Sound Speed Optimization Based on Acoustic Point Spread Function
A constant sound speed of 1.54 mm/mus is usually used by ultrasound imaging systems for focusing delay. In reality, there exists a mismatch between the assumed sound speed and the true sound speed propagated in the tissue. This mismatch can lead to defocusing and geometric distortions in ultrasound images which may degrade the accuracy of clinical diagnoses. We have analyzed this influence in detail. Based on the spatial-frequency characteristic of acoustic point spread function, we develop an algorithm to determine the sound speed which produces the best overall focus quality. The feature of the proposed method, including the effect of the range size is also discussed. We also compare our method with the mean brightness method. Testing results show clear improvement in ultrasound image quality.