As with other digital imaging systems in heavy medical use, it is desirable with magnetic resonance imaging (MRI) to obtain extensive, rigorous system performance measures from a small set of images of one or two relatively simple test objects. Digital analysis of the parallel square rod (PSR) test object introduces digital image system self-evaluation to MRI and extends automated image evaluation to include rigorous measures throughout the imaging volume rather than just average measures over the image. Precise comparisons with theory and between systems can be performed as well as quality control and corrections for nonuniformities. The PSR test object consists of an 18 X 18 X 36 cm rectangular acrylic container enclosing 60 parallel square acrylic rods running the entire length. The inter-rod space is filled with a liquid or gel that produces strong, tissuelike signals in MRI and high contrast relative to the rods for computed tomography (CT). For profiles of slice thickness and separation, the rods are tilted in the test object to intersect the image plane at a 45 degree angle when the test object sides are parallel and perpendicular to the image plane. The test object itself is rotated 6-12 degrees about its major axis so that the sides of the rods make a small angle to the rows and columns of pixels. This allows digital sampling at finer spacing than the pixels for determination of edge response functions.(ABSTRACT TRUNCATED AT 250 WORDS)