The physics of ultrasound

Question 1

What is B mode ultrasound?

Answer 1

Many 2D images can be generated per minute, and a moving image of the heart is made = real-time or B mode ultrasound.
Fig 1.1

Question 2

What is M-mode image=

Answer 2

By sending out only one sound beam instead of many, only the structures associated with that one beam are seen; producing an M-mode image. The structures associated with that one line through the heart keep scrolling on the screen as the heart continues to contract and relax. The M-mpde imager displays depth on the vertical axis and time along the horizontal axis.

Fig 1.2

Question 3

What is Doppler?

Answer 3

Doppler is used in diagnostic ultrasound to provide information on blood flow (spectral and color-flow Dopller) or myocardial motion (tissue Doppler imaging-TDI) of the heart and its vessels. Specific locations can be selected. As in M-mode, the horizontal axis represents time, while the vertical axis represents velocity.
Fig 1.3

Question 4

Sound waves travel in…… lines within the medium

Answer 4

longitudinal

Question 5

Sound waves: The molecules along that longitudinal course of movement in their pathway are alternately compressed (molecules move closer together) and rarefacted (molecules are ………)

Answer 5

spread apart

The time required for one complete compression and rarefaction to occur is one cycle.
(Figure 1.4).

Question 6

What is wavelength?

Answer 6

The distance in millimeters that the sound wave travels during 1 cycle is its wavelength

Question 7

What determines the length of a cycle?

Answer 7

The source of the sound. transducers generate the sound in diagnostic ultrasound. For any given transducers the wavelength is constant.

Question 8

What is the frequency?

Answer 8

The number of cycles per second is the frequency of the sound wave.
Fig 1.5

Question 9

Frequecency is measured in?

Answer 9

Hertz (Hz)

Question 10

1 Hz equals ……….per second.

Answer 10

once cycle

Question 11

Ultrasound has a frequency greater than …….cycles per second

Answer 11

20 000 cycles per second, which is beyond the range of human hearing

Question 12

Since frequency is the number of complete cycles per second; the higher the frequency of the sound wave the ……………..must be.

Answer 12

shorter the wavelength

Question 13

A 5.0 - megahertz (MHz) transducer transmits ………….. cycles per second at 0.31 millimeters (mm) per cycle, while a 2.0 - MHz transducer transmits only ……….. cycles per second at 0.77 mm per cycle.

Answer 13

A 5.0 - megahertz (MHz) transducer transmits 5 million cycles per second at 0.31 millimeters (mm) per cycle, while a 2.0 - MHz transducer transmits only 2 million cycles per second at 0.77 mm per cycle.

Table 1.1 lists wavelengths for sound generated at various frequencies.

Question 14

The speed of sound (V) depends upon the …………. and ……….. of the medium through which it is traveling.

Answer 14

The speed of sound (V) depends upon the density and stiffness of the medium through which it is traveling.

Question 15

Increased density allows sound to travel faster. Does the velocity of sound change within a homogeneous substance? Is the velocity dependent or independent of frequency?

Answer 15

Increased density allows sound to travel faster. The velocity of sound does not change within a homogeneous substance and is independent of frequency

(Figure 1.6 ). Table 1.2 lists the speed of sound in various tissues.

Question 16

The speed of sound through air is very …… because of its low density, while bone allows sound to travel at relatively …….. speeds.

Answer 16

The speed of sound through air is very slow because of its low density, while bone allows sound to travel at relatively high speeds.

Question 17

The average velocity of a sound wave in soft tissue is ……….. meters per second regardless of transducer frequency.

Answer 17

The average velocity of a sound wave in soft tissue is 1,540 meters per second regardless of transducer frequency (Figure 1.7 ).

Question 18

Velocity is calibrated into the ultrasound machine, which then calculates the distance (D) to cardiac structures based upon how long it takes to receive reflected echoes (T):

Hur är formeln?

Answer 18

D = V x T/2

Question 19

Does transducer frequency affect the speed of sound in tissues?

Answer 19

No

Question 20

The number of cycles per second is the frequency of the sound wave. Frequency is measured in Hertz (Hz). One Hz equals one cycle per second.
Hur många cyklar är 5 Hz?

Answer 20

5 cycles/sec

Fig 1.5

Question 21

Increased tissue density allows sound to travel faster. Why will sound generated by a 2.5 - MHz transducer and a 5.0 - MHz transducer have the same velocity within the same tissues?

Answer 21

Sound generated by a 2.5 - MHz transducer and a 5.0 - MHz transducer will have the same velocity within the same tissues since the speed of sound is not affected by frequency. Fig 1.6

Se tabel 1.1 and 1.2

Question 22

Sound travels through soft tissues at an average velocity of ………… m/sec regardless of transducer frequency.

Answer 22

Sound travels through soft tissues at an average velocity of 1,540 m/sec regardless of transducer frequency.

The time required to travel 1 cm at 1,540 m/sec is 6.5 microseconds ( μ sec) one way and 13 μ sec round trip.

Fig 1.7

Question 23

The time (T) required to travel 1 cm is ……….. microseconds or ……..microseconds round trip.

Answer 23

The time (T) required to travel 1 cm is 6.5 microseconds or 13 microseconds round trip.

Even though sound must travel through various tissues with slightly different velocities during an echocardiographic exam, the equipment is calibrated for the average speed of sound in soft tissues (1,540 meters per second). Structures are displayed on a monitor at the calculated depth, and an image of the heart is created. This always creates some degree of error in calculating true structure depth, but the error is generally negligibl

Question 24

What is Acoustic Impedance?

Answer 24

Acoustic impedance is the opposition or resistance to the flow of sound through a medium.

Question 25

Impedance depends upon the density and stiffness of the medium. Is impedance dependent or independent of frequency?

Answer 25

Impedance is independent of frequency.

Very stiff or hard materials are hard to compress and rarefact. Therefore, although increased density increases the speed of sound, if the ability to compress and rarefact a sound wave is limited, the impedance or resistance to sound transmission is high.

Question 26

Contradictory as it sounds, the higher the density and the greater the velocity of sound through a medium, the ……….. the resistance is to sound transmission.

Answer 26

Contradictory as it sounds, the higher the density and the greater the velocity of sound through a medium, the greater the resistance is to sound transmission.

Table 1.3 lists the acoustical impedance of sound in various tissues. Because of its stiffness and inability to compress and rarefact molecules easily, bone has high impedance, while air, because its molecules are easily compressed and rarefacted, has low impedance.

Question 27

High …………….. is what produces a high degree of sound reflection at bony or air interfaces, creating a shadow on the ultrasound image beyond the bone or air due to lack of further sound transmission.

Answer 27

High acoustical impedance is what produces a high degree of sound reflection at bony or air interfaces, creating a shadow on the ultrasound image beyond the bone or air due to lack of further sound transmission.

Question 28

Reflection of sounds depends upon (3)?

Answer 28

1: acoustical mismatch: The greater the difference in acoustical properties the greater the degree of reflection.
2. angle of incidence: Sound striking an organ perpendicularly will have a large amount of sound reflected straight back to the transducer.
3. Depends upon reflecting structure ’ s size: Must be at least 1/4 size of the wavelength. Higher frequency transducers can reflect sound from smaller structures.

Question 29

What is reflection?

Answer 29

Sound that is turned back at a boundary within a medium. These reflected echoes are called specular echoes. When an interface between two tissues with different acoustical impedances is reached, a portion of the sound is reflected back to the transducer. The rest continues on through the tissues.

Question 30

The greater the difference in acoustical impedance the ………….. the degree of reflection.

Answer 30

The greater the difference in acoustical impedance the greater the degree of reflection.

For the same reason, if two boundaries have little or no acoustical mismatch they will not be identifi ed as two different tissues. Therefore interfaces between muscle and fluid, as in the heart, will reflect sound at different intensities while the cells within the homogeneous muscle itself will reflect sound with similar strengths.

All interfaces between muscle and blood - filled chambers in the heart have slightly brighter boundaries on the ultrasound image because of this increased reflection. The interface between tissue and air has an even greater difference in acoustical impedance, and therefore the pericardial sac around the heart is always one of the brightest structures on the ultrasound image.

Question 31

Why is gel placed between the transducer and skin surface?

Answer 31

The gel placed between the transducer and skin surface is used to prevent the large degree of reflection ordinarily seen between a tissue and air interface.

Question 32

The angle at which sound strikes the reflective surface (the angle of incidence) determines the angle of reflection. The angle of reflection is equal to the angle of ……………

Answer 32

The angle at which sound strikes the refl ective surface (the angle of incidence) determines the angle of refl ection. The angle of reflection is equal to the angle of incidence (Figure 1.8 ).

