Fig. 2

The results of the average 2-DIE of the two testing sets. Note: 2-DIE: two-dimensional image entropy (unless otherwise stated, the above measurements are average values); L9: L9 linear array probe, frequency range: 2.5-9.0 MHz, central frequency 6.5 MHz; L14: L14 linear array probe, frequency range: 3.0-14.0 MHz, central frequency 9 MHz; L7: L7 linear array probe, frequency range: 3-7 MHz, central frequency 4.0 MHz; L13: L13 linear array probe, frequency range: 3.6-13.5 MHz, central frequency 8 MHz; P: L9 vs. L14, L7 vs. L13