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Compound Mask for Divergent Wave Imaging in Medical Ultrasound

Zahraa Alzein, Marco Crocco, Daniele D. Caviglia

TL;DR

This work tackles the challenge of optimizing compound weights in Divergent Wave Imaging by deriving a closed-form mapping from Synthetic Aperture Imaging transmit apodization to the DWI compound mask. The method, applicable to both linear and convex probe geometries and arbitrary virtual-source placements, leverages the STAI framework as a reference to reproduce its apodization effects in DWI. Validation through Field II simulations shows that the transformed apodization preserves SAI-like resolution benefits, achieving notable FWHM improvements for both linear and convex arrays, and enabling offline computation to minimize real-time load. The approach broadens DWI applicability, offering a systematic, non-iterative means to enhance spatial and contrast resolution, with future work extending to experimental validation and 3D imaging scenarios.

Abstract

Divergent wave imaging with coherent compounding allows obtaining broad field of view and higher frame rate with respect to line by line insonification. However, the spatial and contrast resolution crucially depends on the weights applied in the compound phase, whose optimization is often cumbersome and based on trial and error. This study addresses these limitations by introducing a closed-form approach that maps the transmit apodization weights used in synthetic aperture imaging into the compound mask applied to divergent wave imaging. The approach draws inspiration from a successful technique developed for plane wave imaging, leveraging synthetic aperture imaging as a reference due to its superior image quality. It works for both linear and convex geometries and arbitrary spatial arrangements of virtual sources generating divergent waves. The approach has been validated through simulated data using both linear and convex probes, demonstrating that the Full Width at Half Maximum (FWHM) in Divergent Wave Linear Array (DWLA) increased by 7.5% at 20 mm and 9% at 30 mm compared to Synthetic Aperture Linear Array (SALA). For Divergent Wave Convex Array (DWCA), the increase was 1.64% at 20 mm and 26.56% at 30 mm compared to Synthetic Aperture Convex Array (SACA), witnessing the method's effectiveness.

Compound Mask for Divergent Wave Imaging in Medical Ultrasound

TL;DR

This work tackles the challenge of optimizing compound weights in Divergent Wave Imaging by deriving a closed-form mapping from Synthetic Aperture Imaging transmit apodization to the DWI compound mask. The method, applicable to both linear and convex probe geometries and arbitrary virtual-source placements, leverages the STAI framework as a reference to reproduce its apodization effects in DWI. Validation through Field II simulations shows that the transformed apodization preserves SAI-like resolution benefits, achieving notable FWHM improvements for both linear and convex arrays, and enabling offline computation to minimize real-time load. The approach broadens DWI applicability, offering a systematic, non-iterative means to enhance spatial and contrast resolution, with future work extending to experimental validation and 3D imaging scenarios.

Abstract

Divergent wave imaging with coherent compounding allows obtaining broad field of view and higher frame rate with respect to line by line insonification. However, the spatial and contrast resolution crucially depends on the weights applied in the compound phase, whose optimization is often cumbersome and based on trial and error. This study addresses these limitations by introducing a closed-form approach that maps the transmit apodization weights used in synthetic aperture imaging into the compound mask applied to divergent wave imaging. The approach draws inspiration from a successful technique developed for plane wave imaging, leveraging synthetic aperture imaging as a reference due to its superior image quality. It works for both linear and convex geometries and arbitrary spatial arrangements of virtual sources generating divergent waves. The approach has been validated through simulated data using both linear and convex probes, demonstrating that the Full Width at Half Maximum (FWHM) in Divergent Wave Linear Array (DWLA) increased by 7.5% at 20 mm and 9% at 30 mm compared to Synthetic Aperture Linear Array (SALA). For Divergent Wave Convex Array (DWCA), the increase was 1.64% at 20 mm and 26.56% at 30 mm compared to Synthetic Aperture Convex Array (SACA), witnessing the method's effectiveness.

Paper Structure

This paper contains 8 sections, 12 equations, 7 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Materials and Methods
  3. Synthetic Aperture Imaging (SA) with Linear and Convex Probes
  4. Divergent Wave Imaging
  5. Relation between transmit apodization in STAI and Compound Mask in DWI
  6. Results AND Discussion
  7. limitations and potential improvements
  8. Conclusion

Figures (7)

  • Figure 1: Comparison of SA Linear and Convex Probe Configurations with distances between image point $(x,z)$ and probe elements coordinates in transmission ($x_t,z_t$) and reception ($x_r,z_r$)
  • Figure 2: Comparison of DW Linear and Convex Probe Configurations with distances between virtual source $(x_v,z_v)$ and image point $(x,z)$ and probe elements coordinates in transmission ($x_t,z_t$); moreover also the distance between image point and probe elements coordinates in reception ($x_r,z_r$) is displayed.
  • Figure 3: Examples of values of H matrix in Eq. 7. Row and column indexes are related to virtual sources and probe elements indexes respectively
  • Figure 4: Comparison of Transmit Apodization Profile (a) and Compound Mask Profile (b)
  • Figure 5: (a) The transmit apodization $v(x_t)$ in STAI for Hanning window with (b) The corresponding compound mask $w(x_i,z_i)$ in DWLA for a fixed $z_i$
  • ...and 2 more figures