Color Duplex Imaging

Question 1

Duplex imaging combines gray scale with Doppler and can appear as 
(A) M-mode and spectrum 
(B) B-mode and spectrum 
(C) color flow imaging and spectrum 
(D) all of the above

Answer 1

(D) All of the above. Color flow images can be used to position a single point, pulsed-Doppler, sample volume, as is the case with more conventional duplex imaging.

Question 2

Doppler color flow imaging produces an image com-
posed of
(A) tissue echoes in gray scale and blood echoes in color
(B) moving soft-tissue echoes in gray scale and blood motion in color
(C) stationary tissues in gray scale and moving tissues in color
(D) stationary tissues in gray scale and stationary blood in color

Answer 2

(C) Stationary tissue in gray-scale and moving tissues in color. All moving tissues in a color flow imaging can produce color. Thus, stationary tissues are in gray scale, whereas moving tissues, including blood, are in color.

Question 3

Color Doppler imaging is a term used to describe
(A) a form of color flow imaging
(B) a form of magnetic resonance imaging
(C) a new form of imaging relying on high-speed
propagation velocities in soft tissues
(D) a form of detecting flow with lasers

Answer 3

(A) A form of color flow imaging. Color flow imaging includes both Doppler and non-Doppler forms of imaging.

Question 4

The Doppler effect occurs
(A) only to waves traveling more than 1,000 m/s
(B) only to ultrasound waves with intensities greater than 500 mW/cm2, SPTA
(C) to all waves coming from a moving wave source
(D) in ultrasound, but only when the targets are moving faster than 1.0 m/s

Answer 4

(C) To all waves coming from a moving wave source.

The Doppler effect happens to all waves coming from a moving source, regardless of propagating velocity or power levels.

Question 5

The Doppler effect depends on
(A) the carrier frequency, the angle between echo source velocity and beam axis, and the reflectivity of blood
(B) the closing velocity between transducer and tissue, carrier frequency, and ultrasound propagation velocity
(C) the lowest Doppler-shift frequency detectable and the highest frequency without aliasing
(D) the largest change in acoustical impedance within the moving blood

Answer 5

(B) The closing velocity between transducer and tissue, carrier frequency, and ultrasound propagation velocity. The Doppler equation looks like the
following,
Df = 2(f/c) V cos 0
where F is the carrier frequency, c is the propaga-
tion velocity, and 0 is the Doppler angle. V cos 0 is the
closing velocity between the transducer and moving
tissue.

Question 6

To calculate blood velocity using color flow imaging, a
sonographer must
(A) place a sample volume in the major streamline or jet within the vessel and set an angle correction parallel to the vessel wall
(B) assume that all flow is parallel to the vessel wall
(C) locate the major streamline and place the sampling angle at 60° to the vessel wall
(D) place a sample volume in the major streamline
or jet and set the angle correction parallel to the
streamline

Answer 6

(D) Place a sample volume in the major streamline or jet and set the angle correction parallel to the streamline. Because the color pattern shows the location of the major streamline or jet, calculating velocity requires correction relative to the flow geometry, not the vessel.

Question 7

To preserve gray-scale texture, digital sampling for
gray-scale images must be at intervals of
(A) 0.6 mm
(B) one wavelength or less
(C) 1.0 mm
(D) 3 dB

Answer 7

(B) One wavelength or less. This is necessary for textural information to reach the display in a digital scan converter.

Question 8

To preserve flow detail, digital Doppler sampling
intervals for a vascular color flow image must be at
intervals of
(A) 1-2 mm
(B) 1-2 cm
(C) one wavelength or more but less than 1 mm
(D) -6 dB

Answer 8

(C) One wavelength or more but less 1 mm. Digital
sampling for vascular flow information requires such
an interval because larger intervals cannot show the
flow patterns within the vessel.

Question 9

Gray-scale tissue texture in a color flow imaging system depends on
(A) transmit focusing only
(B) receive focusing only
(C) the product of transmit and receive focusing
(D) the speed at which the ultrasound beam is moved by the scanhead

Answer 9

(C) The product of transmit and receive focusing. The effective beam width results from the mathematical product of both functions.

