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 PD/PRP x100= DF
The contrast of the display is affected by?
Dynamic Range
What do waves transfer from one location to another?
ENERGY
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
Aliasing
Exceeding the Nyquist Limit causing a wrap around artifact on triplex imaging and a blue, yellow, green duplex vessel color image. NL should be 1/2 the PRF, so to fix aliasing you should raise your scale, which raises the PRF which corrects the aliasing artifact.
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
Order of attenuation in the body
Fat<Muscle<Bone<Air Air is the highest attenuator of US, but the slowest propagation speed
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 Measured in Pascals (Pa)
Pressure
Force per unit area or the concentration of force. Unit: (Pascals Pa) or pounds per square inch(lb/in^2)
What denotes the number of cycles passing a given point each second?
Frequency
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) SPL=1/F If frequency goes down, SPL gets longer. [Think, LOW Hz= LONG WAVES] If frequency goes up, SPL gets shorter. [Think, High Hz= SHORT WAVES]
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
When you switch from a 2.5 MHz to a 5 MHz transducer the sound wavelength: A: Doubles B: Quadruples C: Halves D: Quarters E: Is unaffected
Halves Wavelength is inversely proportional to frequency
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
For better depth resolution you should use higher or lower frequency?
Higher frequency Higher frequency = Shorter wavelengths. With a short wavelength you can resolve smaller structures. Structures that are close together have to be larger than the wavelength to be resolved separately.
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.
range ambiguity
Improper placement of late echoes ( from a previous pulse) received after the next pulse is emitted. Happens when the US machine sends out too many pulses and cannot interpret them causing a misread of one pulse in the place of another when listening causing a deeper appearance of structure being reflected i.e. Range Ambiguity
The linear sequenced array fires the elements...
In groups
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
As the operator increases the maximum imaging depth the Pulse Repetition Period (PRP)...?
Increases As you image deeper you have to wait longer for the signal to come back so you send less pulses per second. So as you increase the depth you increase the time, you increase the PRP.
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 DF=Talking time, or the time the pulse is pulsing, so increasing Hz will increase the amount of pulses, which increases the time the machine is sending a signal or 'talking'
Power/Area=
Intensity
Decibles is the measure for
Intensity of Sound
Density and propagation of speed are ____ related.
Inversely Density & Stiffness are DIFFERENT!
Frequency and Wavelength are:
Inversely related
Rarefaction
Is an area in the sound wave where the molecules are spread wider apart. Be careful not to confuse rarefaction with refraction which is an attenuation artifact.
At the focus you see the best kind of what resolution?
Lateral Resolution
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
How to tell the direction of blood travel on this image Using Doppler Shift.
Locate the Positive Color and put your finger on it and move it toward the Negative Shift. This will tell you the direction of blood traveling in the vessel using the Doppler Shift.
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
Fat Attenuation & Propagation Speed...
Low attenuation and Low Speed
Which has the Slowest Propagation Speed? Water Soft Tissue Bone Lung tissue
Lung Tissue has the slowest propagation speed The lungs have the highest attenuation due to the impedance difference between tissue and air
One dimensional real time images are seen with? Hint (which mode)
M-Mode
Density
Mass per unit volume Unit: (Kilograms per centimeter cubed (Kg/cm^3)
Density
Mass per unit volume Unit: Kilograms per Centimeter Cubed
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.
Number of focal zones, line density and field of view are all related to?
Number of pulses per frame
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 are all affected by changing imaging depth.
Which of the following would most likely have the highest SPTA value?
PW Doppler
Variation in all of the following identify specific waves as acoustic waves except: Pressure, Parameter, Density, Acoustic Variables.
Parameter
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
Axial Resolution is also known as...
Radial, range, longitudinal, or depth reslolution Improved when shortening the Pulse length which happens when dampening is used in PW transducers
Brightness of the display is affected by?
Receiver amplification
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.
