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.

The dimension of a spectral reflector is greater than the wavelength of the ultrasound beam. With specular echo reflection, the sound strikes the target at perpendicular incidence and the sound is reflected back towards the receiver. Specular reflections produce bright echoes.

(FFT) The fast Fourier transformation is a particularly fast and efficient computational method of performing a Fourier transformation, which is the mathematical process by which raw data is processed into a usable image.
The fast Fourier transform analyzer is a common device that performs spectral analysis in ultrasound instruments. In this case, it displays different quadrature Doppler frequencies or reflector velocities when a sample volume cursor is used along time. The Doppler frequency is proportional to the spectral reflector velocity.

See also Proportionality Constant, and Sampling Rate.

The acoustic window or field is the area defined by the pathway of the ultrasound beam between the transducer and the acoustic reflector. The sound reflection to skin boundary should be minimized with an ultrasound gel where this gel acts as an acoustic window through which the image is seen.
Acoustic window refers also to the optimal placing of the transducers so that the areas of interest are clearly imaged.

See also Transforaminal Window, Transcranial Window, Transorbital Window and Transtemporal Window.

The Doppler signal from any range gate is proportional to the number of red blood cells moving through during the periods of its read out, so the amplitude (or loudness) works as an indicator of the number of blood cell reflectors.
High Doppler amplitudes are generated by large pulsed Doppler or color Doppler imaging range gates and large vessels.

See also Amplitude Map, Color Amplitude Imaging.