1
Q
Basic instrumentation process
A
voltages are processed by the machine to reconstruct and image from reflectors in the body
voltages are stored and converted once again into the image we see on the monitor
2
Q
basic instrumentation steps
A
transducer - beam former - signal processor - image processor - display
3
Q
beam former parts
A
pulser - pulse delays - transmit receive switch - amplifiers - ADC’s - Echo Delays - sum - - - - signal processor
4
Q
beam former - pulser
A
- sends the voltage pulse to the probe determining the INTENSITY, OPERATING FREQUENCY, and PRF
- this is what we change when we change power, frequency, depth
5
Q
beam former - pulse delays
A
- applies the delays necessary to accomplish focusing, beam steering and aperture size (how many crystals in the group are firing)
- phasing
6
Q
beam former - transmit receive switch
A
- directs the pulse in the correct direction to protect the sensitive components from large voltage pulses
- gateway for sound to probe and echoes coming back
- traffic cop of probe
7
Q
beam former - amplifiers
A
- pulses that return from the patient are weak and need this to make the trip through the circuitry of the machine
- like a transformer
8
Q
beam former - ADC’s
A
- pulses pass through this and become digitized
- necessary for storage in memory and for manipulation of image later on
- ANALOG TO DIGITAL CONVERSION
- analog is voltage and not stable need to convert to stable digital form
- no missing information in analog
- digital loses insignificant information
9
Q
beam former - echo delays
A
- remember that the echo pulses were delayed and must be “reset” to properly construct and image
- echo delay holds first returning voltage until other catch up
- reduce chance of out of phase destructive interference
10
Q
beam former - sum
A
- adds together the pulses from each element in the segment to form the resulting SCAN LINE
11
Q
digitization ( ADC)
A
- digitization of voltage is crucial to maintain integrity of the data through the system
- involves converting the voltage into a binary number which is more stable
- digitization can occur before or after the echo delay in the beam former but should be digitized early on
12
Q
signal processing
A
- 2 processes
+ ADC
+ the receiver
13
Q
signal processing - the receiver
A
- function is to process the returned echos as analog voltages in preparation for display
- 5 steps
14
Q
5 steps of the receiver
A
- amplification (GAIN)
- compensation (TGC)
- compression (DYNAMIC RANGE)
- rejection
- demodulation ( rectification and smoothing )
15
Q
amplification
A
- returned echos are very weak and must be amplified if they are going to make it through the circuitry of the machine
- WE further the amount of amplification to satisfy the need to brighten or darken the image
- THE CONTROL IS GAIN AND IS EXPRESSED IN DECIBELS
16
Q
compensation
A
- sound attenuates as it travels and thus there is a need to compensate for it
- similar signals from reflectors should have same brightness regardless of how deep you image the reflector
- TGC IS THE CONTROL RESPONSIBLE AND EXPRESSED IN DECIBELS
- can also be called DGC
- operaties in 1cm increments and can correct for MAIN BANG ARTIFACTS (when sound first hits patient) AND ATTENUATION IN FAR FIELD
17
Q
compression
A
- AKA DYNAMIC RANGE
- process of decreasing the difference between the SMALLEST (REJECT LEVEL) and the LARGEST (SATURATION) amplitudes and is expressed in decibels
- log amplification does this
+ gain applied exponentially as function of input signal level and result is compression of dynamic range
18
Q
rejection
A
- THRESHOLD, SUPPRESSION
- used to eliminate or suppresses low level echoes that may represent noise and therefore IMPROVE SIGNAL TO NOISE RATIO
- rejection helps reduce the dynamic range and may or may not be operator controlled
19
Q
demodulation
A
- process that converts radio frequency (RF) signal into a video signal for monitor display
- 2 stage process including rectification and smoothing/enveloping
20
Q
rectification
A
- turns all negative portions of the signal (sine wave) into positive ones
21
Q
smoothing/enveloping
A
- filters the signal to smooth out the bumps
22
Q
image processor parts
A
scan convertor - pre processor - memory - post processor - DAC - - - - display
23
Q
image processor - scan conversion
A
- simple function of scan convertor is to WRITE THE VERTICALLY ACQUIRED ULTRASOUND DATA HORIZONTALLY TO THE MEMORY
- ALLOWED FOR GRAY SCALE
- type of memory
24
Q
analog scan convertor
A
- scan convertor/ memory is similar to CRT (cathode ray tube) except instead of phosphorus face is a WAFER OF SILICON CALLED DIELECTRIC MATRIX
- electrons emitted by the filament pass through the deflection plates and strike the silicon wafer leaving positive charges proportional to the amplitude of the signal strength
- electron beam moves across the dielectric matrix in RASTER FORMAT
25
image processor - pre processing
- any processing of the wave signal before it is transferred and stored in the memory
- different ultrasound machines offer different processing
26
pre processing examples
- receiver functions (gain, tgc, dynamic range)
- maps = extenuate diff parts of gray scale
- interpolation
- edge enhancement
- write zoom
- persistence
27
maps
- curves applies to the shades of gray to accentuate diff levels
- enhance visualization of certain aspects of the image
28
interpolation
- there is a gap present between the scan lines in the image
- interpolation is used which averages pixel gray scale values to fill in information where none exists
- improve appearance but not sure if it is real
- too much interpolation could misrepresent the image
- opposite is OVERRIDING
29
Edge enhancement
- improves look of image
- sharpen boundaries to make them more distinguishable and help make measurements more precise
- a KERNEL is applied to pixels to achieve this
- won't change homogenous tissue
- kernel is swept through image and creates big diff between the grass changes the decibels
30
write zoom
- aka regional expansion expands the image before storage in the memory
- the region of interest (ROI) is adjustable by us
- advantage is that ROI is rescanned and additional scan lines are added which increase spatial resolution, detail and pixel ratio
- good for OB , very accurate, use in moderation
31
persistence
- takes data from several ultrasound frames and averages them before displaying the image to IMPROVE SNR
- sampling over times will decrease temporal resolution so the rate of movement must be small or blurring occurs
- persistence not used in echo or OB
- helps with acoustic speckle
32
post processing
- any process that occurs after the information has been stored into memory
- can be applied to frozen image
- measurements , contrast, enhancement after exam is complete
33
post processing - examples
- measuring
- annotations
- post processing curves
- read zoom
- color doppler mapping
- angle correct
- B color
34
post processing - curves
- can be applied to frozen image and is the assignment of display intensity to a digital value
- operator controlled function accomplished in DAC
- most common LINEAR CURVE
- each manufacturer has different curves
35
read zoom
- magnifies a frozen image by reassigning the pixel size
- decrease in resolution
- bad zoom
36
B color
- instead of shades of gray the operator can assign shades of other colours to each digital
- uses various color schemes form orange to purple to blue
- may help improve contrast resolution of image
37
image processing - DAC
- digital to analog converter
- final step of image processing
- reconvert the digital information into a voltage signal
- DISPLAY SYSTEMS WILL ONLY ACCEPT A VOLTAGE (VIDEO OR ANALOG)
Physics 2
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