Ch 33 - Fluoroscopy PowerPoint

Other words to describe “fluoroscopic”

• Dynamic

• Real Time

• Moving

Other words to describe “static”

• Still Image

ABC

Automatic Brightness Control

FL commonly used for?

Small Bowel Disorder

Who has primary domain of FL?

MD Radiologist (doctors run exam primarily but can ask technician to run during)

function of Input Phosphor

turns x-ray into light

function of photocathode

takes light and produces electrons

function of electrostatic lenses

helps accelerate electrons and focus them down to a focal point

function of output phosphor

convert electrons into light

“Input Screen”

• receives x-ray exiting patient

• emits light photons

Input Phosphor

Input Phosphor: How many light photons are produced per x-ray photon?

1,000 - 5,000

Input Phosphor: What kind of shape does it have and purpose?

Concave shape

• helps control Image Distortion

• Made of cesium and antimony (photo emissive metal)

• Responds to light exiting the input phosphor

• emits electrons

Photocathode

Photocathode: How many photoelectrons are made per light photon?

proportional amount

• Negatively charged

• Focuses the photoelectrons to the output phosphor

• accelerates photoelectrons to anode

• Primary Brightness Gain

Electrostatic Lenses

• placed after positively charged anode - 25kVp

• Converts electrons to light

• emitted isotopically

Output Phosphor

Output Phosphor: How many light photons are produced per electron?

50 - 75x as many as were necessary to create it

Automatic Brightness Control (ABC)

or

Automatic Exposure Control (AEC)

automatically adjust kVp and mA to maintain quantity to image intensifier (II)

This maintains brightness

What does a dark image on an II indicate?

not enough photons / photon starvation

Flux Gain

Increased brightness due to the acceleration of the photoelctrons

Flux Gain Formula

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

Minification Gain

Increased brightness due to same number of light photons being concentrated on a smaller area

Minification Gain Formula

Input diameter² / Output diameter²

What factors will vary FL resolution with Image Intensifier

• electrostatic focal spot

• minification gain

Brightness Gain

The ability of the image intensifier to increase the illumination level of the image

Brightness Gain formula

Minification gain x flux gain

Magnification

• Increase in size of the image

• controlled by changing focal point

  Advantages

  • better spatial resolution

  • better contrast resolution

    Disadvantages

  • increased patient dose, reduced field of view

Magnification formula

input screen diameter / input screen diameter during magnification

Image is more magnified

focal point closer to input

Image is less magnified

focal point is closer to output

Charge-Coupled Devices (CCD)

Used in place of a video camera tube

• Light from image intensifier and turned into electrical signal

  • lets computer change brightness

  • less conversion less patient dose

Artifacts that appear on image

• Veil Glare

• Vignetting

• Quantum Mottle

• Edge distortion

Veil Glare

Internal scatter that reduces contrast to image

Vignetting

Reduction in brightness at the periphery of image

Quantum mottle

Graning of image

Edge Distortion

Straight line bends outward from center of image

Primary source of radiation to medical personnel

patient

mA range of FL

0.5 - 5.0

Minimum source-to-skin distance

• 30 cm mobile equipment (C-arm) (12in)

• 38 cm stationary/fixed systems (15in)

Pixel for Digital Fluoro in μm (micro meter)

200 - 400

lp/min

linepairs/min

Digital R/F unit uses ______ for all exams

1 detector

FPIR

Flat Panel Image Receptor

FPIR use

TFT Technology (thin film transistor)

FPIR composed of

cesium iodide (CsI)/amorphous silicon (a-Si)

Digital Flat Panel detector with pixel pitch (density of pixel) of 141 microns typically yield

3.541 lp/min resolution

Digital FL typically

• 1-2 lp/min

• uses indirect detector technology with TFT

• uses Pulsed FL x-ray exposure timed w/ detector

• 256 shades of gray through 8 bit processing