exam 2 review Flashcards
Pulse duration equation
PD (time)= Period (time) * # cycles
Spatial pulse length equation
SPL (distance)= Wavelength(distance) * # cycles
Frame Time equation
Frame Time= PRP (time) * # lines
Frame time equation with color
Frame Time= PRP * #lines/packet * #packets/frame
Frame Time on steroids equation
Frame Time= 13 ms/cm * ID * #lines/packet * #packets/frame * #foci
Frame rate and Frame time
Reciprocal
FR*FT=1
Pulse repetition period and pulse repetition frequency
Reciprocal
PRP*PRF=1
Pulse repetition period equation
PRP= 13 ms/cm * ID
Duty Factor equation
DT (%)= PD/PRP * 100
Bandwidth equation
BW= F(max) - F(min) BW= 1/PD
Pulsed Wave equation
F(o)=Crystal/2*thickness
F(o)= operating frequency
Continuous wave equation
F(o)= drive voltage frequency
Beam width equation
D/2 @ the focus
D @ 2X the focus
Near zone length equation
D(2)*F(o)/6
OR
D(2)/4y
Beam divergence
1.85/D*f(o)
Longitudinal resolution
SPL/2
Lateral resolution
Beam width in the lateral plane
Elevation resolution
Beam width in elevation plane
Transducers convert one form of ____ into another.
Energy
Piezoelectric effect
Describes the property of certain materials to create a voltage when they are mechanically deformed or when pressure is applied
Transducer construction
- Backing material
- Piezoelectric crystal(s)
- Matching layer
Importance of matching layer and gel
They decrease the reflection at the piezoelectric crystal and skin boundary and increase the percentage of transmitted sound
Band width definition
range of frequencies in the pulse
Beam divergence definition
Describes the gradual spread of the ultrasound beam in the far field.
less divergence= larger diameter, higher frequency
more divergence= small diameter, lower frequency
Axial Resolution
Ability of a system to display two structures that are very close together when the structures are parallel to the sound beams main axis
Determined by the pulse length (shorter pulses have better resolution)
Synonyms= longitudinal, range, radial, or depth resolution
Better axial resolution
- shorter spatial pulse length
- shorter pulse duration
- higher frequencies
Lateral resolution
Ability to distinctly identify two structures that are very close together when they are side by side or perpendicular to the sound beams main axis
Determined by the width of the sound beam (narrower beams have better resolution)
Synonyms= angular, transverse, or azimuthal
Matching layer function
- Located in front of the Piezoelectric crystals at the face of the transducer
- Increases efficiency of sound energy transfer between active element and body
- Protects the active element
- One quarter wavelength thick
Backing material function
- Bonded to the back of the active element
- Reduces the ringing of the PZT
- Dampens emitted sound pulse (enhances axial resolution)
Continuous wave transducer frequency
The frequency is equal to the frequency of the electrical signal
Pulsed wave transducer frequency
Determined by Speed of sound in the PZT and thickness of the PZT
Beam shape characteristics
- focus
- near zone
- focal length/near zone length
- far zone
- focal zone
Focus (Focal point)
The location where the beam is the narrowest
beam shape=1/2 the width of the beam as it leaves the transducer
Near zone (fresnel zone)
Region from the transducer to the focus
The beam gradually narrows or converges within the near zone
Beam shape= 1/2 the width of the active element
Focal length (focal depth or near zone length)
The distance from the transducer to the focus
Far zone (far field, Fraunhofer zone)
Region that starts at the focus and extends deeper
The beam will diverge/spread out
Beam shape= @ beginning of far zone, beam is 1/2 as wide as the transducer. @ deeper depths, the beam is wider
Focal zone
Region around the focus where the beam is relatively narrow
Shallow focus
- smaller diameter PZT
* lower frequency
Deep focus
- larger diameter PZT
* higher frequency
What part of the beam gives the best focus?
Near zone, right before the natural focus
Frame rate
Ability to create numerous frames each second
Determined by speed of sound in a medium and imaging depth
Pulse duration
actual time from start of a pulse to the end of the pulse
Determined by sound source only
Cannot be adjusted by the sonographer
Values= 0.3-2 microseconds
Spatial pulse length
the distance that a pulse occupies in space from start to finish
determined by the sound source and the medium
Cannot be adjusted by the sonographer
Values (in soft tissue)= 0.1-1 mm
Pulse repetition period
the time from the start of one pulse to the start of the next pulse
determined by the sound source and the imaging depth
Can be adjusted by the sonographer
Values= 100 microseconds-1 millisecond
Pulse repetition frequency
number of pulses that a system transmits into the body each second
determined by sound source and imaging depth
Can be adjusted by the sonographer
Values= 1,000-10,000 Hz
Duty factor
percentage of fraction of time that the system transmits a pulse
determined by sound source only
Can be adjusted by the sonographer
Values= 0.2-0.5%
