Ch 14- Pulsed Echo Instrumentation

What are the two major functions of the ultrasound system?

1. preparation and transmission (sending)

2. reception of signals (receiving)

What are the components of the system?

- transducer

- pulser and beam former

- receiver

- display

- storage

- master synchronizer

What is the function of the transducer?

converts electrical energy to acoustic energy and vice versa

What are the functions of the pulser?

excites the PZT

creates sound beams

Is the pulser adjustable?

yes

The pulser controls the brightness of the ____

entire image

What does the pulser determine?

amplitude

PRP

PRF

The pulser is also known as:

output gain

acoustic power

pulser power

energy output

transmitter output

power

gain

Modern machines use ___ ___ or ___ ___

thermal index; mechanical index

Transducer output power is the ability to adjust the ____ of electricity ____ to the PZT

strength (voltage); transmitted

Low voltage results in ____ ultrasound power, ____ echoes, and a ____ image

weak; weak; dark

High voltage results in ____ ultrasound power, ____ echoes, and a ____ image

strong; strong; bright

Low voltage is preferred due to ____

bioeffects

What is noise?

"extra" echoes that degrade the image quality

Noise occurs when voltage output is too ___

low

What is signal-to-noise ratio?

a comparison of the meaningful information (signal) and the amount of noise

A ____ signal-to-noise ratio = strong signal, low noise

high

A ____ signal-to-noise ratio = weak signal, high noise

low

What is PRP?

one on and off time

What is PRF?

number of pulses per second

PRP and PRF are ____ related and ____

inversely; reciprocals

Shallow imaging results in a ____ PRP and a ____ PRF

short; high

Deep imaging results in a ____ PRP and a ____ PRF

long; low

The beam former is part of the ____, and functions during ____ and ____

transmitter; transmission; reception

The beam former generates the ____ that drive the transducer

voltages

The beam former coordinates electrical signals through ____

apodization

What is apodization?

reduces side and grating lobes- stronger signals in the middle of the beam

The beam former controls ____ during reception

dynamic receive focusing

During transmission, the transmit-receive switch changes ____ voltages from the pulser into ____ voltages to protect the ____

strong; weaker; receiver

During reception, the transmit-receive switch directs electrical signals to the ____

receiver

The transmit-receive switch functions during ____ and ____

transmission; reception

What does the channel consist of?

single PZT

beam former / pulser

wire

Most systems have between ___ and ___ channels

32; 256

The receiver is part of the ____

beam former

The receiver processes the ____ echoes from the patient

returning

Receiver order of operation

1. amplification

2. compensation

3. compression

4. demodulation

5. reject

Amplification is also called ____ ____ or ____ ____

overall gain; receiver gain

Receiver gain changes the brightness of the ____ and does not affect ____

entire image; signal-to-noise ratio

Is receiver gain adjustable?

yes

What are the typical values for receiver gain?

60 to 100 dB

Compensation is also known as ____

time gain compensation (TGC)

Compensation corrects ____ and creates ____ ____ images

attenuation; uniformly bright

Is receiver compensation adjustable?

yes

What are the units for receiver compensation?

decibels

What is the TGC curve in order?

near gain

delay

slope

knee

far gain

Near gain is at ____ depths with ____ compensation

superficial; constant

The depth where ____ compensation begins is the delay

variable

In the region of the slope, compensation corrects for the effects of increasing ____ that result from increasing the ____ ____

attenuation; path length

At the depth of the knee, reflections are ____ compensated by the ultrasound system

maximally

The far gain is the ____ amount of compensation that the receiver can provide

maximum

What does a TGC curve look like?

Compression ____ the range of signal amplitudes

decreases

Compression keeps an image's gray scale content within the ____ ____ ____ by the human eye

range of detection

Humans see ___ shades of gray

20

Is compression adjustable? What does it modify?

yes, modifies gray scale mapping

Compression is also called what?

log compression or dynamic range

What effect does compression have on an ultrasound image?

less shades of grey, makes image more black and white

Demodulation processes the ____ signals to make it easier for the machine to display

return

What are the two components of demodulation?

1. rectification

2. smoothing

What is rectification?

converts negative voltages to positive voltages

What is smoothing?

places a smooth line around the "bumps" in a signal and evens them out

Does demodulation have an effect on the image?

no, changes electrical signal only

Is demodulation adjustable?

no

What is the function of reject?

eliminates low-level (weak) echoes ONLY

What is reject also called?

threshold

suppression

Is reject adjustable?

yes on SOME systems

Amplification:

- adjustable?

- signals processed

- effect on image

- yes

- all signals treated identically

- entire image gets brighter/darker

Compensation:

- adjustable?

- signals processed

- effect on image

- yes

- signals treated differently based on reflector depth

- image will be uniformly bright from top to bottom

Compression:

- adjustable?

- signals processed

- effect on image

- yes

- signals treated differently depending on strength

- changes grayscale mapping

Demodulation:

- adjustable?

- signals processed

- effect on image

- no

- prepares electrical signals to be suitable for display

- none

Reject:

- adjustable?

- signals processed

- effect on image

- yes

- only weak signals affected

- weak echoes appear or are eliminated from image

Systems with dynamic frequency tuning use only the ____ frequency part of the reflected pulse's bandwidth to create the ____ portion of the image

high; superficial

Systems with dynamic frequency tuning use only the high frequency part of the reflected pulse's bandwidth to create the superficial portion of the image because higher frequency sound has superior ____ ____

axial resolution

The ____ frequency portion of the bandwidth is used to create ____ portions of the image

lower; deeper

Do all systems have dynamic frequency tuning?

no

Output power vs. receiver gain:

- what changes the brightness of the entire image?

- what alters signal-to-noise ratio?

- what alters patient exposure?

- both

- output power

- output power