Differences in Definity and Optison Microbubble Destruction Rates at a Similar Mechanical Index with Different Real-time Perfusion Systems Carolin Sonne, BS, Feng Xie, MD, John Lof, MS, Joseph Oberdorfer, BS, Patrick Phillips, PhD, E. Carr Everbach, PhD, and Thomas R. Porter, MD, Omaha, Nebraska; Mountain View, California; and Swarthmore, Pennsylvania The purpose of this study was to determine micro- bubble responses to different pulse sequence schemes that exist on low mechanical index (MI) real-time perfusion imaging systems using either intravenous albumin-coated (Optison) or lipid-en- capsulated (Definity) microbubbles. A tissue-mim- icking phantom was created that permitted in- sonation of microbubbles at 3 cm (near field) and 9 cm (far field) from the diagnostic transducer face. Differences in effluent microbubble concentration were measured after they passed through vessels being insonified with pulse sequence schemes that transmitted alternating polarity (pulse inversion Doppler), alternating amplitude (power modula- tion), or both (contrast pulse sequencing) at a sim- ilar MI, frame rate, and transmit frequency. Normal- ized contrast signal intensity within a recirculating chamber was also measured in the near and far field. Pulse inversion Doppler produced less initial normalized contrast signal intensity and greater destruction rates than amplitude varying pulse se- quence schemes like power modulation or contrast pulse sequencing at both the 0.1- and 0.2-MI settings. These differences indicate that the same MI setting on different real-time perfusion imaging techniques will produce different microbubble responses. (J Am Soc Echocardiogr 2003;16:1178-85.) Low mechanical index (MI) imaging (0.25 MI) reduces microbubble destruction and permits the real-time detection of myocardial perfusion after intravenously injected microbubbles. 1,2 Because the low MI will reduce the signal to noise ratio, pulse sequence schemes (PSS) have been developed that increase the nonlinear response from microbubbles while simultaneously reducing background signals produced by tissue and noise. The PSS that have been developed include transmitting pulses of alter- nating polarity, pulse inversion Doppler (PID); trans- mitting pulses of alternating amplitude, power mod- ulation (PM); and transmitting pulses of alternating polarity and amplitude, contrast pulse sequencing (CPS). Because of differences in the averaged ampli- tude of the transmitted pulses between different PSS, differences in the degree of microbubble de- struction may occur even when using a similar frequency, frame rate, and MI setting. This could alter the degree of contrast enhancement and opti- mal system settings when used clinically. The pur- pose of this study was to examine microbubble responses to each of these different PSS when imaging through a tissue phantom at standoffs equiv- alent to what is seen with human transthoracic scanning, and at equivalent frame rates, transmit frequencies, and MI settings. The clinical implica- tions of our findings are then discussed. The micro- bubbles tested were 2 Food and Drug Administra- tion–approved agents that differ in their shell composition: a lipid-encapsulated (Definity) and an albumin-coated (Optison) perfluorocarbon micro- bubble. MATERIALS AND METHODS Microbubble Design Optison is an albumin-coated microbubble containing perfluoropropane. Definity is a lipid-encapsulated micro- bubble containing the same perfluoropropane gas. The mean microbubble concentration of Optison according to the manufacturer is 5 to 8  10 8 bubbles/mL with a size range of 2.0 to 4.5 m. The mean concentration of From the Section of Cardiology, Department of Internal Medi- cine, University of Nebraska Medical Center, Omaha, Nebraska (T.R.P.); Siemens Medical Solutions, Mountain View, California (P.P.); and Department of Engineering, Swarthmore College, Swarthmore, Pennsylvania (E.C.E.). Reprint requests: Thomas R. Porter, MD, University of Nebraska Medical Center, 981165 Nebraska Medical Center, Omaha, NE 68198-1165 (E-mail: trporter@unmc.edu). Copyright 2003 by the American Society of Echocardiography. 0894-7317/2003/$30.00 + 0 doi:10.1067/S0894-7317(03)00680-1 1178