Physics - Imaging with Principle 1

Beam Former

Drives the transducer

Transmit/Receiver Switch

Amplifiers

Analog to Digital Conversion

Summer/Adder -making the scan line

Signal Processor

Involves filtering, detection, compression

Image Processor

Converts the scan lines to images (frame)

Involves preprocessing and image memory (Cine loop)

Display

digital back to analog conversion to create an image

Operating Principle 1 system is composed of:

Beam former

Signal processor

Image processor

Display

Pulser

Voltages (power) that drives the crystals to create the pulse

Where is the frequency initiated?

the pulser

PRF is controlled by

PRP (depth)

Pulse Delays

Array transducers require sequencing, phasing, and varying pulse amplitudes

Channels

Are the pathways or electrical that allow for all of the functions phasing including transmit and receiving, focusing, steering, and sequencing

Transmit/Receive Switch

Whether transmitting or receiving the signal

Beam Former on the Received Signal

Amplification of the received signal from the transducer to the beam former

Returning voltages can be very small (from blood) or higher (from bone) but still too small for _________________ and _____________.

processing and storage

Gain

the difference between the input power to the output power of the amplifier

Gain or power ratio

200 mV (output) / 2 mV (input) = 100

Amplitude ratio is ________.

100, we square it to equal the power ratio = 10,000

10,000 = 40 dB

Gain is expressed in

dB

3 dB rule

if the power is doubled it will equal an increase of 3 dB

10 dB rule

if the power is increased by 10 it will equal an increase of 10 dB

How does an amplifier work?

increases amplitude aka power

Amplification and compensation increase the....

amplitude of the signal to compensate for attenuation

The maximum compensation for TGC is...

about 60 dB of attenuation

At deeper depths if the anatomy is not correctly penetrated turning up the deep TGCs or overall gain will only demonstrate __________ and not tissue brightness.

noise

Digitizer

Analog to Digital Conversion (ADC)

____________ ___________ is converted into numbers/digitized.

echo voltage

What computes dynamic received focusing and steering of the beam?

the digital delay lines

Summer (Adder)

creates the individual scan lines which will be processed in the image processor with all lines to create a frame or image

What aspects are a part of the summer (adder) process?

Reception, apodization and dynamic aperture

Apodization

removing side lobes (low energy signal) of the beam to improve signal - essentially removes noise

The computer only processes...

numbers

Beamformer Review

1. Tells the transducer what to do (Pulser): voltage and intensity, frequency, PRF, depth (PRP)

2. Transmitted beam - scanning, focusing, and apodization

3. Amplification of the received echo voltages

4. Compensation for attenuation both overall gain and time gain compensation

5. Digitizing the echo voltages

6. Received beam: steering and focusing (phased operations) and apodization of the received beam

Signal Processor

works on digital information of the echo voltages

Filtering

bandpass filter allows for only the range of frequencies in that specific transducer's bandwidth For example: a 3-5 MHz transducer's bandpass filter gets rid of frequencies less than 3MHz and greater than 5 MHz

Detection

converts echo voltages from radio frequency to video format

Compression

Dynamic Range, compresses the vast number of shades of gray to a manageable number by assigning similar shades to 1 shade

Compression is measured in...

dB (most systems are around 100 to 170 dB)

Monitors can only display ____ dB and eyes can only detect _____ dB of compression.

30dB; 20dB

Review the Signal Processor - Bandpass Filter, Detection, Compression

1. Bandpass Filter - remove the received frequencies that are above or below the transducer's bandwidth

2. Detection or Demodulation -altering the signal from radio frequency to video format

3. Compression - reassigning or grouping like shades to make fewer shades. The received signal has a huge dynamic range, too big to capture or display

To get ready for display, each scan line is combined to form an image will be stored in _____________ _____________.

image memory

What order does display format or scan conversion place the scan lines in?

in the order of the received signal - linear format or sector or curvilinear at the appropriate depths detected with correct brightness or amplitude

Real-Time Display

Several frames are stored, multiple per second, and displayed

Prior to display various functions called __________________ occurs.

preprocessing

Pixel interpolation

filling in missing pixels based on adjacent brightness because the image gets spread out with curves

Persistence

averaging several frame to make image - averaging removes random noise improving signal strength

Higher numbers of frames per second will improve __________ _______________ but will degrade _____________ ________________.

contrast resolution; temporal resolution

Volume Imaging

acquiring a volume of information in 2 different planes for 3D/4D imaging

What happens during preprocessing?