Question 10

The shape of the sample volume in pulsed Doppler has
a major effect on the content of the Doppler signal.
(A) true
(B) false

Answer 10

(A) True. The sample volume and flow interact in a manner that depends on the geometry of the sample
volume.

Question 11

To form the color patterns in a Doppler color flow
image, a color flow system samples down each Doppler
image line of sight for
(A) the amplitude of the Doppler signal
(B) the velocities of red blood cells
(C) the average Doppler shift frequency
(D) the velocity spread within the sample site

Answer 11

(C) The average Doppler shift frequency. At each sample site, the color flow system determines the average Doppler shift frequency.

Question 12

The Doppler portion of a color flow image is a map of red-cell velocities.
(A) true
(B) false

Answer 12

(B) False. At each sample site, the system determines the average Doppler shift frequency. The display is then either these average frequencies or, in some cases, the calculated closing velocity. This velocity is the rate at which the flow is approaching or moving away from the transducer along the line of sight.

Question 13

Separating moving soft tissue from moving blood in a
color flow image tests for
(A) Doppler signal amplitudes only
(B) tissue signal amplitudes only
(C) Doppler signal frequencies only
(D) the relationship between the amplitudes and frequencies ofthe Doppler signals

Answer 13

(D) The relationship between the amplitudes and frequencies of the Doppler signals. The system will then avoid coloring strong slow-moving echo sources (tissue) but still color moderately fast weak echo sources (blood).

Question 14

A curving vessel within a color flow image shows color
in the vessel when the beam and vessel are parallel
but shows no color as the vessel turns perpendicular
to the beam. The loss of color means that
(A) the vessel is occluded
(B) the vessel is open, but the blood velocity is too
low to complete the image
(C) the dark region is diseased
(D) The Doppler effect works only when the vessel
is parallel to the ultrasound beam.

Answer 14

(B) The vessel is open, but the blood velocity is too low to complete the image. As the vessel curves away from the beam, the Doppler frequencies become too low to be portrayed. The completeness of a color flow image depends on the velocity of the blood flow and the Doppler angle.

Question 15

The smallest vessels that appear in a color flow image
are about 1 mm in diameter. The smaller vessels are
absent because
(A) arterial blood velocities are too low in vessels
that are less than 1 mm in diameter
(B) the smaller vessels are shadowed by the
surrounding soft tissue
(C) soft tissue does not have many vessels that are
less than 1 mm in diameter
(D) the smaller vessels do not reflect ultrasound as
well as the larger vessels do

Answer 15

(D) The smaller vessels do not reflect ultrasound as
well as the larger vessels do. Every living cell in the
body is no more than two cell layers away from a red blood cell. The smaller vessels, however, are not sufficiently echogenic and vanish from the color display
first because of their small echo signals.

Question 16

The color flow image provides information on (1) the
existence of flow, (2) the location of flow in the image,
(3) flow direction relative to transducer, (4) the maximum flow velocity
(A) all of the above
(B) 1, 3, and 4
(C) 3 and 4
(D) 1, 2, and 3

Answer 16

(D) 1, 2, and 3. Color provides information about the existence of flow, its location in the image, its location in the anatomy, the direction of the flow relative to the transducer, the direction of flow within the vessel, the flow pattern within the vessel, and the pulsatility of the flow. It does not indicate the velocity of the flow.

Question 17

Detecting flow in a color flow imaging system depends
on the detection of
(A) changes in Doppler signal amplitude
(B) changes in Doppler signal frequency content
(C) changes in echo signal phase and frequency
content
(D) changes in echo signal phase

Answer 17

(D) Changes in echo signal phase. As with all directional Doppler systems, color flow systems detect the existence of motion with a change in echo signal phase. By measuring the direction of the phase change, the system shows whether the direction of motion is toward or away from the transducer.

Question 18

One begins reading a color flow image by
(A) determining the maximum systolic frequency
(B) knowing the position ofthe scan plane on the patient’s body
(C) knowing the direction of flow relative to the
transducer
(D) determining the Doppler carrier frequency

Answer 18

(B) Knowing the position of the scan plane on the patient’s body. The expected flow pattern in any vessel comes from knowing how the scan plane is positioned on the patient. For example, the patient’s head is always placed on the image left in long axis scans, and the patient’s right side is on the image left in cross-sectional scans.

