Characteristics of contrast agents and 2D imaging

Abstract

Small (encapsulated) gas bubbles in a contrast medium react on an external oscillating pressure field with volume pulsations. Depending on the magnitude of the ultrasound wave the pulsation will be: (1) linear to the applied pressure, or (2) non-linear to the applied pressure. The latter can be split into stationary and transient scattering. For low amplitudes of the acoustic field the instantaneous radius of the bubbles is linearly related to the amplitude of the applied external pressure field. For higher amplitudes of the external field the pulsation of the bubbles becomes nonlinear with the amplitude of the external field. The spectrum of the scattered ultrasound wave contains also higher harmonics of the ground frequency. For even higher amplitudes of the acoustic field the noticed scatter properties of encapsulated bubbles in a contrast medium increase dramatically and become transient. The scattered frequency spectrum containing second and third harmonics broadens. The properties of the encapsulated bubbles change due to rupture, disappearance, change of gas content, etc. Conventional 2D imaging machinery limits the capability of ultrasound contrast agents. Stationary and transient non-linear scattering occurs at acoustic pressures currently employed. Absorption, acoustic velocity, resonance behaviour, frequency and pressure dependency are different from normal tissue. Using these specific characteristics of the agents will open new perspectives in both imaging and analysis for medical diagnosis.