Clinical Application of Harmonic Power Doppler Imaging in the Assessment of Myocardial Perfusion by Contrast Echocardiography

New sonographic techniques for harmonic imaging--underlying physical principles

In this paper, modern harmonic imaging techniques are reviewed and their physical principles are explained. The clinical advantages of these new techniques that are generally used in conjunction with ultrasound contrast agents are highlighted and compared to conventional flow imaging methods. Low/high mechanical index (MI) methods are discussed as well as emerging technologies for future transducer or beamformer generations. Finally the latest safety issues concerning applications of modern (harmonic) imaging techniques with contrast agents are given.

Parametric detection and measurement of perfusion defects in attenuated contrast echocardiographic images

OBJECTIVE

Attenuation of radio frequency (RF) signals limits the use of contrast echocardiography. The harmonic-to-fundamental ratio (HFR) of the RF signals compensates for attenuation. We tested whether HFR analysis measures the left ventricular nonperfused area under simulated experimental attenuation.

METHODS

Radio frequency image data from short axis systolic projections were obtained from 11 open-chest dogs with left anterior descending or left circumflex coronary artery occlusion followed by left atrial bolus injection of a perflutren microbubble contrast agent. Clinical attenuation was simulated by calibrated silicone pads interposed between the epicardial surface and the transducer to induce mild (7-dB) and severe (14-dB) reduction of the backscattered RF signals. Harmonic-to-fundamental ratio values were calculated for each image pixel for 0-, 7-, and 14-dB attenuation conditions and reproducibly showed a "perfused area" and a "nonperfused area." A reference nonperfused area was obtained by manual delineation in high-quality contrast scans.

RESULTS

Correlations of the HFR-detected and manually outlined perfusion defect areas were R = 0.92 for 0 dB, R = 0.94 for 7 dB, and R = 0.90 for 14 dB; the mean difference was less than 0.36 cm(2) (negligible) in all 3 attenuation settings. Conclusions. Attenuation compensation by our HFR method allows precise measurement of myocardial perfusion defect areas in contrast scans with simulated high level of attenuation.