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dorkfork
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Which of the following parameters directly relates to heating of tissues?
- Increase thermal index
- Increased frequency or output power
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Which of the following rod groups scanned from side A would evaluate axial resolution?
Rod group B
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What factors would produce the greatest TI values?
- High frequency
- Narrow focal zone
- Stationary color doppler
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What factors would produce the greatest MI values?
Low frequency, high intensity
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The artifact indicated by the arrow is due to:
- Reverberation/ comet tail
- Large acoustic impedance missmatch
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Which system control manipulations would best limit patient exposure to ultrasound energy?
- Decrease scan time
- M-mode vs. color doppler or pulsed wave
- Decrease frequency
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A transducer has a very wide slice thickness. This may produce:
- Filling defect of a cystic/anechoic structure
- Filling in of vessels / small cyts
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Which of the following produces the split image artifact?
- fat/muscle interface near the surface
- i.e. linea alba
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Which of the following types of tissue will demonstrate the greatest temperature elevation?
- embryo <8 weeks conception
- head, brain, and spine of any fetus or neonate
- eye in any patient
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Which of the following digital scan converters would display the best contrast resolution?
- 8 bit
- 8 is the current standard
- 2n = shades of gray, where n = bits in a computer word
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Bioeffects have been observed in experimental animals with focused intensities greater than:
1 W/cm2
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On an A-Mode display, the height of the spike represents:
The echo intensity
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The System Gain function is performed in the:
Beam former
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What is the maximum number of displayed shades of gray in a 6-bit processor?
26 = 64
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What determines the power of the ultrasound field?
Voltage applied to the transducer
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The typical pulse repetition frequency range for clinical imaging applications is:
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The term signal to noise ratio is:
The ratio of signal amplitude to the variation in noise
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In cardiac imaging, reducing the size of the sector angle will:
Increase the frame rate
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If the imaging depth is quartered, the frame rate will be:
Quadrupled
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The signal processing function that eliminates the negative component of the signal is termed:
Rectification
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Adjusting the TGC controls affects the settings in the:
Beam former
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The ability to distinguish between adjacent structures producing similar echo amplitudes is termed:
Contrast resolution
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When the pulse repetition period is increased:
Imaging depth is decreased
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If the gain is increased by 6 dB, the power has been increased by a factor of:
4
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When comparing Write magnification with Read magnification, Write magnification:
Improves spatial resolution compared to read magnification
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During real time imaging, if the scan line density is reduced to 1/2, the maximum frame rate is:
Doubled
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Preprocessing programs are performed in the:
Image processor
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If the original acoustic power is 100 mW and the power control is increased by 3 dB, the new power is _____ mW.
200
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In real time systems, the range equation is used to determine reflector:
Depth
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The typical dynamic range in the amplifier is:
60-100
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The sonographer has increased the size of the sector width to image a large mass. What can the sonographer do to maintain the same temporal resolution before this adjustment?
Decrease the number of focal zones.
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Increasing the pulse repetition frequency will:
Decrease the maximum imaging depth
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Reflector B is twice the distance from the transducer as reflector A. It takes ______ times as long for an echo to arrive from reflector B as from reflector A.
2
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The computer parameter that limits the number of brightness levels available to display on the image matrix is:
Number of bits in computer word
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The primary method that the sonographer uses to control frame rate during real time imaging is:
Imaging depth
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Which mode has time the unit of measurement on one axis?
M-mode
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Flow through a blood vessel is determined by:
- 1. Pressure difference
- 2. Vascular resistance
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Vessel diameter increase as _____ increases.
Pressure
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Veins or arteries, which are more distensible?
Veins are 6-10 x as distensible as arteries
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Arteries
- Transport blood to tissues
- High pressure
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Arterioles
- Last, smallest branches of the arterial system
- Act as "control valves" for blood flow into capillaries
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Capillaries
Exchange between blood and interstital spaces
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Vasodilitation occurs when?
