Extending the pixel difference metric from 2D to 3D/4D ultrasound

It is frequently of interest to examine differences (e.g., the 1st or 2nd difference) in signals and images. Differencing can be employed for the detection of edges in images, or the detection of events in temporal sequences. One such event is the onset of articulatory movement in ultrasound image sequences of the tongue. It has been quantified using a form of Euclidean distance between successive frames of image scan line data, referred to as Pixel Difference. When applied to 3-D/4-D ultrasound data of the tongue (after scan conversion), Pixel Difference exhibited a surprisingly poor signal-to-noise ratio. In this presentation, we test the hypotheses that (1) scan conversion amplifies the effect of speckle noise near the top of the ultrasound image (i.e. above the tongue), and (2) the Pixel Difference signal-to-noise ratio in 3-D/4-D ultrasound differs from 2-D ultrasound by a power of 3/2 due to the added spatial dimension.