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Book Flashcards

1
Q

Units of length

A

CM, Feet

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2
Q

Units of area

A

Length squared
Cm squared
Ft squared

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3
Q

Volume

A

Length cubed
CM to the third power
FT to the third power

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4
Q

No exponent is between numbers____ and_____

A

1&10

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5
Q

10 to the -6

A

0.000001 is 10 to the -6 or mirco

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6
Q

Hz=

A

Cycles per second

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7
Q

How much bigger is 1 billion than 1 million?

A

1,000 times

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8
Q

Macro - bigger
Micro- smaller

A

True

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9
Q

Biologic effects

A

The effects of a sound wave upon the biologic tissue

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10
Q

Sound is a series of______ and_____

A

Compressions and rarefactions

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11
Q

Compressions

A

Areas of increased pressure and density

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12
Q

Rarefactions

A

Areas of decreased pressure and density

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13
Q

Sound is a mechanical, longitudinal wave

A

True

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14
Q

What are the three acoustic variables?

A

Pressure, density, distance

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15
Q

Pressure*

A

Concentration of force within an area
Force/area
Units-Pascals (Pa)

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16
Q

Density

A

Concentration of mass within a volume
Kg/cm 3

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17
Q

Distance

A

Measure of particle motion
Units- Distance
Ex- mm or cm

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18
Q

Transverse wave

A

Particles move in a perpendicular direction (right angles, or 90°)

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19
Q

Longitudinal wave

A

Particles move back-and-forth in the same direction as the wave

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20
Q

Compressions

A

Regions of higher pressure and density

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21
Q

Rare factions

A

Regions of lower pressure and density

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22
Q

Can a sonographer change period and frequency?

A

No

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23
Q

Can a sonographer change amplitude, power, intensity?

A

Yes

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24
Q

Acoustic variables

A

Identify which waves are sound waves

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25
Q

Acoustic parameters

A

Describe the features of a particular sound wave

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26
Q

Period

A

The time required to complete a single cycle

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27
Q

Frequency

A

How often are cycle sent out

The frequency of a wave is the number cycles of an acoustic variable that occur in one second

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28
Q

Frequency units

A

Per second
Hz

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29
Q

Frequency values

A

2 MHz - 15 MHz

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30
Q

Lower frequency

A

Better penetration with decreased resolution

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31
Q

Higher frequency

A

Poor penetration with increased resolution

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32
Q

Frequency between 20 Hz and 20,000 Hz

A

Audible

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33
Q

Greater than 20,000 Hz

A

Ultrasound

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34
Q

Less than 20 Hz

A

Infra sound

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35
Q

Frequency and period are inversely related

A

When one goes up, the other goes down

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36
Q

When period is unchanged , frequency is____

A

Unchanged

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37
Q

Shorter period uses ____ frequency

A

Higher frequency

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38
Q

Longer period Uses ___ frequency.

A

Lower

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39
Q

Frequency and period equation

A

Frequency x Period

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40
Q

Amplitude, power, intensity. All decrease sound travels.

A

True

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41
Q

Amplitude

A

The difference between the average value and the maximum value of an acoustic variable. The variation of an acoustic variable.

Units
Pressure- Pascals
Density- grams/ cubic cm
Particle motion – centimeters, inches, units of distance

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42
Q

Power

A

The rate of energy transfer
Units- watts *
Power is proportional to the waves amplitude squared

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43
Q

Intensity

A

The concentration of energy in a sound beam
Units- watts/ square cm or watts/cm squared

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44
Q

Amplitude, power, intensity are proportional to each other

A

When one goes up, the other goes up

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45
Q

Wavelength

A

The length or distance of a single cycle and influences image quality (axial resolution)
Units- any units of length
Determined by both the source and the medium

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46
Q

**Wavelength equation **

A

Wavelength(mm) =
prop speed 1.54mm/us divided by frequency (MHz)

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47
Q

Higher frequency sound has shorter wavelengths (better imaging)

Lower frequency sound has longer wavelengths

A
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48
Q

Wavelengths in soft tissue

A

In soft tissue, sound with a 1 MHz frequency has a wavelength of 1.54mm

In soft tissue, sound with a 2 MHz frequency has a wavelength of 0.77mm

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49
Q

Propagation speed

A

The rate that sound travels through a medium (aka- velocity or speed)
Units- meters per second mm/us
Determined by medium only (density and stiffness)

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50
Q

Propagation speed

A

All sound travels at the same speed through any specific medium.

Cant be changed by sonographer

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51
Q

Propagation speed values **

A

1,540m/s
1.54km/s
1.54mm/us

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52
Q

Speed and wavelength are directly related

A

Sound in a slow medium has a short wavelength

Sound in a fast medium has a long wavelength

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53
Q

Tissue types**

A

Lung(air)«fat«soft tissue«bone

Gas(slower)«liquid«solid(faster)

Tissue type: Speed:
Air (slower). 330
Lung
Fat
Soft tissue / blood
Tendon About 1,850
Bone (Faster) 2,000-4,000

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54
Q

Stiffness is related to change in shape “squishability”

Density is related to weight

A

Stiffness & speed- same direction
Density & speed- opposite directions

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55
Q

Bulk modulus *

A

Same as stiffness

When bulk modulus increases, speed increases

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56
Q

Constructive & Destructive interference

A

In phase waves interfere constructively

Out of phase waves interfere destructively

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57
Q

What are the units of intensity?

A

Watts/ cm squared

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58
Q

Units of power?

A

Watts

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59
Q

In diagnostic imaging, short, pulses of acoustic energy are required to create an atomic images

A

Continuous wave sound cannot create an atomic images. CW is used for Doppler.

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60
Q

Pulsed sound

A

 A pulse is a collection of cycles that travel together

A pulse must have a beginning and an end, otherwise the sound is continuous wave

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61
Q

What are the five parameters that describe pulsed sound?

A

Pulse duration
Pulse repetition period
PRF
Duty factor
Spatial pulse length

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62
Q

Pulse duration

A

The actual time from the start of a pulse to end of that pulse

Units-time, seconds
Determined by sound source
Changed by sonographer – no
Typical values – 0.5 - 3us
In clinical Imaging a pulse is comprised of 2 to 4 cycles
Equation- pulse duration= number of cycles x period

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63
Q

Spatial pulse length

A

The distance from the start to the end of one pulse
Units/distance, MM
Determined by the source and the medium
Sonographer cannot change
Typical values/0.1 - 1mm
Equation - SPL(mm)= # of cycles x wavelength(mm)

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64
Q

SPL affects mage quality (Axial resolution)

A

Shorter pulses create higher quality images

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65
Q

Pulse Repetition Period

A

Pulse repetition period (PR) is the time from the start of one pulse to the start of the next pulse. It includes one pulse duration and one listening time.

