Three-dimensional Multistructural Quantitative Photoacoustic and US Imaging of Human Feet in Vivo

Abstract

Background Monitoring the microcirculation in human feet is crucial in assessing peripheral vascular diseases, such as diabetic foot. However, conventional imaging modalities are more focused on diagnosis in major arteries, and there are limited methods to provide microvascular information in early stages of the disease. Purpose To investigate a three-dimensional (3D) noncontrast bimodal photoacoustic (PA)/US imaging system that visualizes the human foot morphologically and also reliably quantifies podiatric vascular parameters noninvasively. Materials and Methods A clinically relevant PA/US imaging system was combined with a foot scanner to obtain 3D PA and US images of the human foot in vivo. Healthy participants were recruited from September 2020 to June 2021. The collected 3D PA and US images were postprocessed to present structural information about the foot. The quantitative reliability was evaluated in five repeated scans of 10 healthy feet by calculating the intraclass correlation coefficient and minimal detectable change, and the detectability of microvascular changes was tested by imaging 10 healthy feet intentionally occluded with use of a pressure cuff (160 mm Hg). Statistically significant difference is indicated with P values. Results Ten feet from six healthy male volunteers (mean age ± standard deviation, 27 years ± 3) were included. The foot images clearly visualized the structure of the vasculature, bones, and skin and provided such functional information as the total hemoglobin concentration (HbT), hemoglobin oxygen saturation (SO2), vessel density, and vessel depth. Functional information from five independent measurements of 10 healthy feet was moderately reliable (intraclass correlation coefficient, 0.51-0.74). Significant improvements in HbT (P = .006) and vessel density (P = .046) as well as the retention of SO2 were observed, which accurately described the microvascular change due to venous occlusion. Conclusion Three-dimensional photoacoustic and US imaging was able to visualize morphologic and physiologic features of the human foot, including the peripheral microvasculature, in healthy volunteers.