System reverse Flashcards Preview

basicas are interchangable between manufactureres

reduces scan time in a clinical setting

know your controls

varies energy transmitted to patient

should be used at lowest level

ALARA limit

higher power=brighter image

operator controlled

determines electrical voltage to pulsar

low voltage=gentle PZT vibration

high voltage=forceful vibration

creates electrical signals that excite the PZT crystals

only functions during transmission

operator controlled

0-500 volts

important in Bioeffects

0-500 volts

high =brighter image

also called output gain, accoustic power, energy output or transmitter output

Thermal Index

Mechanical Index

random and persistant degradation

unwanted low level echoes

power increase raises ratio

quiality improves with increase

determines time between voltage spikes

PRP Pulse repition Period

controlled by operator

determines depth of scan

operator controlled

continuous wave

vascular

pulsed wave

imaging

shorter listening time

shorter PRP

higher PRF

longer listening time

longer PRP

lower PRF

recieves the electrical spike from pulser and distributes to the active elements in an array transducer

used advanced microprocessor tech to produce digital format

proteects the electrical components in the reciever

prepares information from returning echoes for display

5 functions

Amplification

Compensation

Compression

Demodulation

Reject

first function

affects all signal quality

receiver gain

measured in dB

adjustable

Gain/Overall Gain knob

controls degree of echo amplification or brightness or image

too much can fill artifactual echoes into a fluid structure

too little can negate echo information

creates and image of uniform brightness

known as TGC Time Gain Compensation

DGC Depth Gain COmpensation

sompensates for the sound wave as it weakens or attentuates

operator controlled

sliders on console

structures will be same brightness regardless of depth

3rd function

keeps image grayscale content with range of human eye (20 shades)

keeps electrical signal level within accuracy range

called log compression or dynamic range (DR) most common

dB

operator controlled

relative term that compares on one signal to another

important in quantifying strenght of sound beams, electrical signal strenght and brightness of image

notatoin is logarithmic

4th function

two part process that changes electrical signals in reciever into a more suitable form for the CRt or monitor

rectifies and smooths electrical signal

NOT adjustable

no effect on image

5th function

controls whether low level signals will be displayed

low leve signasl can be diagnostic or noise

called threshhold or suppression

operator controlled

Adjustable

all signals affected identically

entire image gets brighter or darker

Adjustable

signals treated differently bases on reflective depth

images will be uniformly bright from top to bottom

Adjustable

Signals treated differently depending on strenght

changes grayscale mapping

NOT adjustable

prepares electrical signals to be suitable for display

NO effect on image

Adjustable

Only weak signbals affected

Strong signals remain unchanged

Weak echoes appear or are eliminated from image

Displays the information from returning echoes

2 user controls

brightness

contrast

patient exposure to sound energy is affected by output power NOT by reciever amplification

changes brightness of image

alters signal to noise ratio

alters patient exposure

bioeffect concerns

decrease this first if image too bright

Changes brightness of entire image

does not affect signal to noise ratio

does not change patient exposure

NO bioeffect concern

increase this first if image is too dark

frame averaging that allows echo information to be accumulated over time

subtle texture differences will be enhanced

allows user to evaluate moving structures more easily

allows image magnification by increasing the pixal size

2 types

Read

Write

occurs after the image is stored

number of pixals or scan lines is the same as original image

Can appear blurry 

Occurs while active scanning

box is placed on screen and the area seen within can be expanded to fill screen

number of pixals and scan lines remain the same

image is not degraded

Markers available to measure distance

linear

ellipsoid

trace

allows the labeling of the image

may be keyboard or preprogrammed keys

may be voice activated

allows the screen to be split in order to show 2 views of an image or compare anatomy of abnormal side to normal side