ARDMS SPI STUDY GUIDE
What is the unit of Duty Factor?
Duty Factor is Unit-less If the ultrasound is produced as a continuous wave (CW), the duty factor will have a value of 1. With Pulsed Wave the whole value of On-Time is fractioned.
What describes the percentage of time that sound is on?
Duty factor is the percentage of time the sound is being transmitted
An ultrasound transducer converts
Electrical energy into Mechanical energy and vice versa
Unexpected low attenuation results in what type of artifact?
Enhancement High attenuation is associated with Shadowing...
A study designed to determine if there is an association between an adverse effect in a population and exposure to a particular agent is a(n):
Epidemiological Study
What should you limit when the Thermal Index TI exceeds 1?
Exposure Time Exposure Time should be limited once the TI exceeds 1.
What is used to process conventional Doppler shift information but is too slow of a method for Color Doppler?
Fast Fourier transform
Lowest attenuating to highest attenuation
Fat-Muscle-Bone-Air
Mechanical Transducers utilize what kind of focusing?
Fixed Focusing: Sonographers cannot determine the location of # of foci. Mechanical Transducers use Cross-Sectional imaging, rotating wheel, wobbler, and oscillating mirror.
pressure
Force per unit area or the concentration of force
Pressure
Force per unit area or the concentration of force. Unit: (Pascals Pa) or pounds per square inch(lb/in^2)
Increasing transmit gain increases everything except:
Frequency Gain is a receiving function •Does not impact how much energy is transmitted to patient (i.e. power)
Along with crystal diameter, the divergence in the far field is also determined by...
Frequency and crystal diameter determines the divergence in the far field
How do you calculate the speed of a wave given the wavelength and frequency?
Frequency (Hz) x wavelength (distance)= Wave Speed
Spatial pulse length is inversely proportional to
Frequency (MHz) (Inversely Proportional means that increased SPL will lower frequency. This is because axial resolution is better with lower frequency)
What color is usually used in Color Flow Doppler variance map to indicate turbulent flow?
Green
Half Intensity Depth is also called
Half-Value Layer Thickness
Mechanical Transducers:
Have moving parts Uses a motor to steer the beam Most transducers are no longer mechanical May be focused with a lens or phased focuses
What is HIPPA? What does it do?
Health Insurance Portability and Accounting Act, which protects the privacy of individually identifiable health information. According to HIPAA, patients have a right to: • See and copy their health record • Update their health record • Get a list of the disclosures that a health care institution has made independent of disclosures made for the purposes of treatment, payment, and health care operations • Request a restriction on certain uses or disclosures • Choose how to receive health information Reviewing your neighbors US scan, in the PACS system would violate HIPPA compliance.
What potential bio effect occurs through absorption of sound energy by tissue?
Heating Why? Sound attenuation in tissue is primarily due to absorption a conversion of ultrasound to heat.
Frequency is measured in
Hertz (Hz) is Cycles per Second Not affected by sonographer Increase Frequency; Decrease Depth or axial focus
The Doppler wall filter is considered a:
High Pass Filter
Higher Frequency=
High resolution with poor penetration Shorter Wavelength
What would you do to create a wave with the highest possible intensity?
Highest intensity would occur with a short distance and low frequency.
A nosocomial infection is defined as one that is?
Hospital Acquired Avoid Nosocomial Infections by: -Wearing New Gloves with Each Exam -Wash Hands -Clean probe -Disinfect the probe using a germicide compatible with the transducer is indicated when the probe is in contact with mucous membranes.
Distance
How far apart objects are AKA vibration or displacement
When will a reflection occur at the boundary of two media?
If the acoustic impedances of the tow media are different.
Along with image depth, which of the following also determines the frame rate?
Image depth and the number of lines per frame determines the frame rate.
Imaging transducers have
Imaging transducers have low quality factors and wide bandwidiths.