Question 19

Changes in the Doppler shift frequencies within a color flow image sample site appear in the image as
(A) nothing; the image only shows changes in phase
(B) different colors (hues)
(C) different levels of color saturation (purity)
(D) different colors (hues) or different levels of saturation (purity)

Answer 19

(D) Different colors (hues) or different levels of saturation (purity). The average frequency within each Doppler sample site is portrayed as a change in either color saturation (purity or whiteness) or hue (color). The object is to use the color to show flow patterns within the vessel lumen or heart chambers.

Question 20

A Doppler color flow image can show changes in the
frequency content at a Doppler sample site by
(A) changes in gray scale
(B) changes in saturation
(C) changes in color hue
(D) the introduction of green markers

Answer 20

(C) Changes in color hue. The variance in Doppler frequencies can be shown with a change in hue, such as green tones with increasing variance.

Question 21

Cardiac color flow imaging shows changes in the frequency content of the Doppler sample site by 
(A) changes in color 
(B) changes in saturation 
(C) changes in color texture 
(D) the introduction of red markers

Answer 21

(A) Changes in color. Cardiac systems change color hues (frequencies) along red and blue lines to show changes in Doppler shift frequencies. Broadening frequencies in a sample site become shades of green.

Question 22

Color flow imaging systems determine the maximum
Doppler shift frequency at each sample site.
(A) true
(B) false

Answer 22

(B) False. Because only one frequency can come to the screen for each Doppler image pixel, all current systems use some estimate of the mean frequency.

Question 23

A measurement of the peak systolic frequency in a
carotid artery with a single-point spectrum will be
lower than a measurement of the color-encoded frequency at the same point.
(A) true
(B) false

Answer 23

(B) False. Because color uses the average frequency at each location, the maximum systolic frequency will always be greater than the mean value.

Question 24

The synchronous signal processing uses a Doppler
carrier frequency that is the same as the imaging center operating frequency.
(A) true
(B) false

Answer 24

(A) True. Because synchronous signal processing uses the same echo signal for both Doppler and gray-scale signal processing, the frequency must be the same.

Question 25

Asynchronous signal processing in color flow imaging
requires the same frequency for both Doppler and
gray-scale imaging.
(A) true
(B) false

Answer 25

(B) False. Asynchronous signal processing can, and often does, use different frequencies for the gray-scale image and the Doppler image. For example, it could image at 5.0 MHz and have a Doppler carrier of 3.0 MHz.

Question 26

Beam steering in asynchronous color flow imaging is
used to provide
(A) a Doppler angle significantly less than 90° to typical blood flow
(B) a way oflooking at the same soft-tissue targets at an angle different from the perpendicular beams
(C) an enlarged Doppler beam to improve Doppler sensitivity
(D) improved Doppler sensitivity to smaller vessels

Answer 26

(A) A Doppler angle significantly less than 900 to typical blood flow. All Doppler imaging requires a Doppler angle. In asynchronous systems that do not use a wedge, the angle comes from beam steering.

Question 27

The mechanical wedge in synchronous color flow imag-
ing is used to provide
(A) improved penetration through impedance matching
(B) improved beam focusing for the gray-scale image
(C) an attenuation system to remove side lobes
(D) a Doppler angle between the typical flow patterns in vessels

Answer 27

(D) A Doppler angle between the typical flow patterns in vessels. Synchronous systems that keep the beams perpendicular to the transducer array (angio-dynography) use a mechanical wedge to obtain the Doppler angle to the flow pattern of the vessel.

Question 28

The ability to see flow in deep vessels is limited by the fact that
(A) blood has scattering units that are about the same size as soft tissue
(B) blood is moving faster than the surrounding tissues
(C) blood has an extremely low attenuation rate
(D) blood reflectivity is about 40-60 dB below that of soft tissue

Answer 28

(D) Blood reflectivity is about 40-60 dB below that of soft tissue. The fact that blood reflectivity is about 1/100th to 1/1,000th that of soft tissues translates into reflectivities that are much lower than those of soft tissues.

