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

Abstract

Purpose Passive acoustic mapping (PAM) has been proposed as a means of monitoring ultrasound therapy, particularly nonthermal cavitation‐mediated applications. In PAM, the most common beamforming algorithm is a delay, sum, and integrate (DSAI) approach. However, using DSAI leads to low‐quality images for the case where a narrow‐aperture receiving array such as a standard B‐mode linear array is used. This study aims to propose an enhanced linear‐array PAM algorithm based on delay, multiply, sum, and integrate (DMSAI). Methods In the proposed algorithm, before summation, the delayed signals are combinatorially coupled and multiplied, which means that the beamformed output of the proposed algorithm is the spatial coherence of received acoustic emissions. We tested the performance of the proposed DMSAI using both simulated and experimental data and compared it with DSAI. The reconstructed cavitation images were evaluated quantitatively by using source location errors between the two algorithms, full width at half maximum (FWHM), size of point spread function (A50 area), signal‐to‐noise ratio (SNR), and computational time. Results The results of simulations and experiments for single cavitation source show that, by introducing DMSAI, the FWHM and the A50 area are reduced and the SNR is improved compared with those obtained by DSAI. The simulation results for two symmetric or nonsymmetric cavitation sources and multiple cavitation sources show that DMSAI can significantly reduce the A50 area and improve the SNR, therefore improving the detectability of multiple cavitation sources. Conclusions The results indicate that the proposed DMSAI algorithm outperforms the conventionally used DSAI algorithm. This work may have the potential of providing an appropriate method for ultrasound therapy monitoring.

Doppler Passive Acoustic Mapping

“…Additionally, the axial point spread function was expected to be larger than the channel itself, thus we could not resolve microbubble velocities across the channel width. Alternative beamforming techniques [23], [77] or hemispherical receiving arrays with larger aperture size [24], [25], [45] may improve the axial-to-lateral resolution ratio of microbubble velocity mapping. With current PAM algorithms, the lateral resolution is far better than the axial resolution.…”

Passive acoustic mapping with absolute time‐of‐flight information and delay‐multiply‐sum beamforming

“…Figure 1b shows a typical example of non‐coaxial alignment where the linear array is parallel to the FUS beam, which is often used for cavitation detection in tissue phantoms and tissues 10,15,26 . In this alignment strategy, the first travel time is given by $$$$\begin{equation}{t_1}\left( {x,z} \right) = \left( {x - {x_t}} \right)/c.\end{equation}$$$$The linear array can also be perpendicular to the FUS beam, as shown in Figure 1c, which is also a common non‐coaxial alignment and mainly applies to the cavitation mapping in an in vitro vascular phantom 12,13,29,37 . Unlike Figure 1a,b, the FUS transducer vertex in Figure 1c is out of the imaging plane.…”

“…DMS was subsequently used in medical ultrasound imaging and photoacoustic imaging, 35,36 and recently modified to enhance RtPAM. 37 It has been verified in B-mode ultrasound imaging that DMS can improve the contrast resolution compared to standard DS due to the decrease in mainlobe width and sidelobe level. 35 As mentioned, PAM is analogous to active ultrasound imaging when passive beamforming utilizes the absolute time-of -flight information.…”

“…The operation of signal combination, multiplication and summation in DMS can be interpreted as the aperture auto‐correlation, which brings a measure of the signal coherence and thus can achieve clutter suppression. DMS was subsequently used in medical ultrasound imaging and photoacoustic imaging, 35,36 and recently modified to enhance RtPAM 37 . It has been verified in B‐mode ultrasound imaging that DMS can improve the contrast resolution compared to standard DS due to the decrease in mainlobe width and sidelobe level 35 .…”

Time-Resolved Passive Cavitation Mapping Using the Transient Angular Spectrum Approach

“…PCM has been proven to be a useful adjunct approach for monitoring FUS, as it provides spatialtemporal information pertaining to the cavitation activity inside the tissue that cannot be obtained by MRI or optical imaging. A variety of PCM algorithms have been developed over the years [19]- [29]. One of the most widely used and straightforward algorithms is the delay-and-sum (DAS) approach, which is also used in B-mode imaging [30] and photoacoustic imaging [31].…”