Chap 6 Lvl 2 Flashcards
What is overall gain control referred to as?
Coarse adjustments
Overall gain control is a broad adjustment used in signal processing.
What does TGC stand for?
Time gain compensation
TGC is a method used to adjust the gain of an ultrasound signal based on depth.
What is the purpose of Time Gain Compensation (TGC)?
To compensate for depth-dependent attenuation
TGC adjusts the gain of the signal as it travels through different depths in the body.
What type of signals are transmitted into the body during ultrasound?
Analog signals
These signals represent sound waves sent into the body for imaging.
What happens to the signals after they return from the body?
They are analog signals that get converted into digital
The returning signals are also in analog format before conversion.
What is the process that all ultrasound systems perform with signals?
Convert from analog to digital format
This conversion is essential for processing and displaying the ultrasound images.
What is the effect of a greater decibel range in internal TGC profiles?
A more decibel range would make the sliders too sensitive
This sensitivity can impact the adjustment of gain in imaging.
What is the relationship between frequency and attenuation?
Higher frequency equals greater attenuation
This means higher frequencies lose strength more quickly as they travel through mediums.
What is the relationship between lower frequency and attenuation?
Lower frequency equals lower attenuation
Lower frequencies maintain strength better than higher frequencies.
What are the three core functions of the scan converter?
- Beamforming the data received
- Converting A-mode lines into B-mode lines
- Organizing the lines of data into a formatted image
These functions are critical for effective ultrasound imaging.
What does linear scan represent in terms of depth increment?
Each depth increment of each A-mode line represents the same physical size in the image.
This ensures consistent representation of depth in the resulting image.
In sector/curved scan, how does the near field compare to the far field?
The nearer field is narrower than the far field.
This results in a varying width between the sector scan lines.
What happens to the width between sector scan lines as it moves from near to far field?
The width between the sector scan lines increases.
This necessitates converting data from a linear coordinate system to a polar coordinate system.
What is scan conversion?
The process of converting lines of data into an image format, requiring grayscale mapping from A-mode to B-mode.
This is essential for creating visual representations in ultrasound.
What is pre-processing in the context of scan conversion?
Any process occurring before the scan conversion.
Pre-processing affects the initial data capture.
What is post-processing in scan conversion?
Any process performed on the stored data after conversion.
This includes adjustments made to a frozen image.
List some pre-processing techniques.
- Transmit frequency
- Transmit power
- Transmit focus
These techniques optimize the data before conversion.
List some post-processing techniques.
- TGC (Time Gain Compensation)
- Speckle reduction
- Edge enhancement
- Compression
- Chroma maps
These techniques enhance the quality of the resulting image.
What is the typical dynamic range for echoes?
80 dB or greater
For Doppler, the dynamic range is significantly greater.
What affects the strength of a reflection in ultrasound?
Acoustic impedance mismatch
How does attenuation vary with depth in ultrasound echoes?
Less attenuation for shallow echoes than for deeper echoes
How many shades of gray can the human eye see?
Up to 64 shades of gray
What is the dynamic range for the human eye?
Less than 36 dB
Why is compression necessary in data processing?
To reduce large signal dynamic range closer to the dynamic range of the human eye