Significance: Photoacoustic computed tomography (PACT) is a fast-growing imaging modality. In PACT, the image quality is degraded due to the unknown distribution of the speed of sound (SoS). Emerging initial pressure (IP) and SoS joint-reconstruction methods promise reduced artifacts in PACT. However, previous joint-reconstruction methods have some deficiencies. A more effective method has promising prospects in preclinical applications.Aim: We propose a multi-segmented feature coupling (MSFC) method for SoS-IP joint reconstruction in PACT.Approach: In the proposed method, the ultrasound detectors were divided into multiple sub-arrays with each sub-array and its opposite counterpart considered to be a pair. The delay and sum algorithm was then used to reconstruct two images based on a subarray pair and estimated a direction-specific SoS, based on image correlation and the orientation of the subarrays. Once the data generated by all pairs of subarrays were processed, an image that was optimized in terms of minimal feature splitting in all directions was generated. Further, based on the direction-specific SoS, a model-based method was used to directly reconstruct the SoS distribution.Results: Both phantom and animal experiments demonstrated feasibility and showed promising results compared with conventional methods, with less splitting and blurring and fewer distortions.Conclusions: The developed MSFC method shows promising results for both IP and SoS reconstruction. The MSFC method will help to optimize the image quality of PACT in clinical applications.
As an emerging optical imaging modality, photoacoustic imaging provides optical absorption contrasts and ultrasonic high resolution. Artifacts appearing in photoacoustic computed tomography (PACT) always deteriorate image quality and resolution, and result in confusion of biological information. On the basis of different causing reasons, they are roughly classified as split artifacts and streak artifacts. Here we present an innovative Feature-Coupling (FC) method to weaken split artifacts with joint reconstruction of speed of sound and a new reconstruction algorithm, termed Contamination-Tracing Back-Projection (CTBP), is proposed for the mitigation of streak artifacts. The utility, effectiveness and robustness of our methods were demonstrated using numerical, phantom, and in vivo experiments.
Photoacoustic imaging relies on diffused photons for optical contrast, and diffracted ultrasound for high resolution. As a tomographic imaging modality, often times an inverse problem of acoustic diffraction needs to be solved to reconstruct a photoacoustic image. The inverse problem is complicated by the fact that the acoustic properties, including the speed of sound distribution, in the image field of view are unknown. During reconstruction, subtle changes of the speed of sound in the acoustic ray path may accumulate and give rise to noticeable blurring in the image. Thus, in addition to the ultrasound detection bandwidth, inaccurate acoustic modeling, especially the unawareness of the speed of sound, defines the image resolution and influences image quantification. Here, we proposed a method termed feature coupling to jointly reconstruct the speed of sound distribution and a photoacoustic image with improved sharpness, at no additional hardware cost. In vivo experiments demonstrated the effectiveness and reliability of our method.
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