The Receiver is the component of the ultrasound machine that receives the current generated in the transducer from the returning sound waves.

See also Blanking Distance, and Range Gating.

A rectal probe is a small ultrasound transducer with high frequency that is inserted directly into the rectum. Transrectal ultrasound is a well established examination for rectal or prostate carcinoma assessment. Rectal probes (e.g., a microconvex probe) generate a much sharper image, caused by the close proximity to the prostate or rectum, and the higher sensitivity.

The elements of a rectangular array transducer (also called matrix transducer) are arranged in a rectangular pattern. Rectangular arrays with unequal rows (e.g. 3, 5, 7) of transducer elements are in real 2D (two-dimensional), but they are termed 1.5D, because the number of rows is much less than the number of columns. Their main advantage is electronic focusing even in the elevation plane (z-plane).
The transducers that are termed 2D have an equal number of rows and columns. 2D transducers have the potential to provide real-time 3D ultrasound imaging without moving the transducer.
Active matrix array transducers have several elements in the short axis and in addition multiple elements along the long axis. This allows electronic focusing in both axes, resulting in a narrower elevation axis beam width in the near field and far field.

Reflection of the sound beam occurs when it hits a boundary between materials having different acoustic impedance. The reflection (echo) is the portion of a sound that is returned from the boundary. The reflection time (the time taken for the wave to return to the probe) can be used to determine the depth of the object.
The reflection within the body produces the ultrasound image, but should be minimized at an ultrasound couplant to skin boundary where the couplant acts as an acoustic window through which the image is seen. The amount of sound waves, which are reflected back at the interface between two tissues is depend on the angle of incidence and the difference between the acoustic impedance values of the two tissues.
If the difference is great, a large part of the sound waves will be reflected back. If too much sound is reflected back and not enough waves are remaining to be able to penetrate the tissue, the imaging will be poor.
If the difference is small, a small amount will be reflected back. Enough sound signal remains to continue with ultrasound imaging.
If the ultrasound beam meets a rough surface or small object, the beam is scattered in all directions and only a small amount will be received by the probe.

See also False Distance Artifact, Target Strength, and Snells Law.

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.