Question 33

When sound is directed perpendicular to a structure the angle of incidence is zero and the sound is reflected straight back to the transducer. If the angle of incidence is 50 ° , then the angle of reflection will be also be 50 ° . When the angle of incidence is 90 ° or parallel to the interface: How will the reflection be?

Answer 33

When the angle of incidence is 90 ° or parallel to the interface, no sound will be refl ected back to the source.

This principle tells us that the best two - dimensional and M - mode cardiac images are obtained when sound is directed perpendicular to the tissues.

Question 34

Not all sound is reflected however, and some continues on through the tissues. These sound waves are refracted if the two tissues are different. What is refraction?

Answer 34

(Figure 1.8 ): Refraction is the change in direction of sound as it travels from one medium to another.

This is similar to what happens when light waves in water create a distorted image.

Question 35

The …………… the mismatch in acoustical impedance between the two tissues the greater the degree of refraction.

Answer 35

The greater the mismatch in acoustical impedance between the two tissues the greater the degree of refraction.

As the refracted sound beam travels in a new direction, the angle of reflection with respect to the original source is different, and posi- tional errors can result since the transducer thinks the received sound is coming from the same direction as the sound waves it generated earlier.

Question 36

The errors produced by refraction during an examination create few problems unless the refracted beam has to travel a great distance. An angle of 1 or 2 degrees at the top of the refracting tissue can result in a several millimeter error in position by the time it reaches the far side of a deep structure. When the two mediums differ enough to create a refractive angle of greater than …… ° (as with soft tissue and bone) then an image is not generated beyond the second structure.

Answer 36

When the two mediums differ enough to create a refractive angle of greater than 90 ° (as with soft tissue and bone) then an image is not generated beyond the second structure.

Question 37

Figure 1.8 : The angle of reflection is equal to?

Answer 37

The angle of reflection is equal to the angle at which sound strikes the tissue. Sound that is directed perpendicular to the tissue is reflected straight back to the transducer producing the best images.

Question 38

Sound is refracted when it crosses a boundary between two different tissues. The greater the ………………. in acoustical properties between the two tissues, the greater the degree of refraction.

Answer 38

Sound is refracted when it crosses a boundary between two different tissues. The greater the difference in acoustical properties between the two tissues, the greater the degree of refraction.

Question 39

Reflection of sound is not only dependent upon the acoustical mismatch of two tissues but also ………….?

Answer 39

Reflection of sound is not only dependent upon the acoustical mismatch of two tissues but also upon the structure’ s size. The structure must be at least one quarter the size of the wavelength for reflection to occur..

Question 40

The short 0.21 - mm wavelengths of a 7.5 - MHz transducer are reflected from structures that are as small as 0.05 mm in thickness, while structures must be at least 0.19 - mm thick for the 0.77 - mm wavelengths of a 2.0 - MHz transducer to be reflected. High frequency transducers then, provide higher resolution images: why?

Answer 40

Because smaller structures reflect their sound waves.

Question 41

↑ Frequency = …. Wavelength = .. Resolution

Answer 41

↑ Frequency = ↓ Wavelength = ↑ Resolution

Question 42

↓ Frequency = .. Wavelength = … Resolution

Answer 42

↓ Frequency = ↑ Wavelength = ↓ Resolution

Question 43

Structures that are small and irregular with respect to the sound wave do not reflect sound but rather ……………..

Answer 43

Structures that are small and irregular with respect to the sound wave do not refl ect sound but rather scatter it in all directions without regard for the angle of incidence (Figure 1.9 ).

Some of this scattered sound is directed back to the sound source and is what allows ultrasound to give us information about tissue character. Scattered sound is important for the generation of images from objects with large angles of incidence to the sound beam or small structure - like cells.

Question 44

Scattered sound is important in ……

Answer 44

In tissue characterization

Question 45

Sound traveling through a medium is weakened by reflection, refraction, scattering, and absorption of heat by the tissues. This loss of energy is called ……….

Answer 45

Attenuation

Question 46

High frequency sound attenuates to a greater degree than lower frequency sound. Why?

Answer 46

High frequency sound attenuates to a greater degree than lower frequency sound because its wavelength allows it to interact with more structures.

This is the reason the deep bass sounds of an orchestra carry farther than the high - pitched sounds. The large degree of attenuation with high frequency sound leaves less energy available for continued transmission through the medium.

Question 47

↑ Frequency = ….. Depth

Answer 47

↑ Frequency = ↓ Depth

Question 48

↓ Frequency = ….. Depth

Answer 48

↓ Frequency = ↑ Depth

Question 49

What is the half-power distance of a tissue?

Answer 49

The half-power distance of a tissue is the distance sound will travel through it before half of the available sound energy has been attenuated.

Table 1.4 lists the half - power distances of various tissues at two different frequencies. The data in this table clearly show that low frequency sound waves are able to penetrate tissues deeper than higher frequency sound waves.

Question 50

Air attenuates half of the sound energy within 0.05 centimeter (cm) when a 2.0 - MHz transducer is used. What happens with sound energy after 0.05 cm?

Answer 50

Therefore, although the density of air creates less impedance for sound, little sound energy is left for image generation from soft tissues after 0.05 cm.

Gel is used to eliminate the air between the transducer and skin, which would otherwise attenuate sound dramatically.

Question 51

What is tissue harmonic imaging?

Answer 51

When ultrasound is transmitted at one frequency and returned at twice or more the transmitted frequency, it is called tissue harmonic imaging.

Question 52

Sound waves change from their sinusoidal shape as they travel through tissues to nonsinusoidal waves. What is this caused by?

Answer 52

This is caused by changes in pressure, with the higher pressure portion of the sound waves traveling faster than the slower portions.

These nonsinusoidal waves contain additional frequencies in multiples of the fundamental or originating frequency. These even and odd multiples of the fundamental frequency are called harmonic frequencies.

Question 53

When using harmonic imaging the fundamental frequency is filtered out and second harmonic waves are used to generate the ultrasound image. This imaging mode is used to enhance what?

Answer 53

This imaging mode is used to enhance the definition of endocardial borders and reduces the generation of artifacts, especially in patients with poor acoustic windows.

Question 54

Poor image quality is usually the result of factors like fat, muscle, and fibrosis that are present before the sound beams have even entered the tissue of interest.

These factors create variations in…?

Answer 54

These factors create variations in the speed of sound and create distortion of the sound beam and the resulting ultrasound image.

Question 55

Where are the harmonic frequencies created?

Answer 55

The harmonic frequencies are created in the chest from the reflected sound and not at the chest wall where most artifacts originate; this results in the alleviation of imaging artifacts especially side lobe artifact. It also enhances contrast resolution of the ultrasound image.

The result is improved image quality with reduced artifact generation, enhanced endocardial details, improved contrast, and decreased noise.

(There are some patients in which harmonic imaging does not improve image quality because of frequency dependent attenuation of sound).

Question 56

Transducers are the source of sound in diagnostic ultrasound. Transducers contain piezoelectric crystals that are deformed by electrical voltage and generate sound. These crystals, often called elements, are also able to receive sound and convert it back into electrical energy. The………….of the crystal dictates the basic operating frequency of the transducer.

Answer 56

The thickness.

Question 57

Wavelength will be one-half of the element thickness so decreased crystal thickness produces ……… wavelengths and ………. frequencies.

Answer 57

Wavelength will be one-half of the element thickness so decreased crystal thickness produces shorter wavelengths and higher frequencies.

Question 58

Transducers used in pulsed - echo applications do not transmit sound ………………. They send sound waves out in ………………………….This is called pulsed ultrasound.

Answer 58

Transducers used in pulsed - echo applications do not transmit sound continuously. They send sound waves out in short bursts and receive sound the remainder of the time. This is called pulsed ultrasound.

Question 59

The number of pulses per second is referred to as the ……………….. which is measured in ……..

Answer 59

The number of pulses per second is referred to as the pulse repetition frequency (PRF). PRF is measured in Hz.

The PRF for example would be 10 Hz if there are 10 pulses per second (Figure 1.10 ).

Question 60

Each pulse may have any number of cycles, but in diagnostic ultrasound, there are generally ……….. cycles per pulse.

Answer 60

Each pulse may have any number of cycles, but in diagnostic ultrasound, there are generally two or three cycles per pulse.
The number of cycles per pulse is controlled by damping materials within the transducer.

Question 61

The duration of a pulse, measured in microseconds, and pulse length, measured in mm, decreases if the frequency of the sound wave ……………… since the wavelengths are shorter (Figure 1.10 ). By the same token, …………. frequency sound waves have longer wavelengths so pulse duration and length are increased.