Determined by Sound source
Units - time, msec
Changed by sonographer- yes
Values- 100us to 1ms

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66
Q

As PR period increases, imaging depth increases.
As PR period decreases, imaging depth decreases.

A
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67
Q

PRF

A

PRF is the # of pulses created by the system in one second.

Hertz, Hz, per second

Determined By sound source

Sonographer can change it

Values In clinical imaging, from 1,000-10,000Hz (1-10kHz) »

• The PRF is determined by imaging depth only.

Shallow image, higher PRF
Deep image, lower PRF

PRP/ PRF- one goes up, other goes down

pulse repetition period (sec) × pulse repetition frequency (Hz) = 1

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68
Q

Duty factor

A

The percentage or fraction of time that the system transmits sound.

Unitless
Determined by sound source
Can be changed by sonographer
Typical values From 0.1% to 1% or 0.001 to 0.01
Shallow image, higher duty factor
(little talking, lots of listening) »
Deep image, lower duty factor
Duty factor is always a small value, typically less than 1%.
With deeper imaging, the duty factor is even smaller.»
Note
An imaging system must use pulsed ultrasound. Therefore,
the duty factor always less than 100%
Continuous wave sound has a duty factor of 100%. CW
cannot create anatomical images.»

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69
Q

shallow imaging
high pulse repetition frequency (PRF)
short pulse repetition period
high duty factor

A

deep imaging
low pulse repetition frequency (PRF)
long pulse repetition period
low duty factor

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70
Q

Pulse duration, and SPL are determined by both source and medium

A

PRP
PRF
DF

All determined by sound source

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71
Q

Intensity

A

The concentration of the power in a beam

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72
Q

Intensity keywords

A

• Peak
the maximum value
• Average the mean value
• Spatial referring to distance or space
• Temporal referring to all time (transmit & receive)
•Pulsed referring only to the time the pulse exists (transmit only)

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73
Q

Intensity descriptions

A

SPTP- spatial peak, temporal peak **highest value
SPTA- spatial peak, temporal average **most relevant for thermal bioeffects
SATA- spatial average, temporal average **lowest value

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74
Q

Intensities

A

SPTA- related to tissue heating
SPTP - greatest
SATA -smallest

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75
Q

Logarithms

A

a novel way of rating numbers, a peculiar combination of
addition and multiplication.
The logarithm of any number represents the number of “1Os” that are multiplied together to create the original number.
What is the log of 100? 10 x 10 = 100, the log of 100 is 2.
What is the log of 1000? 10 x 10 × 10 = 1000, the log of
1,000 is 3.

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76
Q

Decibels

A

A logarithmic scale, a relative, comparison or ratio between the final to the initial strengths
A comparison, therefore, two intensities are needed
calculate decibels.
Db report the of relative bigness of a sound beam

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77
Q

Positive decibels

A

Means getting bigger, the intensity is increasing
3 dB means two times bigger
10 dB means 10 times bigger

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78
Q

Negative decimals

A

Means getting smaller, the intensity is decreasing

-3 dB means 1/2
-10 dB means 1/10

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79
Q

Attenuation

A

A decrease in strength, (intensity, power, and amplitude) have a sound wave as it travels. Unrelated to speed the further sound travels, the more attenuation occurs.

Units -dB/must be negative since attenuation causes intensity to decrease

Less attenuation = shorter distance/lower frequency

More attenuation = longer distance/higher frequency

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80
Q

What are the three components of attenuation?

A

Absorption/primary sound converted into heat
Scattering
Reflection / 1%

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81
Q

Attenuation in different media

A

Air/ much more attenuation, then in soft tissue. Gel is used to remove air from the path of ultrasound.

Lung and bone/bone absorbs and reflects. Lung scatters.

Water/ much less than soft tissue

Air» bone & lung&raquo_space; soft tissue» water

Attenuation and blood is less than that in soft tissue

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82
Q

Attenuation and penetration

A

In soft tissue, lower, frequency results in less attenuation. Thus we penetrate further with lower frequency sound.

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83
Q

Reflection**

A

Occurs when propagating sound energy, strikes a boundary between two media, and some returns to the transducer

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84
Q

Specular reflection

A

Occurs when the wave length is smaller than the irregularities in the boundary

Strongest reflections are produced with normal incidence 90°

These aren’t as well seen when the wave strikes the boundary at angles other than 90°. Example vessel wall.

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85
Q

Diffuse (Backscatter) reflection

A

The reflection of sound generally back towards the transducer, but in a number of directions

When boundary is rough, reflected, sound is disorganized and random

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86
Q

Scattering

A

The distribution of sound randomly in all directions. Higher frequency, sound scatters to a great extent.

**If a reflector is much smaller than the wave length of sound, sound is uniformly distributed in all directions

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87
Q

Rayleigh scattering

A

As frequency increases, scattering increases

Blood is black due to Rayleigh scattering

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88
Q

Attenuation coefficient

A

The amount of attenuation per centimeter. A way to report attenuation without dealing with how far sound travels.

Units- dB, dB per centimeters

As frequency increases, the attenuation coefficient increases

Remains the same, regardless of how far the sound waves travel

Attenuation coefficient is half of the frequency

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89
Q

Impedance

A

A number associated with a medium. *It is Calculated not measured.

Units- Rayls, Z

Reflection of an ultrasound wave depends upon different acoustic impedances of the media on either side of the boundary

*Equation- impedance (rayls) = density (kg/m3) X propagation speed (m/s)

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90
Q

Normal incidence

A

90°

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91
Q

Oblique incidence

A

Not 90°

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92
Q

In soft tissue, attenuation coefficient is directly related to_____

A

Frequency

If frequency, doubles, attenuation coefficient, will double

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93
Q

The amount of Rayleigh scattering is related to____

A

Frequency

If frequency, doubles Rayleigh scattering increases by a factor of 16

2x2x2x2=16

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94
Q

Normal incidence

A

Perpendicular
Orthogonal
Right angle
90°
PORNN

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95
Q

Oblique incidence

A

Anything other than 90°/not at right angles

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96
Q

Reflection and transmission

A

Incident intensity- intensity of a sound wave prior to striking a boundary (100%)

Reflected intensity -the intensity that after striking a boundary changes direction, and returns back from where it came from (less than 1% reflected)

Transmitted intensity - the intensity that after striking a boundary continues on in the same direction that it was originally traveling (99%)

Units W/CMsquared

Incident= reflected + transmitted

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97
Q

Reflection and transmission

A

IRC/ intensity reflection coefficient- the percentage of the ultrasound intensity that bounces back when sound strikes a boundary

ITC/ intensity transmission coefficient- the percentage of the incident intensity that after striking a boundary continues on the same direction that it was originally traveling

No units, percentages

Both are unitless

Range from 0% to 100% or 0 to 1.0

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98
Q

Conservation of energy

A

Exists at a boundary

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99
Q

In biologic media

A

Boundary. Reflection %
Soft tissue -air. 99%
Soft tissue -bone. 50%
Soft tissue- soft tissue. <1%

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100
Q

Reflection with normal incidence

A

**Reflection occurs only if the two media at the boundary have different acoustic impedances

Intensity Reflection Coefficient (%) = Z2-Z1/Z2+Z1 squared

With greater impedance differences between the two media, the IRC increases and the amount of reflection increases.

