An apparatus, a method, and computer-implemented media. The apparatus is to determine a current pixel performance dataset for one or more pixels within a transducer array of pixels located adjoining a first medium with a first acoustic impedance Z1, the transducer array within an imaging device, the current pixel performance dataset obtained from a current pixel performance receive cycle of the one or more pixels against a second medium with a second acoustic impedance Z2 larger than Z1; perform a comparison of the current pixel performance dataset with a baseline pixel performance dataset for the one or more pixels, the baseline pixel performance dataset obtained from a baseline pixel performance receive cycle of the one or more pixels against the second medium, wherein implementation of the current pixel performance receive cycle and of the baseline pixel performance receive cycle is performed without alignment of the second medium with respect to the imaging device; and determine a defective pixel dataset for one or more defective pixels of the one or more pixels based on the comparison.