Phase-frequency compound imaging with extended depth-of-field using a phase-inverted ultrasound transducer

초록

Ultrasound compound imaging techniques combine multiple images acquired at different angles or frequencies to suppress speckle patterns in brightness-mode (B-mode) imaging. Conventional frequency compound (CFC) imaging uses sub-bands within the bandwidth of the transducer and provides full-image compounding, unlike spatial compounding, which is region-limited. However, CFC suffers from degraded image quality in the far field due to the narrow depth-of-field (DOF) of the second harmonic frequency (2f0). To address this, we propose a novel phase-frequency compound (PFC) imaging method that combines an in-phase image at the fundamental frequency (f0) with an out-of-phase image at the 2f0, using a phase-inverted ultrasound transducer (PIUT). By applying out-of-phase processing to the 2f0 image, the DOF is extended, particularly improving far-field signal-tonoise ratio (SNR). These benefits remain after combining the processed 2f0 image with the f0 image. A prototype quartered-aperture transducer was fabricated, and experiments were conducted using wire phantom, tissuemimicking phantom, and ex vivo porcine tissue. In the far-field region, the proposed PFC method improved speckle SNR (SSNR) by 46% in phantom and by 34% in porcine tissue. Compared with the CFC, it maintained the SSNR while increasing the SNR by approximately 7 dB. Therefore, the proposed PFC imaging technique demonstrates the potential to simultaneously suppress speckle patterns and increase far-field SNR, thereby improving overall image quality in B-mode ultrasound imaging.

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