Help

Options

focusNode

Didn't know it?
click below

Knew it?
click below

Don't Know

Remaining cards (0)

Know

retry

shuffle

restart

0:00

Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.

Normal Size Small Size show me how

SPI Must Know

US Physics Must Know from Reynolds

Question	Answer
Sound is	a longitudinal, mechanical wave
In a longitudinal wave	the particles move parallel to the direction of sound travel
One cycle of sound is made up of what?	one compression and one rarefaction
The four acoustic variables are:	pressure, density, temperature, and particle motion
Frequency is	the number of cycles per second
Units for Frequency	Hertz (Hz)
Frequency Range for Audible Sound	20Hz to 20,000Hz
Frequency Range for Ultrasound	20,000Hz to 20kHz
Clinical Imaging Frequency Range	2MHz to 10MHz
Increasing Frequency	Decreases image depth because attenutaion increases
Increasing Frequency	Improves axial resolution because shorter pulses are created
Increasing Frequency	Improves lateral resolution because higher frequencies produce a narrower beam width
Increasing Frequency	Decreases period which decreases pulse duration leading to an improvement in axial resolution
Shorter SPL	Shorter PD
The Narrower the Beam	The better the lateral resolution
Shorter Pulses	Provide for better axial resolution
For Soft Tissue, Wavelength(mm)=	1.54(mm/us)/frequency(MHz)
Increasing the Frequency	Decreases the wavelength which decreases SPL leading to an improvement in axial resolution
The Shorter the Pulse	The better the axial resolution
Average Speed of Sound in Soft Tissue	1540m/s, 1.54mm/us
The Stiffer the Material	The higher the propagation speed
Propagation Speed for Air	333m/s
Propagation Speed for Bone	3500m/s
Amplitude	The strength of the outgoing signal or returning echo
Units for Amplitude	Decibels(dB)
An Increase in Transmit Gain	Increases amplitude, power, pressure, intensity, beam width, depth of penetration, brightness of the signals throughout the display, MI, and the risk of bioeffects.
Units for Power	Watts(W) or milliwatts(mW)
Intensity is	Power(W)/Area(cm^2)
There have been no proven biological effects for	unfocused sound beams below 100mW/cm^2 SPTA unfocused beams or 1W/cm^2 SPTA focused beams
Decibels(dB) are the units for:	amplitude, transmit gain, gain, attenuation, TGC, and dynamic range
An increase in intensity by 40dB represents	An increase in intensity by 10,000 times
For soft tissue, 3dB represents	a 50% loss in original intensity
Another term for stiffness is	Bulk Modulus
For perpendicular incidence	A reflection will occur at the boundary of two media if the acoustic impedances are different
For a soft-tissue interface	Over 99% of the sound energy is reflected with less than 1% of the sound energy transmitted
For a fat-muscle interface	over 99% of the sound energy is transmitted with only 1% reflected
Specular Reflectors	are large, smooth surfaced reflectors that require perpendicular incidence
Scatter Reflectors	are small, rough surfaced reflectors that are not angle dependent, but are frequency dependent
Increase Frequency	Increase Backscatter
The best example of a Rayleigh Scatterer is	the Red Blood Cell
Reflections from scatter reflectors	are weaker than reflections from specular reflectors
Harmonic imaging transmits	a fundamental frequency and processes the second harmonic (twice the fundamental frequency)
Two types of harmonic imaging	contrast harmonic imaging and tissue harmonic imaging
In contrast harmonics	multiples of the fundamental frequency are created by the reflector (e.g. contrast bubble)
Tissue harmonics	are created by the propagation of sound through tissue
Harmonic imaging may be improved by	pulse inversion or power modulation
Harmonic imaging improves	lateral resolution
Harmonic imaging decreases	side lobe/grating lobe artifacts
Harmonic imaging reduces	near field reverberation
Perpendicular incidence (90 degrees)	is also normal incidence
Perpendicular incidence predicts	the amount of reflection (intensity reflection coefficient (IRC)) at a boundary
Perpendicular incidence equation	[(Z2-Z1)/(Z2+Z1)]^2 x 100
Oblique incidence	is present when the US beam strikes a boundary at an angle other than 90 degrees
The reflected angle always equals the	incidence angle
Refraction is	the change in the direction of sound travel and is associated with lateral displacement of structures on the display
Snell's Law (Law of Refraction)	predicts when refraction will occur and how much refraction will occur by predicting the transmitted angle
There will be no refraction if	there is perpendicular incidence or if there is oblique inceidence and the propagation speeds of the two media are equal
The primary cause of attenuation in soft tissue is	absorption (conversion of sound energy into heat)
The attenuation coefficient(dB/cm) for soft tissue is	0.5 dB/cm/MHz (0.5 x frequency)
Total Attenuation(dB)=	0.5 x frequency(MHz) x path length(cm)
The Piezoelectric Effect is	the conversion of electrical energy into sound energy (transmission) and sound energy into electrical energy (reception)
Increasing the Frequency	increases attenuation and decreases depth of penetration
The thinner the piezoelectric element and the higher the propagation speed of the element	the higher the frequency of the element
The Matching Layer	is placed on the front surface of the piezoelectric element, is 1/4 wavelength thick, and reduces the impedance difference between the piezoelectric element and the soft tissue
The Damping Block	is placed behind the piezoelectric element, reduces the ringing of the element, reduces SPL and PD which improves axial resolution
The damping block	increases bandwidth and reduces the QF
