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High frame rate contrast detection

Principal investigator:   Rik Vos


Ultrasound contrast agent (UCA) imaging provides a cost-effective diagnostic tool to assess tissue perfusion and vascular pathologies. However, excessive transmission levels may negatively impact both uniform diffusion and survival rates of contrast agents, limiting their density and thus their echogenicity. Contrast detection methods with both high sensitivity and low contrast destruction rate are thus essential to maintain diagnostic capabilities. Angled plane wave transmission with high number of compounding [Montaldo et al. "Coherent plane-wave compounding for very high frame rate ultrasonography and transient elastography," IEEE Trans. Ultrason., Ferroelect., Freq. Control, vol. 56, no. 3, pp. 489-506, 2009] has been suggested to produce good quality images at pressure levels that do not destroy UCA. We performed a quantitative evaluation of detection efficacy of flowing UCA with either traditional focused scanning or ultrafast plane wave imaging. Amplitude modulation at nondestructive pressure levels was implemented in the ULA-OP ultrasound research platform [MSDLab, Univ. Florence, Italy]. The influence of the number of compounding angles, peak-negative pressure and flow speed on the final image quality was investigated. Results show that the images obtained by compounding multiple angled plane waves offer a greater contrast (up to 12 dB increase) with respect to focused amplitude modulation. This increase is attributed mainly to noise reduction caused by the coherent summation in the compounding step. Additionally, we show that highly sensitive detection is already achieved with a limited compounding number (N<16), thus suggesting the feasibility of continuous contrast monitoring at high frame rate. This capability is essential to properly detect contrast agents flowing at high speed, as an excessive angle compounding is shown to be destructive for the contrast signal, as the UCA motion quickly causes loss of correlation between consecutive echoes.

[J. Viti et al., 'Detection of Contrast Agents: Plane Wave vs Focused Transmission', IEEE Trans. Ultras. Ferr. Freq. 2016]

Figure: Left to right: Focused AM (a) ; Compounded Planewave AM with increasing number of angles (N = 1; 15; 63, respectively). Each image is normalized to its own maximum intenstiy.


We have recently evaluated a TEE 3D matrix probe prototype developed by Oldelft ultrasound [www.oldelft.nl] , and programmed this probe to generate 200 - 600 volumes per second when connected to a Verasonics Vantage-256 research system. With this probe we imaged, as a preliminary test, regular tap-water bubbles in a bucket. Data were processed offline and 3D volume rendering was performed in ParaView 5.1.



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