Use of ultrasound contrast agent microbubbles in preclinical research: recommendations for small animal imaging

Ultrasound contrast imaging techniques represent a real opportunity to improve efficiency in the preclinical drug discovery and development process. Ultrasound contrast agents (UCAs) combined with specific ultrasound contrast detection modes provide real-time, high spatial resolution of both organ and lesion blood perfusion, the so-called dynamic contrast-enhanced ultrasound imaging. With the advent of targeted UCA, ultrasound molecular imaging is gaining momentum in molecular imaging, particularly because of the simultaneous real-time anatomical and functional/molecular imaging capabilities. In preclinical research, contrast-enhanced ultrasound imaging, with either nontargeted or targeted UCA, is a fast-growing imaging modality that has not yet been standardized compared with other imaging modalities. Contrast-enhanced ultrasound imaging is an operator-dependent imaging modality, requiring adherence to rigorous step-by-step protocols. In this article, which is intended for advanced, hands-on researchers, we report key factors that can lead to variability in preclinical results and recommend some preventive methods to limit or cancel their effect on the final results. Standardized procedures are a prerequisite for acceptance of new contrast-enhanced ultrasound imaging methods to eliminate factors that could distort results, improve the reproducibility between different centers and studies, and, therefore, allow translation to clinical application.