Ch. 4: Describing Pulsed Waves Flashcards
In diagnostic u/s, ___ wave sound cannot create anatomic images.
continuous
Define ‘pulsed sound’.
Short bursts of acoustic energy produced by imaging systems to create anatomic pictures; a collection of cycles that travel together.
Pulse duration is…
the actual time from the start of a pulse to the end of that pulse aka transmit/talking/”on” time.
Pulse duration is reported in units of…
time, such as microseconds.
The typical value of pulse duration in diagnostic u/s is…
.3 to 2.0 microseconds.
Pulse duration is determined by the…
sound source only.
Is pulse duration adjustable?
No.
Pulse duration is equal is the ___ in each pulse multiplied by the ___of each cycle.
number of cycles/period
Pulse duration is ___ proportional to the # of cycles in the pulse.
directly. The more cycles, the longer the duration.
Pulse duration is ___ proportional to the period.
directly. The longer the individual period of the cycles, the longer the duration.
Pulse duration is ___ proportional to the frequency.
inversely. The higher the frequency, the shorter the duration must be.
What two characteristics create pulses of LONG duration?
Pulses of long duration have either 1) many cycles in the pulse or 2) individual cycles with long periods.
What two characteristics create pulses of SHORT duration?
Pulses of short duration have either 1) few cycles in the pulse or 2) individual cycles of short period.
(Shorter/Longer) duration pulses are desirable for imaging because they create images of greater accuracy.
shorter
Define ‘spatial pulse length’.
The distance that a pulse ocupies in sace from the start to the end of a pulse.
Spatial pulse length is reported in units of…
distance, such as mm.
In clinical imaging, spatial pulse length in soft tissue ranges from…
.1 to 1.0 mm.
Spatial pulse length is determined by…
both the source and the medium (because the wavelength of each cycle is determined by both, so is spatial pulse length).
Is spatial pulse length adjustable?
No.
Spatial pulse length is equal is the ___ in each pulse multiplied by the ___of each cycle.
of cyles/wavelength
Spatial pulse length is ___ proportional to the # of cycles in each pulse.
directly. The more cycles, the longer the length.
Spatial pulse length is ___ proportional to wavelength.
directly. The longer the individual wavelengths, the longer the pulse length.
Spatial pulse length is ___ proportional to frequency.
inversely. The higher the frequency, the shorter the length must be.
What two characteristics create long pulses?
Long pulses have either 1) many cycles in the pulse or 2) cycles with longer wavelengths.
What two characteristics create short pulses?
Short pulses have either 1) fewer cycles in the pulse or 2) cycles with shorter wavelengths.
Define ‘pulse repetition period’.
The time from the start of one pulse to the start of the next pulse (one ‘on’ time and one ‘off’ time).
Pulse repetition period is reported in units of…
time, such as milliseconds (ms).
In diagnostic u/s, the typical value of pulse repetition period is…
generally 100 to 1000 times longer than pulse duration.
Pulse repetition period is determined by the…
sound source only.
Is pulse repetition period adjustable?
Yes, by adjusting the depth of view.
How are pulse repetition period and depth of view related?
Directly. As one increases, the other increases.
Does the sonographer adjust depth of view by changing the ‘on’ time (pulse) or the ‘off’ time (space between pulses)?
The ‘off’ or listening time.
Define ‘pulse repetition frequency’.
The number of pulses that an u/s sound system transmits into the body each second. (PULSES, not CYCLES.)
Pulse repetition frequency is reported in units of…
hertz (Hz), or ‘per second’.
The typical value of pulse repetition frequency is…
1,000 to 10,000 hertz.
Pulse repetition frequency is determined only by the…
sound source only.
Is pulse repetition frequency adjustable?
Yes, by adjusting the depth of view.
How are pulse repetition frequency and depth of view related?
Inversely. As one increases, the other decreases.
How are pulse repetition frequency and pulse repetition period related?
Inversely (as one increases, the other decreases) and reciprocally (multiplied together, the result is 1).
Define ‘duty factor’.
The percentage or fraction of time that the system transmits a pulse.
Duty factor is reported in units of…
Trick question! Duty factor is a percentage and has no units.
In clinical imaging, the typical range for duty factor ranges from…
.002 to .005 (or .2% to .5%), which means that the system is listening about 500 times longer than it is transmitting.
Duty factor is determined by…
sound source only.
Is duty factor adjustable?
Yes, by changing the depth of view.
How are duty factor and depth of view related?
Inversely. As one increases, the other decreases.
Duty factor is equal is the pulse ___ divided by the pulse ___ times 100.
duration/repetition period
The maximum value for duty factor is…
1 or 100%. But that would be continuously transmitting, so imaging systems are always less than 100%.
The minimum value for duty factor is…
0%. But that would be when the system is totally silent.
Shallow imaging means ___ listening, ___ PRP, ___ PRF, and ___ duty factor.
less, shorter, higher, higher
Deep imaging means ___ listening, ___ PRP, ___ PRF, and ___ duty factor.
more, longer, lower, lower
