US

Question 1

What is the range of human hearing? What is considered US?

Answer 1

20-20,000 HZ

> 20,000 HZ = US

Question 2

Define below and provide units where relevant

Answer 2

Question 3

What is the approximate geometry of an ultrasound beam?

Answer 3

• LONGITUDINAL WAVE: Two distinct regions:

Convergent beam -> near field

Divergent beam -> far field

Question 4

Define reflection. What features dictate reflectivitity? What is the reflection coefficient calculation?

Answer 4

Question 5

Define intensity. What are dB?

Answer 5

Rate at which energy passes through a unit area (= power in wave divided by area over which power spread)

Different units used e.g. include (mW/cm2) and watts per centimeter squared (W/cm2)

dB = RELATIVE INTENSITY. Comparison of intensities converted logarithmically. USED FOR ATTENUATION COEFFICIENT

Question 6

Equation for reflection coefficient AND intensity transmission coefficient

Answer 6

TRANSMISSION COEFFICIENT = 1 - RI!! Just a measure of how much energy transmitted, with 1 = to complete transmission

Question 7

Define acoustic impedance inc. unit and equation

Answer 7

Question 8

Define refraction. What equation is used to describe effect?

Answer 8

Question 9

Define 3 types of reflector

Answer 9

TISSUE INTERACTIONS

• Acoustic scattering: due to small particle reflectors - characteristic of tissue or organ

BOUNDARY

• Non-specular: Approximately same as wavlength or smaller -> ROUGH reflector
• Specular: Large reflector relative to wavlenth -> SMOOTH reflector

Question 10

List 4 factors that influence AMPLITUDE of signal from insonated tissue

Answer 10

• Number of scatters per unit volume (Less amplitude if more scatters)-
• Size of scatterers
• Acoustic impedance differences at scatterer surfaces (Increase amplitude if more impedance)
• Freq (inc scatter from non-specular reflectors with high freq)

Question 11

What interactions are most responsible for attenuation?

Answer 11

SCATTER and ABSORPTION

Question 12

Define attenuation and attenuation coefficient, including units. WHAT IS THE RULE OF THUMB!!

Answer 12

Question 13

What is HVT in US?

Answer 13

Question 14

Define Spatial Pulse Length (SPL)

Answer 14

Question 15

Name 2 methods to improve axial resolution

Answer 15

REDUCE SPL

• Increase frequency (and thus smaller wavelength)
• Shorten pulse duration / number of cycles

Question 16

Calculate SPL and resolution for 5MHz signal (wavelength 0.31mm) and 3 cycle pulse

Answer 16

0.93mm PULSE = SPL

Axial resolution = 1/2 SPL = 0.47mm

Question 17

What factors are most important for AXIAL and TRANSVERSE (Azithmul) resolution?

Answer 17

Axial = SPL

Trans = Beam width

Question 18

Define PRF, PRP and pulse duration

Answer 18

• Pulse repetition frequency (PRF)
  
  • Number of pulses/s (kHz)
• Pulse repetition period (PRP)
  
  • Time from beginning of one pulse to beginning of next (ms)
• PRF RECIPROCAL OF PRP
  
  • As repetition frequency goes up, repetition period goes down
• Pulse duration (microseconds)
  
  • ​Period (of single cycle) x number of cycles per pulse

Question 19

Detail PRF

Answer 19

Question 20

Detail PRP

Answer 20

Question 21

Detail pulse duration

Answer 21

NB: INCORRECT EQUATION -> Wave period X number waves in a pulse

Question 22

Detail duty factor

Answer 22

Question 23

How does frequency in PW doppler compare to CW?

Answer 23

Question 24

Define bandwidth, fractional bandwidth, and quality factor (Q)

Answer 24

Question 25

How does dampening relate to bandwidth and Q factor?

Answer 25

- Increase dampening: DECREASE SPL INCREASE BANDWIDTH DECREASED Q FACTOR

Question 26

Define range and how distances are calculated by US

Answer 26

Question 27

What factors increase acoustic impedance?

Answer 27

- Increased density - Increased propagation speeds THINK ABOUT THE EQUATION!

Question 28

What is the speed of sound in ST?

Answer 28

1540m/s (1.54 mm/microsecond)

Question 29

For a reflector at 5cm depth, calculate pulse round trip time

Answer 29

d = 1/2 (c x t) 100mm = 1/2(1.54mm/mcsec x t) 100 / 1.54 = 65 microseconds (ROUND TRIP TIME) TIme to reflector = round trip time / 2 = 32.5microsec

Question 30

What is the rule that can help with pulse round trip time?

Answer 30

- Pulse round trip time = **13 microseconds / cm** from source to reflector!! \*\*ANSWER NEEDS TO BE DIVIDED BY 2 TO CALCULATE REFLECTOR DISTANCE\*\* 1 sec = 1microsec x10^-6

Question 31

TABLE

Answer 31

Question 32

Define wavelength, propagation speed and frequency. How do they relate?

Answer 32

Question 33

A 5 MHz beam travels from soft tissue into fat. Calculate wavelength in each medium and determine % wavelength change

Answer 33

Frequency = 5MHz (cycles/s) Speed = 1540m/s AND 1450m/s 1540 / 5, 000, 000= 0.000308m = 0.31mm 1450 / 5, 000, 000 = 0.000290m = 0.29mm **Wavelength expressed in mm!!**

Question 34

What is the speed of sound in ST and FAT?

Answer 34

ST = 1540m/s Fat = 1450m/s

Question 35

How do spatial resolution and attenuation relate to wavlength and frequency?

