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Introduction to the Special Issue on High Frame Rate/Ultrafast Contrast-Enhanced Ultrasound Imaging

Since the first injection of air bubbles in blood to enhance the echoes backscattered from within the aorta (Gramick and Shah, 1968), contrast-enhanced ultrasound (CEUS) has seen the development of revolutionary methods for blood flow imaging, tissue perfusion quantification, and molecular targeting. The contrast agents, nowadays typically encapsulated microbubbles with a gas core, offer superb echogenicity from within the blood and can be deactivated by ultrasound at will, enabling quantification of tissue perfusion. Another exciting development in medical ultrasound is represented by high frame rate (HFR) imaging, also known as ultrafast ultrasound, which permits the formation of images at frame rates up to two orders of magnitude higher than the previous line-by-line scanning approach. Since their first introduction, both CEUS and HFR/ultrafast ultrasound have recently seen significant advancements with a substantial acceleration of their clinical application.