Z= impedance

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101
Q

Transmission with normal incidence

A

Whatever is not reflected, must be transmit it 

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102
Q

Reflection and transmission with oblique incidence

A

Transmission and reflection may or may not occur with oblique incidence 

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103
Q

Refraction

A

Transmission with a band. Refraction is a change in direction at sound transmits from one medium to another.

Requires both oblique incidents and different speeds

Snells law describes the physics of refraction

Sin(transmission angle)
—— divided by——-
Sin (incident angle)

=

Propagation, speed 2
——-divided by———-
Propagation, speed one

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104
Q

Angles

A

Smaller angle = slower medium

Greater angle = faster medium

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105
Q

Time of flight

A

The time needed for a post to travel to and from the transducer, and the reflector is called time of flight or round-trip time

What time of flight is measured we can determine reflector Depth

Since the average speed of sound in soft tissue is 1.54 KM/SEC the time of flight and distance that sound travels in the body are directly related.

Time of flight flight is increased by a factor of two. When one reflector is twice as deep as another pulses timer fly is doubled for the deeper reflector.

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4
5
Perfectly
106
Q

The 13 µs (microsecond) rule

A

In soft tissue, every 13 µs of go return time means the reflector is 1 cm deeper in the body. 

Time of flight/Depth/ Distance trvld
13 µs 1 cm. 2 cm.
26 µs 2 cm 4cm

107
Q

Speed equation

A

Speed= distance/ time

108
Q

Piezoelectric effect

A

A property of certain materials to create a voltage when pressure is applied, or when the material is mechanically deformed

109
Q

Piezoelectric materials

A

Synthetic- lead zirconate (PZT) aka/ ferroelectric material.

Natural- quartz, tourmaline

PZT
ceramic
Active element
Crystal

110
Q

Curie temperature
Or
Curie point

A

When PZT is heated above the temperature (approx 360°C or 680°F) its properties are destroyed, depolarized.

Never heat sterilize or auto clave transducers

111
Q

Sterilization

A

The complete destruction of all living microorganisms by means of exposure to heat, chemical agents, or radiation

112
Q

Disinfection

A

The application of a chemical agent to reduce or eliminate infectious organisms.

113
Q

Transducer architecture

A

Wire, case, backing material, crystal, matching layer

Active element- Piezoelectric crystal, also called ceramic, PZT or crystal

It is 1/2 wave length thick

114
Q

Matching layer of transducer

A

The matching layer has an impedance between those of the skin and active element to increase transmission between the active element and the skin

1/4 wave length thick

Impedances - PZT> Matching layer> gel> skin

Going from the PZT crystal to the face of the probe, the impedance of each layer is less than less

115
Q

Damping element, or backing material

A

Short pulses, create more accurate images

Immaterial is bond it to the active element to reduce it’s ringing

Z= impedance

116
Q

Bandwidth and quality factor

A

The range of frequencies between the highest, and the lowest frequency emitted from the transducer

Bandwidth (Hz)= highest frequency-lowest frequency

Imaging probes are wide bandwidth or broadband because they use backing material

Main frequency emitted is called the center, resonant, primary or natural frequency

117
Q

Quality factor

A

A Unitless number related to extent of damping

Low Q= damping, and wide bandwidth, Imaging transducers

High Q= no damping and narrow bandwidth, CW and therapeutic transducers

118
Q

Continuous wave transducers

A

Electrical frequency&raquo_space;> sounds frequency

119
Q

Pulsed transducers

A

The main frequency of sound from a pulse transducer is determined by two characteristics of the Crystal:

1) the thickness
2) propagation speed

The propagation speed of PZT is approximately 4-6 mm/us

When a PZT crystal is half as thick that sounds frequency is twice as high

High frequency // Lower frequency
Thin Crystal. Thick Crystal.
Fast, PZT Slow, PZT

Component // Thickness
PZT crystal 1/2 wavelength thick
Matching layer 1/4 wavelength thick

120
Q

When a transducer is covered with a sterile cover with gel on the inside, what must the transducer avoid touching in order to create an image?

A

Talcum powder

121
Q

Sound beams

A

Narrow beams create better images

Starts out at exactly the same size as the transducer diameter or aperture

Focus or focal point - the location where the beam reaches its minimum diameter

Focal depth -the distance from the transducer to the focus. Also called focal length or near zone length.

Near zone (Fresnel zone)-the zone in between the transducer and the focus. Sound beams coverage in the near zone.

Far zone (Fraunhofer zone)-zone deeper than the focus, beyond the near field . Sound beams diverge in the far zone.

Focal zone -the region surrounding the focus where the beam is sort of narrow and the picture is relatively good

122
Q

Beam diameter

A

See picture

123
Q

Focal depth

A

Distance from transducer to the focal point

Determined by transducer diameter, or aperture and frequency

Shallow Focus.- small diameter/low frequency

Deep focus - large diameter/high frequency

124
Q

Sound beam divergence

A

Describe the spread of the sound beam in the deep far zone

Larger diameter, crystals, producing higher frequency, sound produced beams that diverge less in the far Field

Smaller diameter crystals, producing lower frequency sound produced beams that diverge substantially in the far field

125
Q

Diffraction pattern

A

V- shaped wave, also called Huygens wavelet

126
Q

Huygens principle

A

The hourglass shape of an imaging transducers sound beam

The overall hourglass shape of a sound beam is the result of the constructive and destructive interference of the mini sound wave. Let’s omit it from these numerous sound sources.

127
Q

Axial resolution

A

The ability to distinguish two structures that are close to each other, front to back or along the beams main axis

Units/ distance , mm cm

Not changed by sonographer

Short pulse means a short, spatial pulse length or a short pulse duration

Images are more accurate with shorter pulses

Typical values 0.05 - 0.5 mm

Equation -
Axial resolution (mm)= SPL(mm)/2

128
Q

Axial resolution improves with

A

Less ringing(if you are cycles in a pulse) and higher frequency

Higher frequency, transducers create more accurate images. As frequency increases, the numerical value of the axial resolution decreases.

