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Improving the sensitivity of high-frequency subharmonic imaging with coded excitation: A feasibility study
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Image of FIG. 1.
FIG. 1.

Experimental setup used in (a) attenuation measurements and (b) subharmonic generation studies.

Image of FIG. 2.
FIG. 2.

(a) The number weighted and (b) volume weighted size distribution of Targestar-p TM measured with a CasysTM cell counter and (c) the frequency-dependent attenuation of Targestar-p TM . The error bars represent ±1 standard deviation computed over 5 statistically independent measurements.

Image of FIG. 3.
FIG. 3.

Frequency response of (a) the transmitting transducer (20 MHz nominal center frequency) and (b) the receiving transducer (10 MHz nominal frequency). (c) The measured intensity beam-pattern of the transmitting (20 MHz) and receiving (10 MHz) transducers.

Image of FIG. 4.
FIG. 4.

The frequency response of the broadband membrane hydrophone.

Image of FIG. 5.
FIG. 5.

Experimentally acquired frequency spectra showing the response of contrast agents under three transmission conditions. (a) 1.5 μs, 30 kPa coded-chirps, (b) 0.7 μs, 190 kPa coded-chirps, and (c) 1.5 μs, 190 kPa coded-chirps. Subharmonics were not observed for 30 kPa peak pressures (a) and 0.7 μs pulse durations (b); however, the fundamental and the subharmonic peaks at 20 and 10 MHz were clearly discernable for (c).

Image of FIG. 6.
FIG. 6.

The effect of tapering of excitation pulses on the subharmonic-to-fundamental ratio and the threshold of subharmonic emission. Figure 6(a) shows that the subharmonic-to-fundamental ratio decreased by 20 dB when the excitation pulse was windowed by 50% with a tapered Gaussian window. Figure 6(b) shows that subharmonics were first observed at higher threshold pressures for tapered excitation pulses relative to the rectangular windowed sine-burst.

Image of FIG. 7.
FIG. 7.

Subharmonic-to-fundamental ratio computed from the agent spectra, when the peak-negative-pressure was increased progressively from 60 to 380 kPa, with pulse duration of 1.5 μs.

Image of FIG. 8.
FIG. 8.

(a) Simulated and (c) experimentally acquired acoustic response of the agent to 4 MHz bandwidth chirp excitation with peak-negative pressure of 190 kPa. The subharmonic spectra extracted using the combined Butterworth and match-filtering operation are shown in (b) and (d).

Image of FIG. 9.
FIG. 9.

Shows the simulated (above) and experimental (below) results obtained with 4 MHz coded-chirp for (b) and (f) subharmonic RF pulse and (c), (g), and (h) axial resolution enhancement by pulse compression.

Image of FIG. 10.
FIG. 10.

The simulated (a) and (b) experimentally estimated axial resolution when pulse duration of sine-burst and coded-chirps was varied from 1 to 3 μs.

Image of FIG. 11.
FIG. 11.

The axial resolution obtained when the agent was excited with sine-bursts and coded-chirps. The results were obtained by processing (a) simulated and (b) experimentally acquired RF echo traces.


Generic image for table

List of parameters used in the modified Rayleigh–Plesset model.

Generic image for table

Size distribution estimates of Targestar-pTM


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Improving the sensitivity of high-frequency subharmonic imaging with coded excitation: A feasibility study