Amplitude, Intensity, and Power
Represent the Strength of a beam These three parameters that are adjustable Intensity and Power are directly related
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
Dampening of a sound beam decreases what?
SPL Dampening of the sound beam decreases the SPL by decreasing the number of cycles in a pulse (n).
The formula for Spatial Pulse Length is what?
SPL = # of cycles x λ (wavelength)
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
Beams traveling in a direction different from a single main beam are what?
Side Lobes Side lobes are from a single beam, grating lobes are from an array.
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.
Frequency is determined by:
Sound source only Specifically it is the thickness of the element and the propagation speed of the element that determines frequency.
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.
A reflection from a boundary where the variations on the surface are smaller than the pulse wavelength will be what type?
Specular
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 If Density increases Speed decreases
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.
Range ambiguity results from what assumption?
That the second of two echoes returning is actually the first
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)
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 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.
A side lobe artifact arises from what fact?
The Ultrasound system assumes all reflections arise from the same beam
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 a transmitted sound beam that occurs with oblique incidence and dissimilar propagation speeds.
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
What is the doppler shift?
The difference between the original pulse frequency and the returned pulse frequency.
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
If the transducer freqency is reduced by a factor of 3...?
The doppler shift will be decreased by a factor of 3 Doppler shift and frequency are proportional. Raise one you raise the other. Decrease one you decrease the other. Fd = 2 Fo v / c Fd is the Doppler shift Fo is the original frequency v is the velocity of target c is the propagation speed of interrogating beam through soft tissue
Aliasing is a potential problem in PW Doppler because of...
The doppler signal is a 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.
In which region of the beam is focusing most effective?
The far end of the near zone. This is the natural focal zone
Which of the following would be considered the narrowest part of a sound beam?
The focus is the narrowest part of the beam
Focus is what part of the beam
The highest area of intensity and the narrowest part or diameter at the focus.
Constructive Interference
The interference of a pair of in-phase waves resulting in the formation of a single wave of greater amplitude than either of its components . The resulting wave is larger than either of it component waves.
Destructive Interference
The interference of a pair of out-of-phase waves resulting in the formation of a single wave of lesser amplitude. The resulting wave is smaller than one of its component waves.
Wavelength
The length of a single cycle of sound Distance over which one cycle occurs, or the distance from the beginning of one cycle to the end of the same cycle.
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.
Compression
The part of a longitudinal wave where the particles of the medium are close together. In sound wave propagation, the region with elevated pressure is compression.
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
In the doppler equation Fd = 2 Fo v / c what does c stand for?
The propagation speed of interrogating beam through soft tissue.
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
Refraction
The redirection of a 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 tow 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).
Power is proportional to _____
The waves amplitude squared. They do not have a one-to-one relationship. If amplitude triples then power increases by 9 times
Line density refers to?
The width of the image in relation to the number of scan lines. If you have an image that is 5 cm wide and has 100 scan lines they will be much closer together (denser) than an image that is 10 cm wide and has 100 scan lines.
In order for Refraction to occur, what 2 things must happen?
There must be an oblique angle of incidence and different propagation speeds between the mediums.
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)
Shadowing artifact
US beam is unable to pass through a structure because the structure has a higher than usual attenuation. An anechoic shadow occurs under structure covering all structures deeper.
The frequency ranges for ultrasound are:
Ultrasound frequency is 20 to 20,000 Hz
If the thickness of the 2 substances forming the interface is increased then the amount of beam reflected is...?
Unchanged Reflection = (Z2 - Z1)/(Z2 + Z1) Thickness of the medium isn't involved in this equation.
Two identical systems produce a pulse. One pulse is 0.8 usec in duration while the other is 1.4 usec. The best temporal resolution will be created by which system?
Undetermined. Pulse duration is not related to temporal resolution. Pulse duration (PD) does not affect temporal resolution. Temporal Resolution is equal to frame rate. Frame rate is dependent on PRP x Number of Scan lines. This is why it's important to make your image as small as possible when imaging moving structures.
