Pulse Inversion Imaging of Liver with Microbubble Contrast: Improved Characterization of Tumoral Vasculature in Focal Hepatic Lesions

The challenge presented to ultrasound imaging technology by the advent of microbubble contrast agents is to create a method that detects the echoes from bubbles in preference to the echoes from tissue. Recent progress in ultrasonography is represented by the development of harmonic and pulse inversion imaging (Fig. 1, 2). Pulse inversion imaging is a newly developed one, which uses the full bandwidth image of nonlinear echoes from bubbles in real time, thus overcomes that the conflict between the requirement of contrast and resolution in harmonic imaging (1). At higher acoustic pressures, resonant signals at second, and other, harmonic frequencies start to appear. As sound pressures increase further, phenomena related to microbubble destruction or disruption occur. These include the production of transit ultrasonic signals, an effect referred to as stimulated acoustic emission (SAE) (2, 3). SAE can be visualized as intense transit enhancement on color or gray-scale images (Fig.3).