Physics

Question 1

List 4 Peizoelectric Materials

Answer 1

Lead Zirconate Titanate(PZT) Quartz Rochelle Salts Other Titanates

Question 2

Relationship between Thickness of PZT crystal and wavelength

Answer 2

Thicker crystal = lower frequency = higher penetration

Question 3

Components of a US Transducer Probe

Answer 3

PZT Crystal, Case, Wire, Backing Material, Acoustic Matching Layer, Acoustic Lens

Question 4

List 4 Types of US Probes

Answer 4

Curvilinear (2-5MHz) Linear (5-13 MHz) Phased Array (1-5MHz) Annular Phased Array Transvaginal (6.5MHz) [type of curvilinear

Question 5

Describe the peizoelectric effect

Answer 5

element virbates to generate a sound wave when applied with a voltage (sending sound waves) It also generates a voltage when applied with a vibration (gathering data)

Question 6

Define Frequency

Answer 6

Wavelength = (frequency) x (speed of sound) cycles/second Audible is 20Hz to 20k Hz Medical US is 2MHz to 15 MHz

Question 7

Define Wavelength

Answer 7

Wavelength = (frequency) x (speed of sound) distance between crests of a wave

Question 8

What is the Proporgation Speed of sound in soft tissue? What is its relationship between wavelength and frequency?

Answer 8

Wavelength = (frequency) x (speed of sound) Time it takes for sound to travel through a medium 1.54km/s or 1540 m/s in soft tissue 1.54mm = 1MHz x 1.54km/s Slowest in air, faster in fluid, fastest in solids

Question 9

Period

Answer 9

Period = 1/frequency Time it takes for 1 wavelength

Question 10

Bigness Parameters - things you can adjust

Answer 10

Amplitude (dB) - difference in average and max value of acoustic variable. This is gain, and is affected by pressure, density and distance travelled Power (Watts) - Rate of energy transfer Intensity (Watts/cm^2) - concentration of energy in sound wave

Question 11

Ways US waves can be affected/redirected

Answer 11

Scattering Reflection Refraction Transmission Absorption

Question 12

define

Answer 12

Axial vs Lateral Resolution, Contrast and Temporal Resolution

Question 13

Describe Harmonic Imaging

Answer 13

Multiples of the fundamental frequency, i.e. multiple reflection artifacts from lung pleura *want to turn off when imaging lung

Question 14

Describe compounding

Answer 14

Averaging multiple frames to make a single image can reduce signal to noise ratio at expense of temporal resolution

Question 15

Describe doppler effect

Answer 15

Moving objects will adjust the frequency of sound wave If moving at an angle, there is a loss of this frequency change this term is known as ‘Shift’ Higher frequency shift when moving towards Probe (red) Lower frequency shift when moving away from probe (Blue)

Question 16

Describe Aliasing and the Nyquivist Limit

Answer 16

Pulse Wave Dopper sends pulses of waves at the PRF (Pulse repetition frequency) If magnitude of frequency shift is higher than PRF/2, then you will get inaccurate velocity and range ambiguity. Can adjust Nyquivist limit (Maximum doppler shift in frequency, or PRF/2) to prevent aliasing

Question 17

Compare and Contrast Pulse wave and continuous wave Doppler

Answer 17

Continuous Waves uses 2 crystals - continuous transmissiong and reception. Able to measure high velocities accurate, but more range ambiguity (less resolution) Pulse wave only uses 1 crystal, and unable to measure higher velocities. Better Range Resolution - Can see a specific location within the probe

Question 18

How much time does it take for a sound wave to travel 1 cm within soft tissue and back?

Answer 18

Range Equation 13 microseconds of go-return time is about 1 cm deep in the body 26 microseconds for 2cm deep. so on

Question 19

List 7 US artifacts

Answer 19

Reverberation Comet Tail/Ring Down Mirror Artifact Acoustic Enhancement Acoustic Shadowing Edge Shadowing Anisotropy Grating/Side Lobes Slice Thickness Range Ambiguity Speckle Artifact Clutter Artifact

Question 20

Describe Anisotropy Artifact

Answer 20

Transducer is not perpendicular to structure and structure may not be clearly visualized, or beams will all reflect/refract instead of being reflected back The more perpendicular the beam is to these structure, the better resolution you will have this has higher effect in structures with parallel fibers

Question 21

Describe Grating/Side Lobe Artifact

Answer 21

Extra acoustic energy may be transmitted in directions other than beam’s main axis 2nd copy of a true reflector reflected soundwaves that are slightly off axis will be interpreted as a secondary object that does not exist

Question 22

Describe Mirror Image Artifact

Answer 22

Perceived location of a structure that is not actually there due to a reflection at an angle from a strong reflector

Question 23

Describe Edge Shadowing

Answer 23

Edge Shadowing Oblique incidence and difference in propagation/acoustic impedance, Structures deep to a parallel edge may not be visualized

Question 24

Describe Slice Thickness Artifact

Answer 24

we assume plane is infinitely thin, but reality it isn’t so objectives that are smaller than the beam won’t be seen, and are then replaced by objects that may be coming in from the far field/outside the beam (due to beam divergence

Question 25

3 Ways to QA US Probes

Answer 25

Water Filled Phantom Tissue Phantom Doppler Phantom Works by detecting pins in a model Can assess Axial, Lateral, Contrast Resolution, as well as depth measurement accuracy

Question 26

Describe ALARA and what ‘Thermal Index’ means

Answer 26

As low as reasonable Allowable - radiation/exposure. In US, this is usually in terms of thermal energy Thermal Index is a value that means the highest possible increaes in temperature based on the absorption of soundwaves. e.g. TI of 2 = there is a possible 2C increase in temperature Highest concern in fetal and ocular tissue TI < 1 for eyes, TI < 0.5-1 for fetus for 30 minute scan. if higher TI then shorter scan time