Test 11 1. The following are true about the ultrasound: a. impedance is measured in grams / cm 2 /sec b. the closer the beam to the right angle the less the sound is reflected c. attenuation of ultrasound results in heating of tissues d. A-mode ultrasonography is displayed as a series of spikes e. B-mode ultrasonography is displayed as a series of spikes answera.T   b.T   c.T   d.T   e.T     2. The following are true about the velocity of ultrasound: a. it is dependent on the frequency b. is faster through the soft tissue than the skull c. is faster through the silicone oil than the vitreous d. is about 1540 meters per second through the soft tissue e. is proportional to the compressibility of the medium through     which the sound travels answera.F   b.F   c.F   d.T   e.F Velocity of the ultrasound is independent of frequency.  The velocity is a function of the physical properties of the medium through which the sound travels. It is inversely proportional to the compressibility of the medium. The ultrasound velocity through the skull is greater than the soft tissue and that of the vitreous is greater than the silicone oil.   3. In ultrasound: a. impedance determines the proportion of sound energy reflected     and transmitted at an interface. b. the size of a pulse generated in an A-scan is a measure of the      intensity of the reflected ultrasonic echo. c. the sound travels poorly through air. d. the velocity is faster through a denser materials. e. the velocity is dependent on the temperature of the material through     which it travels. answera.T   b.T   c.T   d.T   e.T The velocity of the ultrasound is dependent on the  compressibility of the materials and hence the density of the materials. Compressibility is also affected by  temperature and will therefore affect the sound velocity.     4. The following are true about ultrasound: a. it is produced by a piezoelectric crystals. b. the frequency of a sound wave is inversely related to its wavelength c. ultrasound is a longitudinal wave form d. ultrasound can be refracted e. ultrasound can be focused answera.T   b.T   c.T  d.T   e.TVelocity of sound = frequency X wavelength. Ultrasound can be focused, reflected and refracted.   5. In ultrasound: a. the acoustic impedance of a material is the product of its density      and the velocity of sound within it b. acoustic impedance determines beam refraction c. as the angle of incidence increases less sound is reflected d. a thicker piezoelectric crystal has a lower resonance frequency e. a thicker piezoelectric crystal has a longer wavelength. answera.T   b.F   c.T   d.T   e.T Acoustic impedance determines beam reflection.