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
What is a consequence of compressing data?
Generally a loss of information
What can result from not changing the compression maps?
Loss of data
What do appropriate compression maps enhance?
Low level echoes to better visualize pathology
Compression maps are crucial for improving image clarity in diagnostic imaging.
What is displayed on the horizontal axis of compression maps?
Signal strength
The vertical axis represents output display intensity.
What does the display intensity range from in compression maps?
Zero (black) to 255 (white)
This range allows for a full spectrum of visual representation.
What are chromamaps used for?
To extend the dynamic range of the human eye with color hues
Chromamaps enhance the visual representation of tissue in imaging.
What is the greatest source of error in area tracing?
Incorrect angle in the 2-D image
This can lead to significant errors in measurement.
What are the two types of mistakes in area tracing?
Overestimating and underestimating the area
Accurate area tracing is essential for correct diagnostics.
What are the two distinct sources of error in longitudinal plane area underestimation?
Location and angle
These factors can lead to inaccurate area measurements.
What happens if the imaging plane does not intersect the object in the center?
Area measurement will be smaller due to foreshortening
Foreshortening affects the accuracy of measurements in imaging.
What is the typical operating frequency of most LCD/LED monitors?
60 Hz
This frequency is standard for display refresh rates.
What occurs if the acoustic frame rate is 180 Hz but the monitor display rate is 60 Hz?
Only every third frame is displayed
This can lead to a loss of detail in the displayed image.
What is the main difference between LED and LCD monitors?
The source of the backlight
LED uses emitting diodes, while LCD uses fluorescent backlighting.
What are the characteristics of LCD monitors?
- Shorter lifespan (around 30,000 hours)
- Less expensive
- Thicker and heavier
- Lower resolution
- Consumes more power
- Generates more heat
- Lower contrast resolution
These characteristics impact their use and performance.
What are the characteristics of LED monitors?
- Longer lifespan (around 50,000 hours)
- More expensive
- Thinner and lighter
- Supports 4K
- More economical
- Generates less heat
- Better contrast and color quality
LED monitors are generally preferred for their superior performance.
What is the positive effect of increasing the number of image lines?
Expands field of view to show larger regions of interest
What is the negative effect of increasing the number of image lines?
Increased frame time decreases temporal resolution
What is the positive effect of using narrower beams?
Improves lateral resolution
What is the negative effect of using narrower beams?
Higher line density needed increases frame time and decreases temporal resolution
What is the positive effect of a larger transmit aperture?
Increased focal depth and penetration depth; beam focus is deeper and narrower
What is the negative effect of a larger transmit aperture?
Wider beam decreases lateral resolution in near field
What is the positive effect of line frame averaging?
Improves SNR, sensitivity, and reduces speckle
What is the negative effect of line frame averaging?
Increased frame timing decreases temporal resolution
What does averaging improve in imaging?
Signal to noise ratio and contrast ratio
What causes speckle in imaging?
Coherent wave interference
What is the effect of high speckle on image quality?
Reduces contrast and detailed resolution
How much does the signal to noise ratio improve when two images are layered?
Improves by 1.4
What is the effect of a larger color packet size in line averaging?
Improves color sensitivity and creates a larger signal noise ratio but reduces temporal resolution
When does frame averaging work best?
When averaging static images
What is a negative aspect of frame averaging?
Time to generate a frame is long enough to allow for significant motion
What happens to signal samples when the sample rate is fast enough relative to changes in the signal?
Each signal sample will add in phase leading to constructive interference
What happens when adding together multiple frames in terms of signal and noise?
Signal increases at a faster rate than noise, improving SNR
What is spatial compound imaging?
A frame averaging technique that creates multiple images over time and averages them to create one image.
Images are formed at varying angles.
What are the three primary benefits of compound imaging?
- Improvement to signal-to-noise ratio
- Reduction of specular reflection
- Speckle reduction
Specular components that cause artifacts are only present in some frames.
How many images are typically used in compound imaging?
Between three and nine images.
Buffing technique replaces the oldest frame with the newest frame.
