shaped regions of interest (ROIs) was scanned using an SPGR sequence and 1-mm slices. Changes in slice sampling rate produced marked effects on volume estimation of irregularly-shaped ROIs. Comparatively little error was associated with changes in slice sampling rates for regularly- shaped ROIs. In addition, there was an interaction between image rotation in non-orthogonal planes and slice sampling rate. The data suggests that the ability to detect anatomical effects may be influenced by an investigator's choices concerning the number of slices included in a region of interest and image rotation when estimating volumes.