Quantification of Tumour Angiogenesis and Perfusion using Contrast-free Super-Resolution Ultrasound Imaging

Introduction. Angiogenesis and blood perfusion are key components of tumour development, which vary between tumour types and patients. Current clinical imaging methods have limited ability to qualitatively or quantitatively assess these parameters. This study describes a novel application of the ultrasound-based imaging modality, super-resolution ultrasound imaging using erythrocytes (SURE), and evaluates its performance against available in vivo and ex vivo imaging methods. Methods. An optimised SURE imaging technique was used to visualise the vasculature in a syngeneic murine model bearing subcutaneous B16-F10 melanoma tumours. For comparison, the tumour was also imaged in vivo with B-mode, colour Doppler, spectral Doppler ultrasound, and ex vivo with micro-CT angiography and immunohistochemistry. Results. SURE imaged the tumour microvasculature, visualising vessels down to ≈ 30 µm in diameter while enabling extensive characterisation of tumour haemodynamics. SURE significantly outperformed colour Doppler and spectral Doppler in visualising vasculature and quantitatively assessing flow. SURE enabled analysis of the variability in perfusion across the tumour section and can enable users to evaluate the health of individual vessels. Vascular density data obtained from SURE did not significantly differ from that obtained by immunohistochemistry, demonstrating comparability even to ex vivo methods. Conclusions . Using only 10 seconds of data acquisition, SURE imaging can provide vascular density in murine tumours at a resolution comparable to ex vivo techniques, along with haemodynamic data across the entire tumour section, distinct regions, or individual vessels. This technique has the potential to identify previously unknown biomarkers of cancer, elucidating characteristics of neoplastic angiogenesis which can be used for early diagnosis and treatment.