Ultrasound attenuation estimation in soft tissue using the entropy difference of pulsed echoes between two adjacent envelope segments = 펄스 에코의 연속적인 포락선 구획사이의 앤트로피 차이를 이용한 연조직에서의 초음파 감쇄계수를 측정하는 방법에 관한 연구
Among several parameters in ultrasonic tissue characterization (UTC), attenuation has gained the most attention since it provides valuable information in clinical diagnosis and in quantitative B-scan imaging. Although attention is intrinsically defined by way of transmission measurement, it can be estimated from analysis of the backscattered echo waveform. But, because of the random spatial variation in the backscattered signal amplitude, the estimator variance becomes very large, making it difficult to estimate the attenuation slope from the back-scattered ultrasound signal. In this thesis, we describe a new method of estimating the ultrasound attenuation coefficient of soft tissue based on the entropy difference between two adjacent envelope segments of narrowband ultrasound pulse echoes. Assuming uniform attenuation in the region under investigation, the attenuation is estimated by minimizing the difference of entropies in the two segments as the attenuation is continuously compensated for. The simulation and experimental results with a tissue equivalent (TE) phantom show that the proposed estimator is quite robust to receiver noise and requires considerably less data length as compared with conventional methods. At present, an experimental result with a TE phantom shows that a resolution of 10 mm X 10 mm can be attained with echoes from a depth of 3 cm using a 2.25 MHz transducer.