Acoustic attenuation properties of the lung: an open question

Between 1961 and 1986, a number of investigators studied the propagation properties of ultrasound (US) in the lungs. These studies revealed high attenuation levels in the lung tissue at all levels of lung inflation. In contrast, some clinical investigators have, in the past decade, used US at 5 to 7.5 MHz to penetrate the collapsed lung effectively during intraoperative thoracic ultrasonography. There is a discrepancy between these clinical imaging results and the high attenuation levels found in the earlier studies of US propagation in the lungs. We studied the attenuation of US in the lungs with an ultrasonic analyzer, designed for highly attenuating materials, and utilizing linear sweep-based transmission measurements. Our data also revealed high attenuation levels at various low levels of lung inflation, inconsistent with the findings of intraoperative thoracic ultrasonography. These results imply that the US attenuation properties of the lung are far from accurately established.