The ultrasound system

what is the ultrasound system

the computer, transducer, and display

beam former

main force behind creating an ultrasound beam. Creates the firing pattern for phased array systems

master synchronizer

makes sure pulses do not overlap (off time) it’s within the beam former. organizes and times their functions to operate as a single integrated system (runs the show)

relationship between depth an PRP/PRF

PRP= directly

PRF= inversely

pulser

responds to the master syncronizer and controls the electrical signals sent to the active elements for sound pulse generation.

What does the pulser determine

the PRP, PRF, Pulse amplitude

transducer

converts electrical into acoustic energy during transmission. Converts returning acoustic into electrical energy during reception

output power

affects brightness by adjusting the strength of the sound waves SENT tothe body from the transducer. Affects patient exposure

low voltage output power affect on the echoes and image

low voltage= weak ultrasound power, weak echoes, DARK image

high voltage output power

high voltage= strong ultrasound power= strong echoes=BRIGHT image

how is the output power adjustable

by the sonographer.

Noise

unwanted and inaccurate portion of the data degrading the quality of our information NOISE IS BAD

signal

meaningful portion of the data. SIGNAL IS GOOD

high signal to noise ratio

meaningful part of our data is stronger than the inaccurate. HIGH QUALITY IMAGE

low signal to noise ratio

the inaccurate part of our data is stronger than the meaningful part. DEGRADES THE IMAGE

what improves the s/n ratio

increasing transducer output improves. (the meaningful strength is increased while the noise level remains unchanged)

receiver

processing the electronic signal produced by the transducer during reception and producing a picture on a display device

5 key steps that occur in the receiver in order

amplification

compensation

compression

demodulation

rejection

(alphabetical order)

amplification

AKA receiver gain, increases the strength of all electrical signals in the receiver

How to adjust amplification

uniform amplification, changes the brightness of the entire image (adjust the gain)

preamplifier

alters the signal before its amplified, performed in the probe

amplification is measured in what

dB

ALARA

when the image is too bright or dark, (increase your gain and decrease your power) minimize patient exposure

if PART of your image is too bright or too dark in one area what is used?

compensation

compensation

makes an image UNIFORMLY bright. uniform brightness from top to bottom. (TGC, DGC) treats echoes differently depending upon the depth at which they arise

relationship between frequency and TGC

higher frequency=more TGC

lower frequency=less TGC.

High frequency attenuates more.

how to adjust TGC on the machine

adjust them at a slope/curved to create an even image

TGC slope

near gain, delay, slope, knee, far gain

what will you adjust if you can’t see reflectors in near field on your image?

adjust the TGC

what will you adjust if you can’t see reflectors in the far field on your image

adjust the TGC

compression

reduces the number of grays in the display (compresses). reducing the total range of signals from smallest to the largest

how to adjust the compression

second compression is adjusted by the sonographer.

purpose of compression

allows us to see all gray shades, decreases the dynamic range. changes the grayscale mapping

with compression how does it relate to decibels

decibels add or subtract. If a signal with a dynamic range of 100dB is compressed by 30dB the dynamic range of the compressed signal is 100-30= 70dB

analogy of compression

grades in a class: 0-100 in class, compressed into A,B,C,D,F

demodulation

detection. change’s the signal’s form to one more suitable for display

is demodulation adjusted by the sonographer

NO

2 steps to demodulation

rectifiaction and smoothing

rectification

turnes negative voltages/amplitudes into positive. Corrects for/eliminates negative voltages

smoothing

aka enveloping. Putting an envelop around the bumps to even them out

rejection

allows the machine to ignore low level echoes/low level noise. (suppression, threshold)

rejection effects on the image

affects only low level signals everywhere on the image but not affect bright echoes

can rejection be adjusted by sonographer

YES, second rejection

AD converter

analog (real word) to digital (computer world). AKA digitizer. assigns a discrete numerical value (binary #) then mapped to the scan converter assigning it to a color

analog numbers

have infinite possibilites

digital numbers are

finite (1,2,3 not 1.24)

summer

responsible for combining all the information into the scan line info for the scan converter

scan converter

AKA memory. changes the data format from penetrations (spokes) to horizontal lines of a display (make gray scale displays possible) goes from storing and displaying

preprocessing

manipulating the data before storage in the scan converter. cannot be reversed or undone. occur in the working memory(while machine is live scanning)

examples of TGC preproccessing

log compression, write magnification, fill-in interpolation, persistence (frame averaging), spatial compounding

post processing

manipulating the data after it ahs been stored in the scan converter but prior to display. Can be undone. performed on FROZEN images

example of post processing

read magnification: 3D rendering

Digital scan converter

a microprocessor digitizes images. Converts the image into numbers stored in memory (digital image data)

the digital scan converter spatial and contrast resolution are limited by what two factors

#of pixels in the scan converter, #of bits assigned

Pixel

smallest element of a digital picture (each square of a checkerboard is a pixel)

pixel density

the more pixels per ince the more detial in image, spatial or detail resolution

spatial resolution on a digital display

determined by the pixel density. related to the number of lines per frame (more lines=good spatial resolution)

bit

binary and a digit. smallest amount of digital storage. is bistable (a group of bits is assigned to each pixel to store the gray scale color assigned to that pixel)

bistable

having a value of either zero or one

the more bits per pixel…

the more shades of gray, the better is the contrast resolution

binary number

a group of bits. a series of zeroes and ones

ex: 0010011001001`

byte

group of 8 bits. 2 bytes=16 bits is a word

word

2 bytes (16 bits)

binary number are based on

2

decimal numbers are based on

10