- During exercise
- After a meal
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Vasoconstriction occurs when?
- In a resting state
- With fasting
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Venules
Collect blood from capillaries and connect to larger veins
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Veins
- Blood returned to heart
- Body contians many more veins than all other parts of the vascular system
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AO/ICV
Have the smallest cross-section area and therefore the highest velocity
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Relationship of velocity to area
Velocity is inverse to area
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Energy derived from the cardiac pump
Potential/pressure energy
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Potential energy
- Pressure/stored energy
- Derived from the cardiac pump
- Distends vessels and stores energy
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Kinetic energy
- Energy of motion
- KE < PE due to distensibility of vessels
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Kinetic energy can increase due to:
- Increase in flow>> i.e. exercise
- Stenosis (increased velocity)
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Movement of fluid between 2 points requires:
- Difference in energy
- Difference in pressure
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Example of low resistance
- Organs
- Low resistance = greater energy difference = greater flow
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Example of high resistance
- Resting muscle
- High resistance = less flow
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Pouseuille's law
Defines relationship between pressure, volume flow, and resistance
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The longer the vessel the _____ the resistance.
- Higher
- High pressure is required to maintain flow
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The shorter the vessel the ____ the flow volume.
Higher
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What has the most significant impact on flow rate?
- Radius of the vessel
- Smaller the radius, the higher the resistance
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Smaller the radius, the _____ the resistance.
Higher (and higher pressure)
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Plug flow
- Flat profile
- Seen in stenotic area
- Same velocity throughout vessel (slower flow at wall)
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Laminar flow
- Most common flow pattern
- Seen during systole in smaller arteries
- Flow in center is highest and gradually tapers as it reaches the wall of the vessel
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Disturbed flow is signified by?
Spectral broadening
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Mathematical number to determine when flow turbulence will occur?
Reynold's number
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Reynolds number for when turbulance will occur
2000 Re or higher
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Harmonic resonance produced by flow turbulence transmitted into vessel walls is known as
audible bruit
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Where is normal disturbed flow visualized throughout the cardiac cycle?
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Significant stenosis
70% blockage
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Tardus parvus
Dampened wave forn distal to a stenosis
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Monophasic flow
- Low resistance, continuous and steady throughout S and D
- Seen in normal arteries that supply low resistance vascular beds -liver, spleen, brain, kidneys
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Triphasic flow
- Highest resistance to flow
- Antegrade/forward flow during systole
- Retrograde/reverse flow during diastole
- Seen in distal AO/iliac arteries
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Cosine of the doppler angle is ______ly related to the doppler angle.
- Inversely related
- Angle of 0 = cosine 1.00
- Angle of 90 = cosine 0
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Increase transmit frequency and _____ the size of the Doppler shift
Increase
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Decrease velocity of flow and _____ the size of the Doppler shift.
Decrease
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Increase the Doppler angle and _____ the size of the Doppler shift.
Decrease
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Decrease the Doppler angle and ______ the size of the Doppler shift.
Increase
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Cosine = 0
- 90 degree angle
- No Doppler shift
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Cosine = 1.00
- 0 degree angle
- Largest Doppler shift
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With spectral analysis the frequency is displayed on which axis?
Vertical y axis
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What is displayed on the X axis of spectral analysis?
Time
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Amplitude or power is displayed as what on spectral analysis?
Brightness
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FFT
- Fast fourier time
- Current computer program for analyzing and displaying spectral representation
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How can aliasing be eliminated?
- Increase PRF (increased nyquist limit)
- Shift baseline
- Increase size of angle
- Decrease transmit frequency
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Main disadvantage of pulsed Doppler is?
