Radiofrequency spectral analysis of attenuated ultrasound signals in experiments with echo contrast microbubbles

Conventional gray-scale myocardial contrast echocardiography cannot disting uish perfused but attenuated from nonperfused myocardium because both may a ppear similar at low image intensity. We hypothesized that with radiofreque ncy spectral analysis of attenuated ultrasound signals, the harmonic-to-fun damental frequency ratio of the peak power spectrum (HFRp) could determine the presence of contrast microbubbles. We measured frequency responses of O ptison microbubbles at defined degrees of ultrasound signal attenuation wit h different formulations of silicone (55D, 80A, and 3M); gray-scale intensi ties of Optison plus water compared with degassed water were analyzed at di fferent attenuation settings (-25, -32, and -44 dB, respectively). HFRp val ues of Optison plus water were significantly higher than reference values o f degassed water at each attenuation setting (55D, -14 +/- 2 dB versus -30 +/- 2 dB, P < .001; 80A, -19 +/- 2 dB versus -30 +/- 3 dB, P < .01; 3M, -22 +/- 2 dB versus -30 3 dB, P < .05), even though conventional videodensitom etric analysis could not distinguish them. HFRp analysis objectively detect s microbubbles in clinically relevant conditions of attenuation.