Answer 35

Resolution -\> increases with smaller wavelength (higher frequency) Attenuation -\> Increases with smaller wavelength (higher frequency)

Question 36

TABLE

Answer 36

Question 37

What features determine size of near field?

Answer 37

- **Unfocused single array:** Tranducer diameter Frequency **- Multiple element array** Effectrive diameter (excitation of groups of elements) INCREASES with increasing width or frequency ("Aperture")

Question 38

What factors affect beam divergence in the far zone?

Answer 38

**APERTURE!** - Frequency: Higher frequency, less divergence - Beam width: Larger width, less divergence

Question 39

List 3 things that can create beam focusing, and 3 things that limit beam focusing

Answer 39

Cause: - Curved elements - Lens - Phasing Limiters: - Wavelength - Aperture - Focal length

Question 40

What dictates focal zone in single element array vs phased array / linear array?

Answer 40

Question 41

List 3 ways harmonic imaging improves image quality

Answer 41

Question 42

What characteristics of of harmonic frequencies are required for successful harmonic imaging?

Answer 42

Question 43

What is harmonic imaging best used for?

Answer 43

- Abdo imaging: requires low freq to achieve penetration -\> can switch to harmonic to improve quality of returning image

Question 44

List 3 types of doppler

Answer 44

Question 45

What 3 factors influence doppler effect?

Answer 45

Question 46

What is doppler shift frequency?

Answer 46

Question 47

What is the general doppler equation

Answer 47

Question 48

What is the doppler equation REARRANGED FOR BLOOD FLOW?

Answer 48

Question 49

What is the doppler shift equation AND rearranged for blood flow?

Answer 49

Question 50

Doppler example: What is the scatterer speed (cm/s) in the below example -\> 2MHz incident freq, 0 doppler angle, shift 1.3kHz. Scatterer moving TOWARDS receiver

Answer 50

(1.3kHz x 1540m/s) / 2 x 2000kHz x cos 0) = 0.5m/s = 50cm/s

Question 51

DOPPLER SHIFT CALCULATION

Answer 51

Question 52

How does doppler shift relate mathmatically to a) blood flow velocity b) operating frequency

Answer 52

**- PROPORTIONAL TO VELOCITY AND FREQ** Increase blood flow -\> increase doppler shift Increase operating frequency -\> increase doppler shift -

Question 53

What effect does increasing doppler angle have on doppler shift?

Answer 53

LARGER ANGLE = LESS SHIFT Remember, maximum shift when angle = 0!!

Question 54

What is the peak veolocity of blood cells?

Answer 54

**200cm/s**

Question 55

What are preferred Doppler angles? Why?

Answer 55

Question 56

What are the 2 major groups of bioeffects to consider in US? What are their respective indices?

Answer 56

Question 57

Which US techniques are considered most likely to contribute to biological effects?

Answer 57

- High power -\> **SPECTRAL DOPPLER,** Colour doppler and M-mode in the middle Gray scale lowest

Question 58

What is GAIN? What is TIME GAIN COMPENSATION?

Answer 58

Question 59

Briefly, detail the components of the BEAM FORMER

Answer 59

Question 60

What is DYNAMIC RANGE?

Answer 60

Question 61

Briefly, detail the functions of the SIGNAL PROCESSOR

Answer 61

Question 62

What are the 4 MAJOR components of the US unit

Answer 62

Question 63

Briefly, detail the components / function of the IMAGE PROCESSOR

Answer 63

Question 64

In what way does US data change formats throughout the ultrasound unit?

Answer 64

Question 65

What is the difference between frame rate and refresh rate?

Answer 65

Question 66

Describe the different US display modes

Answer 66

Question 67

Describe manufacture of piezoelectric material. Which material? Process? Role of curie termperature?

Answer 67

Question 68

What affect does element thickness have on US beam?

Answer 68

Thickness determines OPERATING FREQUENCY -\> Thickness = 1/2 wavelength

Question 69

Briefly detail the DAMPING / BACKING BLOCK

Answer 69

Question 70

What is the role of the MATCHING LAYER

Answer 70

Question 71

Detail the affects of aperture and freq on near field length. What is aperture

Answer 71

Question 72

Detail how LINEAR / CURVED transducers work

Answer 72

Question 73

Detail the differences between sequential and phased array

Answer 73

Question 74

Describe the role of phasing in linear sequential array and phased array probes

Answer 74

Question 75

Briefly detail multifrequency transducers

Answer 75

Question 76

What are the three features that FRAME RATE is affected by?

Answer 76

Question 77

Detail the effects of FOV, DEPTH and LINE DENSITY on frame rate

Answer 77

Question 78

Detail COLOUR DOPPLER

Answer 78

Question 79

Detail POWER DOPPLER

Answer 79

Question 80

Detail TISSUE DOPPLER

Answer 80

Question 81

Describe different types of blood flow

Answer 81

Question 82

What does spectral broadening reflect in PW spectral doppler?

Answer 82

- Disturbed or turbulent flow

Question 83

Briefly, detail what is plotted by spectral doppler. How do flow disturbances manifest?

Answer 83

Question 84

Briefly detail spectral analysis

Answer 84

Question 85

Briefly detail PW doppler

Answer 85

Question 86

Detail the calculation of 3 INDICES related to vascular resistance on spectral doppler

Answer 86

Question 87

Detail the bernoulli effect and modified bernoulli equation

Answer 87

Question 88

Briefy detail the differences in CEUS agents

Answer 88

Question 89

What feature of US units defines capacity for CONTRAST RESOLUTION?

Answer 89

- Number of bits per pixel