An increase in red blood cell velocity will____________Doppler Shift:
Increase increase in rbc velocity increases Doppler shift
What is the best way to increase the near field length of an ultrasound beam?
Increase Transducer Diameter
Increased tissue heating could occur when you
Increase transmit power
What will increase the color flow jet area displayed?
Increasing Color Gain
During performance of an obstetric ultrasound exam, you adjust the system parameters to improve the image. What parameter of sound would increase acoustic exposure?
Increasing Transmit Power
An increase in pulse repetition frequency would lead to:
Increasing pulse repetition frequency, increases duty factor. ↑ PRF ↑ Duty Factor
Power/Area=
Intensity
Decibles is the measure for
Intensity of Sound
Frequency and Wavelength are:
Inversely related
Which artifact is not related to the unexpected reflection of an acoustic sound?
Lateral Resolution
Which transducer fires the elements in groups?
Linear sequenced array fires the elements in groups
A sound pulse travels from the transducer to location A, reflects off of it, and returns to the transducer in 130 μs. How deep is location A?
Location A is 10 cm from the transducer Total travel distance would be 20 cm
Which has the Slowest Propagation Speed? Water Soft Tissue Bone Lung tissue
Lung Tissue
Density
Mass per unit volume
Density
Mass per unit volume Unit: (Kilograms per centimeter cubed (Kg/cm^3)
What type of wave is sound?
Mechanical and Longitudinal Wave
What type of wave is sound?
Mechanical and Longitudinal wave
Propagation speed is determined by
Medium only - density and stiffness of media Bulk Modulus describes the change in the material's volume under external stress.
Which of the following lists is in decreasing order?
Mega, kilo, deca, milli, nano
Micro is denoted as:
Micro is denoted as millionth (µ)
In an unfocused transducer, what is the region between the transducer face and the point where the beam diverges?
Near Field
Inertia
Newton's principle that states that an object at rest stays at rest and an object in motion stays in motion, unless acted on by an outside force.
Does Beam Width directly affect frame rate?
No: The following directly affect frame rate: Depth of Penetration Field of View Number of Focuses and Line Density
What is a reflection arising from a rough boundary?
Non-specular Specular reflection is from a smooth reflector (like mirrors). They return in one direction. Whereas, non-specular is diffuse or scatter, reflection from a rough boundary.
The Nyquist Limit is equal to:
PRF/2 Pulse Repetition Frequency divided by two
What is the highest Doppler shift that can be detected in pulsed wave Doppler without aliasing?
PRF/2 aka Nyquist Limit The maximum Doppler shift frequency equals one-half the sampling rate, given by the Doppler PRF. ... As the depth of interest is increased, the maximum reflector velocity that can be measured is decreased. Importantly, a low-frequency transducer allows higher velocities to be detected.
When the sonographer changes the imaging depth what parameters are changed?
PRP, PRF, Duty Factor
Which of the following would most likely have the highest SPTA value?
PW Doppler
Pressure is typically expressed in:
Pascals (Pa)
Lower Frequency=
Poor resolution with deeper penetration Longer Wavelength
A hydrophone measures...
Pressure Amplitude and Duty Factor
Attenuation denotes
Progressive weakening of the sound beam as it travels
The correct depth placement of reflectors depends primarily upon:
Propagation Speed
"PHI" means
Protected Health Information
Increasing the wall filter during doppler sampling will...
Reduce display of low frequency shifts
The Angle of Incidence
Refers to the angle of deviation from a perpendicular line to the surface of the tissue Therefore, the desired orthogonal(perpendicular) incident wave in ultrasound should be considered to have an angle of incidence of zero. When the angle of incidence is greater, fewer sound waves are reflected back to the transducer resulting in a more hypoechoic (darker) image with less clarity. The optimal reflection with the most sound waves occurs when the angle of incidence approaches zero and is virtually perpendicular (orthogonal) to the tissue of interest.
When time-of-flight is measured, we can determine the ________?
