Exam 3 review Flashcards
Pre-Processing
Takes place before scan conversion and cannot be changed on data that has been stored in the internal system
TGC, receiver, beam former, console, transducer
Scan converter
Where most work is done
A-mode to B-mode, memory, cine loop
Post-Processing
Takes place after scan conversion and can be changed after the data has been stored in the internal system
Display, Storage (PACS), measurement, and printing
Dynamic range
number of available choices, method of reporting the extent to which a signal can vary and still be accurately measured.
Measured in Decibels
When too large, it’s compressed, information is lost
The Receiver
Amplification, compensation, compression, demodulation, and rejection
Amplification
The process of multiplying the received signal to make the signal larger
Compensation
Preformed by TGC and overall gain
Compression
Signal is compressed so the ratio of max and minimum signals is reduced
Demodulation
Takes any signal below the baseline and flips it so it’s above the baseline then smoothes the signals out
Rejection
Any signals below a threshold are eliminated as too weak to be of any value
A-mode
Amplitude mode, shows amplitude and time(or depth)
B-mode
Brightness mode
M-mode
Motion mode, typically used in cardiac imaging, non scanned modality.
Analog vs. Digital
For ultrasound, signals must be in digital form like a computer
Binary
Expressed in 0’s and 1’s, on and off time
Signal to noise ratio
no noise= high signal to noise ratio
Machine averages images to increase SNR and gives a clearer image
Good for ultrasound
Pixel
Picture element
1.5D transducers
Can produce 2D images and improves elevation resolution
2D transducers
Can produce 3D and 4D images and improves elevation resolution
Edge enhancement
optimizes images on their edges, similar to spatial averaging
Spatial averaging
The averaging of pixels to create a smoother image
Spatial resolution
2D “in space”
Pixel size, # of bits, pixel density, lateral resolution, line density all affect spatial resolution
Contrast resolution
Shades of grey
High contrast, low contrast resolution= small # shades (bits)
Low contrast, high contrast resolution= large # shades (bits)
Grey scale map assignment
Digital # in scan converter, takes amplitude and assigns shades of grey to each number
Read magnification
“Magnifying glass”
If image quality is poor, read magnification will be poor as well
Write magnification
Optimizes and rescans in better detail
“Microscope”
Multiple transmit focus
Composite of multiple transmits in the same line, each with a different focus
Advantages: improved lateral resolution
Disadvantages: degraded temporal resolution and banding noise artifact
Dynamic receive focus
Changing the receive focus depending on the depth of the returning reflection, does not change temporal resolution
2 methods:
changing the active window (aperture) of the transducer
changing the delay profile
Parallel processing
A wider transmit beam is sent, the receive beam is broken into two or more parallel groups which are processed simultaneously
Advantages: does not degrade temporal resolution
Interpolation
A process of filling in the gaps for regions of the image where a scan line did not exist, especially in the far field with sector images
Averaging techniques
When more than 1 acoustic line is added together, true signals will add constructively, all averaging techniques improve SNR
Spatial compounding (sono CT, cross beam)
One acoustic line is scanned at different angles and then added together
Advantages: improvement in SNR, reduction of artifacts due to specular reflection
Disadvantages: short duration events might be averaged out
Image persistance
Averaging is done by frame count and/or weighting, there is no angle change
Disadvantage: short duration events can be averaged out
Spatial averaging
An averaging technique at the pixel level, not at frame level.
Averaging pixels results in a reduction in dropout signals or noise
Frequency compounding
Averaging multiple images using different frequencies, done as a parallel process and needs a wide broadband for multiple frequencies
Advantages: does not degrade temporal resolution, improves image texture
Panoramic imaging
Moving the transducer across the patient to build up a 2D image over time
Advantages: the extended field of view can potentially display a whole organ
Adaptive processing (auto optimize, iScan, NTEQ)
The system automatically adapts or controls the system settings depending on the signals it is receiving
Advantages: could result in better scans
Disadvantages: the system assumptions might not be appropriate for the scan