Answer 61

The duration of a pulse, measured in microseconds, and pulse length, measured in mm, decreases if the frequency of the sound wave increases since the wavelengths are shorter (Figure 1.10 ). By the same token, lower frequency sound waves have longer wavelengths so pulse duration and length are increased.

Question 62

Accurate ultrasound images can only be generated if all reflected and scattered echoes are received at the transducer before the next pulse is generated. The transducer assumes that the echoes it receives are products of its last burst. If an echo has not been received before the next burst and it arrives at the transducer shortly after the second burst, then the instrument “ thinks ” very little time has elapsed since it was transmitted and received. Since time is used along with the speed of sound in tissues to determine structure depth, a structure that is actually deeper will be displayed closer to the body surface (Figure 1.11 ). Pulse repetition frequency must ……………. as deeper structures are imaged for accurate depth assessment.

Answer 62

Pulse repetition frequency must decrease as deeper structures are imaged for accurate depth assessment.

Question 63

A sound wave must be transmitted, reflected, and received by the transducer before the next pulse is generated. The number of pulses per second is the ……………

Answer 63

A sound wave must be transmitted, refl ected, and received by the transducer before the next pulse is generated. The number of pulses per second is the pulse repetition frequency. Pulse repetition frequency must decrease for accurate structure localization when interrogating deeper structures.

Question 64

Sound beams generated by transducers are three dimensional. They not only have pulse length and duration but they also have beam ………..and……….

Answer 64

Sound beams generated by transducers are three dimensional. They not only have pulse length and duration but they also have beam widths and thicknesses.

Question 65

Beam diameter determines the …….. within the scan plane and the……….. perpendicular to the scan plane.

Answer 65

Beam diameter determines the width within the scan plane and the thickness perpendicular to the scan plane.

Question 66

Sound beams do not remain the same width as they travel through a medium. In an unfocused transducer the sound beam starts out with a width equal to the transducer diameter and, as it travels through the tissues, it……………….

Answer 66

In an unfocused transducer the sound beam starts out with a width equal to the transducer diameter and, as it travels through the tissues, it diverges (Figure 1.12 ).

Question 67

The distance from the transducer element to where it diverges is the beam’ s …………. The area beyond the near field is the ……….

Answer 67

The distance from the transducer element to where it diverges is the beam’ s near field. The area beyond the near field is the far field.

Question 68

Near field length is directly proportional to the beam diameter and inversely proportional to wavelength (Figure 1.12 ). For two transducers of the same frequency, the ……………….. will be longer for the transducer with the larger diameter.

Answer 68

Near field length is directly proportional to the beam diameter and inversely proportional to wavelength (Figure 1.12 ). For two transducers of the same frequency, the near field will be longer for the transducer with the larger diameter.

Question 69

For two transducers with the same diameter, the near field will be longer for the …………… frequency transducer.

Answer 69

For two transducers with the same diameter, the near field will be longer for the higher frequency transducer.

Question 70

Near field =

Answer 70

radius2 /wavelength

Question 71

Larger beam width =

Answer 71

longer near field

Question 72

shorter wavelength =

Answer 72

longer near field

Question 73

Far field divergence is also dependent upon transducer size. ………… diameter transducers produce less divergence in the far field.

Answer 73

Larger diameter transducers produce less divergence in the far field.

Question 74

………. frequency transducers with ……….. diameters therefore produce the longest near field and the narrowest far field (Figure 1.12 ).

Answer 74

High frequency transducers with large diameters therefore produce the longest near field and the narrowest far field (Figure 1.12 ).

Question 75

When a curved element or lens is used, the beam can be focused and beam width will ………… throughout the entire near field and create a …………. zone, but beam width will diverge rapidly beyond this focal point (Figure 1.13 ).

Answer 75

When a curved element or lens is used, the beam can be focused and beam width will decrease throughout the entire near field and create a focal zone, but beam width will diverge rapidly beyond this focal point (Figure 1.13 ). Many transducers today have variable focal zones that the examiner can set.

Question 76

If multiple pulses are generated and each pulse is set to a different focal zone; then an ………….. focal zone can be created.

Answer 76

If multiple pulses are generated and each pulse is set to a different focal zone; then an elongated focal zone can be created. The transducers simply ignores echoes returning from depts other than the focal depth for any given pulse.

Question 77

Up to this point only single sound beams have been considered. …………………. sound beam is used to generate an M-mode image of the heart.

Answer 77

Up to this point only single sound beams have been considered. A single sound beam is used to generate an M-mode image of the heart. This beam travels through the cardiac structures and a one-dimensional image is generated.

Question 78

B-mode or 2-D imaging uses an array (group) of crystals that are electronically triggered to generate sound waves. It is important to recognize that each sound beam generated by a transducer is affected by…? (4)

Answer 78

pulse length,
beam width,
focal length,
PRF.

Question 79

Linear array transducers have multiple elements arranged in ………….

Answer 79

Linear array transducers have multiple elements arranged in a row. Sequences of elements are electronically stimulated at one time (i.e. elements one through four, then elements two through five, etc) with each group producing one scan line. This producers a high quality image with increased line density within the generated image.

Question 80

Fig 1.12: The distance from a transducer element to where the beam diverges is referred to as the ………. The area beyond that is the …………

Answer 80

Fig 1.12: The distance from a transducer element to where the beam diverges is referred to as the near field. the area beyond that is the far field.

Question 81

Fig 1.13. A sound beam can be focused by using a ………….or……………. This decreases beam width within the near field.

Answer 81

Fig 1.13. A sound beam can be focused by using a curved element or lens. This decreases beam width within the near field.

Question 82

Linear array transducers can be modified into curvilinear formats.

Answer 82

Linear array transducers can be modified into curvilinear formats.

Question 83

Phased array transducers stimulate each crystal with a small time interval (less than a ……………) between them and they are directed through the tissues at slightly different …….. (phased).

Answer 83

Phased array transducers stimulate each crystal with a small time interval (less than a microsecond) between them and they are directed through the tissues at slightly different angles (phased). (fig 1.14). This produces a sector image and these transducers are often called electronic sector transducers.
Rapidly stimulating these elements over and over again in sequence produces the moving cardiac images we call real-time ultrasound.

Question 84

What is resolution?

Answer 84

Resolution is the ability to identify 2 objects as different.

Question 85

Pulse length, beam width, beam diameter, focal length, and PRF are important physical aspects of transducers that affect the …………………..(3) resolution of ultrasound images.

Answer 85

Pulse length, beam width, beam diameter, focal length, and PRF are important physical aspects of transducers that affect the axial, lateral, and temporal resolution of ultrasound images.

Question 86

What is axial resolution?

Answer 86

Ability to differentiate between 2 structures along the length of the sound beam. Axial resolution is also called depth or longitudinal resolution. The smaller the axial resolution is, the better the detail of the image.

Question 87

What is lateral resolution?

Answer 87

Ability to resolve 2 structures in the plane perpendicular to the sound beam

Question 88

What is temporal resolution?

Answer 88

Ability to resolve structures with respect to time, keeping up with the actual events.

Question 89

Transducers ………. plays an important role in axial resolution.

Answer 89

Transducers frequency plays an important role in axial resolution.

Question 90

Axial resolution is equal to half the pulse length; that is?

Answer 90

Axial resolution is equal to half the pulse length; that is 2 structures cannot be closer than half the pulse length to each other in order to be distinguished as 2 separate things.

Question 91

Remember that pulse length depends upon…….? (2)

Answer 91

The wavelength of the sound and upon the number of cycles per pulse.

When one or both of these is reduced axial resolution improves. (Fig 1.15)

Question 92

Is the axial resolution better with 7.5 MHz frequency sound or with 3.5 MHZ frequency sound? Why is it so?

Answer 92

Wavelength decreases as frequency of sound increases, so axial resolution is better with 7.5 MHz.

Question 93

Pulse length and duration are shortened by adding ………?

Answer 93

Pulse length and duration are shortened by adding damping materials within the transducer or electrical damping with the equipment.

Question 94

A pulse may have any number of cycles (generally …..or…. in echo).

Answer 94

A pulse may have any number of cycles (generally 2 or 3 in echo).

Question 95

Pulse length decreases with higher frequency sound because of?

Answer 95

shorter wavelengths

Question 96

Pulse length increases with….?

Answer 96

with lower frequency sound

Question 97

Better axial resolution=

Answer 97

Better image detail. Axial resolution improved with increased frequency and decreased pulse length. 2 things must be farther apart than one-half the pulse length to be identified as 2 different structures. Fig 1.15

Question 98

Axial resolution is equal to?

