A Targeted Molecular Localization Imaging Method Applied to Tumor Microvasculature

Objectives Ultrasound contrast agents, consisting of gas-filled microbubbles (MBs), have been imaged using several techniques that include ultrasound localization microscopy and targeted molecular imaging. Each of these techniques aims to provide indicators of the disease state but has traditionally been performed independently without co-localization of molecular markers and super-resolved vessels. In this article, we present a new imaging technology: a targeted molecular localization (TML) approach, which uses a single imaging sequence and reconstruction approach to co-localize super-resolved vasculature with molecular imaging signature to provide simultaneous anatomic and biological information for potential multiscale disease evaluation. Materials and Methods The feasibility of the proposed TML technique was validated in a murine hindlimb tumor model. Targeted molecular localization imaging was performed on 3 groups, which included control tissue (leg), tumor tissue, and tumor tissue after sunitinib an-tivascular treatment. Quantitative measures for vascular index (VI) and molecular index (MI TML ) were calculated from the microvasculature and TML images, respectively. In addition to these conventional metrics, a new metric unique to the TML technique, reporting the ratio of targeted molecular index to vessel surface, was assessed. Results The quantitative resolution results of the TML approach showed resolved resolution of the microvasculature down to 28.8 μm. Vascular index increased in tumors with and without sunitinib compared with the control leg, but the trend was not statistically significant. A decrease in MI TML was observed for the tumor after treatment ( P < 0.0005) and for the control leg ( P < 0.005) compared with the tumor before treatment. Statistical differences in the ratio of molecular index to vessel surface were found between all groups: the control leg and tumor ( P < 0.05), the control leg and tumor after sunitinib treatment ( P < 0.05), and between tumors with and without sunitinib treatment ( P < 0.001). Conclusions These findings validated the technical feasibility of the TML method and pre-clinical feasibility for differentiating between the normal and diseased tissue states.