Ultrasound Physics Chapter 14

2 major functions of ultrasound system:

1.) the preparation and transmission of electrical signals to the transducer, which creates a sound beam

2.) the reception of electrical signals from the transducer, with subsequent processing into clinically meaningful images and sounds

6 major components of ultrasound system

1) transducer

2) pulse and beam former

3) receiver

4) display

5) storage

6) master synchronizer

During transmission it transforms electrical energy into acoustic energy, and during reception it converts the returning acoustic energy into electrical energy

Transducer

Creates and controls the electrical signals sent to the transducer that generate sound pulses

Pulser and beam former

The pulser determines the:

Amplitude, PRP, and PRF

Beam former determines the:

The firing delay patterns for phased array systems

Transforms the electrical signals from the transducer (produced by reflected sound) into a form suitable for display

Receiver

Presents processed data; may be a flat screen monitor, a transparency, a spectral plot, or a variety of other formats

Display

Archives the ultrasound studies; typical devices include computer hard drives, CD, DVD, videotape, magneto-optical discs, paper printouts, photographs, and USB drives

Storage

Maintains and organizes the proper timing and interaction of the system's components

Master synchronizer

Creates electrical signals that excite the transducer's PZT crystals and create sound beams

Pulser

The pulser functions during ____________

Transmission

Changes in the __________ __________ modify the brightness of the entire image displayed on the system's screen

Pulser voltage

When the pulser is set to a low voltage, the PZT of the transducer vibrates gently, and a weak sound beam is transmitted into the body; the reflected echoes are weak and the entire image tends to be ________

Dark

When the pulser voltage is high, the transducers active element vibrates more forcefully, and transmits stronger sound beams into the body; the reflected echoes are stronger, and the entire image is __________

Brighter

Pulser voltage synonyms

Output gain

Acoustic power

Pulser power

Energy output

Transmitter output

Power

Gain

What synonym fro pulser voltage is particularly vague, and should be avoided?

Gain

Can the sonographer adjust the transducer output?

Yes

What effect on the image does transducer output have?

Brightness of entire image changes

Loosely defined as a random and persistent disturbance that obscures or reduces a signals clarity; contaminates an image with low-level, undesirable info

Noise

Comparison of the meaningful info (signal) in an image, compared to the amount of contamination (noise)

Signal-to-noise ratio

When the signal-to-noise ration is _________, the signal is much stronger than the noise and the image is of high quality

high

When the signal is _________, the strength of the signal is closer to the strength of noise; the image contains a larger amount of visible contamination, and has less diagnostic value

Low

Because noise levels generally remain constant, increasing ____________ ____________ is the most common way to improve (increase) the signal-to-noise ratio

Output power

PRP determines the ___________ _______ _____________

Depth of view

When the PRP is short, the pulse PRF is _________, and the system spends less time listening; the result is ________________ imaging

High, superficial

When the PRP is long, the PRF is _________ and the system listens for a longer time; the result is ___________ imaging

Low, deeper

Considerd part of the transmitter, it functions with array transducers during transmission and reception

Beam former

The beam former also adjusts electrical spike voltages to reduce lobe artifacts in a process called _____________

Apodization

Use advanced microprocessor technology and produce signals in digital format

Digital beam former

Protects the delicate receiver components from the powerful signals that are created for pulse transmission; also directs the electrical signals from the transducer to the appropriate electronic and processing components within the ultrasound system

Switch

Made up of a single PZT element in the transducer, the electronics in the beam former/ pulser, and wire that connects them

Channel

Most systems have how many channels?

32-256 channels

Order of receiver operations:

1) amplification

2) compensation

3) compression

4) demodulation

5) reject

The first function of the receiver, also called receiver gain; each electronic signal returning from the transducer is made larger, required because the electrical signals are too low to be displayed on the monitor

Amplification

Can output power alone make an image of uniform brightness from top to bottom?

No

Can amplification alone make an image of uniform brightness from top to bottom?

No

Can the sonographer alter amplification?

Yes

Amplificaion units?

Decibels (dB)

Typical values for amplification

60 to 100 dB

Process of improving the quality of a signal before it is amplified; occurs as close to the active elements as is practical, often within the transducer itself

Preamplification

What is the role of preamplifiers in processing signals from the transducer during reception?

To prevent electronic noise from contaminating the tiny electronic signals created by the transducers active elements during reception

Compensation

The second function of the receiver; the receiver corrects for attenuation with this process, without it every image would become progressively darker with increasing depth

Compensation creates an image that is uniformly bright from ___________ to ___________

Top, bottom

Can the sonographer adjust compensation?

Yes

Compensation units?

Decibels (dB)

Synonyms for compensation

time-gain compensation (TGC)

Depth-gain compensation (DGC)

Swept gain

At superficial structures, reflections undergo a small, constant amount of compensation called ?