Answer 98

Half the pulse length

Question 99

Higher frequency transducers have better ……..resolution

Answer 99

Better axial resolution

Question 100

Higher frequency = ….resolution

Answer 100

Higher resolution

Question 101

Lower frequency =

Answer 101

Lower resolution

Question 102

Lateral resolution is the ability to ?

Answer 102

The ability to resolve 2 structures as distinct and different in a plane perpendicular to the sound wave and depends upon beam width. 2 structures that fall within the beam width will not be differentiated while 2 structured that are farther apart than the beam width will be identified as separate.

(the axial resolving powers of the system may differentiate 2 structures that fall within beam width when they are offset in depth. Fig 1.16.

Question 103

Lateral resolution is equal to?

Answer 103

Equal to beam width and improves with smaller beam widths.

Question 104

Beam width is affected by?

Answer 104

1) Focusing the sound waves generated by a transducer
2) Transducer diameter
3) Transducer frequency

Question 105

The narrower the beam width the better the ability to differentiate between ….?

Answer 105

The narrower the beam width the better the ability to differentiate between 2 structures in a plane perpendicular to the sound beam. Fig 1.16

Question 106

Beam width varies along the length of the sound wave but is at is narrowest at the focal zone in focused transducers. Lateral resolution is best (smallest) at…..

Answer 106

At the focal zone.

Question 107

What happens with 2 structures that are side by side within the boundaries of the beam width?

Answer 107

2 structures that are side by side within the boundaries of the beam width will not be resolved as 2 different structures. Fig 1.16.
If they are offset a little in depth however, they may be resolved as 2 different structures based upon axial resolving powers of the transducer (fig 1.16).

Question 108

Lateral resolution improves with …………. beam widths.

Answer 108

Lateral resolution improves with narrower beam widths

Question 109

Lateral resolution is usually narrowest at ………… zones of ………….. transducers.

Answer 109

Lateral resolution is usually narrowest at focal zones of focused transducers.

Question 110

Lateral resolution is best within…?

Answer 110

Lateral resolution is best within near field where beam width is narrowest.

Question 111

A high frequency transducer will have better lateral resolution than a lower frequency transducer of the same size. Why?

Answer 111

A high frequency transducer will have better lateral resolution than a lower frequency transducer of the same size because of its longer near field.

Question 112

Long narrow near fields allow more …………………… of the heart to be images; creating less ambiguity about the source of the returning echoes (lateral position errors).

Answer 112

Long narrow near fields allow more specific areas of the heart to be images; creating less ambiguity about the source of the returning echoes (lateral position errors).

Question 113

Longer near field length, focused transducer beams, and less far field divergence also improve image quality by increasing beam ………..

Answer 113

Longer near field length, focused transducer beams, and less far field divergence also improve image quality by increasing beam strength. Stronger beams increase the degree of reflection and can travel farther before all the sound is attenuated.

Question 114

The number of real-time images produced per minute is referred to as the ………..

Answer 114

frame rate

Question 115

The frame rate is dependent upon?

Answer 115

The PRF ( pulse repetion frequency)

Question 116

The faster the frame rate, the faster the …….

Answer 116

The faster the frame rate, the faster the PRF

Question 117

Faster frame rates produces better

Answer 117

Temporal resolution (resolution with respect to time)

Question 118

Logically; rapidly moving structures require fast frame rates in order to prevent ……

Answer 118

slow motion or freeze frame images of cardiac motion.

Question 119

Temporal resolution is dependent upon frame rate. reduce ………in order to improve the frame rate

Answer 119

sector width and reduce image depth

Question 120

Sector transducers that emit multiple pulses with varying focal zones per scan line must wait until ……..?

Answer 120

Sector transducers that emit multiple pulses with varying focal zones per scan line must wait until all sound has returned before generating the next set of pulses. Otherwise range or depth ambiguity results. In doing so the frame rate and temporal resolution of the generated 2 D image is reduced.

Interrogation of deep structures also requires a slower frame rate ans less temporal resolution is possible.

It is possible to increase PRF in both of these settings by reducing sector width and/or image depth since less time is required before the next frame can be produced.

Question 121

Doppler allows detection and analysis of …..

Answer 121

moving blood cells or myocardium

Question 122

Doppler tells us about the direction, velocity, character, and timing of …….or …….

Answer 122

of blood flow or muscle motion

Question 123

The hemodynamic information provided by Doppler echo allows definitive diagnosis in most cardiac examinations by giving information about: (4)

Answer 123

Direction
Velocity
Character
Timing

Question 124

4 types of Doppler used during av echo exam:

Answer 124

Pulsed wave (PW) Doppler
Continous wave (CW) Doppler
Color flow (CF) Doppler
Tissue Doppler imaging (TDI)

Question 125

PW Doppler is ….specific

Answer 125

Site specific: It can be directed and set to sample flow at very specific places within the heart.

Question 126

Limitation with PW Doppler?

Answer 126

Limited in its capacity to detect higher frequency (velocity) shifts

Question 127

CW Doppler has the ability to detect higher frequency shifts: Any limits in flow velocity detection?.

Answer 127

CW Doppler has the ability to detect higher frequency shifts and therefore can record high-flow velocities with virtually no limits.

Question 128

Limitation with CW Doppler

Answer 128

Not site specific: blood cells are examined all along the sound beam. Since sound is continuously transmitted and received in CW Doppler, it is not possible to select and interrogate at specific depths within the heart. However, although this may sound like a disadvantage, the information provided by CW Dopller is very valuable.

Question 129

Color flow Doppler is a form of PW Doppler. Frequency shifts are encoded with varying hues and intensities of color. Flow information is very vivid, and detection of abnormal flow is easier with CW Doppler although ……………….information is limited

Answer 129

Quantitative.

CF Doppler: color codes the various velocities and directions of flow.

Question 130

TDI uses pulsed-wave Doppler to interrogate myocardial motion and velocities. It is used to assess both ……………..and……….myocardial function and synchronicity

Answer 130

Systolic and diastolic myocardial function and synchronicity

Question 131

The Doppler effect: Christian Dopppler found that all types of waves (light, sound, etc) change in wavelength when there is a change in position between…?

Answer 131

……the source of the wave and the receiver of the wave.

Question 132

Using sound; if you were moving toward a sound source; the pitch or frequency of that sound would increase, and if you were moving away from that sound source, the frequency would decrease.
What is the Doppler shift?

Answer 132

The change in wavelength (pitch and frequency) when there is a change in position between the sound source (sound that is transmitted) and the reflecting structure (blood cells in this case) (sound that is received).

Question 133

What happens when the source and the reflecting surface are both stationary?

Answer 133

When the source and the reflecting surface are both stationary, the transmitted (incident) and reflected wavelengths are equal (Fig 1.17).

Question 134

What happens when the reflecting structure is moving toward the source?

Answer 134

Sound waves are encountered more often, resulting in an increased number of waves (= increased frequency) being reflected back toward the source.

Question 135

What happens when the reflecting structure is moving away from the source?

Answer 135

they travel ahead of the transmitted wave front and sound waves are encountered less frequently resulting a decreased number of sound waves (lower frequency) reflected back to the source.

Question 136

Positive frequency shift?

Answer 136

Cells moving toward the transducer reflect an increased number of sound waves, and so the received frequency is greater than the transmitted frequency.

Question 137

Negative frequency shift?

Answer 137

Cells moving away from the transducer reflect fewer sound waves, and the received frequency is less than the transmitted frequency.

Question 138

Everyday ex of Doppler shift include any loud sound moving toward or away from you such as sirens, trains, marching bands, etc.

The sound of a siren as it approaches you will increase in pith (frequency increases) and then as it passes you, the pith will decrease (frequency decreases).
Doppler radar uses this principle when policemen determine the speed of your car; Howecome?

Answer 138

Since the frequency shift is used to determine velocity.

Doppler radar is also used in forecasting weather

Question 139

The Doppler shift as we utilize it in diagnostic ultrasound is?

Answer 139

The difference in frequency transmitted by the transducer and received frequency reflected from blood cell.

Question 140

The Doppler-derived frequency shift (fd) is equal to reflected frequency minus transmitted frequency. Therefore; objects moving toward the source result in …………. frequency shifts while objects moving away from the source result in …………frequency shifts.

Answer 140

Therefore; objects moving toward the source result in positive frequency shifts while objects moving away from the source result in negative frequency shifts.

Question 141

The site (gate) for Doppler flow interrogation is selected by the examiner and is represented on the Doppler display as a line (baseline). Positive frequency shifts (flow moving ………….. the transducer) produce waveforms up from the baseline while negate frequency shifts (flow moving ……………from the transducer) produce downward deflection of the Doppler tracings.

Answer 141

Positive frequency shifts (flow moving toward the transducer) produce waveforms up from the baseline while negate frequency shifts (flow moving away from the transducer) produce downward deflection of the Doppler tracings.
Figure 1.18.

These images are called spectral tracings.

Question 142

The velocity range is split between the positive and negative directions of flow. What happens when the baseline is located in the middle of the spectral display?

Answer 142

The total velocity range is displayed equally above and below the baseline (Figure 1.19).

When the baseline is moved all the way to the top of the image, the entire velocity range is allocated to downward flow. When it is moved to the bottom of the image, the entire velocity range is allocated to upward flow.

Question 143

PW Doppler: pulsing the sound waves allows a transducer to act as receiver for the signal only during the time interval specified by a sample depth. With PW Doppler the transducer will record frequency shifts only during ………………………

Answer 143

With PW Doppler the transducer will record frequency shifts only during the time interval dictated by the depth of the sample site ignoring all other returning echoes.
Fig 1.20
New sound waves will not be transmitted until the transducer has received the echoes from the previous burst.

Question 144

PW Doppler: The ability to measure velocity within a small cell at a specified depth along the ultrasound beam is referred to as ……………….., and the site at which sampling is set to occur is referred to as the …………..

Answer 144

The ability to measure velocity within a small cell at a specified depth along the ultrasound beam is referred to as range resolution, and the site at which sampling is set to occur is referred to as the gate. The gate is manually set by the examiner while watching a 2D image.

Question 145

CW Doppler: continuously sends out sound and continuously receives sound. Is it possible to range gate CW Doppler?

Answer 145

No, because the transducer has no way of detecting the depth of the reflected signal. CW Doppler detects frequency shifts all along the ultrasound beam with no range resolution.

Question 146

CW Doppler is steered in one of two ways:
1) ………….. CW systems use a cursor representing the Doppler sound beam. The cursor is placed over the 2D image and frequency shifts are calculated all along the beam.

2)………………CW systems use a dedicated CW probe without the luxury of a 2D image.

Answer 146

1) Imaging CW systems use a cursor representing the Doppler sound beam. The cursor is placed over the 2D image and frequency shifts are calculated all along the beam.
2) Non-imaging CW systems use a dedicated CW probe without the luxury of a 2D image.

These systems require recognition of characteristic flow profiles.

Question 147

Velocities along the beam vary, and a full spectrum of frequency shifts is detected with CW Doppler. When CW Doppler is used properly, the highest ………………..long the line of interrogation are recorded.

Answer 147

When CW Doppler is used properly, the highest velocities along the line of interrogation are recorded.
Figure 1.21.

The highest velocities are generally what is of interest and diagnostically important. Lower velocity flow found along the Doppler line of interrogation are hidden within the higher flow profiles.

Flow patterns for the various valves and vessels in the heart are very characteristic and usually are easily identified with both PW and CW Doppler.

Question 148

Doppler ultrasound can determine blood cell velocity within the heart or in peripheral vessels based upon the Doppler shift. Blood cell velocity (V) is determined using the following formula:

Answer 148

se Equation 1.3 s 18

Shows that V is equal to the speed of sound in tissues (C) times the frequency shift (fd) in kHz, divided by the transmitting frequency of the transducer f0 (2.5, 3.5, 5.0 etc) times the cosine of 0 where 0 where 0 is equal to the intercept angle of the ultrasound beam with respect to the blood flow.

The speed of sound in tissues is a constant (1.540 m/sec), leaving the interrogation angle, 0, and transducer frequency as variables that can be controlled.

Question 149

Velocity measurement: Accurate measurements are affected by? (2)

Answer 149

1. Transducer frequency

2. Intercept angle

Question 150

Angle of Interrogation: The closer to …………… the transmitted wave is with the direction of blood flow being interrogated, the more accurate the velocity measurement.

Answer 150

The closer to parallel the transmitted wave is with the direction of blood flow being interrogated, the more accurate the velocity measurement.
(Fig 1.22)

Question 151

When the Doppler equation is changed to calculate for the frequency shift, you can see that the cosine of the intercept angle directly affects the frequency shift (fd)

Answer 151

Equation 1.4

Since the speed of sound in tissues (C) and the transmitting frequency (f0) is known, the calculated frequency shift and therefore the calculated flow velocity is directly dependent upon the cosine of the intercept angle. The cosine of 0 grader (symbol) is one. The value increases, and by the time an angle of 90 grader is reached, the cosine is zero.

Question 152

Table 1.5 lists the cosines for several angles. Larger intercept angles and cosines of less than one falsely decrease the recorded frequency shift of blood flow. Generally, interrogation angled greater than ….-…… grader are considered unacceptable.

Answer 152

Generally, interrogation angled greater than 15-20 grader are considered unacceptable.

The graph in Figure 1.23 shows the relationship between the cosine of the angle of incidence with respect to blood flow and the calculated velocity for a 5.0 MHz transducer.

Question 153

Can velocity be overestimated?

Answer 153

Velocity cannot be overestimated, just underestimated, when interrogation angles with respect to flow become larger than zero.

Question 154

PW Doppler measures the frequency shift at very specific locations within the heart. Just like 2D and M-mode imaging, the reflected signal must be received before the next pulse is transmitted or there will be ambiguity in the recorded signals. The time interval between pulses must be ….. times the sample depth and is also referred to as the …………….

Answer 154

The time interval between pulses must be 2 times the sample depth and is also referred to as the pulse repetition frequency (PRF).

Question 155

Decreased PRF decreases the ………………… shift that can be accurately measured.

Answer 155

Decreased PRF decreases the Doppler frequency shift that can be accurately measured.

Fig 1.24 shows how sampling frequency affects your perception of events. As the sampling frequency decreases, information is lost. Time on the clock in Figure 1.24 is perceived correctly until the sampling frequency decreases to two times per minute. At that rate it is not possible to determine whether the hand on the clock is moving clockwise or counterclockwise. This is similar to what happens in movies when wheels on vehicles appear to rotate backwards.

Question 156

The sampling rate (PRF) must be at least 2 times the frequency shift for unambiguous flow information to be received by the transducer. Equation 1.5 states the maximum Doppler shift that can be recorded accurately is equal to one-half the PRF.

Answer 156

Doppler shift = 1/2 PRF

Equation 1.5

Question 157

The best Doppler recordings at any given depth are obtained with ……………… frequency transducers.

Answer 157

The best Doppler recordings at any given depth are obtained with lower frequency transducers.

Question 158

…………….. of the PRF is referred to as the Nyquist limit. When the Nyquist limit is exceeded signal ambiguity results. This ambiguity is called ……………….

Answer 158

One-half of the PRF is referred to as the Nyquist limit. When the Nyquist limit is exceeded signal ambiguity results. This ambiguity is called aliasing.

Figure 1.25 shows an aliased Doppler display.

Question 159

When the Nyquist limit is exceeded ny larger degrees, the aliased signal no longer displays the characteristic flow profile and direction can no longer be determined (Figure 1.26). Switching to …………. allows flows velocities that exceed the Nyquist limit to be recorded accurately.

Answer 159

Switching to CW Doppler allows flows velocities that exceed the Nyquist limit to be recorded accurately.

Equation 1.6 is used to determine the maximum velocity a PW system can record accurately without aliasing of a given transducer frequency (f0) and sampling depth (D).

The equation 1.6 shows that the maximum velocity that can be recorded at any given depth with no ambiguity is inversely proportional to transducer frequency.

Question 160

The best recordings of higher velocity jets at any given depth are obtained from a ……………. frequency transducer. This is opposite of what produces the best M-mode and 2D exams where higher ………………… transducers produce the best images.

Answer 160

The best recordings of higher velocity jets at any given depth are obtained from a lower frequency transducer. This is opposite of what produces the best M-mode and 2D exams where higher frequency transducers produce the best images.

Question 161

Table 1.6 lists the maximum velocities that can be accurately recorded at a variety of depths and transducer frequencies.

Answer 161

Table 1.6 lists the maximum velocities that can be accurately recorded at a variety of depths and transducer frequencies.

Question 162

Effect of Sampling (Gate) Depth

Answer 162

Equation 1.6 also shows that the maximum velocity that can be recorded without aliasing is inversely proportional to depth for any given transducer frequency.

Question 163

What to do about Aliasing?

Answer 163

1. Move the baseline up or down
2. Find an imaging plane where less depth is necessary
3. Use a lower transducer frequency
4. Switch to CW Doppler

Question 164

When the Nyquist limit is exceeded, aliasing occurs. When the Nyquist limit is not exceeded by degree, we can still see the typical flow profile; however, it wraps around the image. This type of aliasing can be eliminated by moving the baseline up or down in order to see the entire flow profile. Fig 1.25

Answer 164

Fig 1.25

Question 165

Normal blood flow is typically ……..

Answer 165

laminar

Question 166

Laminar blood flow: All blood cells within a vessel, outflow tract, or chamber are moving in the same direction with very similar flow velocities.

Vessel and chamber walls do create friction for the blood cells moving adjacent to their surface and velocities are generally somewhat slower along the …………….. of the flow stream than in the center of the flow stream.

Answer 166

Vessel and chamber walls do create friction for the blood cells moving adjacent to their surface and velocities are generally somewhat slower along the periphery of the flow stream than in the center of the flow stream.

Nevertheless velocities are similar enough that a velocity profile is produced that has little variance.

Question 167

PW Doppler always appears hollow with little spectral broadening when the following occurs:

Answer 167

1) Flow is laminar,
2) intercept angles are close to zero,
3) the Nyquist limit is not exceeded

The signals are hollow when flow is laminar because there is little variance in velocity.
(Figure 1.27)

Question 168

Spectral ……….. is the filling in of the typically hollow wave-form

Answer 168

Spectral broadening is the filling in of the typically hollow wave-form. (Figure 1.28)

CW Doppler displays always show spectral broadening because of the many velocities detected along the CW sound beam. PW Doppler may she spectral broadening when gain is too high, when intercept angles are large or when flow becomes turbulent

Question 169

Spectral broadening in a pulsed-wave signal may be due to….(3)

Answer 169

1) improper gain settings,
2) a large intercept angle,
3) non-laminar (turbulent) flow.

Question 170

PW: When velocities dramatically exceed the Nyquist limit, normal flow profiles are lost and it is impossible to determine flow direction or velocity (Fig 1.26)

Answer 170

PW: When velocities dramatically exceed the Nyquist limit, normal flow profiles are lost and it is impossible to determine flow direction or velocity. Switching to CW Doppler allows the high velocity flow of mitral regurgitation to be recorded accurately. (Fig 1.26)

Question 171

When flow becomes abnormal it is generally turbulent. Turbulent flow has blood cells moving in many directions and at variable velocities. This kind of flow is seen with stenotic lesions, shunts, and valvular regurgitation. Doppler signals produced from turbulent flow have a lot of spectral broadening because of the many velocities and flow directions present in the jet. Why does CW Doppler always shows spectral broadening?

Answer 171

CW Doppler always shows spectral broadening even when flow is laminar because flow velocities detected all along the transmitted sound beam vary tremendously. (Fig 1.28)

Question 172

Color flow Doppler is a form of …….. Doppler. RT images and CF mapping are done at the same time with alternating scan lines dedicated toward RT image generation and Doppler signals.

Answer 172

Color flow Doppler is a form of PW Doppler. RT images and CF mapping are done at the same time with alternating scan lines dedicated toward RT image generation and Doppler signals.

Question 173

Remember that PW Doppler is range gated in that a specific sampling site i chosen and the ultrasound machine ignores signals that come back from any other point along the line of interrogation. This can be done by knowing the speed of sound i ………….. and the depth of the ………..

Answer 173

Remember that PW Doppler is range gated in that a specific sampling site i chosen and the ultrasound machine ignores signals that come back from any other point along the line of interrogation. This can be done by knowing the speed of sound i tissues and the depth of the gate.

Question 174

CF mapping involves the analysis of information all along hundreds of interrogate lines, each with hundreds of gates, until a wedge is filled with color. Each gate sends frequency shift information back to the ………… This frequency shift info is sent to a ……………., which calculates the mean velocity, direction, and location of blood cells at each gate. Info from each gate is assigned a color and position on the image.

Answer 174

CF mapping involves the analysis of information all along hundreds of interrogate lines, each with hundreds go gates, until a wedge is filled with color. Each gate sends frequency shift information back to the transducer. This frequency shift info is sent to a processor, which calculates the mean velocity, direction, and location of blood cells at each gate. Info from each gate is assigned a color and position on the image.
Fig 1.29.

Question 175

Blood flow is color mapping is perceived by the machine as either moving toward the transducer or away from it via a negative or positive frequency shift. By convention, flow moving toward the sound source is plotted in hues of ………, and flow moving away from the transducer is mapped in shades of …………. although this can be changed by the operator.

Answer 175

Blood flow is color mapping is perceived by the machine as either moving toward the transducer or away from it via a negative or positive frequency shift. By convention, flow moving toward the sound source is plotted in hues of red, and flow moving away from the transducer is mapped in shades of blue although this can be changed by the operator. Fig 1.30

Question 176

No flow generates no ……………, and no color is assigned.

Answer 176

No flow generates no frequency shift, and no color is assigned.

Question 177

Enhanced color maps, available in most equipment, display ………….. information as well as ………

Answer 177

Enhanced color maps, available in most equipment, display flow velocity information as well as direction.

Question 178

Color range from deep ……… for slow flow to bright ……….. for rapid blood flow toward the transducer. Slow blood flow away from the transducer is mapped in deep ………. colors while more rapid flow away from the transducer is mapped in shades of light b…….. and ………

Answer 178

Color range from deep red for slow flow to bright yellow for rapid blood flow toward the transducer. Slow blood flow away from the transducer is mapped in deep blue colors while more rapid flow away from the transducer is mapped in shades of light blue and white.

Question 179

CF Doppler quality is dependent upon 2 important factors; ……………. and ………………. of the transducer.

As with spectral Doppler the ……… of the sound source dictates the maximal velocity, which can be accurately mapped at any given depth before aliasing occurs.

Answer 179

CF Doppler quality is dependent upon 2 important factors; pulse reception frequency and frequency of the transducer. As with spectral Doppler the frequency of the sound source dictates the maximal velocity, which can be accurately mapped at any given depth before aliasing occurs.

Question 180

Aliasing in CF Doppler involves a reversal of color and the result is a mosaic or mixing of the blue and red hues.
Aliasing can occur while using …….. frequency transducers when in actuality there is normal flow and the aliasing is only a function of transducer frequency. The aliasing would be eliminated if a ………. frequency transducer were used.

Answer 180

Aliasing in CF Doppler involves a reversal of color and the result is a mosaic or mixing of the blue and red hues. (Fig 1.31: Aliasing secondary to high velocity or turbulent flow is displayed as a mosaic of color).
Aliasing can occur while using high frequency transducers when in actuality there is normal flow and the aliasing is only a function of transducer frequency. The aliasing would be eliminated if a lower frequency transducer were used.

Question 181

CF Doppler: May aliasing be seen even when flow is normal?

Answer 181

Aliasing occurs at lower velocities due to sampling time requirements. Therefore; aliasing may be seen even when flow is normal.

Question 182

…….. maps are found in many ultrasound machines (Fig 1.32). These machines map turbulent flow in hues other than blue or red, typically green.

Answer 182

Variance maps are found in many ultrasound machines (Fig 1.32). These machines map turbulent flow in hues other than blue or red, typically green.
(All CF images in the textbook by Boon use enhanced and variance color maps.

Question 183

Frame rate refers toP

Answer 183

Frame rate refers to the number of times a B-mode or color-flow image is generated per minute.

Question 184

A frame rate of at least ……. times per minute is required for smooth transitions and the appearance of a continuously moving image.

Answer 184

A frame rate of at least 15 times per minute is required for smooth transitions and the appearance of a continuously moving image.

Question 185

CF Doppler: Frame rate in a 2D image is equal to?

Answer 185

Frame rate in a 2D image is equal to PRF divided by scan lines per color sector (which is superimposed upon a 2D image).

Question 186

The width of the color sector can be altered by the operator. Decreasing the color wedge …………. the amount of time necessary for sampling and ……….. the fram rate.

Answer 186

The width of the color sector can be altered by the operator. Decreasing the color wedge decreases the amount of time necessary for sampling and increases the fram rate.

Question 187

The operator can also eliminate the real time image; which extends beyond the width of the color sector. This also decreases the time necessary for image generation and enhances ……. mapping.

Answer 187

The operator can also eliminate the real time image; which extends beyond the width of the color sector. This also decreases the time necessary for image generation and enhances CF mapping.

Question 188

Many machines allow the operator to decrease the depth of the color wedge. Does this has an effect on the fram rate?

Answer 188

This typically has no effect on fram rate on most ultrasound machines since total image depth is unchanged. It merely decreases the info the mind has to process by eliminating processed info from the display.

Question 189

What is the packet size?

Answer 189

The numer of times each line of sound (within a color sector) is sampled is referred to as its packet size.
(Fig 1.34)

Increasing packet size improves image quality (because more samples can be taken) and fills in the color display, but this is at the expense of frame rate as more time is necessary.

Question 190

Packet sizes can be selected by the operator on some equipment. Decreasing packet size will ……………. your frame rate but decrease sampling time. Information may be lost with very short sampling times. This may be necessary however with rapid heart rates. Increasing packet size will increase the time required for sampling and ……………. the fram rate, but it will be able to map velocities and color with greater color filling.

Answer 190

Packet sizes can be selected by the operator on some equipment.

Decreasing packet size will increase your frame rate but decrease sampling time (decrease the number of times each scan line is sampled): so color info is not as complete, but frame rate is higher.

Information may be lost with very short sampling times. This may be necessary however with rapid heart rates. Increasing packet size will increase the time required for sampling and decrease the fram rate, but it will be able to map velocities and color with greater color filling.

Question 191

How can CF imaging be optimized?

Answer 191

1. Decrease transducer frequency
2. Decrease color sector width
3. Eliminate real-time image
4. Increase packet size: Decreases fram rate however.
5. Decrease packet size: Decreases sampling time and good for high heart rates but may lose information

Question 192

CF Doppler: Variance maps display turbulent (aliased) flow by ….

Answer 192

By adding green to the mapped flow

Question 193

CF Doppler: Enhanced maps mix and reverse color and all the hues when ……

Answer 193

when flow becomes turbulent.

Question 194

CF Doppler: Small color sector: ….. time required.

= ……………. frame rate.

Answer 194

CF Doppler: Small color sector: Less time required.
= increased frame rate.
Fig 1.33. Better temporal resolution is then possible.

Question 195

Large color sector = ………time required.

= ………….. frame rate.

Answer 195

Large color sector = more time required

= decreased frame rate.

Question 196

Eliminate image outside color sector = ………. time required.
= ……………………. frame rate.

Answer 196

Eliminate image outside color sector = less time required.
= increased frame rate.
Improved color flow mapping.

Question 197

Tissue Doppler Imaging -TDI (or tissue Doppler echo-TDE) involves ………?

Answer 197

Acquiring myocardial velocities.

Question 198

While blood cells reflect …….. amplitude signals at high velocity, myocardial motion has ………….-amplitude signals but low velocity.

Answer 198

While blood cells reflect low amplitude signals at high velocity, myocardial motion has high-amplitude signals but low velocity.

Question 199

Standard Doppler interrogation of blood flow filters out …….. velocity signals. TDI however bypasses the ……. velocity filter.

Answer 199

Standard Doppler interrogation of blood flow filters out low velocity signals. TDI however bypasses the low velocity filter.

Question 200

TDI can employ PW signals only or can be used in conjunction with …….. Doppler.

Answer 200

TDI can employ PW signals only or can be used in conjunction with CF Doppler.

Question 201

Color TDI uses a …….. sector of color (to keep frame rates high) placed over a section of myocardium.

Answer 201

Color TDI uses a narrow sector of color (to keep frame rates high) placed over a section of myocardium.

Question 202

A PW gate can be placed anywhere over the color sect after the fact from stored video loops.

Answer 202

A PW gate can be placed anywhere over the color sect after the fact from stored video loops (Fig 1.35)

Question 203

When using PW Doppler TDI, the spectral ………. is placed over a color Doppler sector in the area of interest on the myocardium and a spectral trace of myocardial motion is displayed in real-time.

Answer 203

When using PW Doppler TDI, the spectral gate is placed over a color Doppler sector in the area of interest on the myocardium and a spectral trace of myocardial motion is displayed in real-time. (Fig 1.36)

Question 204

The advantage of PW TDI to color TD?

Answer 204

The advantage to color TDI is that myocardium anywhere under the color sector can be interrogated, after the fact all at the same time, and compared.

Question 205

Limitations of PW TDI ?

Answer 205

PW TDI is limited to recording myocardial velocities taken i RT under the gate.

PW TDI, however, provides the highest temporal and velocity range resolution.

Question 206

TDI uses both apical, poarasternal, and transverse images of the heart.
A typical TDI display shows systolic myocardial motion directed ………… into the ventricular chamber and diastolic motion directed ……….. from the center of the chamber on transverse or long-axis parasternal images.

Answer 206

TDI uses both apical, poarasternal, and transverse images of the heart.
A typical TDI display shows systolic myocardial motion directed centrally into the ventricular chamber and diastolic motion directed away from the center of the chamber on transverse or long-axis parasternal images.

Question 207

On an apical 4-chamber view of the heart, systolic motion is directed ………… the transducer, while during diastole, myocardial motion is directed ……………… the transducer.

Answer 207

On an apical 4-chamber view of the heart, systolic motion is directed upward to the transducer, while during diastole, myocardial motion is directed away from the transducer.

Question 208

Color-tissue Doppler uses a narrow sect of color placed over myocardium. Off-line analysis allows gates to be placed over the myocardium anywhere within the color sector. Myocardial velocity corresponding to the selected gate or gates is displayed

Answer 208

Color-tissue Doppler uses a narrow sect of color placed over myocardium. Off-line analysis allows gates to be placed over the myocardium anywhere within the color sector. Myocardial velocity corresponding to the selected gate or gates is displayed.
Fig 1.35

Question 209

PW tissue Doppler also uses a narrow sector of color placed over myocardium. A PW gate is placed over the myocardium anywhere within the color sector. Instantaneously myocardial velocity corresponding to the selected gate is displayed. Myocardial velocity from only one gate at a time can be displayed.

Answer 209

PW tissue Doppler also uses a narrow sector of color placed over myocardium. A PW gate is placed over the myocardium anywhere within the color sector. Instantaneously myocardial velocity corresponding to the selected gate is displayed. Myocardial velocity from only one gate at a time can be displayed. Fig 1.36

Question 210

Give ex of some common echo artifacts

Answer 210

Inability to resolve 2 structures as separate entities both in the lateral and longitudinal planes.
Timing artifacts related to temporal resolution.
Aliasing
Other artifacts are created as a result of patient movement, and respiration, improper gain settings, peripheral sound beams, or strong reflectors.

Question 211

What can be done to minimize echo artifacts?

Answer 211

Selecting the most appropriate transducer for the application will minimize these artifacts.
Using harmonic imaging during the echo examination helps eliminate many artifacts.

Question 212

Respiratory motion moves the transducer farther and closer to the cardiac structures. The resulting M-mode image will have excessive cardiac motion simply due to this perceived cardiac motion by the equipment when in actuality it is only movement of the transducer with respect to the heart. Movement of the transducer closer to and farther away from the heart is interpreted by the equipment as cardiac motion.

Answer 212

Respiratory motion moves the transducer farther and closer to the cardiac structures. The resulting M-mode image will have excessive cardiac motion simply due to this perceived cardiac motion by the equipment when in actuality it is only movement of the transducer with respect to the heart. Movement of the transducer closer to and farther away from the heart is interpreted by the equipment as cardiac motion. Fig 1.37.

Question 213

What is temporal artifacts/inaccuracy?

Answer 213

Temporal artifact is the inaccurate timing of CF Doppler information. Temporal inaccuracy is often created secondary to reparatory movement. Color is encoded for a chamber or vessel at a location on the screen that has moved before the info is processed. This usually appears as a sheet of color. Frame rates that are too slow for sampling in hearts with rapid heart rates will result in color being placed over the heart during the wrong phase of the cardiac cycle.
Fig 1.38.

Question 214

What is a side lobe artifact?

Answer 214

All transducers produce a central beam. They also all produce peripheral beams. These peripheral beams are directed laterally with respect to the central beam. When they intercept structures and are reflected back to the transducer, the equipment does not have the ability to recognize that the info presented did not come from the central beam. Lateral structures are then superimposed upon centrally located structures (such as within an echo-free space like a chamber in a RT image) and are called side lobe artifacts. Fig 1.39.

Question 215

Are side lobe artifacts always easily detected?

Answer 215

Side lobes are much weaker than central beams and thus returning echoes are also weaker. Often the potential artifact is not even seen since main beam structures have stronger reflections. When other structures are not there to overshadow them, however, they are easily visible. The most common place to see side lobe artifact is within a dilated left atrium or ventricle. This empty space allows eager side lobe echoes to be displayed. Fig 1.40.
When side lobe reflections are seen, they typically appear as a curved line extending from the side of the sector into a fluid-filled space or an irregular density within a chamber. Make sure you see a structure in several imaging planes to eliminate possible misinterpretation of these reflections.

