Pixels, Dynamic Rang, Harmonics Flashcards
Name the receiver functions, briefly define.
~Amplification: increase the the received sound echoes to of which it was sent out
~Compensation: it makes up for the lower amplitude of the echoes that attenuated more due to being in the tissue for longer.
~Compression: Combining some of the similar amplitudes for a smaller dynamic range (gray scale) for our poor little eyes to see.
~Demodulation: Invals Smoothing (further compressing amplitudes
for the mechiens sake)
Rectification, makes the negative amplifications -
positive
~Regection: taking out the amplitudes bellow the base line, considering it noise
What is the process of displaying the scan’s information?
~Transducer sends sound beam out to tissue and sound is reflected back and into the transducer to go through the receiver functions
What is the scan converter?
This is where the final data of exam is stored, converting the data from a spoke to image format.
What are the different ways to display the data on screen?
Old way- TV (CRT) Cathode ray tube
New/current way- LCD screens
How does the CRT display the information of the exam?
Sends charged electrons to a phosphate screen which glows when hit making an image. the image is made up of 525 horazantal lines, odd lines displayed first then even line, to avoid noticable flickering, which happens between frames if odd and even lines where displayed all at once.
These odd and even lines are interlaced and make 1 frame when added together.
What does newer display modes use?
Pixel
What is biscale?
Biscale: 2 color choices (Black and White)
- high constrast - Low dynamic range
What is grayscale?
Includes black, white and all the gray inbetween
- Gives more detail in images - Higher dynamic range - Better contrast resolution (able to see separate structures based on there grayscale)
What is involved in what is called the writing phase of the scan converter?
This is the storing/converting phase of the image information. This is looking at live data from patient at which we can zoom and still add to the line density improving spatial resolution.
Transduser-analog (spoke format) Display- digital (horazantal format)
What does it mean for the scan converter to Read information?
This is the output information, of which we are looking at old data, for example we can not zoom and improve resolution. We use this when measuring, and using cine.
Analog vs Digital
Analog Old techology Digital New technology
- difficult to manage. •easier to manage - Imposible digits (5.9876). •Desecrate digits (57)
What is the Analog scan converter and its Benifits?
Electrons projected to a silicon wafer or dialect matrix and stored as information.
~Store large amount of information
~Many electrons + high amount of image information
~Good spatial resolution.
What are some cons of Analog scan converters?
- Images fade
- image flickers
- Instability
- Degeneration
What is the digital scan converters?
Final data is stored as digital format, using 1s (on) and 0s (off), like the matrix.
the 1s and 0s are reassessed to recreate images for display, using Pixes and bits.
What are the pros digital scan converters?
Uniform- no charges to degrade Stable- no change to information Durable- unchanged by time or environmental conditions Fast- able to access data instantly Accurate- error free
Whats are pixels?
They are the picture element of a digital converter.
Pixel density = pixels per inch
Higher density = better for spatial resolution
Smaller pixel size = higher density
What is a bit?
This is a binary digit either 1s or 0s (on or off), which is used to store data for images.
Amount of bits determine grayscale
Many bits = large dynamic range
Large DR = better contrast resolution
What is dynamic range?
Describes the range of shades of gray that can be used in a image
-Reported in dB which is determined by the largest and smallest of the measurement.
-Decreases with image proessing, and display example;
transducer= 120 dB Display = 20-30dB
How do calculate dynamic range?
For every 0 in the largest number of a voltage ratio there are 20 dB
ex 100:1 =40 dB
How do you calculate shades of gray?
Bi = 2^N N + # of bits pixel with bits —> 2^4 =2x2x2x2=24 —— ——>24/2=16 shades of gray
What is the 5 step process to convert between analog and digital?
1- Analog signals from transducer changed to 0s and 1s by the A to D Convertor
2- Info stored in Scan Converter (Preprocessing)
3-Postprocessing occurs
4- D to A Converter for display of image (CRT only)
5- Image displayed
What is done in Preprocessing?
~TGCs, 2D, depth, width, focus, frequency
~Wright zoom
What happens with wright zoom?
~Increase in pixel density ~Increase in line density ~Improved spatial resolution ~Always better! ~Adjust depth, then zoom
Name the methods of storage.
Old method- Paper, film VHS, CDs
MO Disk- Magneto-optical storage
High volume, low degradation
PACS- Picture Archiving and Communicating System
Instant access to images
Stores prior imaging, organizes by patient
Multiple viewers can access data
What are hermonics?
Creation of an image based on reflection that are twice the fundamental frequency
They have greater penetration then the fundamental frequency, two ways of accomplishing harmonic imaging:
tissue harmonics
Contrast hermonic
What describes a Non linear wave propegating through tissue?
Tissue harmonics
How do tissue harmonics work?
It happens when the sound beam passes through tissue with varying propegation speeds, stiffness, and density.
it occers down the length of the beam AND ALTERS a portion of the beams wavelenth, creating higher frequencies so better resolution.
What are Contrast Harmonics?
This is like the amplified vertion of tissue harmonics, working under the same principles, through the use of injecting or swallowing contrast agents.
How do contrast agents work?
A contrast agent is made of gas filled micro bubbles, which contracts when encountering the sound wave due to the higher pressure of the compressed part of the wave and epand in the rarfraction phase, releasing energy. This energy causes harmonic frequency that is reflected back to the transducer.
What is the mechanicle index?
Determines how much harmonic effect will occur based on fundamental frequency and pressure of sound wave
MI = Peak Negative Pressure Root Fund Freq
Why is the mechanical index importent?
It is a way to to figure out the risk of bioeffects.
How is the mechanical index related to (1) peak rarefaction pressure and (2) fundamental frequency?
(1) Directly and (2) indirectly
Considering the mechanical index what would be the best range (Low, mid or high) for harmonics and Why?
Mid = 0.1 - 1.0
Low = 1 Very strong harmonic effect Bubble instability (bad! bioeffects)
