Exam 1 Flashcards

Question

Define Spatial Pulse Length units? typical values ? determined by ? equals ? adjustable?

Answer 1

-is the distance that a pulse occupies in space from the start to the end of a pulse. -Units: mm -Typical values: in soft tissue 0.1 to 1.0 mm -Determined by: both the source and medium -It equals the number of cycles in each pulse times the wavelength of each cycle. Since wavelength is determined by both, so is the spatial pulse length. -NOT adjustable

Answer 2

SPL = # cycles x wavelength Directly proportional to the number of cycles in the pulse Inversely proportional to frequency.

Answer 3

Bone (3,500 m/s) Liver (1,560 m/s) Water (1,480 m/s) Air (330 m/s)

Answer 4

-Is the rate at which a sound wave travels through a medium. -Units: meters per second, mm/us, or any distance divided by time. -Typical values: 500 m/s to 4000 m/s depending on the tissue through which it travels. -Not adjustable by sonographer, just by traveling from one medium to a different medium.

Answer 5

If both mediums are identical and the incidence was normal then only transmission occurs because the impedances of the media are the same.

Answer 6

If both mediums are different with a normal incidence and different impedance, both reflection and transmission occur.

Answer 7

Oblique incidence (not normal) Different propagation speeds of the two media

Answer 8

Pulse repetition period and imaging depth are directly related As depth of view increases, the pulse repetition period increases.

Answer 9

lengthen shorten

Answer 10

Is the time it takes a wave to vibrate a single cycle, of the time from the start of one cycle to the start of the next cycle Units: microseconds (um), seconds Typical values: 0.06 to 0.5 microseconds (us) Determined by: sound source only Not adjustable by sonographer.

Answer 11

is the number of pulses that an ultrasound system transmits into the body each second. Units: Hertz (Hz) or per second Typical values: 1,000 or 10,000 hertz or one to ten thousand pulses per second. Determined by Sound source only and maximum imaging depth Yes adjustable by sonographer by adjusting depth of view NOT related to frequency

Answer 12

transducer has 2 crystals, one for sending and one from receiving. It does this at the same time. It never stops. It is unable to produce a picture. It will average all velocities scanned.

Answer 13

is the actual time from the start of a pulse to the end of that pulse. Is a single transmit, talking, or “on” time. Typically contain 2 to 4 cycles Shorter duration pulses are desirable for imaging because they create images of greater accuracy. Units: microseconds (us) Typical values: 0.3 to 2.0 us Determined by: sound source only NOT adjustable

Answer 14

is the time from the start of one pulse to the start of the next pulse. Includes one pulse duration plus one listening time Units: milliseconds, seconds, etc Typical values: 100 microseconds (us) to 1 millisecond (ms) Generally about 100 to 1000 times longer than pulse duration. Determined by: sound source only and imaging depth Adjustable by sonographer (adjust depth of view PRP also adjusted). NOT related to period

Answer 15

(near field, Fresnel zone) is the region from the transducer to the focus (blue arrow). The beam gradually narrows, or converges, within the near zone. For a continuous wave, disc-shaped crystal, the diameter of the sound beam as it leaves the transducer is the same as the diameter of the active element. At the end of the near zone, the beam narrows to only one-half the width of the active element. The focus is located at the end of the near zone.

Answer 16

(far field) the far zone is the region that starts at the focus and extends deeper (purple arrow). Within the far zone, the beam diverges, or spreads out. At the beginning of the far zone, the beam is only one-half as wide as it is at the transducer. From the focus, the beam continues to diverge. When the beam is two near zone lengths from the transducer, the beam is again the same size as the active element. At depths more than two near zone lengths, the beam is wider than the active element.

Answer 17

They both help form the focal zone which is a region around the focus where the beam is relatively narrow. Reflections arising from the focal zone create images that are more accurate than those from other depths.

Answer 18

Near zone is closer to the transducer and starts off the same width as it then narrows, while the far zone is further from the transducer starts off narrow and ends at the same width as the transducer.

Answer 19

Absorption (Most sizeable component of attenuation)

Answer 20

Is the acoustic resistance to sound traveling in a medium. Calculated by multiplying the density of a medium by the speed at which sound travels in the medium. Reflection of an ultrasound wave depends on the difference in acoustic impedances of the two media at a boundary. Units: rayls (Z) Typical values: 1,250,000 to 1,750,000(1.25 to 1.75 Mrayls) Determined by: medium only Also called Characteristic impedance

Answer 21

right through it

Answer 22

(far field) the far zone is the region that starts at the focus and extends deeper (purple arrow). Within the far zone, the beam diverges, or spreads out. At the beginning of the far zone, the beam is only one-half as wide as it is at the transducer. From the focus, the beam continues to diverge. When the beam is two near zone lengths from the transducer, the beam is again the same size as the active element. At depths more than two near zone lengths, the beam is wider than the active element.