129
Q

Lateral resolution

A

The minimum distance that two structures are separated by side to side or perpendicular to the sound beam

Units - distance mm

Lateral resolution = being diameter

Beam diameter, and lateral resolution varies with depth. Also called beam width variation, or point spread artifact

Best at the focus or one near zone length from the transducer

Degrades at deeper depths in the far zone

130
Q

High frequency pulsed ultrasound

A

Improved axial resolution

Improved lateral resolution in far field

131
Q

Phased array

A

Adjustable or multi focusing

Better overall lateral resolution

Sonographer can move the focus to anatomic region

132
Q

Focusing alters beam three ways

A

Narrow waist in the beam
Shallower focus
Smaller focal zone

Focusing is effective, mainly in the near field and focal zone

133
Q

Two types of focusing

A

Fixed- conventional or mechanical

Adjustable by electronics called phased array

134
Q

Mechanical scanning

A

One disc shaped element

Active element mood by a motor, oscillating crystal or mirror

Focusing/conventional or fixed

Image shape/sector (fan)

Defective, crystal/destroys entire image

135
Q

Transducer arrays

A

A collection of active elements in a single transducer

PZT cut into separate pieces called elements

Combination of electronic circuitry, the wire, and the element

Linear array/a collection of elements in a line. Linear switched (or sequential) and linear phase array

Annular array/a group of ringed elements (bull’s-eye) with a common center

Curvilinear array/elements arranged in an arc. Curvilinear, switched, or curvilinear phased.

136
Q

Linear arrays (switched, or sequential)

A

Approximately 200 rectangular shaped elements

3 -10 but not all are fired at exactly the same time to create a narrow directional beam. Improving lateral resolution.

No steering

Parallel lines / rectangular shaped

Defective crystal/drop out, extending from superficial to deep

137
Q

Phased array’s

A

Adjustable, focus or multi focus electronically

Approximately 200 rectangular shaped elements

Electronic pulses delivered to mini or all elements and various patterns for each sound pulse.

Sector shaped

Time delays are called phase delays

If one element malfunctions the staring and focusing become erratic

Curvature pattern can change focal depth and amount of focusing

The beam former creates the electronic patterns. 10 ns delays.

Provides many focusing at many depths during reception 

138
Q

Annular phase arrays

A

Rings, cut from the same circular slab a PZT. Looks like a bull’s-eye target.

Small number of ring-shaped elements

Selected focal zones. Inner crystals for shallow regions and outer crystals for deep regions.

Small diameter rings, have a shallow focus, but divert rapidly

Large diameter rings, have a deep focal length

The image is pointed, fan, or sector shaped

Multi focusing provides electronic, focusing and all planes at all depths

Improved elevational resolution

Steering is mechanically

Defective, crystal/horizontal side to side drop out

139
Q

Curvilinear arrays

A

PZT crystals arranged in a curve to provide a natural sector image

Approximately 200 rectangular shaped elements

Blunted sector, fan shaped image

140
Q

Multi dimensional, arrays

A

2D arrays create 3D or 4D images

3D imaging more accurately measure is volumes of structures, such as cysts

4D Imaging is real time 3D imaging

3D Imaging quality is determined by the number of slices

3D Imaging provides more accurate value measurements

141
Q

Vector arrays - trapezoidal imaging

A

Combined linear sequential and linear phased array technologies

Trapezoidal shape / sector with a flat top

Sector scanners are less useful when imaging superficial structures

142
Q

Contrast resolution

A

Dynamic range

Visualizing variety of gray shades in an image

143
Q

Spatial resolution

A

Detail

Affected by axial and lateral resolution, line density, and monitor

144
Q

Temporal resolution

A

The ability to accurately locate moving structures are any particular incident in time

Resolution pertaining to time

**Depends only on frame rate. More images per second improves temporal resolution.

Units / Hertz or per second

Values / 20Hz - 100 Hz

**Frame rate is determined by Imaging, depth and number of pulses

**Limited by speed of sound, and imaging depth

145
Q

Higher frame rate=

A

Better temporal resolution

146
Q

Deeper imaging =

A

Lower frame rate

147
Q

4 settings that affect temporal resolution

A

Sonographer controlled

Maxximum Imaging depth
Multi focus systems
Sector size
Line density

148
Q

Temporal resolution improves-

A

When image is shallower or made of fewer pulses
Less time to create an image
More frames created each second

149
Q

Temporal resolution, degrades-

A

When image is deeper or made of more pulses
More time to create an image
Frame rate decreases

150
Q

Imaging depth

A

Shallow depth of you makes a frame faster and improves temporal resolution

If Imaging depth is doubled, the frame rate will be halved 

151
Q

Temporal resolution continued

A

Shallow Imaging
Higher frame rate
Better temporal resolution

Deep Imaging
Lower frame rate
Worse temporal resolution

152
Q

Single versus multi focus

A

Single focus- fewer pulses
Higher frame rate
Better temporal resolution

Multi focus - more pulses
Lower frame rate
Worst temporal resolution

153
Q

Sector size

A

Narrow sector- fewer pulses
Higher frame rate
Better temporal resolution

Wide sector - more pulses
Lower frame rate
Worst temporal resolution

154
Q

Line density

A

Low line density- fewer pulses
Higher frame rate
Better temporal resolution

High line density - more pulses
Lower frame rate
Worst temporal resolution

155
Q

Improved and reduced temporal resolution

A

Factors that shorten the time required to make each frame increase frame rate and improve temporal resolution

Factors that lengthen the time required to make a frame will reduce frame rate and reduce temporal resolution

156
Q

Frame rate vs. image quality

A

As temporal resolution improves (higher frame rate) image quality made degrade

As temporal resolution degrades (lower frame rate) image quality may improve

Increasing the line density degrades, temporal resolution, but improves spatial resolution

Using multi focus, degrades temporal resolution by improves lateral resolution

157
Q

Frame rate(FR) and time to create a frame (Tf)

A

Tf and frame rate are reciprocals

Equation - Tf x FR = 1

Ex- 1/10th x 10 = 1
When one frame is created in 1/10 of a second, then the frame rate will be 10/second or 10 HZ

158
Q

System components

A

Master synchronizer/organizes, synchronizes and times their functions so as to operate as a single integrated system

Pulser/ controls the electrical signals sent to the elements. Creates the firing pattern for phased array system called being former.

