Chapter 14 Flashcards
Pulsed Echo Instrumentation
What is an ultrasound system?
A highly sophisticated device that creates sound pulses, retrieves the reflections, and produces images and audio signals from these reflections.
The ultrasound system has two major functions:
- Preparation and transmission of electrical signals
- Reception of electrical signals
What are the seven major components of an ultrasound system (in order)?
Transducer
Pulser
Beam Former
Receiver
Display
Storage
Master Synchronizer
The ____ transmits electrical energy into acoustic energy and converts acoustic energy into electrical energy.
Transducer
The ____ creates electrical signals that excite the transducer’s PZT crystals.
Pulser
The pulser determines the ____, ____, and ____.
Amplitude, pulse repetition period, and pulse repetition frequency.
What functions during transmission?
The pulser
The sonographer can adjust the ____ of the electrical voltage spike
Magnitude
Changes in pulser ____ adjust the brightness of the entire image.
Voltage
Two measurements that are related to transducer output (acoustic power) and measure bioeffects are:
- Thermal Index (TI)
- Mechanical Index (MI)
____ is a random and persistent disturbance that obscures or reduces the clarity of the image.
Noise
Signal-to-Noise ratio is the comparison of ____ ____ (signal) to ____ (noise)
Meaningful information; Contamination
With high signal-to-noise ratio the signal is ____ than the noise.
Stronger
With low signal-to-noise ratio, the signal is ____ to the strength of the noise
Close
Increasing the output power will ____ the signal-to-noise ratio (good).
Increase
Increasing the ____ ____ is the only way to improve the signal-to-noise ratio
Output power
The sonographer controls the PRP and PRF by adjusting the ____ ____ ____
Depth of view
The ____ ____ is the part of the transmitter that controls the electrical signals.
Beam former
The beam former determines the ____ ____ ____ for phased array systems.
Firing delay pattern
The ____ ____ receives the single electrical spike from the pulser, and distributes it to all the active elements of an array transducer.
Beam former
True or false: The beam former functions during transmission and reception.
True
During transmission, the beam former reduces lobe artifacts through ____.
Apodization
During reception, the beam former controls ____ ____ by varying the number of PZT crystals used during reception.
Dynamic aperture
What is used in the most modern ultrasound systems to produce signals in digital format?
Digital beam formers
The beam former switch does two things:
- Protects the delicate receiver components from the powerful transmission signals
- Directs the electrical signals from the transducer to the appropriate electrical and processing components.
The ____ is a single PZT active element in the transducer, the electronics in the beam former/pulser, and the wire that connects them.
Channel
What transforms electrical signals from the transducer into a form suitable for display?
Receiver
What are the receiver operations in order?
Amplification
Compensation
Compression
Demodulation
Reject
What is the first function of the receiver?
Amplification (overall gain)
During ____ each electronic signal returning from the transducer is made larger.
Amplification
Is amplification adjustable?
Yes (overall gain)
What are the units for amplification?
dB
____ the process of improving the quality of a signal before it is amplified.
Preamplification
What is the second function the the receiver?
Compensation (TGC’s)
What is the first function of the compensation?
It corrects for attenuation and creates an image that is uniformly bright from top to bottom.
Without ____, images become increasingly dark with depth due to attenuation.
Compensation
What are the units for compensation?
Decibels
On a TGC curve the ____ indicates the amount of amplification.
X-axis
On a TGC curve the ____ indicates the reflector depth.
Y-axis
What is the third function the the receiver?
Compression (dynamic range)
____ keeps an image’s grayscale content within the range of detection of the human eye (about 20 shades of grey).
Compression
What are the units for compression?
Decibels
Is compression adjustable?
Yes
What is the fourth function of the receiver?
Demodulation
What is the function of demodulation?
It is a two-part process that changes the electrical signals in the receiver into a form suitable for display on a monitor.
Name the terms used to describe the two part process of demodulation.
Rectification and smoothing (enveloping).
____ converts all the negative voltages into positive voltages.
Rectification
____ places a smooth line around the “bumps” and evens them out
Smoothing (enveloping)
Can demodulation be adjusted?
No
____ has no visible effect on the image.
Demodulation
What is the fifth function of the receiver?
Reject
What is the function of reject?
Allows sonographers to control whether low-level gray scale info within the data will appear on the displayed image.
Can reject be adjusted by the sonographer?
Yes
____ presents the processed data.
Display
____ archives the ultrasound studies. Most use PACS systems.
Storage
____ ____ maintains and organizes the proper timing and interaction of the system’s components.
Master synchronizer
Dynamic frequency tuning amplifies a more ____ range of frequencies depending upon the depth of the returning signals.
Limited
Can dynamic frequency tuning be adjusted by the sonographer?
No
The most important distinction between output power and amplification relates to ____.
Bioeffects
Patient exposure to sound energy is affected by alterations in ____ ____, but not ____.
Output power; amplification
ALARA principle stands for:
As Low As Reasonably Achievable
If the image is too dark, increase ____ ____ (overall gain) first.
Receiver gain
If the image is too bright, decrease ____ ____ first.
Output power
You are scanning a patient, you notice that the image is good except that it is a little dark in the far field. What should you do?
Adjust lateral and vertical gains (TGC’s)
compensation is adjusted
