Ultrasound Physics 1 (ch. 4-5)

pulsed sound is different from continuous sound because it has

short bursts/pulses

pulse is made up of _____ and travels as a ______

individual cycles; single unit

transmit time is also called ___ or ____

talking or “on” time

receive time is also called ___ or ___

listening or “off” time

actual time from the start of the pulse to the end of that pulse

pulse duration

pulse duration is also called ___ or ___

talking or “on” time

units for pulse duration

microseconds (μs), units of time

values in U/S for pulse duration; adjustable?

0.3-2.0 μs; not adjustable

usual number of cycles per pulse (for pulse duration)

2-4 cycles

pulse duration is ____ proportional to number of cycles in the pulse and period

directly

pulse duration is ____ proportional to frequency

inversely

distance that a pulse occupies in space from the start to the end of a pulse

spatial pulse length (SPL)

units of spatial pulse length (SPL)

mm, units of distance

values in U/S for spatial pulse length; adjustable?

0.1-1.0 mm; not adjustable

spatial pulse length (SPL) is created by ___ and ___

source and medium

spatial pulse length (SPL) is ___ proportional to the number of cycles and wavelength

directly

spatial pulse length (SPL) is ___ proportional to frequency

inversely

in SPL, shorter pulses create more ___

accurate images

time from the start of one pulse to the start of the next pulse

pulse repetition period (PRP)

pulse repetition period (PRP) includes one ___ plus one ___

pulse duration; listening time

units of pulse repetition period (PRP)

ms, units of time

values in U/S for pulse repetition period (PRP); adjustable?

0.1-1.0 ms; yes adjustable

as depth of imaging increases, PRP ___

increases

what part of the pulse repetition period (PRP) changes

the length

number of pulses that a U/S system transmits into the body each second

pulse repetition frequency (PRF)

units of pulse repetition frequency (PRF)

Hz, per second

values is U/S for pulse repetition frequency (PRF); adjustable?

1,000-10,000 Hz; yes adjustable

pulse repetition frequency (PRF) and depth of view are ___ related

inversely

when the image depth is shallow, the pulse repetition frequency (PRF) is

higher

when the image depth is deeper, the pulse repetition frequency (PRF) is

lower

pulse repetition period (PRP) and pulse repetition frequency (PRF) are ___ related

inversely

percentage or fraction of time that the system transmits a pulse

duty factor

units of duty factor

none (it is %)

values in U/S for duty factor; adjustable?

0.2%-0.5%; yes adjustable

maximum value for duty factor is

1 (100%)

minimum value for duty factor is

0%

duty factor is related to both ___ and ___

pulse duration and pulse repetition period (PRP)

shallower imaging has a/an ___ duty factor

increasing

deeper imaging has a/an ___ duty factor

decreasing

what are each determined by (source/medium/both)

1. pulse duration

2. pulse repetition period (PRP)

3. pulse repetition frequency (PRF)

4. spatial pulse length (SPL)

5. duty factor (DF)

1. source

2. source

3. source

4. both source and medium

5. source

beam’s power divided by its area

intensity

for intensity measurements, evaluate…

maximum intensity

spatial considerations refer to ___ or ___

location or space

the beam’s intensity at the location where it is maximum

spatial peak intensity

across the beam’s entire cross-sectional area

average intensity

temporal refers to

time

what does SPTP stand for

spatial peak, temporal peak

what does SATP stand for

spatial average, temporal peak

what does SPPA stand for

spatial peak, pulse average

what does SPTA stand for

spatial peak, temporal average

what does SATA stand for

spatial average, temporal average

what does SAPA stand for

spatial average, pulse average

rank from largest to smallest

• SPPA

• SATA

• SPTP

• SPTA

1. SPTP (largest)

2. SPPA

3. SPTA

4. SATA (smallest)

what is the most relevant intensity with respect to tissue heating

SPTA

PRP is unrelated to___ and related to ___

unrelated to period, related to depth of view (ONLY)

PRF is unrelated to ___ and related to ___

unrelated to frequency and related to depth of view (ONLY)

shallow imaging is

• ___listening

• ___ PRP

• ___PRF

• ___duty factor

• less listening

• shorter PRP

• higher PRF

• higher duty factor

deeper imaging is

• ___listening

• ___PRP

• ___PRF

• ___duty factor

• more listening

• longer PRP

• lower PRF

• lower duty factor

when adjusting imaging depth, the system changes the ___, ___, and ___

PRP, PRF, and duty factor

spatial peak intensity is always ____ than spatial average intensity

higher

temporal intensities from largest to smallest: (4)

I tp (temporal peak), I max, I pa (pulse average), I ta (temporal average)

all intensities have units of ___

W/cm²

refers to distance or space

spatial

refers only to the transmit time

pulsed

Which of the following is adjustable?

• pulse duration

• PRP

• PRF

• SPL

• duty factor

PRP, PRF, duty factor are all adjustable