A Histogram Analysis of the Pixel Grayscale (Luminous Intensity) of B-Mode Ultrasound Images of the Subcutaneous Layer Predicts the Grade of Leg Edema in Pregnant Women

The technique most widely used to quantitatively measure leg edema is only a pitting edema method. It has recently become possible to digitize B-mode ultrasound images and accurately quantify their brightness using an image-analysis software program. The purpose of this study was to find new indices of the grade of leg skin, to study whether or not analyses of the subcutaneous layer of leg skin on ultrasound images using image-editing software program can be used to evaluate it and to digitize it. Images of 282 subcutaneous layers of leg skin in 141 pregnant women were obtained using a B-scan portable ultrasound device. Rectangular photographs (vertical: skin thickness; horizontal: width of probe) were obtained using an image-editing program, and the luminous intensity (pixel grayscale: 0-255) and thickness of the skin were calculated using a histogram. We investigated the correlation between these parameters and the grade of pitting edema (0-3). There was a significant positive correlation between the grade of pitting edema and the average luminous intensity value, its standard deviation, and the skin thickness (? = 0.36, ? = 0.22, ? = 0.51, p < 0.0001, respectively). In particular, there was strong positive correlation between the grade of pitting edema and both the total number of pixels in a rectangle x (multiplied by) the average luminous intensity value and the total number of pixels in a rectangle x the standard deviation of the average luminous intensity value (? = 0.58 and ? = 0.59, p < 0.0001, respectively). We could quantitatively evaluate the grade of leg edema by analyzing ultrasound photographs of the subcutaneous layer of the leg skin using an image-editing software program and found new indices to digitize it.

Automated summary

The most commonly used technique for quantitatively measuring leg edema is the pitting edema method. Recent advancements in image-analysis software have allowed for the digitization and accurate quantification of brightness in B-mode ultrasound images. This study aimed to find new indices for evaluating the grade of leg skin and determine if ultrasound image analysis using image-editing software can be used to digitize it. Analysis of the obtained images showed a significant positive correlation between the grade of pitting edema and various parameters, such as luminous intensity and skin thickness. Particularly, there was a strong positive correlation between the grade of pitting edema and the total number of pixels multiplied by the average luminous intensity value. This study demonstrates the potential of using image-editing software to quantitatively evaluate leg edema and provides new digitization indices.