Question 29

Levels of output power and intensity for color flow imaging are generally higher than those for conventional gray-scale imaging.
(A) true
(B) false

Answer 29

(A) True. Because the reflectivity of blood is low, many color flow systems improve color penetration by greatly increasing the power of the transmitted Doppler output.

Question 30

Because Doppler signal processing requires more energy, synchronous signal processing always produces Doppler power levels that are higher than those for gray-scale imaging.
(A) true
(B) false

Answer 30

(B) False. Synchronous signal processing systems are limited by the power levels of the common transmitter used for both gray-scale imaging and Doppler imaging. As a result, imaging with and without Doppler produces similar power levels.

Question 31

In general, tissue ultrasonic intensity levels are higher for single-point spectra than for color flow imaging with the same system.
(A) true
(B) false

Answer 31

(A) True. The single-point spectrum requires the ultrasound beam to linger over its position longer than is the case in either real-time gray-scale imaging or color flow imaging.

Question 32

Moving from gray-scale only to full-screen color flow
imaging in a system means that the image frame rate
will probably do which of the following?
(A) decrease
(B) increase
(C) stay the same
(D) color signal processing has no effect on frame rate

Answer 32

(A) Decrease. Color flow imaging requires dwelling on each line of sight for as few as four pulse-listen cycles to as many as 32 pulse-listen cycles. Various systems have different dwell times. The typical end result is a reduction in image frame rate for color flow imaging.

Question 33

Color flow imaging in the heart uses larger Doppler
sampling intervals to increase the image frame rate
than does vascular imaging.
(A) true
(B) false

Answer 33

(A) True. Real-time color flow imaging of the heart requires relatively high frame rates. In general, Doppler requires dwelling on each line of sight for some period of time. In addition, each Doppler sample site requires processing time to extract the average Doppler shift frequency. Restoring suitable cardiac frame rates requires decreasing the number of color flow lines of sight and the number of samples along each line.

Question 34

Cardiac color flow imaging also works well in the vascular system because the design can handle the high attenuation rates in cardiac imaging.
(A) true
(B) false

Answer 34

(B) False. Cardiac color flow imaging does not work well for vascular imaging because the Doppler sampling intervals are too large. Imaging the heart also involves a problem with reflectivities, not with tissue attenuation.

Question 35

Sampling intervals for cardiac color flow imaging and
vascular color flow imaging are similar.
(A) true
(B) false

Answer 35

(B) False. Doppler sampling for vascular imaging may be well below intervals of 1 rom. In contrast, sampling for echocardiography may be at intervals or several millimeters or more.

Question 36

Cardiac color flow imaging is limited with a mechanical sector scanner because
(A) the cardiac attenuation rate is too high
(B) the ultrasound beams are always moving
(C) the beam has a fixed focal point
(D) the beam has too many side lobes

Answer 36

(B) The ultrasound beams are always moving. This is the case because mechanical systems lack a special motor that could move the beam in small steps. Because Doppler signal processing is keyed to relative movement, and the beam is always moving, color does not work well in mechanical systems.

Question 37

The phased array sector scanner and the linear array
share common beam forming properties of (1) a stationary beam at each line of sight, (2) increased grating lobes with beam steering, (3) three-dimensional
dynamic focusing on receive, (4) the same aperture
sizes for dynamic focusing.
(A) 1 and 2
(B) 1, 2, and 4
(C) 2, 3, and 4
(D) all of the above

Answer 37

(A) 1 and 2. The linear phased array and the phased linear array have stationary ultrasound beams at each line of sight in the scanning plane. Both arrays also have increased grating lobes with beam steering. They do not have three-dimensional dynamic focusing or apertures necessarily of the same size.

Question 38

Color flow imaging in the peripheral vascular system 
typically uses 
(A) 	the phased sector scan 
(B) 	the linear array scan 
(C) 	the curved linear scan 
(D) 	a combination of A and B

Answer 38

(B) The linear array scan. The linear array with a rectangular scanning field is the geometry used for vascular imaging. The sector-scanning geometry makes reading color ambiguous in the straighter segments of a vessel.