What does FIFO stand for in the context of compound imaging?
First In, First Out.
This refers to the buffering technique used in compound imaging.
What is compound imaging?
It is an averaging technique that transmits multiple frames at varying angles to improve image quality.
This results in decreased specular reflection artifacts and improved signal-to-noise ratio.
What is frequency compounding/fusion?
A technique that transmits with a broadband signal and simultaneously processes multiple images at different frequencies.
Each image is captured at a different frequency.
What is the difference between compound imaging and fusion imaging?
Compound imaging averages frames taken over time at varying angles, while fusion imaging fuses multiple images taken at different frequencies simultaneously.
Fusion does not reduce temporal resolution.
What are two key differences between persistence and spatial imaging?
- The angle is not changed between frames
- A weighted average is applied to each frame, counting new frames more than old ones.
This highlights how persistence maintains frame angle consistency.
What are the two varied parameters for image persistence?
- How many frames are averaged together?
- The weighting function applied to each frame.
These parameters affect the persistence technique’s effectiveness.
What is spatial averaging?
A technique that reduces noise by averaging data from different frames and smoothing data based on neighboring pixels.
It focuses on one pixel and the surrounding pixels.
What is a composite beam?
A variable focus receive beam that can be in focus at all depths, created by the simultaneous effects of transmit and receive beams.
The lateral resolution of the composite beam varies based on the width of the transmit and receive beams.
What is active single focus?
A transmit technique used to create sequential images that can adjust focal depth to improve lateral resolution.
This technique enhances image quality as adjustments are made.
What is the purpose of multiple transmit focus?
To improve lateral resolution by transmitting multiple beams in the same direction at varying focal depths and combining the zones of best resolution.
More transmit focuses increase the time to produce a line and affect temporal resolution.
What is synthetic aperture?
The effective aperture created by adding signals from individual elements.
Synthetic aperture improves the resolution of images in imaging technologies.
Define ultra fast imaging.
Any image generation methodology that results in significantly faster frame rates than conventional sequential imaging.
Sequential imaging operates under 100 Hz frame rate, while ultra fast imaging is 100 times faster.
What is multi line acquisition?
Imaging that generates more than one receive line simultaneously.
What is parallel processing in imaging?
An increase in frame rate and temporal resolution using a wide beam with multiple receive beams instead of narrow beams with a single beam.
What characterizes zone imaging?
No transmit focus, increased frame rates, and a wider beam that decreases lateral resolution.
What is a dynamic receive focus?
A technique that improves lateral resolution but requires increased processing power.
What is the advantage of single focal sequential imaging?
Good detailed resolution.
What is a disadvantage of single focal sequential imaging?
Limited temporal resolution.
What is the advantage of multifocal sequential imaging?
Improves lateral resolution.
What is the disadvantage of multifocal sequential imaging?
Degrades temporal resolution.
What is the advantage of multi line acquisition?
Increased temporal resolution.
What is the disadvantage of multi line acquisition?
Decreased lateral resolution unless retrospective focusing is employed, may cause grouping artifacts.
What is the advantage of multiline transmit?
Increased frame rate.
What is the disadvantage of multiline transmit?
Grading lobes and cross talk between simultaneously transmitted beams.
What is a synthetic aperture using a single element?
Ability to create high resolution focus for both transmit and receive, but has poor signal noise ratio.
What is a disadvantage of synthetic aperture using a single element?
Image from a single element has poor signal noise ratio; temporal resolution is similar to a single transmit focus.
What is a synthetic aperture using multiple elements?
Ability to create high resolution focus for transmit and receive beam with better signal to noise ratio than single element.
What is a disadvantage of synthetic aperture using multiple elements?
Requires massive amounts of processing power.
What is retrospective transmit focus?
Improved lateral resolution but requires significant processing power.
What is the advantage of compounded plane/diverging wave with retrospective transmit focus?
Improved temporal resolution and potential increased contrast resolution.
What are the disadvantages of compounded plane/diverging wave with retrospective transmit focus?
Grading globe, artifacts, and image degradation.
