Intravascular ultrasound imaging with directional synthetic aperture focusing and coherence factor weighting

Abstract

Purpose: Intravascular ultrasound (IVUS) is widely used to visualize vascular structures and assess atherosclerotic plaques, particularly for evaluating the risk of rupture. Although increasing the center frequency of the transducer can enhance spatial resolution, it also increases attenuation, which substantially degrades image quality at greater depths. To mitigate this trade-off, synthetic aperture focusing (SAF) techniques have been studied; however, when applied to single-element rotational IVUS systems, they have yielded only minimal improvements and introduced undesirable artifacts. Methods: In this work, a directional SAF (dSAF) method is proposed to address these limitations. The convex nature of the point spread function in rotational IVUS scanning is analyzed to track the true direction of echo signals, enabling the selective exclusion of off-axis signals. By focusing only on valid signals during synthesis, resolution degradation and artifact formation are prevented, and the fidelity of the reconstructed image is preserved. Results: Validation through simulations and phantom experiments indicates that the dSAF method achieves an average 37.3% improvement in lateral resolution and an 8.6% increase in contrast-to-noise ratio, without degrading penetration depth. Conclusion: These findings suggest that directional echo screening effectively mitigates the limitations encountered with conventional SAF in IVUS imaging, offering a robust pathway to improved image quality. Additionally, the proposed approach can be integrated into existing IVUS workflows, potentially expediting clinical adoption and advancing intravascular diagnostic capabilities.