Three-dimensional Visualization of Ultrasound Backscatter Statistics by Window-modulated Compounding Nakagami Imaging

Abstract

In this study, the window-modulated compounding (WMC) technique was integrated into three-dimensional (3D) ultrasound Nakagami imaging for improving the spatial visualization of backscatter statistics. A 3D WMC Nakagami image was produced by summing and averaging a number of 3D Nakagami images (number of frames denoted as N) formed using sliding cubes with varying side lengths ranging from 1 to N times the transducer pulse. To evaluate the performance of the proposed 3D WMC Nakagami imaging method, agar phantoms with scatterer concentrations ranging from 2 to 64 scatterers/mm were made, and six stages of fatty liver (zero, one, two, four, six, and eight weeks) were induced in rats by methionine-choline-deficient diets (three rats for each stage, total n = 18). A mechanical scanning system with a 5-MHz focused single-element transducer was used for ultrasound radiofrequency data acquisition. The experimental results showed that 3D WMC Nakagami imaging was able to characterize different scatterer concentrations. Backscatter statistics were visualized with various numbers of frames; N = 5 reduced the estimation error of 3D WMC Nakagami imaging in visualizing the backscatter statistics. Compared with conventional 3D Nakagami imaging, 3D WMC Nakagami imaging improved the image smoothness without significant image resolution degradation, and it can thus be used for describing different stages of fatty liver in rats.

Hepatic Steatosis Assessment Using Quantitative Ultrasound Parametric Imaging Based on Backscatter Envelope Statistics

“…Compared with one-dimensional or two-dimensional envelope statistics parametric imaging, three-dimensional envelope statistics parametric imaging can offer an enhanced characterization of hepatic steatosis, which involves the construction of the three-dimensional envelope statistics parametric image. Currently, only three-dimensional Nakagami imaging has been proposed for hepatic steatosis assessment [19]. Three-dimensional parametric imaging based on other envelope statistics parameters can be explored for characterizing hepatic steatosis in future developments.…”

“…Because of its low computational complexity, the Nakagami distribution has become the most widely used statistical model in the field of medical ultrasound; typical applications of Nakagami model have been summarized by Tsui et al [30]. The estimation methods of Nakagami m parameter mainly include moment-based estimators [19,31,32] and maximum likelihood estimators [30,32,33]. It should be noted that window-modulated compounding (WMC) Nakagami imaging was proposed by Tsui et al [34] for simultaneous improvement of image resolution and smoothness of Nakagami images.…”

“…Animal models [19,31] and clinical studies [35] have shown that the m parameter estimated by the moment-based estimators increases with the increasing severity of hepatic steatosis. Using a rat model (n = 24), Ho et al [31] reported that ultrasound Nakagami imaging is well correlated with the amount of the total cholesterol (r = 0.86; p < 0.0001) and triglyceride (r = 0.79; p < 0.0001) in the liver tissue, respectively.…”

“…Using a rat model (n = 24), Ho et al [31] reported that ultrasound Nakagami imaging is well correlated with the amount of the total cholesterol (r = 0.86; p < 0.0001) and triglyceride (r = 0.79; p < 0.0001) in the liver tissue, respectively. Zhou et al [19] investigated three-dimensional WMC Nakagami imaging for characterizing hepatic steatosis in a rat model (n = 18); the Nakagami m parameter had a correlation r 2 = 0.94 with the methionine-choline-deficient diet weeks. Wan et al [35] investigated ultrasound Nakagami imaging for assessing hepatic steatosis of 107 patients; the reference standard was an ultrasonographic scoring system [36].…”

“…QUS envelope statistics [17] extracts statistical information from the envelope of backscattered RF signals and is related to liver tissue microstructures. Envelope statistics techniques, both statistical model-based [18][19][20] and non-model-based [21,22], have shown potential for hepatic steatosis characterization. However, a state-of-the-art review of hepatic steatosis assessment using envelope statistics techniques is still lacking.…”