Contrast-free Super-Resolution Ultrasound Imaging for Microvascular Assessment of Murine Subcutaneous Tumour Models in Preclinical Oncology

Introduction . Tumour vascularity is an important biomarker of tumour growth and therapeutic response. Current in vivo imaging methods have a limited ability to detect individual tumour vessels due to the small vessel size and low flow rates commonly observed in murine oncology models. This paper presents three pilot studies which together aim to assess the performance of a developing imaging method, Super-resolution Ultrasound using Erythrocytes (SURE), for subcutaneous tumour imaging. Methods . Across three experiments, we qualitatively compared the vascular imaging sensitivity and clinical applicability of SURE imaging with colour Doppler imaging and ex vivo immunohistochemistry. Two murine oncology models were investigated: the LNCaP (lymph node carcinoma of the prostate) xenograft model (n = 3) and the B16-F10 melanoma model (n = 7). Optimal SURE post-processing parameters for subcutaneous tumour imaging were characterised. Results . SURE outperformed Doppler imaging, detecting flow with higher spatial resolution in corresponding tissue regions. SURE successfully visualised tumour microvasculature, detecting vessels approximately 30 µm in diameter while enabling haemodynamic characterisation. Optimal post-processing involved a trade-off between vascular imaging sensitivity, final signal-to-noise ratio, and image artefact prevalence. Vascular density measurements obtained using SURE did not differ significantly from those obtained by immunohistochemistry. Conclusions . SURE represents a significant advance in in vivo microvascular imaging. While post-processing time, image artefacts, and limited quantitative analysis currently limit preclinical application, the technique demonstrates strong potential for tumour vascular characterisation in both preclinical research and clinical oncology.