Tomographic Imaging of Attenuation with Simulation Correction for Refraction

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Abstract
Beam refraction in soft tissue and phase cancellation at the receiver can cause large errors and prevent tomographic reconstruction of attenuation. The method developed in this study incorporates simulation of ultrasound propagation into tomographic imaging to correct these effects. The method is based on input scan data of time-of-flight and received signal amplitude. The speed of propagation is estimated from the time-of-flight scan data. Based on this estimate, the simulation generates scan data of signal amplitude. This scan data represents the loss from refraction and phase cancellation with zero attenuation, and is used to correct the input amplitude scans. We evaluate the accuracy of the method, and investigate the trade-off between various scanning and filtering parameters. The evaluation is based on scan data generated by a comprehensive simulation including refraction, attenuation, phase cancellation, finite beam width, several target shapes and sizes with sound parameters consistent with biologic values, and discrete translational and rotational transducer positions. In several cases with large refraction distortions, attenuation images are accurately reconstructed which are not feasible using standard tomographic methods.