1Ultrasound Division, GE Healthcare, 2Department of Gastroenterology and Hepatology, Toho University Omori Medical Center, 3Department of Clinical Functional Physiology, Toho University Omori Medical Center
Purpose: To elucidate the mechanism behind the so-called “bamboo blind” sign frequently observed on B-mode images as multiple low-echoic lines in nonalcoholic steatohepatitis and highly fatty liver cases. Subjects and Methods: Six types of acoustic shadowing artifacts that might be the cause of the bamboo blind sign were defined. B-mode images were acquired for 21 fatty liver cases (inc. 9 highly fatty liver cases). The cases were then pathologically diagnosed. A phantom experiment was also performed to investigate whether the refraction occurs due to the gap of sound velocity between two different media. Results and Discussion: The mechanism of the bamboo blind sign corresponded well to the acoustic shadowing from small vessels in the liver. The phantom experiment validated the same phenomenon at a larger gap in sound velocity, which can be regarded as the same level as that in highly fatty liver cases. Conclusion: The refraction between blood vessels and highly fatty liver parenchyma with decreased sound velocity is the dominant reason for the bamboo blind sign.