A new imaging strategy utilizing wideband transient response of ultrasound contrast agents

High resolution clinical systems operating near 15 MHz are becoming more available, however, they lack sensitive harmonic imaging modes for ultrasound contrast agent (UCA) detection, primarily due to limited bandwidth. When an UCA is driven to non-linear oscillation, a very wideband acoustic transient response is produced that extends beyond 15 MHz. We propose a novel strategy utilizing 2 separate transducers at widely separated frequencies and arranged confocally to simultaneously excite and receive acoustic transients from UCAs. Experiments were performed to demonstrate that this new mode shows similar resolution, higher echo amplitudes and greatly reduced attenuation compared to transmission at a higher frequency, and superior resolution compared to transmission and reception at a lower frequency. The proposed method is shown to resolve two 200 μm tubes with centers separated by 400 μm. Strong acoustic transients were detected for rarefaction-first 1-cycle pulses starting at peak-negative pressures ranging from -300 to -400 kPa. The results of this work may lead to uses in flow and/or targeted imaging in applications requiring very high sensitivity to contrast agents.