Modern US transducers	have wide bandwidths with low QF
The Near Field (Fresnel zone, near zone)	is the sound beam region located between the transducer face and the focal point
Beam width decreases where?	In the near field
The focal point	is the narrowest portion of the sound beam where intensity is the greatest and lateral resolution is the best
The Far Field (Fraunhofer zone, far zone)	is where the sound beam diverges, intensity decreases, and lateral resolution is poor
The near field length (NFL) can be increased by what?	By increasing the transducer diameter (best way) and/or by increasing the frequency
Focusing	decreases the beam width in the near field, improves lateral resolution but does not extend the near field and increases beam divergence in the far field
Internal focusing curves what?	The piezoelectric element
External focusing	places a curved lens on the piezoelectric element or transducer face
Electronic transmit focusing	curves the pulses going to the piezoelectric element
Electronic receive focusing	uses delay lines to focus the returning echoes
Only transmit focusing is controlled by?	The sonographer
Lateral Resolution is dependent upon what?	Beam width (the narrower the beam width, the better the lateral resolution)
Lateral resolution is improved by what?	Increasing the transducer diameter, frequency, harmonics, and/or by focusing
Axial resolution is dependent upon what?	The spatial pulse length and pulse duration (the shorter the pulse, the better the axial resolution)
Axial resolution is improved by what?	Increasing the frequency (sonographer) or by damping (manufacturer)
The linear sequenced array transducer	is a large electronic transducer which creates a linear display
The sector phased array transducer	is a small electronic transducer where all the piezoelectric elements are fired but with a brief time delay in order to beam steer and beam focus
The annular array transducer	utilizes piezoelectric elements arranged in a circle, is electronically fired and electronically focused, but is mechanically steered
The mechanical transducer	creates a cross sectional image by placing a piezoelectric element on a motor, is fixed focus where an acoustic standoff may be used to alter the placement of the focus
Beam scanning infers what?	That the sound beam is being swept through the tissue manually, mechanically, or electronically to create a cross sectional image
Beam steering is what?	Mechanically or electronically directing the sound beam toward a certain direction
Beam focusing is what?	Mechanically (internal/external focus) or electronically (transmit/receive) decreasing the sound beam width in the near field
The range equation uses what?	The propagation speed and the round trip time (divided by 2) to determine he distance to a reflector
For soft tissue, how long does it take for an US pulse to travel 1 cm round trip?	13 us
Pulse Repetition Frequency (PRF)	is the number of pulses created per second
PRF is determined primarily by what?	Image depth since only one pulse can travel in the body at one time
Image depth and PRF are related how?	Inversly (increase depth, decrease PRF; decrease depth, increase PRF)
Duty Factor(DF) is	the percentage of time the machine spends producing a pulse; it is unitless
The pulser delivers the electrical impulse to what?	The piezoelectric element
The sonographer can control what with the transmit gain control?	The pulser
Amplification(gain, receiver gain, overall gain) does what?	Amplifies all returning signals regardless of depth, increases the strength of all the echoes throughout the display and is a safer gain to use as compared to transmit gain
Compnesation(TGC, DGC) compensates for what?	Attenuation
Compression reduces what?	The dynamic range
Rejection eliminates what?	Low amplitude signals and noise
Demodulation has two components:	rectification and smoothing
Dynamic Range (dB) is what?	The range of echo amplitudes that a particular component can process.
Dynamic range can be influenced by:	the sonographer (compression, log compression, dynamic range)
Decreasing Dynamic Range	Will increase contrast
Increasing Dynamic Range	Will increase the shades of gray displayed
A-mode displays returning echoes as what?	Spikes
B-mode displays returning echoes as what?	Bright dots
B-mode displays what?	The strength of the returning signals(amplitude) and the depth at which they are located.
M-mode is a B-mode operation displaying what?	Motion over time with excellent temporal resolution.
A frame is a collection of what?	Pulses where one pulse equals one scan line.
A frame contains how many scan lines?	100-150 scan lines (pulses)
What is the standard frame rate?	30 frames per second (30 Hz)
Temporal resolution is improved how?	By increasing the frame rate.
To improve temporal resolution (to increase frame rate)	decrease image depth, field of view, number of foci, and/or line density
What is the heart of the memory?	The scan converter
What is the digital scan converter?	A computer which uses the binary system where the number column is the multiple of 2 and the digits for the binary system are 0 and 1.
The digital scan converter is composed of what?	A matrix(s) or "checkerboards" with pixels able to hold a binary digit (0 or 1)
The more bits per pixel	the greater the number shades of gray
The number of shades of gray that a particular digital scan converter can display can be calculated how?	By the formula 2 to the power of x (e.g. a 4 bit scan converter can display 16 shades of gray)
Preprocessing occurs when?	Before memory
Postprocessing is what?	The assignment of gray shades to numbers leaving the memory.
