A Theoretical and Experimental Study of the Double Aorta Artefact in B-Mode Imaging

Abstract

Artefacts arise in ultrasound B-mode images due to propagation effects and limitations in system performance. The ‘double aorta’ artefact has been described previously and ascribed to refraction through superficial tissues, such as the abdominal muscles, in which the speed of sound is significantly higher than values in the abdominal organs. A phantom was designed and constructed to model the abdominal muscles as a pair of lens-shaped sections of tissue mimicking material with speed of sound similar to that of muscle. Scanning a standard test object through these sections in a water bath resulted in double images of the various anechoic and filament structures within the test object. At a depth of 3 cm below the ‘muscle’ mimics, a 7-mm diameter cystic structure appeared as two overlapping objects with centres separated by 5.1 ± 1.8 mm. A theoretical model was established assuming straight line propagation, Snell's law and measured and quoted speeds of sound within the muscle mimic, water and the test object. Derived values for the separation agreed with experimental measurements to within the calculated uncertainties. These observations support the view that the double aorta artefact can be explained by refraction through the abdominal muscles.