Transducer/converts electrical into acoustic energy during transmission

Receiver/ the electronics associated with processing the electronic signal, produced by the transducer during reception, and producing a picture on display device

Display/monitor, audio speakers

Storage/computer memory, hard drives

159
Q

Pulser

A

Receives timing signal from synchronizer. Produces electrical voltage up to 100 V that excites PZT Crystal during transmission.

When the sonographer increases output power higher electrical voltages are created that strike the PZT crystals. This increases the sound intensity, created by the transducer and sent into the patient.

160
Q

Pulser modes

A

Continuous wave/ continuous electrical signal
Electrical frequency = sounds frequency

Pulsed wave, single Crystal /short, duration, electrical, spike, one electrical spike per Ultrasound pulse

Pulsed wave, arrays/mini elements fired for each ultrasound pulse. For phased array systems, the pulsar is also called the beam former.

161
Q

Output power

A

Output power change the brightness of the entire image

Signal-to-noise ratio changes

Determined by the excitation voltage from the pulser

PZT crystal vibrates with a magnitude related to pulser voltage

Sonographer can change

Brightness of the entire image changes

162
Q

Signal to noise ratio
(S/N)

A

High S/N ratio- high quality image

Low S/N ratio- low quality image, degrades

Increasing output power is the primary way to improve S/N ratio

163
Q

Receiver functions order

A

Gain, TGC, dynamic range, reject

Or

Amplification
Compensation
Compression
Rejection

164
Q

Gain

A

Changes the brightness of the entire image.

S/N ratio unchanged

Adjusted by sonographer

Units dB

Every signal is treated identically (uniform amplification)

Preamplification alters the signal before gain is applied. Usually performed in the probe

Gain kill’s resolution

165
Q

Compensation or TGC

A

Used to create uniform brightness

Makes all echoes from similar reflectors appear identical regardless of depth

Uniform from top to bottom

Higher frequency = more TGC

Lower frequency = less TGC

166
Q

Dynamic range

A

Adjusts the grayscale range within the image

Allows us to see all gray shades and differentiate tissues

Changes the gray scale mapping

Sonographers can adjust



167
Q

Reject

A

Illuminates, low level noise in our images

Affects only low level signals everywhere on the image, but does not affect bright echoes. Fewer shades of gray.

Sonographer can adjust 

168
Q

Contrast agents

A

Micro bubbles of gas entrapped in a shell

There is a large impedance difference between contrast agents and biologic tissues

169
Q

Requirements for contrast agents

A

Safe
Strong, reflector ultrasound
Long persistence
Metabolically inert

170
Q

Output power vs gain

A

Adjustments to either output power, or gain alter the brightness of the entire image

Output power affects patient exposure
Gain doesn’t affect patient exposure

Output power affects brightness, by adjusting the strength of the sound waves sent to the body from the transducer

When the image is too bright due to high output power, the lateral and longitudinal resolution degrade

Gain affects the brightness by changing the amplification of the electronic signals before returning to the receiver

With increased gain, the electronic signals in the receiver, are boost it in the image will be brighter 

171
Q

ALARA

A

As low as reasonably achievable

172
Q

Lower frequency, transducers

A

To image deep, it is better to use a low frequency, transducer rather than increase output power

173
Q

Harmonics

A

Harmonics are multiples of the transducer frequency

Creates ULTRASOUND images by using reflections that are twice the transmit frequency.

Harmonics are created in the tissues, not in the transducer

Nonlinear behavior creates harmonics

Nonlinear is uneven

Sound moves slightly faster in regions of compression (higher pressure)

Sound travel, slightly slower in regions of rarefaction. (lower pressure.)

174
Q

Pulse inversion, harmonic imaging

A

The major disadvantage is that the frame rate is half that a fundamental imaging. Pulse inversion, imaging degrades, temporal resolution (lower frame rate) well improving spatial resolution (image detail)

Transducer bandwidth must include transmit and harmonic frequencies

175
Q

Harmonics are multiples of the transducer frequency?

True or false

A

True

176
Q

Bistable vs. Grayscale.

A

Bistable:
black or white
On or off
High contrast *
Narrow dynamic range *
Poor contrast resolution

Grayscale :
Many shades of gray
Multiple levels
Low contrast
Wide dynamic range
Good contrast resolution

177
Q

Brightness*

A

 Related to the brilliance of the image, how ‘lit up’ is the image

178
Q

Contrast

A

Determines the range of brilliance is that are displayed. Are the whites white? Are the blacks black?
Bistable images are high contrast

179
Q

Analog and digital

A

Analog:
Real world/a variable obtains, a continuum of values
Ex- actual weight of an individual

Digital:
Computer world/a variable attains only discrete values
Ex- measuring weight on a digital scale

180
Q

Scan converters

A

Changes the data format from penetrations to horizontal lines of a display

181
Q

Computer memory is called…

A

RAM
Random Access Memory

182
Q

Digital scan converter

A

A microprocessor digitizes images. This converts the image into zeros and ones which are stored in memory. The numbers (*digital image data) can be processed and then re converted for display as an image

183
Q

Pixel

A

The smallest element of a digital picture **

Pixel density- the more pixels per inch, the more detail in the image, spatial or detail resolution **

Low pixel density/ poor spatial resolution

High pixel density/ good spatial resolution

*spatial resolution on a digital display is determined by the pixel density (the # of pixels per inch)

  • spatial resolution is also related to the # of lines per frame
184
Q

Bit

A

*Binary digit, the smallest amount of digital storage

*a bit is a bistable, having a value of either zero or one

*a group of bits is assigned to each pixel to store the gray scale color assigned to that pixel

*the more bits per pixel the more shades of gray, and the better the contrast resolution

Binary number- group of bits. A series of zeroes and ones
Digital (computer based) means binary
Ex- 101 or 00110011

*Byte- a group of 8 bits is a byte.
2 bytes (16bits) is a word
Ex-
Byte 12345678
Word 12345678 12345678

Note-
Binary numbers are based on 2
Decimal numbers are based on 10 *

185
Q
  • how to calculate the # of gray shades that a collection of bits can represent
A

How many bits are assigned to each pixel.

Multiply the number 2 by itself the same number of times as there are bits. Thats the answer.

Ex- what # of shades that can be represented by 10 bits?

2x2x2x2x2x2x2x2x2x2= 1024
Or
2 to the 10th power

So the largest # of shades represented by 10 bits is 1024

Note- digital means binary, not decimal

Examples pg 106

186
Q

Image processing
Pre-processing

A

Manipulating the data before storage in the scan converter.