Reflector Depth
Non-specular Reflectors
Reflectors that are smaller than the wavelength of the incident beam
What is least likely to cause Attenuation?
Refraction, because absorption, reflexion, and scattering will happen naturally and cause bits of attenuation, but refraction usually stays the same in soft tissue.
Directly Related
Relationship that implies that if one variable decreases, the other also decreases or if one variable increases, the other also increases; also referred to as Directly Proportional
Inversely Related
Relationship that implies that if one variable decreases, the other increases or if one variable increases, the other decreases; also referred to as inversely proportional
In soft tissue, if the frequency of a wave is increased the Propagation Speed (PS) will...
Remain the Same because stiffness and density affect Propagation Speed.
Multiple echoes, equally spaced originating from a gas bubble is called
Ring Down
Which of the following has the lowest intensity
SATA is the lowest of the intensities because average intensities have the lowest value
The most relevant intensity with respect to tissue heating
SPTA, PW has the highest SPTA.
The rank of intensities from largest to smallest is
SPTP > Im > SPPA > SPTA > SATA
Highest intensity value is?
SPTP- Spatial Peak Temporal Peak because PEAK measurements are more intense than Average measurements
Backscatter
Scattered sound waves that make their way back to the transducer and produce an image on the display
The most common type of transducer used in echo is:
Sector Phased Array
What term is defined as the body's pathologic response to illness, trauma or severe physiologic or emotional stress?
Shock
A strongly focused transducer implies a:
Short focal length and Increased Beam Divergence
What describes the physics of refraction mathematically?
Snell's Law
What describes the amount of refraction that occurs at an interface?
Snell's law Refraction: the redirection of the transmitted sound beam Snell's law describes the angle of transmission at an interface based on the angle of incidence and the propagation speeds of the two media.
Continuous Wave
Sound that is continuously transmitted
Ultrasound
Sound waves of frequencies exceeding the range of human hearing 20-20,000Hz
Ultrasound
Sound waves with frequencies above 20,000 Hz.
The speed of sound in soft tissue is
Speed of sound in soft tissue is 1540 m/s
the ability of an object to resist compression and relates to the hardness of a medium?
Stiffness. Think: ↑ Stiffness ↑ Speed ↓ Density ↑ Speed
Capacitive Micromachined Ultrasound Transducers
Technology used to create comparable transducer technology to piezoelectric materials
Which type of resolution is an accurate representation of moving structures?
Temporal resolution, also known as frame rate, is the ability to display moving structures in real time.
What is Q-factor or Quality Factor?
The "Q factor" describes the bandwidth of the sound emanating from a transducer Transducer Q Factor (Q = Quality) is associated with two characteristics of the crystal • purity of their sound and • length of time the sound persists (Unitless measurement) Fundamental Frequency(Hz)/Bandwidth(range of frequency in the pulse)
Pulse duration is determined by
The Sound Source only, not by the medium through which the sound travels. Pulse Duration is the time it takes for one pulse to occur.
Elasticity
The ability of a material to bounce back after being disturbed
Axial Resolution
The ability to accurately identify reflectors that are arranged parallel to the ultrasound beam
Pulse Duration (PD)
The actual time from the start of a pulse to the end of that pulse; a single transmit, talking, or "on" time. Time the pulse is on typically measured in (ms).
What type of transducer that utilizes elements arranged in a concentric pattern?
The annular array transducer ultilizes elements arranged in concentric rings
Refraction
The change in direction of the transmitted sound beam that occurs with oblique incidence angles and dissimilar propagation speeds.
Which of the following is the part of the transducer that stops the ringing of the element?
The damping material helps stop the ringing of the transducer
Wavelength
The distance between two corresponding parts of a wave
Pulse Length
The distance of the pulse start to end or the duration or length of a single pulse Pulse Length is typically measured in (mm).