1. Decrease noise

2. Removes Artifact

3. Careful not to remove diagnostic artifacts

Panoramic Imaging - during preprocessing

Before a frozen image

Still acquiring, that's why its during preprocessing

Seeing a wider field of view in a 2-dimensional image

3D acquisition - a volume set

This is preprocessing as it is acquiring the information

3D acquisition post-processing

allows for imaging and different renderings of the images

What does freezing do?

looking at a single frame pulled from image memory

What is cine review doing?

ability to look at previous frames

Pixels and Bits

The matrix is the number of pixels (like a checkerboard)

Bits

the number of layers of the matrix

More bits or layers will provide...

the ability to display more shades of gray

More pixels the ___________ (better/worse) resolution of the images.

better

Typically, ___ to ___ bits per pixel

4 to 8

The number of bits is the __________.

power

Read Zoom or Non-Acoustic

will just magnify a frozen image - simply blowing up the pixels - poorer image quality

Write Zoom or Acoustic Zoom

magnifies a live image rewriting the information - higher quality images

With modern equipment is the difference between read and write zoom noticeable?

no

After images are stored in ___________.

memory

B Color is a form of...

mapping - assigning different shades of color to different amplitudes or brightness of echoes

Digital to Analog Conversion

After digital numbers are retrieved from memory and post processing functions are completed, numbers are converted to voltages to be display

What are the brightness of the displayed echos based on?

they are driven by the voltages to match the original amplitudes received in the beam former

Reviewing Functions of the Image Processor

The received signal has gone through many functions starting at the beam former where it is initially digitized. The signal process gets the received information ready for the image processor to its work to create an image

1. Scan conversion

2. Preprocessing items - persistence, spatial compounding, 3D acquisition, we will cover more later

3. Memory storage - cline loop

4. Post processing after the image is frozen - mapping, 3D rendering

5. Getting ready for Display

6. Digital to Analog Conversion

PACS

Picture Archiving and Communication Systems

Digital Imaging and Communications in Medicine (DICOM)

standardized format to talk to multiple workstations

What does digitizing analog waveforms allow?

allow us to see an image and measure

To increase penetration what two things can we do?

Increase power or decrease frequency

Compensation is apart of?

beam former - compensates for attenuation

Pulser drives?

frequency, depth - PRP/PRF, gain, voltage, intensity

preprocessing involves?

pixel interpolation, persistance, averaging

4 bits =

4 bits = 2^4 = 16 shades of grey

Signal

what comes back from the patient - what is truly there

How do we increase the signal to noise ratio?

averaging, persistence, spatial compounding

How many frames make an image (on average)?

10

What is the front end? What does it include?

all the processes before digital to analog conversion - beam former, signal processor, image processor

Noise is _____________, which is why mechanism like persistence works.

random

Spatial Compounding

method of using several different imaging angles to produce a single image - improves signal to noise ratio

Scan converter

combines the scan lines

the signal processor receives __________ signals.

digital

Humans can only perceive _____ shades of grey.

64

Refresh rate

The number of times per second the image is retrieved from memory and displayed

Frame time

amount of time to make 1 frame

Frame time equation

PRP x # of scan lines

Frame rate

frames per second

Frame rate formula

1/frame time

Real time frame rate should be...

30Hz

Multi focus imaging increases _________ __________ and decreases ________ ___________.

frame time; frame rate

2 types of focus

transmit - we tell the beam where to focus

receive - dynamic focusing - automatic

How many transmitted focuses per acoustic line? Received?

1 transmit focus

infinite receive focus

Label whether these receive digital or analog: display, workstation, and storage

display: analog

workstation: analog

storage: digital

units for amplitude? power?

volts; watts