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.
Interference
Waves lose their individual characteristics and form a single beam.
Enhancement occurs when sound passes through a ___ attenuating structure.
Weakly
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.
The term Heterogeneous in relation to a sonographic image means?
When the imaged structure has a non-uniform, uneven appearance
Near Zone Length (NZL)
Where we get our image =d²/4λ Diameter Squared divided by 4x Wavelength NZL = D²f / 4c How to actually find the NZL you take the diameter of the crystal squared x frequency divided by 4 propagation speed. If the diameter of the Crystal goes up the NZL goes up Diameter is directly related to NZL NZL is inversely related to Wavelength If WL goes down the NZL will go up
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)
In a stenotic vessel, where is the velocity the highest?
Within the stenosis. In the center of the lumen. Proximal flow is slowed because it rushes up to the stenosis. In the stenosis it must compensate to maintain the same rate of flow so it speeds up. Distally as blood exits the stenosis turbulence is created thus slowing the blood flow.
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 from lowest to highest...
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
Power is proportional to or directly related to.....
amplitude squared If power decreases then amplitude decreases
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)
What is the formula for Axial resolution?
axial resolution = 1/2 the Spatial Pulse Length (SPL)
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
Mass per unit volume is the equation for what?
density
The inertia of the medium describes its:
density
Pulse Length is related to pulse duration how?
directly
Depth and PRP
directly related Shallow images have lower PRP Deep images have higher PRP
Wavelength is measured in
distance Unit: (mm) Speed/frequency c/f
path length
distance to reflector
Doppler Shift =
doppler shift = reflected frequency - transmitted frequency
For every 3dB the intensity will what?
double
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
What will improve a system's temporal resolution?
increasing PRF
How is time related to frequency
inversely
Depth and PRF are ___ related.
inversely DEPTH and PRF are inversely related. When you increase Depth the PRF decreases When you decrease Depth the PRF increases
Wavelength and Frequency are
inversely proportional to each other
Density and propagation of speed are ____ related.
inversely related
relationship between wavelength and frequency
inversely related
Shadowing
is produced by high attenuation In US, Calcification will render a bright mass showing a shadow beneath it with tissue appearing to the left and right of the calcific Echogenic area, but no echoes below (shadow) due to the strength of the strong reflector attenuating the sound beam causing an absence of echoes creating an anechoic cast of information below.
Infrasound
less than 20 Hz
Decibel notation is associated with which scale
logarithmic
Decibel notation is associated with which scale?
logarithmic +3 double -3 half
Greatest attenuation would occur at:
long distance with high frequency
Lowest Attenuation is found at
lowest frequency, with the shortest path length.
Ultrasound Transducers Convert
mechanical to electrical energy and vice versa
Impedance is determined by
medium only (Stiffness & Density)
Micro-
metric prefix that denotes one-millionth 10^-6
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 indirectly related to frequency Pd=1/Frequency
Acoustic Variables
pressure, density, distance
Pulse Duration Formula
pulse duration (μs) = # cycles in pulse/frequency(MHz) PD= Number of cycles in Pulse/ Frequency(Hz) or PD= Number of cycles in Pules x Period (T)
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
Enhancement artifact
rendering an impression more visible through physical, photographic, chemical, or digital methods.