Spatial Pulse Length (SPL) (measurement)
The distance that a pulse occupies in space from the start to the end of a pulse. (mm)
Interface
The dividing line between two different media
Aliasing is a potential problem in PW Doppler because of...
The doppler signal is sample rather than recorded continuously Aliasing only happens with PW Doppler. The reason why is because CW Doppler is talking and listening 100% of the time.
Which of the following would be considered the narrowest part of a sound beam?
The focus is the narrowest part of the beam
Wavelength
The length of a single cycle of sound
What does the mechanical index indicate on an ultrasound system?
The likelihood of cavitation during an ultrasound exam
What transducer would be considered an advantage of linear array over a phased array transducer?
The linear array has a wider near field of view compared to a phased array transducer
Amplitude
The maximum or minimum deviation of an acoustic variable from the average value of that variable; the strength of the reflector
Frequency (Hz)
The number of cycles per second
Pulse Repetition Frequency
The number of pulses that an ultrasound system transmits into the body each second. Unit: Hz. Typically 4-15 KHz. PRF and Depth of View are inversely related. When the system is imaging deeper, the pulse repetition frequency is lower, as well as, the number of pulses created each second.
You are performing a sonographic examination and notice that the TI reading is 1. What does this indicate?
The output level is high enough that temperature could increase as much as 1°C if the transducer were held stationary is a 1 TI reading.
Intensity Reflection Coefficient (IRC)
The percentage of sound reflected at an interface. The percentage of the sounds intensity that is reflected when sound hits a boundary or tissue Interface is the dividing line between 2 different media.
Intensity Transmission Coefficient (ITC)
The percentage of sound transmitted at an interface -or- The percentage of intensity that continues forward after beam strikes an interface
Duty Factor
The percentage of time that sound is actually being produced
Scattering
The phenomenon that occurs when sound waves are dispersed into different directions because of the small reflector size compared with the incident wavelength
Damping
The process of reducing the number of cycles of each pulse in order to improve axial resolution
Attenuation Coefficient
The rate at which sound is attenuated per unit depth
Beam Uniformity Ratio
The ratio of the center intensity to the average spatial intensity; also referred to as the SP/SA factor or beam uniformity coefficient
Snell's Law
The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for a given frequency. Law used to describe the angle of transmission at an interface based on the angle of incidence and propagation speeds of the two media
Beam Properties
The ultrasound beam propagates as a longitudinal wave from the transducer surface into the propagation medium, and exhibits two distinct beam patterns: - a slightly converging beam out to a distance specified by the geometry and frequency of the transducer (the near field), and - a diverging beam beyond that point (the far field).
The transducer frequency is primarily determined by the transducer element's what?
Thickness For pulsed transducers..the main or center frequency of the transducer is determined by the thickness and the propagation speed of the piezoelectric material.
Duty factor describes the relationship of beam intensities with what?
Time DF is unitless with a value between 0 and 1 0=off 1=on
Period is measured in
Time (μs)
Intensities may be reported in various ways with respect to
Time and Space
Unit of measurement for Pulse Duration, Duty Factor, PRP, and Period
Time, (μs)
Absorption is a sound parameter that relates to....
Tissue Heating
A 3MHz sound beam travels through two media. It attenuates 5 dB in medium A and 6 dB in medium B.
Total attentuation is 11 dB Attenuation simply adds up as sound travels.
Which gain will increase the risk of bioeffects?
Transmit
Which instrument control affects the amplitude (db) of the outgoing signal?
Transmit Gain; Amplitude can be affected by the sonographer
PRP is determined by
Transmit time and receive time.
Spectral Broadening Suggests
Turbulent Flow
A 3 dB gain would indicate an increase in intensity by:
Two Times 3 dB results in doubling of intensity (or power)
The frequency ranges for ultrasound are:
Ultrasound frequency is 20 to 20,000 Hz
The unit of duty factor is:
Unitless
To practice the ALARA principle, what technique should you employ?