Answer 23

Longitudinal waves (particles moves in the same direction that the wave propagates) Mechanical waves

Answer 24

Compression (most) Rarefaction (less)

Answer 25

less than 20 Hz (0.02 kHz or 0.0002 MHz)

Answer 26

Between 20 Hz and 20 kHz (0.02 kHz- 20 kHz 20 Hz - 20,000 Hz 0.0002 MHz - 0.02 MHz)

Answer 27

Greater than 20 kHz (0.02 MHz ro 20,000 Hz)

Answer 28

Some people believe that hertz means “cycles per second” Hertz are actually a two part process: Hertz means events per second To which event are we referring?

Answer 29

a region around the focus or focal point where the beam is relatively narrow and an area where the image detail is superior. Reflections arising from the focal zone create images that are more accurate than those from other depths.

Answer 30

the focal length is the distance from the transducer to the focus (narrowest part of the beam). focus location can be changed adjustable

Answer 31

is the location where the beam is the narrowest (red arrow) for a disc shaped crystal, the width of the sound beam at the focus is one-half the width of the beam as it leaves the transducer. Located at the end of the near zone, the beginning of the far zone, or the middle of the focal zone.

Answer 32

Ultrasound, no

Answer 33

Infrasound, No

Answer 34

Pulse duration "on" time or talking determined by sound source not adjustable units: microseconds

Answer 35

1) Pressure: concentration of force in an area Units: pascals (Pa) 2) Density: concentration of mass in a volume Units: kg/cm^3 3) Distance: measure of particle motion Units: cm, mm, um, feet, mile

Answer 36

Soft tissue average 1540 m/s Online: 1565 m/s

Answer 37

function of the receiver that is performed twice. First compression: keeps the electrical signal levels within the accuracy range of the system’s electronics. Second compression: keeps an image’s gray scale content within the range of the detection by the human eye.

Answer 38

is a change in direction of wave propagation when traveling from one medium to another.

Answer 39

is the distance or length of one complete cycle Units: mm, meters, any other length Typical ranges: 0.1-0.8 mm Determined by both the source and medium Not Adjustable

Answer 40

Frequency (1/T)

Answer 41

concentration of mass in a volume. Describes the relative weight of a material Characteristics of a medium that affects the speed of sound When equal volumes of two materials are compared, the dense material weighs a lot, whereas the non-dense material weighs little. Steel is dense, aluminum is not Inversely related to speed Units: kg/cm^3

Answer 42

is the rate at which a sound wave travels through a medium. Units: meters per second, mm/us, or any distance divided by time Typical values: 500 m/s to 4000 m/s depending on the tissue Is determined only by the medium through which the sound is traveling. All sound, regardless of the frequency, travels at the same speed through any specific medium. Ex: sound with a frequency of 5 MHz and sound with a frequency of 3 MHz travel at the same propagation speed in the same medium. Not adjustable by sonographer, just by change of medium

Answer 43

is the percentage or fraction of time that the system transmits a pulse Units: none Determined by sound source only Inversely related to imaging depth Is higher at shallow depths, and lower at greater depths. Adjustable by changing depth of view Duty factor (%) = ( Pulse duration / pulse rep. period ) x 100

Answer 44

is a mechanical wave in which particles in the medium move The molecules in the medium vibrate back and forth from a fixed position. Cannot travel thru a vacuum, must travel through a medium Where molecules are alternatively compressed and rarefied Travels in a straight line Are longitudinal waves

Answer 45

describes the ability of an object to resist compression. Characteristics of a medium that affects the speed of sound. Directly related to speed Also called Bulk modulus Elasticity and Compressibility are the opposite

Answer 46

is 1.0 (100%) for continuous wave sound, because the system is always transmitting. Pulse wave duty factor is somewhere in between 0 and 100%

Answer 47

Propagation Speed

Answer 48

Pressure Density Distance Temperature Particle motion *vary with location and time

Answer 49

The interference of a pair of out-of-phase waves results in the formation of a single wave of lesser amplitude than at least one of its components.

Answer 50

It measures the ability of a system to display two structures that are very close together when the structures are parallel to the sound beam’s main axis. Units: mm or any other distance unit Determined by spatial pulse length (spatial pulse is determined by both sound source and medium) Not adjustable

Answer 51

Shorter pulses improve axial resolution.

Answer 52

the ability to distinctly identify two structures that are very close together when they are side by side, or perpendicular to the sound beam’s main axis. Units: mm, cm, or any unit of distance (smaller numbers are preferable) Determined by: width of the sound beam

Answer 53

narrower beams have better resolution

Exam 1 Flashcards

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