Lecture 4 Flashcards
4 Things sonographer must know to accurately place echo
- Direction of sound entering patient
- Propagation speed
- Distance of reflector
- Time to reflector
What must US machine know to adjust brightness?
Strength/amplitude of reflector
4 characteristics of a pulse
- Burst of sound energy
- Collection of waves
- Waves travel together
- Beginning, middle, end
Definition of Pulse Repetition Frequency (PRF)
Number of pulse emitted in 1 sec.
Unit for PRF
Hertz (KHz)
Limitations to PRF (2)
- Echo must be received before another pulse is transmitted
2. Deeper the reflector, the longer the echo takes to return
PRF is influenced by (3)
Distance (depth), frequency, and damping
(T/F) PRF is set by the sound source
True
What can the sonographer change to adjust PRF?
Depth
Definition of Pulse Repetition Period
The time from the beginning of a pulse to the beginning of the next pulse
Components of PRP (3)
Idle time, pulse duration, period
Equation for PRP & PRF
PRF = 1/PRP, reciprocals AKA inversely related!
Frequency sets the _____ of the pulse
Period
Frequency relation to period
Inversely related
Frequency ↑, period ↓
Frequency relation to pulse duration
Inversely related
Frequency ↑, pulse duration ↓
Frequency relation to spatial resolution
Directly related
Frequency ↑, resolution ↑ (smaller resolution # is better!)
AR = 1/2 x SPL,
Frequency relation to PRP
Inversely related
Frequency ↑, PRP ↓ (because pulse duration decreases)
Frequency relation to PRF
Directly related
Frequency ↑, PRF ↑
(Frequency decreases PRP because pulse duration is decreased. PRP & PRF are inversely related!)
Definition of Pulse Duration
Time of an ultrasound pulse (from start to finish)
Equations for Pulse Duration (2)
PD = idle time + pulse duration PD = # of cycles/frequency
What does damping determine?
The number of cycles in the pulse.
↑ damping, ↓ number of cycles
Damping is built into into the probe, NOT user adjustable
Damping relation to pulse duration
Inversely related
↑ damping, ↓ pulse duration
(b/c # of cycles ↓ and PD = # of cycles/freq.)
Damping relation to PRP
Inversely related
↑ damping, ↓ PRP
(damping decreases pulse duration & PRP = pulse duration + idle time)
Damping relation to PRF
Directly related
↑ damping, ↑ PRF
(damping decreases PRP, PRP is inversely related to PRF)
What sets the idle time of an image?
Depth, which is user adjustable AKA idle time is adjustable
Depth relation to idle time
Directly related
↓ depth, ↓ idle time
Depth relation to PRP
Directly related
↓ depth, ↓ PRP
(b/c PRP = pulse duration + idle time & less depth decreases idle time)
Depth relation to PRF
Inversely related
↓ depth, ↑ PRF
(b/c less depth = less PRP; PRP & PRF are inversely related)
(T/F) Pulse duration can be changed by altering depth
False, pulse duration is changed by altering dampening
Definition of Duty Factor
Fraction of time the ultrasound machine is sending a pulse
Equation for Duty Factor
DF = pulse duration/PRP
What is the duty factor for a continuous wave transducer
1 or 100%
Depth relation to duty factor
Inversely related
Depth ↓, duty factor ↑
Definition of SPL
Spatial Pulse Length; the distance a pulse travels
Equation for SPL (2)
SPL = wavelength x number of cycles SPL = propagation speed x # of cycles/frequency