If the image is frozen, what is being utilized?	Postprocessing (preprocessing does not allow for manipulation of a frozen image)
The display	is a television cathode ray tube (CRT) or computer monitor which writes in the raster scan format and is able to display up to 60 frames per sec (Hz)
Step 1 in the processing of echo information	pulser to transducer
Step 2 in the processing of echo information	reflection to transducer
Step 3 in the processing of echo information	receiver functions applied to the reflection (amplification, compensation, compression, demodulation, rejection)
Step 4 in the processing of echo information	analog to digital conversion (preprocessing) with storage of the binary number in the memory (scan converter)
Step 5 in the processing of echo information	the assignment of a shade of gray to the binary number leaving the memory
Step 6 in the processing of echo information	the display as a bright dot (B-mode)
The five resolutions are:	axial, lateral, temporal, contrast, and elevational
What is the Doppler principle?	The change in the frequency of sound due to motion of the sound source and/or the observer.
What is the Doppler shift?	The difference between the transmit frequency and the received frequency; is in the audible range; can be positive or negative
An increase in transmit frequency or RBC velocity will increase what?	The magnitude of the Doppler shift
To avoid aliasing, Doppler utilizes what?	Lower frequencies as compared to imaging.
The best way to perform a Doppler exam is what?	To be parallel (0 degrees) to blood flow
Fast Fourier Transform (FFT) is what?	The method used for spectral analysis in conventional (PW, CW) Doppler
What do the x, y, and z axis represent for the FFT?	The x axis represents time, the y axis represents velocity, and the z axis represents the amplitude (strength) of the returning signal
What is the Doppler wall filter?	The Doppler wall filter is a high pass filter which eliminates high amplitude (strong)(e.g. wall motion) and low velocity signals.
What is spectral broadening?	The vertical thickening of the Doppler spectrum, results in window fill-in and indicates turbulent flow.
CW Doppler requires how many piezoelectric elements?	Two
The primary advantage of CW Doppler is what?	It resolves high velocities without aliasing (no inherent sampling rate).
The primary disadvantage of CW Doppler is what?	Range ambiguity
PW Doppler requires how many piezoelectric elements?	One
The primary advantage of PW Doppler is what?	Range resolution (range discrimination)
The primary disadvantage of PW Doppler is what?	Aliasing due to the Nyquist limit (PRF/2)
What can you do to avoid aliasing?	Increase velocity scale, decrease image sampling depth, decrease transducer frequency, alter the baseline, increase Doppler intercept angle (e.g 0 degrees towards 90 degrees), utilize high PRF or CW
What is color flow Doppler?	A multigate PW Doppler technique which presents the mean velocity of blood flow.
Can aliasing occur in color flow Doppler?	Yes, because it is a PW technique. It may occur in normals because the PRF is lower as compared to imaging and appears as apparent flow reversal.
What is packet size?	The number of pulses sent down one line to create one scan line of color.
Increasing the packet size will improve what?	The estimation of the mean velocity, but it will decrease the frame rate.
What will increase the color Doppler frame rate?	Decreasing image depth, packet size, field of view, and/or line density.
What is autocorrelation?	The rapid technique of converting Doppler shift information into color.
What does a mosaic flow represent?	Turbulent flow
Green may be added to indicate what?	Variance (turbulent flow)
What is ghosting or flash artifact?	The placement of color on moving tissue structures.
What are reverberations?	Multiple echoes, equally spaced usually located close to the transducer.
Refraction may result in what?	Lateral displacement of structures (e.g side-by-side double image of a structure) or edge shadowing
What will result in a resolution artifact?	Structures being too close axially, laterally, or in the elevational plane to be distinguished.
What are side lobe and grating lobe artifacts?	Extraneous ultrasound energy emanating from the primary beam.
What are two types of reverberation artifact?	Ring down (originating from a gas bubble) and comet tail(originating from a highly reflective structure e.g bullet).
If the propagation speed of a material is less than 1540 m/s, then reflectors will be placed where?	Too far from the transducer.
If the propagation speed of a material if greater than 1540 m/s, then reflectors will be placed where?	Too close to the transducer.
Shadowing involves what?	A highly attenuating structure resulting in a low amplitude signal.
Enhancement involves what?	A low attenuating structure resulting in a high amplitude signal.
When will range ambiguity occur?	If depth of penetration(cm) x number of foci x lines per frame x frame rate is greater than 77,000.
What is the best way to practice ALARA?	To reduce the scanning time and transmit gain.
Bioeffects may be what?	Thermal, cavitation, or direct mechanical
What is stable cavitation?	The expansion and contraction of a gas bubble which may result in microstreaming.
What is transient cavitation?	The implosion of a gas bubble and may lead to a significant bioeffect.
What indicates the risk of cavitation?	The mechanical index (MI)
What indicates the risk of an unsafe rise in temperature?	The thermal index (TI)
A cracked ultrasound transducer can result in what?	An electrical shock to the patient.

Created by: jmontroy

"Know" box contains:
Time elapsed:
Retries: