chapter 25 fluoroscopy

fluoroscopy is

dynamic

diagnostic radiography is

static

fluoroscopy uses

x-ray tube

__ viewed during exposure for non-digital systems

image receptor

__ used for digital systems

flat panel receptors

fluoro invented by

edison in 1896

fluoro screen made of

zinc cadmium fluoride

first fluoroscopes held by

hand

radiologist stood in front of

patient and tube

later units added

mirror and lead shielding

image intensification tubes developed in

1948

__ replaced mirror systems

video camera and monitor systems

non-image intensified fluoroscopy requires time for eyes to adjust to low light levels

adaptation time

radiologists would wear __ prior to performing the exam

red goggles for 30 minutes

fluoro screens use

rods (scotopic)

image intensifiers use

cones (photopic)

photopic or scotopic vision better?

photopic

fluoro x-ray tube designed at

low mA (less than 5 mA) for long periods of time

SID is around

20” so small focal spot is needed

FSS is usually

.3 to .6 mm

kVp varies based on

part being examined

3 brightness control settings

-Automatic Brightness Control

-Automatic Dose Control

-Automatic Brightness Stabilization

A function of the fluoroscopic unit that maintains the contrast and density of the image.

automatic brightness control

ABC operates by monitoring either

-current through image intensifier

-output phosphor intensity

ABC can be slow to respond to __ as it is moved

changes in patient thickness and density

input exposure rate should be

0.1-0.4 μGya/s

Fluoroscopic chain

x-ray tube

image intensifier

recording system

viewing system

An electronic vacuum tube that amplifies a fluoroscopic image to reduce patient dose

image intensifier tube

image intensifier tube developed in

1948

conversion for image intensifier

1. remnant beam

2. light

3. electrons

4. light

5 basic parts of image intensifier

-input phosphor

-photocathode

-focusing lens

-accelerating anode

-output phosphor

image intensification enables use of

photopic vision

image intensification designed to

electronically amplify brightness of image

image intensification increases image brightness

500-8,000 times

compared to radiography or conventional fluoroscopy uses __ mAs

significantly less

primary beam strikes

input screen of image intensifier

Electrons are accelerated by the potential difference between the

anode and cathode

also focus and accelerate the electron beam

electrostatic lenses

is from the acceleration and focusing of the electron beam

primary brighthness gain

output screen is at the __ of the tube

anode

input phosphor made of

0.1-0.2 mm layer of cesium iodide

input phosphor ranges from __ in diameter

6” to 23”

input phosophor absorbs __ and emits __

xray energy

light

photocathode made of

cesium and antimony

photocathode absorbs __ and emits __

light photons

electrons

process of absorbing light and emiting electrons

photoemission

number of electrons emitted is ___ to the intensity of the the incident image-forming x-ray beam

proportional

electrostatic focusing lenses made of

Negatively charged electrodes/plates

electrostatic focusing lenses located

inside glass tube

fucntion of electrostatic focusing lenses

focuses and accelerates electron stream

The concavity of the input screen reduces __ in electrostatic focusing lenses

distortion

Circular plate with a hole in the middle through which electrons pass to the output phosphor

accelerating anode

accelerating anode located near

output phosphor

accelerating anode sets

electron stream in motion

accelerating anode is __ charged

positively

output phosphor made of

Silver-activated Zinc-Cadmium Sulfide

is input or output phosphor smaller?

output

output phosphor absorbs __

electrons to emit light

output phosphor increases

image brightness

electron beam contains an

electronic image

electronic image has a focal point similar to

optical lens

A measurement of the increase in light photons due to conversion efficiency of output screen

flux gain

if 1 electron produces 50 light photons, flux gain is

50

greater flux gain decreases

image quality

flux gain formula

Number of output light photons/Number of input x-ray photons

Large number of electrons are produced at input screen

minification gain

minification gain is not an improvement in

quality or number of photons

minification gain formula

input screen diameter)²/(output screen diameter)²

an expression of the ability of an image intensifier tube to increase the brightness of the image.

brightness gain

Traditionally, brightness gain was found by multiplying the

flux gain by the minification gain

t is now common practice to express the increase in brightness with the term

conversion factor

brightness gain deteriorates as much as __ a year

10%

An expression of the luminance at the output phosphor divided by the input exposure rate.

conversion factor

conversion factor is __ times the brightness gain

.001 (1%)

The image intensifier’s ability to increase brightness deteriorates with

tube age

when brightness detiorates, does patient dose increase or decrease?

increase

Internal scatter from x-rays, electrons and light, can reduce the contrast of image intensifiers – called

veiling glare

Voltage is increased to the

electrostatic lenses

Manipulation of the electronic focal point/spot can produce

image magnification

magnification has focal spot moves __ the input screen

toward

magnification increase voltage to tighten the

electron stream diameter

tubes can have how many different sizes of input phosphors

4

the different sizes of input phosphors is called

multifield

resolution can be increased up to __ when magnification mode is used

50%

magnification formula

Input screen diameter/diameter of input screen during magnification

when going from a 12” to 6” field

multifield image intensifiers

Unequal magnification of an image creates a ___ and loss of brightness around the periphery.

pincushion appearance

a loss of brightness around the edges is called

vignetting

When originally introduced, the image from the image intensifier was viewed using a

mirror optics system

conventionally, viewing system is now a

television monitor

2 types of viewing system television monitor

camera tube

charge coupled device

what kind of circuit is television monitor

closed

Visible light from output phosphor converted to an

electronic video signal

The difference between the camera tube and CCD is in their

size and readout process

how many people could view the image for mirror and lenses

1

Convert light image to an electronic signal that is sent to the television monitor

video cameras

Video camera tubes include

vidicon, orthicon and plumicon

camera tube most often used is a

vidicon tube

The vidicon tube is connected to the output phosphor of the image intensifier by either a

fiberoptic bundle or optical lens system

maintains vacuum

glass envelope