Use the lowest transmit power that allows adequate tissue visualization. USE HIGH GAIN and low transmit power to best practice ALARA.
To minimize the risk of biologic effects of ultrasound to the fetus, which imaging mode tradeoff is used?
Using M-mode instead of pulsed-wave Doppler to measure the fetal heart rate.
What action should the sonographer take when receiving a verbal order for an exam?
Verbally repeat the order back to the referrer to verify the correctness.
If frequency doubles, what happens to the wavelength?
Wavelength is decreased by 1/2
What is described as the distance over which one cycle occurs?
Wavelength is distance over which one cycle occurs, or the distance from the beginning of one cycle to the end of the same cycle. Remember, it asks for distance over which one cycle occurs.
The units for wavelength is
Wavelength units are (Millimeters)
Sound wave can be described by five characteristics
Wavelength, Amplitude, Time-Period, Frequency and Velocity or Speed.
Longitudinal Wave
Waves in which the molecules of the medium vibrate back and forth in the same direction that the waves are traveling.
Enhancement is caused by
Weakly attenuating structures
C: Complete the diagnostic scan in a timely fashion at the lowest output power that achieves a quality image.
What action below would be most in keeping with the ALARA principle while performing a diagnostic ultrasound examination? A: Allow multiple students to scan an obstetrical patient because the fetus is in a good position for imaging. B: Prolong the sonogram to make videos of the fetus for each family member. C: Complete the diagnostic scan in a timely fashion at the lowest output power that achieves a quality image. D: Maximize the acoustic output to brighten the overall image. E: Extend the sonogram beyond the intended scope of the exam requisition.
Clinical imaging transducers are:
Wide bandwidth; Low Q factor Wide range of frequencies in the pulse and short period of time that the sound is emitted (pulsed wave)
Hydrophone
a device used to measure the output intensity of the transducer
Piezoelectric Materials
a material that generates electricity when pressure is applied to it, and one that changes shape when electricity is applied to it; also referred to as the element or crystal
Scientific Notation
a method of expressing a quantity as a number multiplied by 10 to the appropriate power
What has the lowest propagation speed?
air technically has the lowest propagation speed at 300 m/s
Increasing Propagation Speed
air: 330 m/sec fat: 1450 m/sec water: 1480 m/sec soft tissue: 1540 m/sec liver: 1550 m/sec kidney: 1560 m/sec blood: 1570 m/sec muscle: 1580 m/sec bone: 4080 m/sec
For continuous wave ultrasound the beam is
always on and the pulse average and temporal average intensities are the sameSPTA = SPPA and SATA = SAPA
oblique incidence
angle of incidence is less than or greater than 90° to the interface
The range for ultrasound begins:
at 20,000Hz or 20KHz (Useful Frequency Range for Clinical Imaging is 2MHz-10MHz)
Ultrasound pulses contain a range of frequencies called
bandwidth
What is the range of frequencies produced by a dampened PZT element?
bandwidth
Diagnostic Ultrasound
between 2 and 15 MHz (or higher) Mega M- Million 10^6 2,000,000-15,000,000Hz
Audible Sound
between 20 Hz and 20 kHz
Giga (G)
billion 10^9
The different measurements of intensities are important in the study of
bioeffects
Lowest attenuation to highest
bone, muscle, fat, air
Acoustic Variables
changes that occur within a medium as a result of sound traveling through that medium
path length
distance to reflector
Doppler Shift =
doppler shift = reflected frequency - transmitted frequency
The ____ of a wave is the number of wavelengths that pass a fixed point in a second.
frequency Frequency is the number of wavelengths that pass a fixed point in a second
A Doppler (high pass filter) eliminates?
high amplitude signals, low velocity flow
hecto (h)
hundred 10^2
centi (c)
hundredth 10^-2
How is time related to frequency
inversely
Wavelength and Frequency are
inversely proportional to each other
Infrasound
less than 20 Hz
Greatest attenuation would occur at:
long distance with high frequency
Lowest Attenuation is found at
lowest frequency, with the shortest path length.
