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Ultrasound Physics > Lecture 4 > Flashcards

Lecture 4 Flashcards

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1
Q

4 Things sonographer must know to accurately place echo

A
  1. Direction of sound entering patient
  2. Propagation speed
  3. Distance of reflector
  4. Time to reflector
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2
Q

What must US machine know to adjust brightness?

A

Strength/amplitude of reflector

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3
Q

4 characteristics of a pulse

A
  1. Burst of sound energy
  2. Collection of waves
  3. Waves travel together
  4. Beginning, middle, end
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4
Q

Definition of Pulse Repetition Frequency (PRF)

A

Number of pulse emitted in 1 sec.

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5
Q

Unit for PRF

A

Hertz (KHz)

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6
Q

Limitations to PRF (2)

A
  1. Echo must be received before another pulse is transmitted

2. Deeper the reflector, the longer the echo takes to return

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7
Q

PRF is influenced by (3)

A

Distance (depth), frequency, and damping

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8
Q

(T/F) PRF is set by the sound source

A

True

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9
Q

What can the sonographer change to adjust PRF?

A

Depth

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10
Q

Definition of Pulse Repetition Period

A

The time from the beginning of a pulse to the beginning of the next pulse

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11
Q

Components of PRP (3)

A

Idle time, pulse duration, period

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12
Q

Equation for PRP & PRF

A

PRF = 1/PRP, reciprocals AKA inversely related!

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13
Q

Frequency sets the _____ of the pulse

A

Period

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14
Q

Frequency relation to period

A

Inversely related

Frequency ↑, period ↓

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15
Q

Frequency relation to pulse duration

A

Inversely related

Frequency ↑, pulse duration ↓

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16
Q

Frequency relation to spatial resolution

A

Directly related
Frequency ↑, resolution ↑ (smaller resolution # is better!)
AR = 1/2 x SPL,

17
Q

Frequency relation to PRP

A

Inversely related

Frequency ↑, PRP ↓ (because pulse duration decreases)

18
Q

Frequency relation to PRF

A

Directly related
Frequency ↑, PRF ↑
(Frequency decreases PRP because pulse duration is decreased. PRP & PRF are inversely related!)

19
Q

Definition of Pulse Duration

A

Time of an ultrasound pulse (from start to finish)

20
Q

Equations for Pulse Duration (2)

A 
PD = idle time + pulse duration
PD = # of cycles/frequency
21
Q

What does damping determine?

A

The number of cycles in the pulse.
↑ damping, ↓ number of cycles
Damping is built into into the probe, NOT user adjustable

22
Q

Damping relation to pulse duration

A

Inversely related
↑ damping, ↓ pulse duration
(b/c # of cycles ↓ and PD = # of cycles/freq.)

23
Q

Damping relation to PRP

A

Inversely related
↑ damping, ↓ PRP
(damping decreases pulse duration & PRP = pulse duration + idle time)

24
Q

Damping relation to PRF

A

Directly related
↑ damping, ↑ PRF
(damping decreases PRP, PRP is inversely related to PRF)

25
Q

What sets the idle time of an image?

A

Depth, which is user adjustable AKA idle time is adjustable

26
Q

Depth relation to idle time

A

Directly related

↓ depth, ↓ idle time

27
Q

Depth relation to PRP

A

Directly related
↓ depth, ↓ PRP
(b/c PRP = pulse duration + idle time & less depth decreases idle time)

28
Q

Depth relation to PRF

A

Inversely related
↓ depth, ↑ PRF
(b/c less depth = less PRP; PRP & PRF are inversely related)

29
Q

(T/F) Pulse duration can be changed by altering depth

A

False, pulse duration is changed by altering dampening

30
Q

Definition of Duty Factor

A

Fraction of time the ultrasound machine is sending a pulse

31
Q

Equation for Duty Factor

A

DF = pulse duration/PRP

32
Q

What is the duty factor for a continuous wave transducer

A

1 or 100%

33
Q

Depth relation to duty factor

A

Inversely related

Depth ↓, duty factor ↑

34
Q

Definition of SPL

A

Spatial Pulse Length; the distance a pulse travels

35
Q

Equation for SPL (2)

A 
SPL = wavelength x number of cycles
SPL = propagation speed x # of cycles/frequency

Ultrasound Physics (11 decks)

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