Preprocessing cannot be reversed

TGC
Dynamic range
Write magnification
Fill in interpolation
Persistence / frame averaging
Special compounding

187
Q

Image processing
Post processing

A

Manipulating the data after it has been stored in the skin, converter memory, but prior to display. This can be undone

  • post processing is performed on frozen images

Read magnification
3-D rendering

188
Q

Analog digital conversion

See pg 107/ pix

A

Analog / real world that we live in is analog

Digital/ computers is digital

Analog to digital conversion/electrical signals, created by the PZT are analog However, a digital scan converter can only process computer information.
The analog signal must be converted into digital form for the input into the scan converter this is done by analog to digital converter

189
Q

Read and write magnification

A

Read magnification-
Post processing
Does not rescan, only reads old image data in memory
Same line density
Larger pixels
Spatial resolution not improved
Temporal resolution unchanged

Write magnification -
Preprocessing
Rescans and requires new data, discard old image data
Increased line density
More pixels
Improved spatial resolution *
Temporal resolution can change

**If pixel size is unchanged, the number of pixels increase (write magnification)

If number of pixels is unchanged, pixel, size increases (read magnification)

190
Q

Spackle artifact

A

Imaging artifact

*Grainy appearance and tissues, that does not represent actual tissue anatomy

  • created by interference effects of scattered sound

Spackle reduces image contrast, and spatial resolution

191
Q

Clutter artifact

A

Doppler artifact

With Doppler blood velocity measurements, the reflection from blood cells are weak. Reflections from anatomic structures are much stronger. These strong reflections are called clutter. 

192
Q

Fill in interpolation

A

Preprocessing

Improves image detail (spatial resolution) by filling in the missing data, especially for deeper parts of a sector shaped image.

Example/edges of a circular structure will be better defined

193
Q

Spatial compounding

A

Creating an image by averaging images obtained from different angles.

Scan lines are steered by the system in different angles or views

Phased array transducers only

Frames are averaged, improving signal to noise ratio

-artifacts reduced
-spatial resolution (detail) improved
-temporal resolution (frame rate) reduced
- shadows and edge shadows are reduced or eliminated

194
Q

Temporal compounding or Persistence

A

Creating an image by overlaying images obtained at different times

Also called temporal averaging
Used in color flow Doppler

Resulting image is a consolidation of past frames

Temporal resolution is decreased

Moving anatomic structures appear blurred
Improves dynamic range, and contrast resolution

195
Q

Frequency compounding 

A

Creating an image by averaging frames obtained from different frequency sub-bands.

Images are averaged, improving signal-to-noise ratio

*Spackle artifact is reduced

Spatial resolution is improved

196
Q

Dynamic aperture

A

Improves lateral resolution

*A form of electronic receive focusing

*Accomplished, by varying the number of elements used to receive the reflected signal

Minimizes beam width variation

197
Q

Edge enhancement

A

Increases the contrast at a boundary to make image appear sharper

Most useful to emphasize different tissues

Distinguish interfaces

198
Q

Coded excitation

A

Takes place in the pulser

Improves :
Axial resolution
Penetration
Spatial resolution
Contrast resolution

coded excitation creates long sound pulses that contain a complex pattern of frequencies and cycles, called a code.
Special mathematical techniques process the long reflected codes, creating high quality images

199
Q

Elastography

A

a dynamic technique that produces images, called
elastograms, based on the deformation (change in shape) when an force is applied to tissue. The force is exerted a sound pulse from the transducer. Tissue stiffness is often related to underlying disease.
identifies tissues of different mechanical properties,
or different stuffiness

200
Q

Dynamic range

A

Ratio* of the largest to the smallest signal strength that each component processes, the number of choices indicates the number of gray shades on an image.

Can eliminate low level noise*

Units - dB*

Transducers process using the widest dynamic range.

Recoding device date has the lowest dynamic range

201
Q

Recording and Archiving

A

PACS-
Picture archiving and communications system

DICOM-
Digital imaging and communications in medicine

NAS-
Network attached storage

202
Q

Hemodynamics

Steady, pulsatile & phasic flow

A

Steady, pulsatile & phasic flow

Steady flow- fluid moving at a constant speed

Pulsatile-
Arterial
Cardiac
High rate
Higher pressure

Phasic-
Venous
Respiration
Low rate
Lower pressure

203
Q

Hemodynamics

Flow vs velocity

A

Flow-
Volume
How much?
Volume/ time
Liters/ min

Velocity-
Speed
How fast?
Distance/ time
Meters/ sec

204
Q

Laminar flow

A

Plug or parabolic

Plug flow
Layers travel at same speed

Parabolic flow
Layers travel at individual speeds, highest in the center of the lumen

205
Q

Turbulent flow

A

Chaotic flow in many directions and speeds

Associated with cardiovascular pathology and increased velocities (ex stenosis)

*Turbulence may be identified as doppler spectral broadening

Vortex- swirling pattern

Eddy currents- turbulent flow

206
Q

Reynolds number

A

A unitless number, indicating whether flow is laminar or turbulent

Reynolds #. Flow
Less than 1500 Laminar
Between 1500 and 2000 ????
Greater than 2000 Turbulent

207
Q

Bernoulli’s principle

A

Law of conservation of energy

Describes the relationship between pressure (potential energy,) and flow
(kinetic energy)

208
Q

Doppler shift
Or
Doppler frequency

A

a change or difference in the frequency of sound as a result of motion between the sound source and the receiver.

Greater velocities create greater Doppler shifts.

*difference between received and transmitted frequencies»

positive/ change (or shift) when source and receiver are approaching each other. Reflected frequency is higher than transmitted.*

negative/ change when the source and receiver are moving apart. Reflected frequency is less than transmitted frequency.

*doppler measures frequency shift not amplitude

Units- Hertz, cycles per second

Values- * 20 Hz - 20kHz *audible
Created when sound reflects off of moving red blood cells

We still use 2 MHz to 10 MHz transducers to perform a
Doppler ultrasound study. but the change in frequency (Doppler shift) ranges from 20-20,000 Hz.•

Demodulation extracts the Doppler frequency from the transducer frequency and is performed by a demodulator. Bidirectional Doppler is analyzed with phase quadrature processing.

Doppler shift = received frequency - transmitted frequency

209
Q

Doppler Equation
***

A

Doppler shift =
2 x reflector speed x incident frequency x cos (angle)
—— Divided by ———
Propagation speed

*** in order to accurately determine velocity, the angle between the directions of flow and sound beam must be known 

210
Q

Doppler shift is directly related to the……
**

A

Blood cell speed
Transducer frequency
Cosine of the angle between flow and the sound beam

211
Q

Doppler shift is inversely related to…
**

A

The speed of sound in the medium

212
Q

What does the 2 in the doppler equation represent?

