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Reducing the Number of Elements in Order to Enhance the Speed of the Ultrasound Tomographic Imaging Systems

Rasouli Jokandan, Fatemeh | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 58282 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Kavehvash, Zahra; Hakakzadeh, Soheil
  7. Abstract:
  8. Transmission-mode ultrasound computed tomography (USCT) has emerged as a novel, safe, and cost-effective method for quantitative imaging of biological tissues, especially in breast screening. Despite technological advancements, challenges such as reduced accuracy in heterogeneous media, incomplete acoustic field coverage, sensitivity to initial conditions, and phenomena like cycle skipping still limit image quality and reconstruction speed in these systems. In this thesis, aiming to improve the speed and performance of USCT imaging, three reconstruction algorithms have been designed, implemented, and evaluated: a travel-time-based Gauss-Newton method, frequency-domain full waveform inversion (FWI), and a novel hybrid algorithm based on adaptive integration of these two approaches. In the structure of the hybrid algorithm, the Gauss-Newton method is used not only for initial estimation but also iteratively during intermediate reconstruction stages for model correction. This strategy effectively reduces cycle skipping, accelerates convergence, and enhances the final reconstruction accuracy. To further enhance imaging speed, another key innovation of this research is the introduction of a novel excitation technique termed steered single-beam excitation with simultaneous activation of adjacent sources. By employing beam steering and multi-transmitter activation, this technique enables the generation of more focused acoustic fields with wider angular coverage and increased received energy in each transmission. Importantly, it achieves a significant improvement in data acquisition speed and input data quality without requiring changes to the structure of existing reconstruction algorithms. The simulation and performance evaluation of the proposed framework were conducted using the K-wave numerical environment in MATLAB on two different phantoms—one simple for controlled analysis and the other realistic based on breast CT images. The results demonstrate that the combination of the hybrid algorithm with the proposed steered excitation yields more accurate and faster reconstruction of sound speed and attenuation maps compared to individual algorithms. Simulation results show that, compared to the baseline method, the proposed approach improves image quality (PSNR) by approximately 17%, reduces reconstruction error (RMSE) by about 49%, and increases the SSIM index by nearly 20%
  9. Keywords:
  10. Computed Tomography (CT) ; Ultrasound Computed Tomography (USCT) ; Image Reconstruction ; Sound Velocity ; Steered Beam Excitation ; Acoustic Attenuation ; Steered Beam Excitation

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