Knobology Flashcards
What is the pathway to which Echo Images are made?
- Electrical Voltage applied to crystals in the probe
- Crystals (probe) vibrate
- Vibration –> Sound pulses Made
- TEE sends out the ultrasound sound pulses
- Pulses bounce off of objects and reflect back (Echo)
- Returning echos cause 2nd vibration in crystals
- Vibrating crystals create an electrical voltage difference
- Voltage difference is used to create an image
- Image displayed on the screen
What is A mode?
Amplitude Mode
(Not used anymore but strength of echo was plotted as amplitue)
What is B-Mode?
Brightness Mode
What is M-Mode?
Motion Mode
What is 2-D grayscale imaging?
Multiple M-modes to create 2D images
What are the axis of M-mode?
X-axis = Time
Y-axis = Depth
What is the frame rate of M-Mode?
1000
What does Brightness in M-Mode reflect?
Strength
What is seen here at the Aortic Valve in M-Mode?
HOCM
- Early closure of aortic valve leaflets
- Below is another image of this
What is a 2D: Phased array?
Multiple Scan Lines
- M-Mode of an entire scan plane
Multiple Pulses frorm multiple crystals
Real 2D images on the Screen
What is the basics of ultrasound physics when referring to Sound (Wave) and Medium?
Sound = Mechanical Longitudnal Wave
- Sound waves are compressions and rarefraacations in the molecules in the medium
Medium = Vibrates left/right as sound travels L –> R
What type of wave is Sound Not? (Odd question, but often confused)
Sound is NOT a Transverse Wave (it is a longitudinal wave)
What is the velocity of sound in media?
1540 meters/sec
What is a sound wave by definition?
Compression and Rarefactions in the molecules in the medium
Rarefactions* are areas of ultrasound wave having low pressure as the distance of their particles is far while *compressions are areas having high pressure as the distance of their particles is close.
What is the period in terms of ultrasound waves?
The amount of time it takes to complete a single cycle (Single wavelength time period).
What is frequency in terms of wave properties?
The number of cycles per second
What is frequency in relationship to period in terms of ultrasound waves?
1/Period = Frequency
What is pulse duration?
The amount of time it takes to complete an entire pulse
(Period of time it takes to complete pulse cycle)
What is pulse repetition period?
Period between pulses including listening time (Blank space)
(Includes pulse duration and listening time)
What is the pulse repetition frequency?
The inverse of the pulse repetition period
AKA the number of pulses per second
(# of pulses per second)
Why is PRF important (Pulse repetition frequency) important?
*2 reasons*
- Determines temporal resolution
- Determine nyquist limit
What is the max doppler shift?
What is the max doppler shift if how it relates to pulse repetition Frequency (PFR)?
Max Doppler Shift = Nyquist Limit
1/2 (50%) of the Pulse Repitition Frequency
What is spatial pulse length?
Spatial pulse length in ultrasound imaging describes the length of time that an ultrasound pulse occupies in space.
Mathematically, it is the product of the number of cycles in a pulse and the wavelength.
How does a shorter spatial pulse length affect axial resolution?
A shorter spatial pulse length results in higher axial resolution (Still able to differentiate two close objects)
Spatial pulse length can be reduced by heavier damping or use of a higher frequency transducer 1.
What are the 3 components that affect strength of an ultrasound?
- Amplitude
- Power
- Intensity
What is power as it relates to wavelength ultrasound physics?
The amount of work (Joules/sec = Watts) the ultrasound beam can do?
ALSO
Power = Rate of energy transfer (Rate at which work is performed)
What is intensity as it relates to wavelength ultrasound physics?
Why is intensity important?
Power / Area (Watts/cm2)
Intensity determines bioeffects
The mechanical bioeffect of ultrasound refers to damage caused by the actual oscillation of the sound wave on tissue
What is amplitude as it relates to wavelength ultrasound physics?
The difference between average acoustic variable vs. max acoustic variable.
The higher the amplitude, the higher the pulse.
What are the two types of resolution?
- Spatial Resolution
- Temporal Resolution
What is spatial resolution?
Ability to discern the correct space (Place) of a structure
What are the three types of spatial resolution?
How are they each related to the pulse/beam?
- Axial (Pulse length)
- Lateral (beam width)
- Elevational (beam height)
“ALE” - Best to worse in terms of optimal
What is the axial resolution equal to?
Half of the spatial pulse length
What is the relationship to Frequency, Spatial Pulse Length and Axial resolution?
Higher frequency = Shorter SPL = Better axial resolution
How does frequency relate to period?
Frequency = 1/Period
What is frequency?
of cycles per second
What is audible sound Hertz?
What is ultrasound Hertz?
Audible = 20-20 KHz
Ultrasound > 20KHz
As we increase frequency, what happens do our axial resolution?
it improves because we decrease our spatial pulse length
What is the downside of increasing frequency?
More attenuation (Not able to penetrate as deep)
Attenuation = Decrease in power as you penetrate structures at a high frequency
What is the definition of resolution?
The ability to accurately image structures
What is spatial resolution?
Ability to accurately create images of small structures in their correct anatomic position
What is temporal resolution?
Ability to accurately determine the position of a structure at a particular instant in time
What are the influential factors of temporal resolution?
- How much something moves
- Frame rate = # of frames/sec = # of images / sec
- Number of pulses per scan
- Line Density (# of lines/image)
- Image Depth (listening time)
- Sector width
What is gain in terms of ultrasound terminology?
Amplification
(Amplifies the returning signals)
When you increase the gain, what are you doing to the pulses transmitted from the probe to the body?
NOTHING
Does not alter the pulses
How does gain relate to power?
Gain DOES NOT correlated to power
If you change the power of the transducer, how does this affect the echo?
Power changes the strength of the pulses transmitted and the echos received.
- Strength of emitted pulses increases
When is the only time you will turn down the power?
When probe/machine is overheating
- Turn power down and turn gain up
What is the time gain compensation?
Time Gain Compensation = Depth Gain Compensation
i.e. compensates for attenuation
A way to overcome ultrasound attenuation is time gain compensation (TGC), in which signal gain is increased as time passes from the emitted wave pulse. This correction makes equally echogenic tissues look the same even if they are located in different depths.
The basis of this is that of returned ultrasound echoes from tissues. It is known that early echoes represent wave reflections in superficial layers, while late echoes come from deeper layers. This is the base of axial localization in ultrasound.
What is lateral gain compensation?
Changes in vertical position
Used to compensate for attenuation
Corrects enhancement artifact
Lateral gain compensation fine tunes the image in the lateral direction by increasing or decreasing gain as a function of lateral position (beam or vector position)
How does compression affect dynamic range?
Less compression = Larger dynamic range
More compression = Smaller dynamic range
What is the relationship between dynamic range and compression
Inversely proportional to one another
How does compression affect white/dark images?
Less compression = Less white/dark
More compression = Brighter brights and darks
How does compression affect grey images?
More compression = Fewer grays
Less compression = Less compression
How does compression affect contrast?
More compression = Highly contrasted image
Less compression = Less contrasted image
If you adjust gain, it changes what to the ultrasound signals?
Amplification