Mega (M)
million 10^6
What results in the most attenuation?
most attenuation occurs at the high frequency and long distance.
A period is the length of time it takes for
one complete wavelength to pass a fixed point
Acoustic Variables
pressure, density, distance
Pulse Duration Formula
pulse duration (μs) = # cycles in pulse/frequency(MHz) PD= Number of cycles in Pulse/ Frequency(Hz)
What is bandwidth?
range of frequencies in a pulse
Specular Reflections
reflections that occur when the sound impinges upon a large, smooth reflector at a 90° angel
Rayleigh scattering
small scattering reflectors
Spatial pulse length is determined by
sound source and medium
pulsed wave
sound that is sent out in pulses
Deca (da)
ten 10^1
Spatial Pulse Length is directly proportional to
the Number of Cycles in the Pulse and the Wavelength (Directly Proportional means that increased SPL will increase both the number of cycles in the pulse and the wavelength if increased).
Pulse Duration (PD)
the actual time from the start of a pulse to the end of that pulse. Time during which the sound is actually being transmitted.
Law of Reflection
the angle of incidence is equal to the angle of reflection
The most sensitive structures of developing fetus with regards to cavitation are:
the brain, the eye, the lung and bone-tissue interfaces.
Half-Intensity Depth
the depth at which sound has lost half of its intensity
Spatial Pulse Length
the distance that a pulse occupies in space from the start to the end of a pulse. Length of a pulse
Reflection
the echo; the portion of sound that returns from an interface.
rate
the fixed quantity owed as the sound beam travels through tissue (related to attenuation)
normal incidence
the incident sound beam strikes the boundary at exactly 90 degrees
Acoustic Speckle
the interference pattern caused by scatterers that produces the granular appearance of tissue on a sonographic image
The mechanical index (MI) is a value that attempts to quantify...
the likelihood of cavitation by an ultrasound beam This value is readily displayed on the ultrasound screen and it is recommended that it is kept below 1.9 to remain safe.
particle motion
the movement of molecules due to propagating sound energy
pulse repetition frequency
the number of pulses that an ultrasound system transmits into the body each second
What is duty factor?
the percentage or fraction of time that the system transmits a pulse[PDxPRF] The actual time from the start of a pulse to the end of that pulse.
Intensity
the power of a wave divided by the area over which it is spread; the energy per unit area
The spatial pulse length is defined as:
the product of the wavelength and the number of cycles in a pulse? SPL = wavelength x cycles
Power
the rate at which work is performed or energy is transmitted
Impedence
the resistance to the propagation of sound through a medium.
The intensity of the ultraosund beam is usually greater at the focal zone because of
the smaller beam diameter
The beam uniformity coefficient (SP/SA factor) describes
the spread of a beam in space, it is unitless, with a value of 1 or greater
period
the time it takes for one cycle to occur
total attenuation
the total amount of sound (in dB) that has been attenuated at a given depth
Pulse Duration is controlled by
the ultrasound system and transducer
kilo (k)
thousand 10^3
milli (m)
thousandth 10^-3
propagate
to transmit trough a medium
transverse waves
type of wave in which the molecules in a medium vibrate at 90° to the direction of travel
propagation speed
v = fλ the speed at which a sound wave travels through a medium.
All intensities have are measured in what units?
watts/cm²
Enhancement is caused by:
weakly attenuating structures
Using Gain Does Not:
-Increase Tissue Heating (no) -Increase Risk of Cavitation(heating)no -Cause Fluid Particle Streaming (Gas heating) no -Increase Sound Absorption (heating) no
Typical values for spatial pulse length in soft tissue.
0.1 to 1.0 mm
What is the speed of a wave with a wavelength of 3 m and a frequency of .1 Hz?
