Comparison of synthetic aperture focusing and delay‑and‑sum compounding for 3D ultrasound tomography of the breast

Synthetic aperture focusing technique (SAFT) and delay-and-sum (DAS) compounding are two reconstruction methods commonly used in ultrasound computed tomography (USCT). In our 3D USCT device, SAFT is performed with reduced resolution due to the long acoustic paths and uncertainties in speed of sound, using signal detection and broadened pulses. In contrast, DAS compounding avoids signal detection and preserves speckle patterns that enhance the representation of tissue texture. Using a volunteer breast dataset, we systematically varied the transmitter–receiver neighborhood (23°–85° solid angle) and Transducer Array Systems (TAS) subset spacing (all TAS to every 32nd TAS), and qualitatively assessed contrast, small-structure visibility, and glandular texture. Larger neighborhoods improved texture continuity, while progressively spaced TAS subsets unexpectedly increased contrast, suggesting residual propagation uncertainties for closely spaced TAS. The results show that SAFT emphasizes strong reflectors but may miss weaker signals, whereas DAS provides more continuous tissue texture at the cost of partial blurring and parameter-dependent contrast. The choice of method should be guided by the diagnostic focus.