AbstractIn this study, we theoretically analyze the interaction of ultrasound waves in a liquid with suspended gas microbubbles confined in region of the liquid. In ultrasound harmonic imaging, gas microbubbles are used to contrast image by accentuating the generation of backscattered second-harmonic waves. However, these waves are attenuated twice as much as the fundamental. To delineate the harmonic amplification effect from excess attenuation, we study the nonlinear interaction of ultrasound with a region containing microbubbles. Considering an incident plane wave interacting with a spherical cloud of microbubbles, the solutions for the linear and the second-harmonic scattered waves are derived. The results are obtained for both monochromatic and period pulsed waves, including the effects of attenuation, and diffraction. These results provide the mathematical framework for estimating and compensating the effect of attenuation in the harmonic backscattered wave.