0.3 m/s wave speed= frequency x wavelength
The wavelength in a material having a propagation speed of 1.5 mm/µs employing a transudcer frequency of 5.0 MHz is:
0.3 mm wavelength = c/f 1.5 mm/µs / 5 MHz = 0.3 mm
How many meters is 1000mm
1 meter
The typical range of frequency for diagnostic ultrasound imaging is
1-20 Mhz is the typical range of frequency for diagnostic ultrasound imaging.
Parameters of Sound
1. Frequency 2. Period 3. Amplitude - "bigness" 4. Intensity - "bigness" 5. Wavelength 6. Power - "bigness" 7. Propagation Speed
What are the four acoustic variables?
1. Temperature 2. Density 3. Particle Motion 4. Pressure
Propagation Speed in SOFT TISSUE
1.54 mm/μs (1540 m/sec)
Continuous wave Doppler has a duty factor of
100% CW Doppler is always transmitting sound making it's duty factor 100%
How many mm is 1 cm
10mm
The speed of sound in soft tissue:
1540 m/s
What is the speed of a wave with a frequency of 2 Hz and a wavelength of 87 m?
174 m/s 2Hz x 87m= 174m/s speed of a wave: frequency x wavelength
What is the audible range?
20-20,000Hz >20,000Hz=Ultrasound
A sound wave is traveling in the body and propagates from muscle to air. What percentage of the sound wave is most likely reflected at the muscle-air boundary?
75%
Attenuation
A decrease in the amplitude and intensity of the sound beam as sound travels through tissue. When the ultrasound beam travels through the tissues there is some energy loss. This loss is called attenuation.
sound
A disturbance that travels through a medium as a longitudinal wave A traveling variation in pressure
What will decrease beam divergence in the far field?
A large crystal diameter and high frequency would decrease the beam divergence in the far field
will increase the near zone length?
A large crystal diameter with high frequency would increase the near zone length
Parameter
A measurable quantity Can be described as Directly Related or Inversely Related One Parameter can affect the other ex.
Hertz (Hz)
A unit of frequency
Decibels
A unit that establishes a relationship or comparison between two values of power, intensity, or amplitude
What term and philosophy relates the amount of exposure time for the sonographer and patient during a diagnostic ultrasound examination?
ALARA - As Low As Reasonably Achievable
stiffness
Ability of a tissue to resist a load Greater stiffness = greater magnitude load can resist The ability of an object to resist compression and relates to the hardness of a medium
The primary advantage of CW Doppler is:
Absence of Sampling Rate
The conversion of sound energy to heat
Absorption
The thermal index is most affected by which type of interaction between sound and tissue?
Absorption Absorption is responsible for tissue heating and SPTA is also associated with tissue heating. ALARA operates off of not increasing the tissue heat over 1 degree Celsius to be within diagnostic and medical limits.
Which operator control most directly adjusts the intensity of the transmitted pulse?
Acoustic Output (Transmit) Power Pulse repetition frequency PRF can also affect the intensity, specifically the I(SPTA), because it affects the duty factor. DF= the percentage or fraction of time that the system transmits a pulse[PDxPRF]
The motion of particles in a fluid is sometimes observed in an intense ultrasound beam. This is termed
Acoustic Streaming Acoustic streaming is defined as an acoustically generated transport of fluid within the body of insinuated fluid tissue. This mechanical interaction of tissue and sound, where the beam literally pushes the medium. If the medium is a fluid and fluid is free to move, or if particles in the medium are free, then they can move in directions determined by the beam and any obstacles that are present, such as interfaces
When scanning with PW Doppler adjusting PRF does what?
Affects the Acoustic Exposure
Which media has the greatest attenuation and the slowest speed?
Air Air > Bone & Lung > Soft Tissue > Water
List propagation speed from lowest to highest
Air-Fat-Muscle-Bone
B-mode displays reflector:
Amplitude and Distance
What happens to intensity if the amplitude of a signal is halved?
