Ultrasonographic, quantitative comparison of lower extremity lymphedema versus normal control. Technical note with case reports

Abstract

Characterization of tissue by ultrasonography (CATUS) is a modern-day research endeavor intended to improve visual perception and image quantification. Visual perception increases with color. Quantification focuses on pixel echo brightnesses. A previously presented case report demonstrated reappearance of lymphatic channels a few days after manual drainage. Ultrasonographic images (US) of lymphatic leg and foot were quantitated and compared to a normal extremity based on proportions of pixels in specific brightness intervals. Anatomy evaluated included control- subcutaneous and lymphatic compartments. US with 256 brightness levels were obtained at the proximal, mid and distal leg and foot. Control and lymphatic Gray Scale Medians (GSM) and histograms were compared using t-test and Chi-square statistics. Average GSM was 97±9 (SD) (82-114, n=12 images) for control, greater than 51±15 (24-69, n=12) for lymphedematous leg/foot (P99% of pixels with brightness in the muscle-fiber range (41-196), in contrast to 62% for the lymphatic extremity (P<0.001). Lymphedema averaged 7%, 3%, 15% and 14% of pixels in blood, blood/fat, fat and fat/muscle-like regions (0-4, 5-7, 8-26, 27- 40 brightness intervals). Such regions were visually interpreted as lymphatic channels or lakes. Visual perception by colorization is subjective, but most people perceives details better, for example, during the day than at night. Furthermore, US images have 16 times more shades of gray, 256, than that perceived by the human visual system, 16 on average. Colorization improved perception of lymphatic channels and lakes by transforming blood echoes into red and lymphatic liquid with echoes similar to fat into yellow. Pixel proportions in low brightness intervals were higher in the lymphatic than in the normal extremity. Lymphedema severity was quantified. The CATUS technique may be used to monitor treatment effects or disease evolution.