A

In clinical Doppler, there is a double Doppler shift. The first occurs when the sound strikes the blood cell. The second shift results from sound wave, reflecting off of the moving blood cell and returning back to the transducer. 

213
Q

Speed versus velocity

A

*Doppler measures velocity not speed

Speed/ magnitude only
Velocity/magnitude and direction *

Doppler frequency depends on direction. The magnitude of shift depends upon the cosine of the angle between the sound being in the direction of motion.

You need to know the angle to accurately evaluates velocity

Equation -
Velocity (measured)=
True velocity x cos (angle)

Angle Cosine
0° 1 (100% of the info parallel)
60° 0.5
90° 0

Maximum doppler shift at 0°
No Doppler shift at 90° 

214
Q

Continuous wave Doppler

A

Two crystals in the transducer
> one crystal is continuously transmitting
> the other is continuously receiving

Advantage/high velocity is our accurately measured.*

Disadvantage/echoes arise from entire length of overlap between the transmit and receive beams called range ambiguity (doesn’t focus on specific area.)

Range means depth

CW can be thought of as a ‘Jet Sniffer’

215
Q

Pulsed wave doppler

A

One Crystal, alternates between sending, and receiving *

Echoes arise only from the area of interrogation, the sample volume or gate. We locate the gate.(center of the lumen, parallel to vessel walls.)*

Disadvantage/aliasing, errors in measuring high velocities

And imaging and pulse Doppler can be performed with a single Crystal transducer

Simultaneous Imaging and Doppler is known as duplex, ultrasound

Axes-
>the horizontal axis (or X axis, side to side) of a doppler spectrum is time.
> the vertical axis (or Y axis, up and down) of a Doppler spectrum is Doppler shift or velocity.

216
Q

Aliasing

A

High velocities appear negative. With pulse Doppler, high velocity, measurements are inaccurate if the pulsed doppler sampling rate, the PRF, is too low in comparison to measured Doppler shift.

Aliasing grows from top or bottom, never from the baseline

Wrap around aliasing / with extremely high velocities

High frequency transducers tend to show aliasing

217
Q

Nyquist frequency

A

The doppler frequency at which aliasing occurs, equal to half the PRF

Equation-
Nyquist limit (kHz) = PRF/2

218
Q

Eliminating aliasing

A

1) use CW doppler (CW has no aliasing)
2) use a lower frequency transducer/ it reduces the doppler shift & shrink the spectrum
3) select new view with shallower sample volume (this increases PRF & nyquist limit)
4) increase the scale
5) baseline shift (move baseline)

*when the transducer frequency is halved, the measured doppler shift is halved

*the calculated velocity will be the same regardless of the transducer’s frequency

perform doppler at angles closer to 90°

219
Q

Relationship between sample volume size and Doppler spectrum
**

A

Smaller sample volumes create doppler spectra with cleaner spectra window

Larger sample volumes create Doppler spectra with filled in spectra (spectral broadening)

220
Q

Gray shades on a Doppler spectrum are related to:

*

A

Amplitude or strength of the reflected signal

Or

Concentration of blood cells creating the reflection

221
Q

Pulsed vs cw

Imaging vs doppler

A

Pg 124

See picture chart

222
Q

Color Doppler is based on pulsed ultrasound and is subject to:

A

Range resolution, or specificity*
Aliasing *

223
Q

Color Doppler provides information regarding :

A

Flow direction

224
Q

Average or mean velocity

A

Color flow measures mean velocities (average)

Pulsed and CW space Doppler measures. Peak velocity is.

225
Q

Color Maps

A

Top color/ always flow toward or closer to the transducer

Bottom color/ always flow away from the transducer

Velocity mode/colors on map do not vary side to side

Variance mode/ colors on map very side to side

226
Q

No color in a vessel

A

The vessel is without color due to 90° incidence between sound being and flow

The cosine of 90° zero

227
Q

Flow directions with color/sector probe

A

For a sector shaped image, look at the map. The flow direction is always from the top color to the bottom color.

What is the vertical black line in the center of the vessel on a sector image?
No Doppler shift because a normal incidence

228
Q

Velocity & Variance mode

A

Velocity mode/ colors show information on flow direction

Variance mode/ colors show information on flow direction AND the presence or absence of turbulence
Left side-laminar or parabolic (normal)
Right side-turbulent or disturbed (pathology)

229
Q

Doppler Packets

A

Multiple pulses are called a packet, or ensemble length

Small packets-
Less accurate doppler
Less sensitive to slow velocity or low flow
High frame rate, improved temporal resolution

Large packet-
More accurate doppler
More sensitive to fast velocity or flow
Lower frame rate, reduced temporal resolution

Advantages-
Greater accuracy of velocity measurements
Sensitivity to low flows

Disadvantages-
More time to acquire information
Frame rate and temporal resolution are reduced

The packet size must balance between accurate velocity measurements and temporal resolution

Color doppler measures mean velocity

** color flow measures mean velocity

**pulsed and CW measures peak velocity

230
Q

Color power doppler

A

Energy mode, color angio

Direction and velocity are not calculated.

Any measured doppler shift is simply colorized without consideration of direction or speed

Advantages-
*increased sensitivity to slow flows (venous flow, small and deeper vessels)
*angle independent, not affected by doppler angles, unless the angle= 90°
no aliasing

Limitations-
*low frame rates, poor temporal resolution
No information on velocity or direction

231
Q

Roles for doppler modalities

A

CW doppler- identifies highest velocity anywhere along length of ultrasound beam

PW doppler- accurately identifies the location of flow (range resolution)
Has good temporal resolution.

Color flow doppler- provides 2-D flow information directly on anatomic image.

Power mode doppler- greatest sensitivity. Allows the use of color with low velocities or small volumes of blood flow

232
Q

Spectral analysis

A

Spectral analysis is performed to extract or identify the individual frequencies making up the complex signal. It is used to interpret individual velocities in the signal.

*Techniques:
Pulsed and CW doppler= fast fourier transform (FFT)
Color flow- autocorrelation or correlation function

*both FFT and autocorrelation are digital techniques that are performed by computers

  • Autocorrelation used for color doppler
    -determines average velocities
    -used for variance mode (pg128)
233
Q

Doppler artifacts
Using the wall filter

A

*Also known as high pass filter

Wall filters serve as a reject for doppler. Removed low level doppler shifts around the baseline.

