Technical introduction to echocardiography.
Pulse-echo ultrasound can be used to measure distance along a narrow beam with resolution limited by the wavelength and, ultimately, by attenuation. Time-position (M-mode) recording can be used to study structure motion. Real-time two-dimensional imaging can be achieved with mechanical scanning or electronically controlled phase array transducers, the frame rate being limited by the depth of penetration and the image line density. Blood flow can be detected by the Doppler effect. Continuous wave Doppler systems lack depth discrimination, but this can be provided by pulsed Doppler although range-velocity ambiguities may occur. Blood flow volume rate can be estimated from measurements of velocity and area; the simultaneous use of wide and narrow beams reduces the errors. Duplex scanning uses two-dimensional real-time imaging for Doppler sample volume localization. Two-dimensional colour-coded images of blood flow can be produced in real time. Endoscopic scanning avoids problems due to bone and gas. Contrast agents can be used to enhance the echogenicity of blood.
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D004452:Echocardiography / Q000295:instrumentation*; D015150:Echocardiography, Doppler / Q000295:instrumentation*; D006321:Heart / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans