Week 4 US machine Flashcards
The US machine: describe power output
power output = output, transmit, dB, power
controls overall power
Set power as low as possible but still produces diagnostic image
NOT gain
The US machine: describe pulser
pulser converts continuous electrical signals into pulses
has a timer and sends timing signals to the receiver and memory
Pulse Repetition Period (PRP)
PRP is time required to send 1 pulse and wait for echos
Pulse Repetition Frequency (PRF)
What is the relationship between depth and PRF?
Why do we want high PRF?
PRF is # pulses per second
incr depth = incr PRP = decr PRF
incr PRF = incr frame rate (good for fast moving images) and better doppler
The US machine: describe beam former
btw pulser and transducer
adds time delays to control beam focus/steering
controls dynamic focusing of received echos
The US machine: describe receiver
receives electrical signal from transducer
performs amplification, compensation, and signal processing
The US machine: describe memory (RAM)
RAM is Rapid Access Memory
remembers several minutes of data, you can “freeze” and scroll back
RAM is deleted if you “freeze/unfreeze” or store cine
Where are US exams stored permanently
Defn of Lossy versus Lossless for file transfer
PACs system
DICOM is best format (highest res)
Lossy = decr file size and degrade image (DICOM to JPEG)
Lossless = not as much decr in file size (DICOM to GIF or TIFF)
The US machine: describe display types
LCD vs LED vs OLED
LCD = Liquid Crystal Display; image is angle dependant (not good)
LED = Light Emitting Diode; used today; thinner, brighter and less power than LCD
OLED = Organic LED; better black display than LED but more expensive
Analog vs Digital signal
Analog - continuous format like clock with hands
Digital - discrete exact events like a digital watch that changes every minute or second
How did the Analog US machine work?
used until 1990s
Disadvantages?
scan converter received electrical signal and converted it for display on cathode ray tube (analog to analog)
recorded onto VCR
Disadv
- info wasn’t permanent and tended to fade and drift
- could not alter stored info
- devices needed lots of servicing
today we use digital computers
How does scan converter convert analog signal to digital display
screen is a matrix (grid) made up of pixels
each pixel corresponds to a location in the body (x,y)
a binary number representing the amplitude of the echo is stored in the pixel and represents the shade of grey we see
bit
A bit is like a letter
binary - 0 (off) or 1 (on)
computers smallest unit of data
byte
A byte is like a word
group of 8 bits
computers smallest unit of memory (length of command)
byte size
storage of computer… how many gigabytes?
bit depth
defn and formula
what happens when you incr bit depth
of parallel options for 1 piece of data (in US, this is number of shades of grey for pixel)
L = 2^n
L is bit depth
n is bit size
incr bit depth = contrast res
most US machines are 8 bit. What does this mean?
8 bit means “8 grids/matrix deep”
L = 2^n = 2^8 = 256
each pixel on the matrix can display any 1 of 256 pieces of info/shades of grey.
convert 5 to binary system
8 4 2 1
1 0 1
101
Scan converter - reading versus writing; freeze
writing - actively collecting data and making image; “real time” image on screen
reading - puts data on screen (takes data out of matrix, converts it, sends info to monitor)
freeze - stops everything
rectification
negative components are flipped and become positive
demodulation
converts RF waveform into a smoother shape
interpolation
filling in the gaps so image appears continuous (during image writing)
pixel density
what happens when you incr pixel density?
size of matrix
incr pixel density = improves spatial res
