(PWD) Pulsed wave (PW) Doppler is a Doppler ultrasound mode that evaluates blood flow velocities in a range specific area along the length of the sound beam. Measured are changes in received frequency due to relative motion (flow) between a sound source (transducer) and sound receiver (transducer).
PW Doppler produces an audible signal as well as a graphical representation of flow. The Doppler shift produced by moving blood flow is calculated by the ultrasound system.

See also Amplitude Indicator, Pulsed Ultrasound.

Quadrature detection is used in Doppler ultrasound as well as in magnetic resonance imaging and is also called quadrature demodulation or phase quadrature technique. Quadrature detection is the acquisition of Mx and My simultaneously as a function of time by using two separate detector channels. This signal processing method is used for directional Doppler in which the signal reference frequency for the two channels has a phase shift of 1/4 period. The output Doppler signal phase for both channels also depends on the Doppler shift whether positive or negative.
The fast Fourier transform analyzer performs spectral Doppler analysis in ultrasound machines and displays different quadrature Doppler frequencies, when a sample volume cursor is used along time.

The reflector is a stationary plate component of a flowprobe used in Doppler ultrasound. Each transducer alternately emits an ultrasound beam which is reflected from this reflector to the receiving transducer. The fixed distance of the reflective pathway is critical to the measurement of the ultrasonic transit time and the accurate measurement of volume flow.

See also Target Strength.

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Stress echocardiograms are used for detection of coronary artery disease, or to determine the cardiac performance. Stress echocardiograms are less performed to evaluate pulmonary artery pressures, pulmonary hypertension or the significance of valvular heart disease.
Stress increases the degree to which the heart contracts. After a myocardial infarction there will be a region of the heart muscle that contracts abnormal at rest. This area may worsen with stress. A coronary artery blockage most often do not impairs the function of the heart at rest. With stress, a region of the heart does not receive enough blood to work effectively and wall motion abnormalities occur. The echocardiographer compares rest and exercise and can determine the presence and severity of a coronary artery blockage.

Stress echocardiograms involve:
A bicycle stress echocardiogram involves transthoracic echocardiography performed at the rest baseline and after or during different stages of physical exercise.
A dobutamine stress echocardiography uses the drug dobutamine instead physical exercise.
Transthoracic echocardiograms are routinely performed during stress and rest.
Cardiovascular stress represents a minimal risk to the patient.

See also Transesophageal Echocardiography, Echocardiography, M-Mode, Curved Transducer, Doppler Ultrasound, History of Ultrasound and History of Ultrasound Contrast Agents.