US Flashcards
What is the range of human hearing? What is considered US?
20-20,000 HZ
> 20,000 HZ = US
Define below and provide units where relevant


What is the approximate geometry of an ultrasound beam?
- LONGITUDINAL WAVE: Two distinct regions:
Convergent beam -> near field
Divergent beam -> far field

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

Define intensity. What are dB?
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

Equation for reflection coefficient AND intensity transmission coefficient
TRANSMISSION COEFFICIENT = 1 - RI!! Just a measure of how much energy transmitted, with 1 = to complete transmission

Define acoustic impedance inc. unit and equation

Define refraction. What equation is used to describe effect?

Define 3 types of reflector
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

List 4 factors that influence AMPLITUDE of signal from insonated tissue
- 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)
What interactions are most responsible for attenuation?
SCATTER and ABSORPTION
Define attenuation and attenuation coefficient, including units. WHAT IS THE RULE OF THUMB!!

What is HVT in US?

Define Spatial Pulse Length (SPL)

Name 2 methods to improve axial resolution
REDUCE SPL
- Increase frequency (and thus smaller wavelength)
- Shorten pulse duration / number of cycles
Calculate SPL and resolution for 5MHz signal (wavelength 0.31mm) and 3 cycle pulse
0.93mm PULSE = SPL
Axial resolution = 1/2 SPL = 0.47mm
What factors are most important for AXIAL and TRANSVERSE (Azithmul) resolution?
Axial = SPL
Trans = Beam width

Define PRF, PRP and pulse duration
-
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

Detail PRF

Detail PRP

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

Detail duty factor

How does frequency in PW doppler compare to CW?

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

How does dampening relate to bandwidth and Q factor?
- Increase dampening:
DECREASE SPL
INCREASE BANDWIDTH
DECREASED Q FACTOR

Define range and how distances are calculated by US

What factors increase acoustic impedance?
- Increased density
- Increased propagation speeds
THINK ABOUT THE EQUATION!
What is the speed of sound in ST?
1540m/s (1.54 mm/microsecond)
For a reflector at 5cm depth, calculate pulse round trip time
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
What is the rule that can help with pulse round trip time?
- 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

TABLE


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

A 5 MHz beam travels from soft tissue into fat. Calculate wavelength in each medium and determine % wavelength change
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!!
What is the speed of sound in ST and FAT?
ST = 1540m/s
Fat = 1450m/s
How do spatial resolution and attenuation relate to wavlength and frequency?
Resolution -> increases with smaller wavelength (higher frequency)
Attenuation -> Increases with smaller wavelength (higher frequency)
TABLE


What features determine size of near field?
- Unfocused single array:
Tranducer diameter
Frequency
- Multiple element array
Effectrive diameter (excitation of groups of elements)
INCREASES with increasing width or frequency (“Aperture”)
What factors affect beam divergence in the far zone?
APERTURE!
- Frequency: Higher frequency, less divergence
- Beam width: Larger width, less divergence
List 3 things that can create beam focusing, and 3 things that limit beam focusing
Cause:
- Curved elements
- Lens
- Phasing
Limiters:
- Wavelength
- Aperture
- Focal length
What dictates focal zone in single element array vs phased array / linear array?

List 3 ways harmonic imaging improves image quality

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

What is harmonic imaging best used for?
- Abdo imaging: requires low freq to achieve penetration -> can switch to harmonic to improve quality of returning image
List 3 types of doppler

What 3 factors influence doppler effect?

What is doppler shift frequency?

What is the general doppler equation

What is the doppler equation REARRANGED FOR BLOOD FLOW?

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

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

DOPPLER SHIFT CALCULATION


How does doppler shift relate mathmatically to
a) blood flow velocity
b) operating frequency
- PROPORTIONAL TO VELOCITY AND FREQ
Increase blood flow -> increase doppler shift
Increase operating frequency -> increase doppler shift
-
What effect does increasing doppler angle have on doppler shift?
LARGER ANGLE = LESS SHIFT
Remember, maximum shift when angle = 0!!

What is the peak veolocity of blood cells?
200cm/s
What are preferred Doppler angles? Why?

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

Which US techniques are considered most likely to contribute to biological effects?
- High power -> SPECTRAL DOPPLER,
Colour doppler and M-mode in the middle
Gray scale lowest
What is GAIN? What is TIME GAIN COMPENSATION?

Briefly, detail the components of the BEAM FORMER

What is DYNAMIC RANGE?

Briefly, detail the functions of the SIGNAL PROCESSOR

What are the 4 MAJOR components of the US unit

Briefly, detail the components / function of the IMAGE PROCESSOR

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

What is the difference between frame rate and refresh rate?

Describe the different US display modes

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

What affect does element thickness have on US beam?
Thickness determines OPERATING FREQUENCY
-> Thickness = 1/2 wavelength

Briefly detail the DAMPING / BACKING BLOCK

What is the role of the MATCHING LAYER

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

Detail how LINEAR / CURVED transducers work

Detail the differences between sequential and phased array

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

Briefly detail multifrequency transducers

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

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

Detail COLOUR DOPPLER

Detail POWER DOPPLER

Detail TISSUE DOPPLER

Describe different types of blood flow

What does spectral broadening reflect in PW spectral doppler?
- Disturbed or turbulent flow
Briefly, detail what is plotted by spectral doppler. How do flow disturbances manifest?

Briefly detail spectral analysis

Briefly detail PW doppler

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

Detail the bernoulli effect and modified bernoulli equation

Briefy detail the differences in CEUS agents

What feature of US units defines capacity for CONTRAST RESOLUTION?
- Number of bits per pixel