Near gain

Depth at which variable compensation begins

Delay

In this region compensation corrects for the effects of increasing attenuation that result from increasing path length

Slope

At this depth, reflections are maximally compensated by the ultrasound system

Knee

Indicates the maximum amount of compensation that the receiver can provide

Far gain

The third function of the receiver; performed twice, first to keep the electrical signal levels within the accuracy range of the systems electronics and second to keep an image's gray scale content within the range of detection by the human eye

Compression

Can sonographer adjust compression?

Yes, modifies the gray scale mapping of ultrasound image

What effect does compression have on the image?

Changes the gray scale characteristics of the image

Synonyms for compression?

Log compression

Dynamic range

Units for compression

Decibels (dB)

Log compression is an adjustable compression where small differences in __________ __________ a displayed and seen as different gray scale levels

Weak signals

What is log compression clinically important?

Because most meaningful backscattered signals from biological tissues are very weak and the sonographer must be able to see differences in these weak reflections

The fourth function of the receiver; 2 part process that changes the electrical signals within the receiver into a form more suitable for display on a monitor

Demodulation

2 parts of demodulation

Rectification

Smoothing (enveloping)

Converts all negative voltages into positive voltages; corrects for, or eliminates, negative voltages

Rectification

Places a smooth line around the " bumps" and evens them out

Smoothing (enveloping)

Can the sonographer adjust demodulation?

No

What is the effect of demodulation on the image?

None

The fifth function of the receiver; allows the sonographer to control whether low-level gray scale info within the data will appear on the displayed image

Reject

Synonyms for reject

Threshold

Suppression

Can the sonographer adjust reject?

Yes, 2 levels of reject; one is built into the system and the other is user adjustable

What effect does reject have on the image ?

Affects all low-level signals on the image, regardless of their location; doesn't affect bright echoes

Patient exposure to sound energy is affected by alterations in _____________ _____________ but not by changes in amplification

Output power

As Low As Reasonably Achievable; states that when modifications to either output power or receiver gain can improve the image's diagnostic quality, the first and best choice is the one that will minimize the patients ultrasound exposure

ALARA principle

If the image is too dark, first increase the _____________ ___________, which does not increase patient exposure

Receiver gain

If the image is too bright, first decrease the __________ _____________, which decreases patient exposure

Output power

This type of pulser generates a single electrical spike, which ultimately creates a single sound pulse.

pulsed wave, single crystal

This type od pulser generates numerous electrical spikes, which ultimately create a single sound pulse

pules wave, phased array

The acoustic power of a sound beam emitted from the transducer is determined bu the __ of the pulser’s signal

voltage

true or false: amplification processes all reflected signals in a similar manner

true

True or false: compensation processes all reflected signals in a similar manner

false

This type of pulser creates a constant electrical signal in the form of a sine wave:

continuous wave

This type of pulser generates a single electrical spike, which ultimately creates a single sound pulse:

pulsed wave, single crystal

This type of pulser generates numerous electrical spikes, which ultimately create a single sound pulse:

pulsed wave, phased array

The acoustic power of a sound beam emitted from a transducer is determined by the ___ of the pulsars signal

voltage

All of the following are functions of the receiver except:

-demodulation

-suppression

-amplification

-attenuation

attenuation

T/F: amplification processes all reflected signals in a similar manner

true

T/F: compensation processes all reflected signals in a similar manner

false

Which of the following is to considered a component of an ultrasound system?

-master synchonizer

-pulser

-receiver

-image intensifier

image intensifier

T/F: the pulser of a mechanical transducer is typically more complex than that of a phased array transducer

false

What is the typical pulser output voltage that excites a PZT crystal?

40 volts

What is the typical voltage of the signal that is the input to the receiver of an ultrasound system?

10 µV

The output of an ultrasound pulse are determines the ___ of the acoustic pulse

Receiver gain

True or false the sonographer can alter the pulser power

true

Which of the following will improve the signal to noise ratio:

-inc dynamic range

-inc receiver gain

-inc output power

-inc time-gain compensation

inc output power

Which of these functions are performed by the receiver of an US system?

• amplification

• threshold

• copensation

• demodulation

all

which of the following tasks is not performed by the receiver of an US system?

-recification

-smoothing

-compression

-degaussing

degaussing

True or false the sonographer can adjust the receiver gain

true

true or false: the signal to noise ratio remains unchanged when a sonographer adjusts the receiver gain

true

True or false: the sonographer can make an image of uniform tightness by adjusting both output power and receiver gain

false

Which of the following is a typical value for the amplification of a signal by the receiver?

• 50-100 watts

• -50 to -100 dB

• 50 to 100 dB

• 5 to 25 W/cm²

• 50 to 100 dB

What is the process of adjusting for path length related attenuation called?

compensation

Which receiver function creates an image of comparable brightness from top to bottom?

swept gain compensation