Figure 3.

Signal intensity of the multimodal contrast agent and the effect of the incubation time on labeled cells. (A) US, PA, and MPI signals of the nanobubbles are shown as a function of the concentration in a phantom. Iron oxide nanoparticles (IO; 5.5 mg/mL) and Stoba silica (SiO₂) nanoparticles (Si; 5 mg/mL) are positive controls for MPI and US, respectively; water is a negative control. There is a linear relationship in detection in these modalities, which is an important aspect in quantifying the number of labeled cells present. (B) US imaging of hMSCs treated with nanobubbles from 0.25 to 24 h (concentration = 240 μg/mL). (C) US and PA imaging quantification at various times up to 24 h. The signal was detected at 4 h of incubation for both modalities, compared to the negative control (water). * and ** indicate p values < 0.05 compared to the negative control. (D) PA imaging of hMSCs treated with nanobubbles from 0.25 to 25 h (concentration = 240 μg/mL). (E) MPI quantification of hMSCs treated with nanobubbles from 1 to 24 h (concentration = 240 μg/mL). * indicates p values < 0.05 compared to the negative control (water); nanobubbles (NBs, 24 μg/mL) and IO (5.5 mg/mL) are positive controls. (F) MPI imaging data of hMSCs treated with nanobubbles at varying times from 1 to 24 h (concentration = 240 μg/mL). The MPI signal was detected at 4 h of incubation. Error bars represent the standard error (n = 8). Scale bars are 4 mm.