Question 39

Color flow imaging in the heart typically uses 
(A) the phased sector scan 
(B) the linear array scan 
(C) the curved linear scan 
(D) a combination of A and C

Answer 39

(D) A combination of A and C. Color flow imaging of the heart uses the phased array sector scan and the curved-linear array sector scan. These scanheads permit cardiac imaging from intercostal and subcostal
windows.

Question 40

You are imaging a small vessel using 7.5 MHz DCFI
with the lowest displayable velocity of 6.0 cm/s. Changing only the carrier frequency to 5.0 MHz will change the lowest displayable velocity to
(A) 1.5 cm/s
(B) 9 cm/s
(C) 6.0 cm/s; the vessel does not change
(D) 15 cm/s

Answer 40

(B) 9 cm/s. Lowering the Doppler carrier frequency means that the same Doppler shift frequency requires a higher velocity to be just visible.

Question 41

Doppler color flow imaging is unique because it does not have a major problem with high-frequency aliasing.
(A) true
(B) false

Answer 41

(B) False. Like all pulsed Doppler systems, color systems will alias when the Doppler frequencies exceed the PRF sampling limit.

Question 42

Both the color and a point spectrum in a stenosis show
high-frequency aliasing. One strategy for removing
the aliasing involves
(A) doing nothing. Aliasing cannot be removed from
the system.
(B) decreasing the system PRF
(C) decreasing the carrier frequency
(D) decreasing the Doppler angle toward zero

Answer 42

(C) Decreasing the carrier frequency. This moves all Doppler frequencies downward and may bring the high aliasing frequencies below the aliasing limit.

Question 43

Increasing a sonograph’s output power levels and PRF
to increase penetration and frame rates opens the system to the following artifact:
(A) high-frequency aliasing
(B) loss of low velocities
(C) tissue mirroring
(D) range ambiguity

Answer 43

(D) Range ambiguity. High frame rates (high PRF) and high output power permit structures from outside the field of view to enter the image as a range ambiguity artifact.

Question 44

The color coding of red arteries and blue veins and the
slow high-resolution frame rates make the identity of
arteries and veins in the abdomen direct and easy.
(A) true
(B) false

Answer 44

(B) False. The large fields of view for abdominal imaging slow the frame rate. In addition, vessel anatomy goes in all directions. Sorting out arteries and veins requires the spectrum to determine pulsatility.

Question 45

Turbulence in a vascular color flow image appears as
(A) a mottled pattern of colors
(B) a mottled pattern of red and blue with changing saturations
(C) a mottled green region
(D) A or B

Answer 45

(D) A or B. In vascular color flow imaging, turbulence appears as broken streamlines. The image then takes on a mottled appearance either in color or in color saturation.

Question 46

Turbulence in a cardiac color flow image appears as
(A) a mottled pattern of colors
(B) a mottled pattern of red and blue with changing saturations
(C) a bright red region
(D) a mottled green region

Answer 46

(D) A mottled green region. In color flow echocardiography, the sampling intervals are too large to show turbulence. As a result, the system determines
the spectral variance at each sampling site and expresses increased turbulence (increased variance)
with increasing tones of green.

Question 47

Power Doppler Imaging is so named because
(A) it increases output power for image improvement
(B) it encodes the power spectrum of the Doppler signal into color
(C) it uses the phase of the amplitude to detect flow
(D) none of the above

Answer 47

(B) It encodes the power spectrum of the Doppler signal into color. Power Doppler looks at only the amplitudes of the Doppler signals in the I and Q channels.

Question 48

Power Doppler Imaging is limited because
(A) it has a serious aliasing problem
(B) it does not work with low carrier frequencies
(C) it does not show the directionality of vessel flow
(D) A and B

Answer 48

(C) It does not show the directionality of vessel flow.
Power Doppler uses only the amplitudes of the signals in the I and Q channels. Without phase information, power Doppler cannot show the direction of flow.

Question 49

Power Doppler imaging is a good choice when you
(A) want to show tissue perfusion
(B) want to show tissue velocity
(C) want to easily separate blood flow form simple tissue motion
(D) A and B

Answer 49

(A) Want to show tissue perfusion. Power Doppler will show wherever the system detects Doppler signal amplitudes. Thus, the color will distribute according to this signal map for both arteries and veins.