Ultrasonic Imaging of Organ Perfusion with SH U 563A 1 Albrecht Bauer, Harold Becher, Martin Blomley, Adrian Borges, David Cosgrove Edward Leen, Reinhard Schlief, Klaus Tiemann RATIONALE AND OBJECTIVES Ultrasound (US) diagnosis uses B-mode images to pro- vide anatomic information and uses Doppler analysis to measure the velocity of blood flow. It has recently been discovered that the active acoustic response of US con- trast agents, acoustic emission, allows detection of some contrast agents in the microvascular compartment and even as stationary contrast with color Doppler imaging (1–3). The underlying phenomenon is the complex interaction between the incident ultrasound wave and microbubbles. The incident ultrasound can drive the microbubbles into oscillation, and depending on the size of the microbubbles and the properties of their shells, that oscillation can be- come resonant. As the microbubbles undergo nonlinear oscillation, they emit signals containing harmonic compo- nents of the fundamental frequency as well as broadband signal components. In principle, the microbubbles act as an active sound source within the US field (4). The sig- nals originating from microbubbles due to stimulated acoustic emission can be used for specific detection of the US contrast agent with different techniques: conventional color Doppler imaging; and more complex pulse se- quences, such as wideband harmonic imaging (5,6), in new high-end US equipment. With color Doppler imag- ing, the induced acoustic emissions are detected as signals with a random value, resulting in a peculiar mosaic pat- tern varying with time. The underlying mechanism is that color Doppler flow mapping depends on the correlation between successive pulses. This is infringed by the non- linear response of SH U 563A (Schering, Berlin, Ger- many) resulting in a loss of correlation of the pulses dur- ing the destruction of the microbubble. Because this tech- nique is not using color Doppler imaging in its original fashion, it may also be described as “loss of correlation” (LOC) imaging, to distinguish this technique from vascu- lar color Doppler imaging. Although the same technique, color Doppler imaging, is used, the image content is changed from a flow image based on correlation to a map of the contrast distribution based on LOC and destruction of the microbubbles during the scanning process (1). The contrast agent distribution, the localization map, is gener- ated by the presence of the random color spots, with varying color in the image and between subsequent im- ages. The information on tissue perfusion during the vas- cular phase and the distribution of active reticuloendothe- lial system (RES) cells after uptake is provided by this map. It gives a direct image of the microvascular com- partment and the RES compartment, independent of flow velocity. SH U 563A is a novel polymeric US contrast agent, optimized for this nonlinear acoustic response. Due to the durability of the polymer shell, no degradation is ob- served during the capillary passage in the vascular phase, allowing a complete delineation of the microvascular compartment. Therefore, SH U 563A may be considered as an ideal perfusion tracer, demonstrating, in theory, the blood volume distribution. Acad Radiol 2002; 9(suppl 1):S46–S51 1 From Clinical Development, Ultrasound Contrast Media, Schering AG, 13342 Berlin, Germany (A. Bauer, R.S.); the Department of Cardiology, Uni- versity of Bonn, Bonn, Germany (H.B., K.T.); the Department of Imaging, Hammersmith Hospital, London, England (M.B., D.C.); the Department of Cardiology, Charite, Berlin, Germany (A. Borges); and the Department of Radiology, Royal Infirmary, Glasgow, Scotland (E.L.). Address correspon- dence to A. Bauer. © AUR, 2002 S46