Passive Acoustic Mapping with the Angular Spectrum Method

Abstract

In the present proof of principle study, we evaluated the homogenous angular spectrum method for passive acoustic mapping (AS-PAM) of microbubble oscillations using simulated and experimental data. In the simulated data we assessed the ability of AS-PAM to form 3D maps of a single and multiple point sources. Then, in the two dimensional limit, we compared the 2D maps from AS-PAM with alternative frequency and time domain passive acoustic mapping (FD- and TD-PAM) approaches. Finally, we assessed the ability of AS-PAM to visualize microbubble activity in vivo with data obtained during 8 different experiments of FUS-induced blood-brain barrier disruption in 3 nonhuman primates, using a clinical MR-guided FUS system. Our in silico results demonstrate AS-PAM can be used to perform 3D passive acoustic mapping. 2D AS-PAM as compared to FD- PAM and TD-PAM is 10 and 200 times faster respectively and has similar sensitivity, resolution, and localization accuracy, even when the noise was 10-fold higher than the signal. In-vivo, the AS-PAM reconstructions of emissions at frequency bands pertinent to the different types of microbubble oscillations were also found to be more sensitive than TD-PAM. AS-PAM of harmonic-only components predicted safe blood-brain barrier disruption, whereas AS-PAM of broadband emissions correctly identified MR-evident tissue damage. The disparity (3.2mm) in the location of the cavitation activity between the three methods was within their resolution limits. These data clearly demonstrate that AS-PAM is a sensitive and fast approach for PAM, thus providing a clinically relevant method to guide therapeutic ultrasound procedures.

Combined passive acoustic mapping and magnetic resonance thermometry for monitoring phase-shift nanoemulsion enhanced focused ultrasound therapy

“…By utilizing an array of transducers as passive detectors it becomes possible to spatially resolve the location of cavitation activity. Such passive acoustic mapping (PAM) makes use of time (Gyongy and Coussios 2010, Gateau et al 2011b) or frequency-domain (Salgaonkar et al 2009, Arvanitis et al 2016, Haworth et al 2012) beamforming methods to reconstruct the distribution of acoustic sources such as cavitating microbubbles (O’Reilly et al 2014, Deng et al 2016, Choi and Coussios 2012). PAM has been utilized for various FUS applications including monitoring of ablation in tissue (Jensen et al 2012), microbubble activity in the brain (Arvanitis et al 2013, Vignon et al 2013), transfection of cells (Lee et al 2015, Myers et al 2016) and investigation of microbubble targeting (Crake et al 2015).…”

MRI‐guided transurethral insonation of silica‐shell phase‐shift emulsions in the prostate with an advanced navigation platform

“…Previous studies have found that bubble activity from droplets or microbubbles can provide controlled heating and can be monitored with passive ultrasound imaging techniques . In order to reduce the inconsistencies in the experimental treatment arms observed in this study, the acoustic output should be modulated based on feedback of cavitation activity via passive cavitation imaging, plane wave B‐mode imaging, or color Doppler imaging …”

“…Previous studies have found that bubble activity from droplets or microbubbles can provide controlled heating 21,23,24,29,64 and can be monitored with passive ultrasound imaging techniques. 65 In order to reduce the inconsistencies in the experimental treatment arms observed in this study, the acoustic output should be modulated based on feedback of cavitation activity via passive cavitation imaging, [66][67][68] plane wave Bmode imaging, [69][70][71] or color Doppler imaging. 72,73 The observation of thermal fixation with histology was related to some qualitative features of T 2 W and diffusionweighted imaging, suggesting that such enhanced heating could be ascertained in vivo, independently from histopathological analysis.…”

Delay multiply and sum beamforming method applied to enhance linear‐array passive acoustic mapping of ultrasound cavitation

“…Arvanitis et al . have described a fast PAM using the angular spectrum method, which is operated in frequency domain, so it is also a frequency‐domain method. By using a spectral propagator to form two‐dimensional images on a line‐by‐line basis rather than a point‐by‐point basis, this method can greatly improve the computational speed but yields poor image quality comparable to that of conventional TEA algorithm.…”

“…38,39 The presented results show that frequency-sum beamforming can provide a smaller point spread function (PSF) for single source, but may fail when multiple unknown sources are present. Arvanitis et al have described a fast PAM using the angular spectrum method, 40 which is operated in frequency domain, so it is also a frequency-domain method. By using a spectral propagator to form two-dimensional images on a line-by-line basis rather than a point-bypoint basis, this method can greatly improve the computational speed but yields poor image quality comparable to that of conventional TEA algorithm.…”