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Physics 2 > Module 2 : Basic Instrumentation > Flashcards

Module 2 : Basic Instrumentation Flashcards

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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

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2
Q

basic instrumentation steps

A

transducer - beam former - signal processor - image processor - display

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3
Q

beam former parts

A

pulser - pulse delays - transmit receive switch - amplifiers - ADC’s - Echo Delays - sum - - - - signal processor

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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
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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
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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
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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
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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
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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
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10
Q

beam former - sum

A
  • adds together the pulses from each element in the segment to form the resulting SCAN LINE
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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
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12
Q

signal processing

A
  • 2 processes
    + ADC
    + the receiver
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13
Q

signal processing - the receiver

A
  • function is to process the returned echos as analog voltages in preparation for display
  • 5 steps
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14
Q

5 steps of the receiver

A
  • amplification (GAIN)
  • compensation (TGC)
  • compression (DYNAMIC RANGE)
  • rejection
  • demodulation ( rectification and smoothing )
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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
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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
Q

image processor - pre processing

A
  • any processing of the wave signal before it is transferred and stored in the memory
  • different ultrasound machines offer different processing
26
Q

pre processing examples

A
  • receiver functions (gain, tgc, dynamic range)
  • maps = extenuate diff parts of gray scale
  • interpolation
  • edge enhancement
  • write zoom
  • persistence
27
Q

maps

A
  • curves applies to the shades of gray to accentuate diff levels
  • enhance visualization of certain aspects of the image
28
Q

interpolation

A
  • 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
Q

Edge enhancement

A
  • 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
Q

write zoom

A
  • 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
Q

persistence

A
  • 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
Q

post processing

A
  • 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
Q

post processing - examples

A
  • measuring
  • annotations
  • post processing curves
  • read zoom
  • color doppler mapping
  • angle correct
  • B color
34
Q

post processing - curves

A
  • 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
Q

read zoom

A
  • magnifies a frozen image by reassigning the pixel size
  • decrease in resolution
  • bad zoom
36
Q

B color

A
  • 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
Q

image processing - DAC

A
  • 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 (8 decks)

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