Attenuation coefficient and propagation speed estimates of intercostal tissue as a function of pig age

Attention coefficient and propagation speed of intercostal tissues were estimated from chest walls removed postmortem (pm) from 15 5.3+/-2.3-day-old, 19 31+/-6-day-old, and 15 61+/-3-day-old crossbred pigs. These ultrasonic propagation properties were determined from measurements through the intercostal tissues, from the surface of the skin to the parietal pleura. The chest walls were placed in a 0.9% sodium chloride solution, sealed in freezer bags, and stored at -15 degrees C prior to measurements. When evaluated, chest-wall storage time ranged between 1 and 477 days pm. All chest walls were allowed to equilibrate to 22 degrees C in a water bath prior to evaluation. There was an age dependency of the intercostal tissue propagation speed, with the speed increasing with increasing age. The attenuation coefficient of intercostal tissue was shown to be independent of the age of the pig at the discrete frequencies of 3.1 and 6.2 MHz. For pig intercostal tissues, the estimated attenuation coefficient over the 3.1-9.2 MHz frequency range was A = 1.94f(0.90) where A is in decibels per centimeter (dB/cm) and f is the ultrasonic frequency in megahertz. In order to determine if there was an effect of storage time pm on estimates of attenuation coefficient, a second experiment was conducted. Five of the youngest pig chest walls measured on day 1 pm in the first experiment were stored at 4 degrees C prior to the first evaluation then stored at -15 degrees C before being measured again at 108 days pm. There was no difference in the estimated intercostal tissue attenuation coefficient as a function of storage time pm.