Answer #56

The correct answer is B: backscatter.
Backscatter occurs when the wavelength of the ultrasound is similar to irregularities in the boundary. It results in scattering in many different directions but all backward and usually therefore toward the transducer. This form therefore is the most useful for generating an image.

Rayleigh scattering occurs when the wavelength of the reflecting object is much smaller than the wavelength of ultrasound sending waves in all different directions, only some of which get back to the transducer. Specular reflection occurs when the object has a much larger wavelength than the ultrasound. The angle of incidence equals the angle of reflection and a mirror image is created, but this doesn't make up a large portion of ultrasound image creation since the more of the beam that reflects, the less that transmits. Refraction is a different phenomenon altogether where the beam is bent by different in speed of ultrasound through different media.