Rayleigh scattering
small scattering reflectors
Intensity is determined by
sound source (initially) Intensity is essentially equal to the power of a wave divided by the area over which the power is distributed
Spatial pulse length is determined by
sound source and medium Frequency and Stiffness/Density of tissue will determine the Spatial Pulse Length. Low PRF in normal soft tissue yields a longer spatial pulse length. Higher PRF in normal soft tissue yields a shorter spatial pulse length.
pulsed wave
sound that is sent out in pulses
Axial resolution is determined by
spatial pulse length Longer SPL cannot see close together objects along the beam path. -Ron
Multi-Path Artifact
structure appearing deeper than reality because of elongated path length. Generally the total image quality is lost. Echo leaves TD hits a tangent and bounces off hitting another object and then returning. With Multi-Path Artifact, there are objects all around sending beams in directions. Muddy Image
Deca (da)
ten 10^1
PRP is determined by
the Sound Source and Imaging Depth PRP is the time from the start of one pulse to the start of the next pulse, and therefore, it includes the ON (Transmit) and OFF (Listening) time. RED ARROW ON IMAGE
Lateral Resolution
the ability to accurately identify reflectors that are arranged perpendicular to the ultrasound beam
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.
Absorption
the creation of heat in the tissue as sound travels, is a significant contributor to attenuation.
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 or is producing sound UNIT: % PERCENTAGE DF=PD/PRP PRP is inversely related to PRF, So an increase in PRF would lead to an increase in DF because PRF and DF are directly related 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
Attenuation Coefficient
the rate at which sound is attenuated per unit depth Frequency/2
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 The ultrasound system and transducer allocate the Frequency, which is inversely relates to time as a reciprocal. So, if the PRF goes up, then the PRP goes down due to an increase of vibrations causing shorter Wavelengths, which cause shorter Pulse Durations. HIGHER PRF- SHORTER PRP LOWER PRF- Longer PRP
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
Density in regards to ultrasound...
ultrasound doesn't detect tissue density. Rather, it detects sonotransmission (the passage or reflection of sound). Highly dense tissues such as bone or kidney stones readily reflect echoes and, therefore, appear bright white on an ultrasound.
Pascals (Pa)
unit of pressure measurement Pounds per square inch
Propagation Speed
v = fλ Rate at which sound travels through a medium Unit: mm/us
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 (such as a cyst)
Lateral resolution is determined by
width of the sound beam Focusing the beam, or a narrow beam improves Lateral resolution.
SPL=
# of cycles x wavelength
Pulse Repetition Frequency
- the number of pulses that is transmitted into the body each second - interested in the # of pulses created each second UNITS: HZ (per second) - PRF is determined only by the sound source - ADJUSTABLE - can be adjusted by adjusting the depth of view of a scan - when imaging shallow, PRF is higher (and vice versa) - PRF and depth of view are INVERSELY related (as depth of view increases, PRF decreases) (as depth of view decreases, PRF increases)
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 SPL= 0.1 - 1.0mm
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
What is the upper limit intensity for the SPTA of a focused ultrasound wave with no observed bio-effects?
1 W/cm2 Bioeffects intensity limit: SPTA >100 mW/cm2 Unfocused >1 W/cm2 or 1000 mW/cm2 Focused Exam duration has the greatest effect on patient exposure. HIGHEST output intensities used with pulsed doppler. Lowest output intensities are with gray-scale imaging.
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.
Medical Diagnostic Ultrasound Frequency
1-20MHz 1MHz is the lowest, and in some specialized imaging exams transducers can reach as high as 70MHz. Best answer is 1-20, but 2-15 is acceptable too...
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)
Beam at the Focus is
1/2 the diameter of the Crystal
With a frame rate of 20 Hz the time to construct a frame is?
1/20 of a second Hz = cycles per second. So 20 cycles per second. The rate is 1/20th of a second.
A typical ultrasound system will have how many scan lines per image?
100
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
The diameter of a disc shaped, unfocused piezoelectric crystal is 5 mm. Estimate the minimum lateral resolution of the system.
2.5 mm The beam width at the focus is 1/2 the diameter of the crystal
What is the audible range?
20-20,000Hz >20,000Hz=Ultrasound
An acoustic wave has a 40 lb/in2 maximum density and a 20 lb/in2 minimum density. What is the amplitude of the wave?
40 lb/in2 max-min / 2
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%
Ultrasound is defined as sound with a frequency....
