Image Processing Flashcards
What are the five functions of the receiver?
Amplification, compensation, compression, demodulation, reject.
What is the purpose of amplification?
Voltages coming back from the transducer are very tiny and need to be made larger to be useful.
What is the purpose of compensation?
Compensation refers to the TGCs. This provides the operator the ability to boost deeper echoes and reduce shallower echoes.
What are some archaic terms used for controls that are now done automatically?
Delay, Slope, Knee
What is the purpose of compression?
Compression controls the range of gray shades.
High-value:Wider range of grays.
Low value:Fewer shades of gray.
Essentially compression controls the DIFFERENCE between the strongest and the weakest voltages, thus reducing or increasing the image contrast.
What are the units used to describe levels of compression?
Decibels.
What is the purpose of demodulation?
Demodulation rectifies an AC signal. AC signals are positive and negative crossing the baseline. Rectifying converts the AC signal into a DC signal, whereby all of the voltages are above the baseline. This is critical for display because display devices present values from zero (blacks) and above (i.e. 100: whites) yes. They cannot represent values that are negative.
What is the purpose of reject?
Reject cancels out low-level echoes to varying degrees to enhance image clarity. The low-level stuff is probably just noise.
What is the purpose of harmonics or tissue harmonics?
This is a special process where the machine evaluates the harmonic instead of the fundamental frequency. This often provides a better image. Especially useful for deep imaging such as Echo, not very useful for superficial imaging.
What is the scan converter?
Scan converter stores image information as voltages then sends it to the display. It essentially translates the echo information into a video format
What gets stored?
The position and grayscale value of pixels.
What is dynamic range?
Dynamic range refers to the range of shades of gray in the display. This relates back to log compression is given in decibels and the higher the decibels the more shades of gray.
What is the difference between analog scan converters and digital scan converters?
Analog scan converter store the grayscale values as voltages.
Digital scan converters Store information has bits designated in binary numbers.
How do you determined the maximum number of shades of gray when given a bit value?
The value equals two to the power of bits. For example five bits = two to the power of five = 32 shades of gray.
Eight bits = two to the power of eight = 256 shades of gray.
What does preprocessing refer to?
Preprocessing is adjusting the image information before it gets to the scan converter. These changes are irreversible.
