Chapter 14 Flashcards
Transducer
During transmission it transforms electrical energy into acoustic energy. During reception, it converts the returning acoustic energy into electrical energy.
Pulser and Beam Former
Creates and controls the electrical signals sent to the transducer to generate sound pulses.
Receiver
transforms the electrical signals from the transducer into a form suitable for display
Display
Presents processed data on a monitor (CRT or LCD)
Storage
Archives the data images onto a network, system hard drive, or other media (flash drive, DVD, older media such a photopaper, transparent film, videotape)
Master Synchronizer
Maintains and organizes the proper timing and interaction of the system’s components
Signal
displayed reflections arising from true structures
Intended, meaningful, constructs image
Noise
displayed low level reflections not arising from true structures
Unintended, unmeaningful, contaminate image
The Pulser
creates and sends the electrical signal that excites the crystal(s) to create the sound beam, thus functions during transmission
Beam Former
receives the electrical spike from the pulser and distributes it to the active elements in an array transducer
It coordinates the electronic slope, electronic curvature, apodization, and dynamic aperture
The Receiver
prepares the information contained in these minuscule signals for eventual display
Order of Receiver Operations are in alphabetical order
Amplification
Compensation
Compression
Demodulation
Reject
Amplification
each electrical signal returning from the probe to the receiver is made larger
adjusted by sonographer
knob: receiver gain
units: decibels
typical values: 60-100 dB
Preamplification
prevent noise from contaminating the tiny signals; maintaining the quality of the signal
Compensation
creates an image that is uniformly bright from top to bottom
adjusted by sonographer
AKA: time gain compensation (TGC), depth gain compensation (DGC), swept gain (SWC)
units: dB
Anatomy of a TGC Curve
X axis = TGC, Y axis = depth
Near gain: at superficial depths reflections undergo a small constant amount of compensation
Delay: depth at which variable compensation begins
Slope: area of variable compensation
Knee: depth at which maximal compensation has been reached
Far Gain: represents the maximum amount of compensation the receiver can provide
Compression (Automatic)
the system adjusts the dynamic range of electrical signals into a range that a system device can process accurately
Dynamic range
range of electrical signals that a device can process accurately
Compression (Sonographer Adjusted)
The sonographer uses the compression knob to assign the echo data signals amongst more or fewer shades of gray
AKA compress, log compression, or dynamic range knob
Demodulation
this fourth receiver function is a two part process that changes the electrical signal into a form more suitable for display
Rectification and Smoothing
automatic
Rectification
converts all the negative voltages into positive voltages
Smoothing(enveloping)
places a smooth line around the “bumps” in the voltage signal
Reject
this fifth receiver function eliminates low amplitude signals suspected to be noise
AKA: reject, threshold, or suppression knob
Dynamic Frequency Tuning
The receiver processes only the high frequency signals to create the superficial portion of the image because they provide superior axial resolution
Lower frequency signals are used to create the deeper portions of the image because they are all that remain (the higher frequencies have attenuated)
Output power
Entire image is brighter because stronger pulse is sent into the body
Higher output power increases patient exposure
Improves signal to noise ratio
Receiver Gain
Amplifies the returning signals affecting the entire brightness of the image
It does not alter the signal to noise ratio since both signal and noise are boosted
Nor does it impact patient exposure to US