>20,000Hz 20kHz
lead zirconate titanate (PZT)
A ceramic piezoelectric material Transducers have material inside of them that, when electronically stimulated, produces ultrasound waves. These Materials most likely consist of some form of lead zirconate titanate. Lead zirconate titanate is an inorganic compound with the chemical formula Pb[ZrₓTi1−ₓ]O₃. Also called lead zirconium titanate, it is a ceramic perovskite material that shows a marked piezoelectric effect, meaning that the compound changes shape when an electric field is applied.
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
Comet Tail Artifact
A form of reverberation artifact in which there is a band of echoes that taper distal to a strong reflector ex. Gallbladder with a highly Echogenic calcification showing a diminishing tail due to reverberation.
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.
Sound Waves
A series of compressions and rarefactions... Sound Waves are Mechanical and Longitudinal waves. Sound Waves are pressure waves, which are created by a mechanical action, like vocal cords or piezoelectric element vibrating. Longitudinal Waves are waves where the molecules vibrate in a direction that is parallel to the direction of wave travel.
The term Hypo-echoic in relation to a sonographic image means?
A structure that appears darker than the surrounding structures Hypo means "under". For example a hypodermic needle is one that goes under (hypo) the skin (derma). This is also good to know for hypothyroid. Underperforming thyroid.
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
Stiffness in regards to propagation speed
Ability of a tissue to resist a load of compression and relates to hardness of a medium Greater Stiffness = Greater Magnitude a load can resist STIFFNESS has the greatest impact on propagation speed!
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
Doppler Ghosting Artifact
An artifact that occurs when blood flow appears outside of a blood vessel due to pulsation. A high pass filter (Wall filter, or low velocity reject) can be used to eliminate Doppler Ghosting Artifact.
Medium
Any form of matter; Solid, Liquid, or Gas
Compression
Area of high pressure and density are referred to as compression.
Rarefaction
Areas of low pressure in a sound wave.
Propagation Speed Errors
Artifact that occurs because the actual propagation speed of the tissue is greater than or less than 1540 m/s, the machine places the reflector at the wrong location on the display
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 produces a shadow artifact?
Attenuation through a highly reflective structure A highly reflective structure basically returns the whole sound beam and leaves nothing to image the structures behind. So you have a black, empty space. A shadow. Just like your body blocks all the light and leaves a dark space.
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
What media has the greatest attenuation and the fastest speed?
BONE
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
WL measurements in clinical imaging
Between .1 and .1mm
What structure in the body has the highest Propagation Speed?
Bone
Which of the following would have the highest propagation speed?
Bone has the highest propagation speed, at 2000-4000 m/s.
Wavelength is determined by
Both the source and the medium Sound Source (Frequency det. by Transducer) Medium (Propagation Speed in Medium)
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 High frequency waves attenuate in more shallow surfaces, so in order to image deeper a low penetrating wave must be propagated to visualize deeper structures more clearly.
Attenuation
Decrease in the amplitude and intensity of the sound beam as sound travels through tissue. There are 3 Mechanisms of Attenuation: ABSORPTION, REFLECTION, SCATTERING
The diameter of the beam in the Fresnel zone/near zone does what?
Decreases
If the frame rate increases the time to generate a single frame...?
Decreases These are inversely proportional. If you image something a centimeter under the skin. The echo returns quickly so a new frame can be made quickly. In one second you can make more frames. So there a more frames per second displayed.
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. Directly Related ↓ Density ↑ Speed. Indirectly Related
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)
Reverberation Artifact
Due to reflections between two parallel highly reflective surfaces. Looks like multiple equidistantly spaced linear reflections. ex. parallel lines within the vessel because of bouncing off top and bottom intima causing a reverberation artifact.
The percentage of time that the ultrasound instrument is emitting ultrasound is called?
Duty Factor The maximum value is 1, the minimum is 0
