Figure 8.

PA image from Fig. 4d showing filtering technique to remove comet-tail artifacts; (a) unfiltered PA image of the horizontal needle, The FFT of the signal shows one frequency peak at the center frequency of the transducer (7 MHz) and one at a lower frequency around 3 MHz, representing the signal from the comet tail; (b) result of bandpass filtering demonstrating incorrect choice of cut-off frequencies (3 to 10 MHz), low-frequency components are still present, blurring out the artifacts; and (c) correct bandpass filtering (4 to 10 MHz), which eliminated the comet-tail artifact. Contrast-to-noise ratios in (a), (b), and (c) were calculated to be 39.3, 38.2, and 32.5 dB, respectively.