Amplitude halved will result in intensity quartered amplitude = intensity2
Compression
An area in the sound wave of high pressure and density
Rarefaction
An area in the sound wave of low pressure an density
Medium
Any form of matter; Solid, Liquid, or Gas
The attentuation coefficient in soft tissue is equal to:
Attentuation Coeffcient = 1/2 (one half of the frequency in soft tissue) The attentuation coeffcient (in dB/cm) is the rate at which sound is attentuated per unit depth.
What is used to convert Doppler shift information into color?
Autocorrelation
What happens to axial resolution with Pulse Wave Doppler
Axial Resolution Degrades when using Pulse Wave Doppler
Which resolution is best in the clinical imaging?
Axial resolution is best in imaging
A thermal index greater than one will cause the greatest temperature in
BONE Higher density means more absorption, which means more heating.
What is the definition of the beam uniformity ratio?
Beam Uniformity Ratio = Spatial peak / Spatial average
Which of these media has the lowest attenuation and the greatest speed? bone tendon lung fat air
Bone Air > Bone & Lung > Soft Tissue > Water Bone is more stiff than air (remember ↑ stiffness, ↑ speed)
Which of the following would have the highest propagation speed?
Bone has the highest propagation speed, at 2000-4000 m/s.
PZT is also called
Ceramic, Active Element, or Crystal
What should you do to avoid nosocomial and cross infection with sonographic probes?
Clean probe and disinfect with germicide compatible with transducer when probe is in contact with mucous membranes.
Areas of high pressure and density are referred to as:
Compressions
Which intensity parameters aren not applicable for continuous-wave ultrasound?
Continuous Wave is on 100% of the time and does not calculate a Pulse Average, so SPPA and SAPA are intensity parameters that only apply to Pulsed Wave US
Increasing wavelength will_______frequency?
Decrease
As imaging depth increases, the pulse repetition frequency (PRF) must:
Decrease As imaging depth increase, pulse repeition freqency (PRF) decreases. ↑ Imaging Depth ↓ PRF
The diameter of the beam in the Fresnel zone/near zone does what?
Decreases
What would cause an increase in frame rate?
Decreasing the imaging depthwould increase the frame rate When you decrease the imaging depth it can work faster (increase frame rate) because it doesn't have to go as deep.
What is the most common cause of localized vertical non-uniformity in real-time B-Mode images?
Defective Transducer Element... Why- When we read vertical we want to imagine the crystal being broken causing a vertical stripe from front to back of the image. This can happen along the image in different places.
The inertia of the medium describes its:
Density. Inertia is described by Newton's principle - an object at rest will stay at rest. An object in motion stays in motion, unless acted on by an outside force.
What affects frame rate?
Depth of Penetration, Field of View, Number of Focuses, and Line Density. Frame Rate= Number of Frames/Second
Snell's Law
Describes the relationship between the angles and the velocities of the waves. When an ultrasonic wave passes through an interface between two materials at an oblique angle, and the materials have different indices of refraction, both reflected and refracted waves are produced In ultrasound, Snell's Law is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant, for a given frequency.
An increase in the number of pixels on the display will improve:
Detail Resolution
What is considered the memory of an ultrasound instrument?
Digital Scan Converter
Stiffness and propagation speed are
Directly Related Also remember: ↑ Stiffness ↑ Speed ↓ Density ↑ Speed
Between ultrasound exams, what should you do with your gloves?
Discard them, sanitize hands, and apply new gloves
The unit for wavelength:
Distance (mm)
Particle Motion
Distance molecules travel in a back-and -forth motion Units: (feet, inches, centimeters, or miles)
Doppler Shift Equation
Doppler shift = 2fv cos/ c 2xTransducer Frequency x Velocity x Cosign of TD angle/ Speed of Sound in Soft Tissue (1.54mm/ms)
The percentage of time that the ultrasound instrument is emitting ultrasound is called?
Duty Factor The maximum value is 1, the minimum is 0
