Parametric imaging of three-dimensional engineered tissue constructs using high-frequency ultrasound

Abstract

The goal of this study was to use high-frequency ultrasound to nondestructively characterize three-dimensional engineered tissues. We hypothesized that backscatter spectral parameters, such as the integrated backscatter coefficient (IBC), can be used to quantify differences in cell concentration in engineered tissues. We chose the IBC parameter since it estimates the backscattering efficiency of scatterers per unit volume. In this study, acoustic fields were generated using single-element, focused transducers (center frequencies of 30 and 40 MHz) operating over a frequency range of 13 to 47 MHz. Three-dimensional engineered tissue constructs were fabricated with mouse embryonic fibroblasts homogenously embedded within agarose. Constructs with cell concentrations ranging from 1x104 to 1x106 cells/mL were investigated. The IBC was computed from the backscatter spectra, and parametric images of spatial variations in the IBC were generated. Results showed that the IBC increased linearly with cell concentration. Further, we demonstrated that parametric images detected spatial variations in cell concentration within engineered tissue constructs. Thus, this technique can be used to quantify changes in cell concentration within engineered tissues and may be considered as an alternative to histology. Furthermore, because this technique is nondestructive, it can be employed for repeated monitoring of engineered tissues throughout the duration of fabrication.