The Doppler ultrasound twinkling artifact on crevices etched in silicon wafers

The twinkling artifact, or rapid color shifts, are observed when imaging kidney stones and other mineralizations. The current theory is that scattering from bubbles in micron-sized crevices causes twinkling. Our objective is to investigate the effect of ultrasound frequency and crevice size and number on twinkling of silicon wafers. Ten or 100 randomly positioned cylindrical crevices with diameters of 1, 10, or 100 μm and depths of 10 μm were dry-etched on wafers. A research ultrasound system was used to image wafers at 5, 7.8, and 18.5 MHz; IQ data were post-processed to calculate twinkling or Doppler power. Twinkling for all crevice sizes and numbers followed the trend 5 MHz>7.8 MHz>18.5 MHz. For crevice size, at 5 and 7.8 MHz, twinkling was higher for 1- or 10-μm crevices compared to 100 μm; at 18.5 MHz, twinkling was only observed on 100-μm crevices. Increasing the number of crevices increased twinkling for 1 μm crevices at 5 and 7.8 MHz and 10 μm crevices at 7.8 MHz; no differences were noted at 18.5 MHz. These results support previous work showing twinkling is frequency-dependent and suggest that even 10, 1-μm crevices are sufficient to cause twinkling. [Work supported by SURIEA, NSF CAREER-1943937.]