UniSA Module 1 2023 with complete solution question and answers

A 10dB difference in signal intensity is equivalent to a ... Tenfold The reflection coefficient between water and air is ... Nearly 100% The reflection coefficient between water and air interface is nearly 100%. Air prevents the sound from entering the body. It is for this reason that a coupling gel is necessary. How much will a 3.5MHz pulse be attenuated after passing through 2cm of soft tissue? 3.5dB. A rule of thumb approximating the attenuation coefficient of a reflected echo in soft tissue is 0.5dB/cm/MHz. Thus, the attenuation coefficient will be one - half of the operating frequency. Attenuation (dB) = attenuation coefficient (dab/cm) x path length (cm) dB = 1.75dB/cm x 2cm = 3.5dB If frequency increases, the wavelength will ... Decrease If frequency increases, the wavelength decreases c = fλ The equation that describes the relationship among propagation, wavelength and frequency is ... c = fλ (c = velocity/speed, f = frequency, λ = wavelength) An example of a nonspecular reflector is... Red blood cells Structures smaller than a wavelength will scatter sound in all directions and are sometimes called diffuse reflectors Wavelength is a measure of ... Distance Wavelength is the distance between two identical points on the waveform. Increasing the frequency of an ultrasonic longitudinal wave will result in ... the velocity of that wave. No change The velocity of sound propagation depends on the material through which it is being transmitted and is independent of frequency. Increasing the frequency will decrease the wavelength, not change the velocity. The change in direction of an ultrasonic beam when it passes from one medium to another, in which elasticity and density differ from those of the first medium is called... Refraction As frequency increases, the resolution will... Increase The period of an ultrasound wave is... The time of one wavelength. Speculator reflection occurs when... The reflector surface is smooth as compared with the wavelength. In physical science, the word period donates... The time it takes to complete a single cycle. If frequency decreases the wavelength will... Increase The average velocity of ultrasonic waves in soft tissue is... 1540 m/s When particle motion of a medium is parallel to the direction of a wave propagation, the wave being transmitted is called a... Longitudinal wave If a 2MHz frequency is used in human soft tissue, the wavelength is approximately... 0.75mm The wavelength can be determined by rearranging the wavelength equation. c = fλ. λ = c/f Ultrasound wave propagation causes displacement of particles in a medium. The regions of lowest particle concentration are called... Rarefractions The wavelength in a material having a wave velocity of 1500 m/s employing a transducer frequency of 5 MHz is... 0.3mm Wavelength = velocity/frequency. Wavelength = 1.5/5 = 0.3mm The abbreviation 5 MHz denotes... Five million cycles per second 1 mega = 1 million. Therefore, 5 MHz = 5 million cycles per second or 5 million Hz Refraction occurs due to a difference in ... across an interface between two materials. Refraction is described by Snell's law, which relates the incident angle (θi) to the transmitted angle (θt) to the relative velocities of the two media making up the interface sinθi/sinθt = c1/c/2 Which of the following is the least obstacle to the transmission of ultrasound? Blood Attenuation of an ultrasound beam can occur by... Divergence of a beam, scattering of a beam and reflection of a beam. The factor that determines the amount of reflection at the interface of two dissimilar materials is... The specific acoustic impedance Ultrasound can be described as a (an) Mechanical vibration that can be transmitted through matter. Sound wand ultrasound are mechanical vibrations that can propagate in matter, such as liquid and solid. However, sound or ultrasound cannot travel in a vacuum. Ultrasound waves in tissue are called... Longitudinal The attenuation for soft tissue is... Increased with tissue thickness. Attenuation is the product of the attenuation coefficient and path length. Which of the following can occur when an ultrasound beam reaches the interface of two dissimilar materials? Reflection, refraction & mode conversion. Reflection refers to echoes, refraction refers to the bending of the beam; mode conversion refers to a change in the propagation mode transverse, shear, surface, or longitudinal waves. Reflection factor at an interface between two materials, depends primarily on the change in ... across the interface. Acoustic impedance The velocity of sound waves is primarily dependent on... The material through which the sound is being transmitted and the mode of vibration. What happens to the ultrasound beam beyond the critical angle? 100% is reflected Beyond the critical angle, 100% of the sound beam is reflected and 0% is transmitted. A waveform transfers ... from one point in space to another point in space. Energy Acoustic impedance The density of tissue x the speed of sound in tissue The term Hertz denotes... Cycle per second. The acoustic impedance of a material is... Equal to the product of density and velocity Ultrasound wave propagation causes displacement of particles in a medium. The regions of greatest particle concentration are called... Compression What percentage of intensity of an ultrasound pulse incident on an interface of 0.25 and 0.75 rayls is reflected? 25% The reflection coefficient (R) is equal to R =[(Z2-Z1/Z2+Z1)² = (0.75-0.25)/(0.75+0.25)]² = 0.25 Attenuation denotes... Progressive weakening of the sound wave as it travels. Attenuation occurs because of absorption, reflection and scatter. Acoustic impedance is not dependent on which of the following... Frequency Acoustic impedance is dependent on density and stiffness. It does not depend on frequency. If the amplitude is double, the intensity is... Increase by four times Intensity equals the square of the amplitude. Longitudinal waves are characterised by... Motion of particles parallel to the axis of wave propagation.