Liver glycogen and water storage: effect on ultrasound attenuation

Glycogen has been shown in vitro to have a high specific absorption coefficient (ultrasound absorption in water per concentration) compared to other proteins. Depending on the amount of water which may accompany glycogen flux into and out of liver cells, the ultrasound attenuation coefficient of the liver may rise and fall with stored hepatic glycogen. This paper reports ex vivo studies on rats and in vivo studies on normal human volunteers before and after fasting. The results show a statistically significant difference in liver attenuation between well fed and fasted individuals. Generally, the attenuation difference is greater than 10%, and indicates that liver wet weight may not be strictly constant over glycogen storage cycles, as suggested in classic works. In contrast, no significant change in ultrasound backscatter is noted. The results point to the possible role of ultrasound attenuation measurements as a sensitive indicator of tissue physiology, and suggest that glycogen (feeding or fasting) must be controlled in tissue characterization experiments which compare liver attenuation coefficients of individuals and groups.