High-accuracy measurements of the average speed of sound in biological tissues based on improved focusing method

The speed of sound (SoS) is expected to be a biomarker for liver diseases such as fatty liver and cartilage diseases such as osteoarthritis. We have developed an improved method to measure the average SoS with high accuracy in liver and cartilage based on the focusing method. In the case of the liver, a plane wave is transmitted to a strong scatterer such as a blood vessel in the liver, and the average SoS is measured with high accuracy by performing phase aberration correction using a virtual central element on the received waves. In the case of cartilage, a focused wave is transmitted to the subchondral bone to generate a pseudo-point scattered wave, and the average SoS is measured by applying the focusing method to the received wave. The correctness of the proposed method was first verified by simulations. Then, the effectiveness was investigated by experiments using phantoms and the excised liver and cartilage tissues from animals. The results while heating the liver showed that the proposed method could capture a change of 1.5 m/s/°C and had the ability to achieve high-accuracy SoS measurements. The SoS measured in the cartilage agreed with the reference value obtained by the standard pulse transmission method.