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Ultrasound Physics > Ch. 4: Describing Pulsed Waves > Flashcards

Ch. 4: Describing Pulsed Waves Flashcards

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1
Q

In diagnostic u/s, ___ wave sound cannot create anatomic images.

A

continuous

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2
Q

Define ‘pulsed sound’.

A

Short bursts of acoustic energy produced by imaging systems to create anatomic pictures; a collection of cycles that travel together.

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3
Q

Pulse duration is…

A

the actual time from the start of a pulse to the end of that pulse aka transmit/talking/”on” time.

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4
Q

Pulse duration is reported in units of…

A

time, such as microseconds.

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5
Q

The typical value of pulse duration in diagnostic u/s is…

A

.3 to 2.0 microseconds.

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6
Q

Pulse duration is determined by the…

A

sound source only.

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7
Q

Is pulse duration adjustable?

A

No.

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8
Q

Pulse duration is equal is the ___ in each pulse multiplied by the ___of each cycle.

A

number of cycles/period

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9
Q

Pulse duration is ___ proportional to the # of cycles in the pulse.

A

directly. The more cycles, the longer the duration.

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10
Q

Pulse duration is ___ proportional to the period.

A

directly. The longer the individual period of the cycles, the longer the duration.

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11
Q

Pulse duration is ___ proportional to the frequency.

A

inversely. The higher the frequency, the shorter the duration must be.

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12
Q

What two characteristics create pulses of LONG duration?

A

Pulses of long duration have either 1) many cycles in the pulse or 2) individual cycles with long periods.

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13
Q

What two characteristics create pulses of SHORT duration?

A

Pulses of short duration have either 1) few cycles in the pulse or 2) individual cycles of short period.

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14
Q

(Shorter/Longer) duration pulses are desirable for imaging because they create images of greater accuracy.

A

shorter

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15
Q

Define ‘spatial pulse length’.

A

The distance that a pulse ocupies in sace from the start to the end of a pulse.

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16
Q

Spatial pulse length is reported in units of…

A

distance, such as mm.

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17
Q

In clinical imaging, spatial pulse length in soft tissue ranges from…

A

.1 to 1.0 mm.

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18
Q

Spatial pulse length is determined by…

A

both the source and the medium (because the wavelength of each cycle is determined by both, so is spatial pulse length).

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19
Q

Is spatial pulse length adjustable?

A

No.

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20
Q

Spatial pulse length is equal is the ___ in each pulse multiplied by the ___of each cycle.

A

of cyles/wavelength

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21
Q

Spatial pulse length is ___ proportional to the # of cycles in each pulse.

A

directly. The more cycles, the longer the length.

22
Q

Spatial pulse length is ___ proportional to wavelength.

A

directly. The longer the individual wavelengths, the longer the pulse length.

23
Q

Spatial pulse length is ___ proportional to frequency.

A

inversely. The higher the frequency, the shorter the length must be.

24
Q

What two characteristics create long pulses?

A

Long pulses have either 1) many cycles in the pulse or 2) cycles with longer wavelengths.

25
Q

What two characteristics create short pulses?

A

Short pulses have either 1) fewer cycles in the pulse or 2) cycles with shorter wavelengths.

26
Q

Define ‘pulse repetition period’.

A

The time from the start of one pulse to the start of the next pulse (one ‘on’ time and one ‘off’ time).

27
Q

Pulse repetition period is reported in units of…

A

time, such as milliseconds (ms).

28
Q

In diagnostic u/s, the typical value of pulse repetition period is…

A

generally 100 to 1000 times longer than pulse duration.

29
Q

Pulse repetition period is determined by the…

A

sound source only.

30
Q

Is pulse repetition period adjustable?

A

Yes, by adjusting the depth of view.

31
Q

How are pulse repetition period and depth of view related?

A

Directly. As one increases, the other increases.

32
Q

Does the sonographer adjust depth of view by changing the ‘on’ time (pulse) or the ‘off’ time (space between pulses)?

A

The ‘off’ or listening time.

33
Q

Define ‘pulse repetition frequency’.

A

The number of pulses that an u/s sound system transmits into the body each second. (PULSES, not CYCLES.)

34
Q

Pulse repetition frequency is reported in units of…

A

hertz (Hz), or ‘per second’.

35
Q

The typical value of pulse repetition frequency is…

A

1,000 to 10,000 hertz.

36
Q

Pulse repetition frequency is determined only by the…

A

sound source only.

37
Q

Is pulse repetition frequency adjustable?

A

Yes, by adjusting the depth of view.

38
Q

How are pulse repetition frequency and depth of view related?

A

Inversely. As one increases, the other decreases.

39
Q

How are pulse repetition frequency and pulse repetition period related?

A

Inversely (as one increases, the other decreases) and reciprocally (multiplied together, the result is 1).

40
Q

Define ‘duty factor’.

A

The percentage or fraction of time that the system transmits a pulse.

41
Q

Duty factor is reported in units of…

A

Trick question! Duty factor is a percentage and has no units.

42
Q

In clinical imaging, the typical range for duty factor ranges from…

A

.002 to .005 (or .2% to .5%), which means that the system is listening about 500 times longer than it is transmitting.

43
Q

Duty factor is determined by…

A

sound source only.

44
Q

Is duty factor adjustable?

A

Yes, by changing the depth of view.

45
Q

How are duty factor and depth of view related?

A

Inversely. As one increases, the other decreases.

46
Q

Duty factor is equal is the pulse ___ divided by the pulse ___ times 100.

A

duration/repetition period

47
Q

The maximum value for duty factor is…

A

1 or 100%. But that would be continuously transmitting, so imaging systems are always less than 100%.

48
Q

The minimum value for duty factor is…

A

0%. But that would be when the system is totally silent.

49
Q

Shallow imaging means ___ listening, ___ PRP, ___ PRF, and ___ duty factor.

A

less, shorter, higher, higher

50
Q

Deep imaging means ___ listening, ___ PRP, ___ PRF, and ___ duty factor.

A

more, longer, lower, lower

Ultrasound Physics (23 decks)

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