Question 216

What is a reverberation artifact?

Answer 216

Reverberation artifact occurs when strong reflectors are encountered within the thorax. These structures send such strong echoes back to the transducer that the sound is both received by the transducer and reflected from it. The same sound beams travel through the heart again, and when they are sent back to the transducer for a second time they are perceived as having taken twice as long. This produces a mirror image below the first one. Fig 1.41.

Question 217

When does reverberation artifact/mirror image artifact commonly occur?

Answer 217

Reverberation artifact often occurs in cardiac imaging when strong reflectors like the pericardium and lung interface cause echoes to bounce back and forth.

Reverberation artifact can also be produced between two strong reflectors within the thorax or heart. The sound may bounce back and forth between these two highly dense structures one to several times before traveling all the way back to the transducer. Multiple images of the same strutters are created, each equally spaced and deeper in the image.

Question 218

How can reverberation artifacts be minimized?

Answer 218

Reverberation artifact can be minimized by making sure depth settings are adequate for the heart size and not so deep was to see a double image.

Question 219

What is a mirror image artifact?

Answer 219

When spectral Doppler flow shows up on both side of the baseline, it is refereed to as mirror image artifact. Fig 1.42.
Depending upon where blood flow is being sampled, it is still possible to decide which flow direction is the correct one. This artifact is created ny high gain settings creating a situation similar to reverberation artifact. It may also be produced as a result of large angles of incidence with respect ot blood flow.

Question 220

Summary: Transducers sent out sound waves that travel in cycles. The number of cycles per second determines transducer frequency. High frequency transducers generate more cycles per second and so have …….. wavelengths.

Answer 220

Transducers sent out sound waves that travel in cycles. The number of cycles per second determines transducer frequency. High frequency transducers generate more cycles per second and so have shorter wavelengths.

Question 221

The average speed of sound, sent out from transducers) in soft tissue is …….m/second ?

Answer 221

1,540 m/second

Question 222

Is the average speed sent out from transducers dependent of transducer frequency?

Answer 222

No, the speed is independent of transducer frequency.

Question 223

Acoustic impedance increases with increased tissue ……… and ………… This is also independent of transducer frequency.

Answer 223

Acoustic impedance increases with increased tissue density and stiffness. This is also independent of transducer frequency.

Question 224

An acoustical difference between ……………… causes sound to be reflected back to the transducer.

Answer 224

An acoustical difference between two tissues causes sound to be reflected back to the transducer.

Question 225

Bone, being very stiff and dense, impedes the flow of sound tremendously and reflects almost …… sound.

Answer 225

Bone, being very stiff and dense, impedes the flow of sound tremendously and reflects almost all sound.

Question 226

Scattered sound generates the images from within …………….. tissues where acoustical properties are similar and structures are small and irregular with respect to wavelength.

Answer 226

Scattered sound generates the images from within homogenous tissues where acoustical properties are similar and structures are small and irregular with respect to wavelength.

Question 227

A structure must be at least ………… the size of the wavelength to be reflected.

Answer 227

A structure must be at least one-quarter the size of the wavelength to be reflected.

Question 228

High frequency sound with shorter wavelengths can reflect sound from smaller structures and produce better images.

Drawback with high frequency transducers?

Answer 228

High frequency sound with shorter wavelengths can reflect sound from smaller structures and produce better images.
Sound attenuates rapidly with these short wavelengths, however, since they interact with more structures. High frequency transducers therefore create high-resolution images but lose strength rapidly and cannot penetrate as far into tissues as sound from low frequency transducers.

Question 229

Transducers contain piezoelectric crystals, which function to generate sound and receive sound. the sound is sent out in pulses and the number of pulses per second is the ……. of the transducer?

Answer 229

Pulse repetition frequency

Question 230

One of the factors affecting axial resolution is the …..?

Answer 230

The pulse length of a transducer.

Question 231

Higher frequency transducers will have better axial resolution since their …… wave and pulse lengths can differentiate smaller structures.

Answer 231

Higher frequency transducers will have better axial resolution since their short wave and pulse lengths can differentiate smaller structures.

Question 232

………. resolution is dependent upon several factors one of which is beam width. The wider the beam width the poorer the lateral resolving power since structures must be farther apart than the beam width to be differentiated.

Answer 232

Lateral resolution is dependent upon several factors one of which is beam width. The wider the beam width the poorer the lateral resolving power since structures must be farther apart than the beam width to be differentiated. Therefore, lateral resolution is best with smaller diameter transducers.

High frequency transducers have longer near fields before the beam diverges, and this enhances the lateral resolution of deeper structures.

Question 233

Current technology allows multiple focal points along each sound beam in a phased array or annular array transducer. Correct timing of cardiac motion and flow is dependent upon ……………… resolution.

Answer 233

Current technology allows multiple focal points along each sound beam in a phased array or annular array transducer. Correct timing of cardiac motion and flow is dependent upon temporal resolution.
As multiple focal zones are used or as deeper structures are imaged, the pulse repetition frequency is decreased.
This may not allow fast enough processing of information, and temporal resolution will suffer.
Decreasing the width of the RT sector will increase the PRF as will decreasing the depth of interrogation and using no more than one focal zone.

Question 234

What is the Doppler shift?

Answer 234

The change in frequency between sound transmitted by the transducer and sound received by the transducer is the Doppler shift.

Question 235

Blood cells moving toward the transducer will create a positive frequency shift and be displayed above the baseline, while blood moving away from the transducer produces a negative frequency shift and flow profiles below the baseline.

Answer 235

Blood cells moving toward the transducer will create a positive frequency shift and be displayed above the baseline, while blood moving away from the transducer produces a negative frequency shift and flow profiles below the baseline.

Question 236

PW Doppler is range gated in that it samples blood at indicated sites within the heart. It is however limited in the highest velocity it is capable of measuring accurately.

Answer 236

PW Doppler is range gated in that it samples blood at indicated sites within the heart. It is however limited in the highest velocity it is capable of measuring accurately.

Question 237

Continuous-Wave Doppler samples blood flow all along the sound beam and while not site specific, it has no ………. limit.

Answer 237

Continuous-Wave Doppler samples blood flow all along the sound beam and while not site specific, it has no Nyquist limit.

Question 238

The Nyquist limit is dependent upon….?

Answer 238

The Nyquist limit is dependent upon PRF and thus transducer frequency. The Nyquist limit for any transducer frequency decreases as blood flow is sampled at increasing depths. Lower frequency transducers are capable of accurately recording higher flow velocities at any given depth before aliasing occurs.

Question 239

Accurate velocity measurements are also dependent upon having an angle of interrogation that is ……………with flow. Deviations of the Doppler beam away from parallel result in underestimation of flow velocities.

Answer 239

Accurate velocity measurements are also dependent upon having an angle of interrogation that is parallel with flow. Deviations of the Doppler beam away from parallel result in underestimation of flow velocities.

Question 240

………… flow creates a Doppler signal with little variance in velocity and little spectral broadening. Spectral broadening is seen when flow becomes turbulent or when CW Doppler is used since many frequency shifts are received by the transducer.

Answer 240

Laminar flow creates a Doppler signal with little variance in velocity and little spectral broadening. Spectral broadening is seen when flow becomes turbulent or when CW Doppler is used since many frequency shifts are received by the transducer.

Question 241

CF Doppler is a form of PW Doppler. Frequency shift info is encoded with color. The most commonly used color map uses a blue away and red toward (BART) format.

Aliasing typically occurs at ………… velocities in CF Doppler because of the increased time necessary for flow analysis at multiple gates. Aliasing in CF Doppler results in a mosaic of color. As in spectral Doppler, ……………..frequency transcoders will increase the Nyquist limit.

Answer 241

CF Doppler is a form of PW Doppler. Frequency shift info is encoded with color. The most commonly used color map uses a blue away and red toward (BART) format.

Aliasing typically occurs at lower velocities in CF Doppler because of the increased time necessary for flow analysis at multiple gates. Aliasing in CF Doppler results in a mosaic of color. As in spectral Doppler, lower frequency transcoders will increase the Nyquist limit.

Question 242

Artifacts are common in diagnostic ultrasound and may be created by…?

Answer 242

The physical properties of transducers
Patient-related factors
Tissue characteristics
Operator-related errors.

Selecting the most appropriate transducer for the exam, calming the patient, and realizing the limitations of diagnostic ultrasound will help eliminate many of these problems or allow intelligent decision making.