Aliasing
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Nyquist Limit
- 1/2 the PRF
- Exceeding this produces aliasing
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PRF control
Changed the number of pulsed emitted per second
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Primary advantage of CW Doppler
No velocity limit/ no aliasing
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Main disadvantage of CW Doppler
- Large fixed sample volume
- POOR RANGE RESOLUTION
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Color Doppler
- Qualitative, NOT quantitative information
- Will produce aliasing
- Good range resolution
- BART
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How to eliminate color aliasing
- Increase PRF (scale setting)
- Decrease sample volume depth
- Use larger Doppler angle
- Lower transmit frequency
- Go from triplex(color, image, spectra) to duplex (color, image)
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Power Doppler
- Encodes amplitude of blood cells
- Provides no info on direction of flow
- NO aliasing and less angle dependant
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Components of pulsed Doppler instrumentation:
- Pulser
- Gated detector
- Spectral analysis
- Memory
- Display
- Speakers
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Length of pulses produced by pulser
5-30 cycles
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The time period for acquisition of Doppler signal is determined by the _____.
Size of the gate
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Phase shift means
Motion is present
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Rhythmic cycles or beats produced when waves of different frequencies produce interference are added together and termed
Beat frequency
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Minimum number of cycles per pulse is?
4
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Number of cycles required for fast flow
6-10
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Number of cycles needed for gray scale
2-3 cycles
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Number of cycles needed for slow flow
20-30
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Typical sampling rate
25,600 times per second
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High pass filter
- Rejects all frequencies below the threshold vaule
- Usually 100Hz
- Removes wall thump but not slow flow
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Low pass filter
- Eliminates high frequency noise
- Improper adjustment can eliminate high frequency (fast) flow
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One speed estimate has a _____ pulse minimum.
Three
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More than 3 pulses are required in order to:
- Improve accuracy of the estimate
- Determine the variance
- Improve detection of slow flow
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Typical ensemble length range
10-20 pulse
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Increasing ensemble length will ___ frame rate.
Decrease
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Ensemble length
- AKA pulse packet size
- The number of pulses required to produce one color scan line
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Transient cavitation refers to :
- AKA collapse cavitation or normal cavitation
- Bubble oscillation so large that the bubble collapses
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No thermal effects have been documented when the temperature elevation is below ___ degrees.
2
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A Thermal Index (TI) value of one (1) indicates:
Potential to increase tissue temperature by 1 degree
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The artifact indicated by the white line can be eliminated by:
Aliasing
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Which mode has the potential for the highest thermal production?
Color doppler
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A device commonly used to measure the output of diagnostic ultrasound systems is:
Hydrophone
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A tumor has a slower propagation speed than the soft tissue average propagation speed. This will result in:
Shadowing
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A long near zone can be obtained by:
Increase frequency (decrease λ)
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Higher the ____ the shorter the SPL
Frequency
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Shorter the SPL the better the ____ resolution
axial
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SPL=
- SPL= λ x # of cycles in pulse
- Shorter the SPL the better the axial resolution
- Higher the frequency the shorter the SPL
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Longitudinal or axial resolution is directly dependent on:
- Spatial pulse length
- SPL= λ x # of cycles in pulse
- Shorter the SPL the better the axial resolution
- Higher the frequency the shorter the SPL
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Generally, ultrasound transducers have better _____ resolution than ________ resolution.
Better axial resolution than lateral resolution
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Which equipment assumption is violated when refracted echo information is processed?
All echoes come from straight ahead
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To reduce the Mechanical Index (MI), the sonographer would:
Decrease acoustic power, increase the number of focal zones
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Mechanism through which ultrasound energy can produce a biological effect
Stable caviatation, transient cavitation, increase in temperature
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The artifact indicated by " A" is indicates:
Large acoustic impedance missmatch
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If the focal zone is decreased to 1/5 of its original area, the intensity will:
Increase by 5
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Which rod groups scanned from side C would evaluate lateral resolution?
Rod group C
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Side lobe artifact produces which of the following sonographic characteristics?
- Energy distribution outside main beam profile
- Horizontal linear extensions from specular reflector (i.e. septa)
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The risk of cavitation is considered low when the MI value is ____ or lower.
0.5
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PhThe area of the sound field characterized by violent intensity changes is:
Near field
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