*rejects clutter

Increasing scale will eliminate clutter

*Wall filter may eliminate end diastolic flows from the spectral display, since they are the lowest velocities

234
Q

Cross talk

A

Found in spectral doppler only

“Mirror image”

Causes-
Doppler gain set too high
Incident angle near 90 degrees when flow is at focus

235
Q

What feature does pulsed wave Doppler have that continuous wave Doppler does not?

A

Pulsed wave Doppler has a receive gate that is adjusted by the sonographer.

236
Q

*hyperechoic

A

Tissues that appear brighter than normal

“Brighter”

237
Q

Hypoechoic

A

Tissues that appear less bright than normal

238
Q

Anechoic

A

Without echoes

239
Q

Isoechoic

A

Equal echo brightness

240
Q

Homogenous

A

Similar echos

241
Q

Heterogeneous

A

Different echos within the image

242
Q

Artifacts

A

Reverberations-
Multiple equally spaced
Parallel to the sound beam
Appears like a ladder
Created when ultrasound ping-pongs between reflectors

Comet tail or ring down -
Single, solid, hyperechoic line
Parallel to sound beam

Shadowing -
Shadow is background color (too few reflections on the scan)
Too much attenuation
Hypoechoic or anechoic region beneath
Absence of true anatomy on scan in the region of the shadow
Parallel to sound beam

Edge shadow or shadowing by refraction -
Eliminated by spatial compounding *
Hypoechoic color
Often along the edge of a curved reflector

Enhancement -
Results from too little attenuation in the structure above the artifact
Hyperechoic

Mirror image -
Extra reflections on the skin
Artifact located deeper than the true reflector

243
Q

Propagation speed errors

A

*Speed errors appear as a step off, split, or cut

When speed is faster than soft tissue / reflector beneath will be placed to shallow on the display

When speed is slower than soft tissue/ reflector beneath will be placed too deep on the display

Fat/ sound travel slower than 1540 ms in fat. Reflectors beneath that may be placed too deep on the display.



244
Q

Refraction artifact

A

Cannot identify refraction artifact from true anatomy with a single static image

-Artifact appear side-by-side with the true anatomic structure
-Sound can change direction or bend while transmitting
-Occurs with oblique, incidence and different speeds

Degrades lateral resolution

245
Q

Side lobes and grating lobes

A

-Artifact appearance, side-by-side with the true anatomic structure
-occurs when reflections arise from off axis sound

  • mechanical transducers create side lobes
  • array transducers create grading lobes
  • grating lobes can be reduced by dividing each element into even smaller pieces. This is called subdicing.

Grading lobes are further reduced by exciting the sub diced elements with different voltages. Center of the sound beam are excited with high voltages and outer most further away from the center. Excited with low voltage is. This is called apodization, which reduces lobes.

  • lobe artifacts, degrade lateral resolution

With lobe artifact, the assumption that reflections arise from the beams, main axis are violated

246
Q

Slice thickness

A

Slice thickness, artifact occurs when beam has a greater width than the reflector
This is called elevational resolution

Phil and I have an anatomic structure is called partial, volume artifact, or section thickness, artifact

*Generally, linear array transducers, have poor, elevational resolution

247
Q

Speckle

A

*Grainy appearance

  • created by interference effects of the scattered sound



248
Q

Range ambiguity artifact

A

Created by reflection from structure, located deeper than the maximum imaging depth

Fixed by changing depth

249
Q

Doppler phantom

A

Tests flow

Used to assess the accuracy of pulsed, continuous wave and color flow systems

Vibrating string and moving belt phantoms maybe used to evaluate dollar systems

250
Q

Sensitivity performance measures

A

When adjustments make changes in display or echo brightness from scarcely visible to fully saturated, sensitivity is being assessed

251
Q

Organizations

A

SDMS/society of diagnostic medical sonographer’s
-Assists in acquisition of data
* acquires, and reviews data

OSHA / occupational safety, and health administration
-Regulatory agency
* regulates

252
Q

Measuring the output of ultrasound machines

A

Hydrophone/a small needle with a Piezoelectric crystal at the end. Measures the pressure in a sound beam.

Calorimeter/a transducer that turns acoustic energy into heat

Thermocouple/ a small device and better in absorbing material. The intensity at specific locations are measured.

** the exam duration is the greatest way to decrease exposure

253
Q

In-VIVO and in-Vitro

A

In VIVO- in the natural setting
In vitro- anything else; literal meaning in glass

Difficult to study in vivo(living tissues) due to absorption, scattering, and reflection

254
Q

Dosimetry

A

The science of identifying, and measuring those characteristics of an ultrasound field, which are especially relevant to its potential for producing biological affects

255
Q

AIUM

A

American Institute of Ultrasound in medicine

Evaluates science

256
Q

FDA

A

Food and drug administration

Regulates

257
Q

Bioeffects intensity limit-

A

SPTA

100mW/cm squared unfocused
1,000mW/cm squared focused

258
Q

Study techniques

A

Mechanistic approach/
Identify “cause-effect” relationship

Empirical approach/
Identify “exposure-response”. relationship

259
Q

Thermal mechanism

A

Tissues/bone is an absorber

Fetal tissues/fetal soft tissues adjacent to bone are of great concern/greater harm than adults

SPTA/related to tissue heating

Any exam that causes the temperature elevation two greater than 41°C is considered potentially harmful to a fetus

Thermal index is a number proposed in the most recent AIU, and guidelines that relates to tissue
Heating

260
Q

Non-thermal (cavitation) mechanism

A

Gaseous nuclei/ microbubbles

Mechanical index/a number proposed in the a RUM guidelines that relates to cavitation
Higher with peak rarefaction pressure and lower frequency sound.
-Micro bubbles get bigger during the rarefactions
-cavitation is more likely to occur in lung than other tissues
Equation-
*MI=peak rarefaction pressure/freq

261
Q

Stable cavitation

A

Bubbles intercept, redirect and absorb acoustic energy.

Effects
*shear stresses & microstreaming in surrounding fluids

262
Q

Transient cavitation

A

Bubbles expand during rare factions, and the bubbles burst

TIN-
Transient
Inertial
Normal

Threshold is 10% greater than stable cavitation

Highly localized violent effects/
Enormous pressures/mechanical stress
Colossal temperatures /thousands of degrees

263
Q

Epidemiology and statistics

A

Population studies/large number of patients, clinical studies, ultrasounds

***Best study is perspective and randomized **

Limitations
Often retrospective
Ambiguities
Other risk factors, such as age nutrition Etc

Potential benefits should outweigh the risks
AIUM suggests/
Don’t perform studies without reason
Don’t prolong studies
Minimize exposure
ALARA principal - use minimum output, power, and highest game

SPI ESP (2 decks)

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