Unit 6 Exam - Fluoroscopy

When was fluoroscopy discovered?

1896

Who discovered the fluoroscope?

Thomas Edison

Red Adaptation Goggles

Invented in 1916 by Wilhelm Trendelenburg to help physicians’ eyes adapt for greatest visual acuity

Who invented the image intensifier?

Dr. John Coltman in 1916

What can fluoro help diagnois?

Pathologies of soft tissue structures

Fluoro mA range

0.5-5.0 mA

Diagnostic tube mA range

50-1,200 mA

What is the purpose of the image intensifier?

Improve image brightness

Glass Envelope

Protective enclosure which maintains a vacuum seal and lined with 2mm of lead

What is the material of the input phosphor?

Cesium Iodide (Csl)

Input Phosphor (screen)

Converts x-ray photons into light photons

What is the material of the photocathode?

Cesium and antimony compounds

Photocathode

Bonded to input phosphors; converts light photons to electrons via photoemission

What is the charge of the electrostatic focusing lenses?

Negative

Electrostatic focusing lenses

Negatively charged; focus electrons towards the anode and accelerate the electrons

What is the charge of the anode?

Positive

Anode (accelerating)

Positively charged, layers of aluminum with hole in center to attract electrons from photocathode

What is the material of the output phosphor?

Cadmium sulfide

Output Phosphor

Small fluorescent screen that converts electrons back into light photons; the exit light carries the latent image in a minified form

Magnification

An increase in voltage causes a smaller diameter of input phosphor and shifts the focal point closer to the input phosphor

Benefits of magnification

Reduces contrast problems and increases spatial resolution

Magnification Factor

Input phosphor diameter / Input phosphor diameter during mag mode

What does magnification do the the x-ray tube?

Causes excessive heat

Minification gain

Input phosphor diamter² / output phosphor diameter²

Flux gain

# of light photons from output phosphor / # of x-ray photons striking input phosphor 

What does flux gain represent?

Tube’s conversion efficiency

Total brightness gain

The overall increase in image brightness achieved by an image intensifier  

Total brightness gain will decrease roughly _____ each year due to aging of the tube

10%

Total brightness gain equation

Flux gain x minification gain

What is another method to identify brightness gain?

Conversion factor

Conversion factor

Intensity of output phosphor(cd/m²)/ exposure rate at input phosphor (mR/sec) 

Conversion factor is equivalent to approximately _____ the brightness gain

1%

Coupling

Takes light from II to next component in imaging chain 

Fiber optics

Bundle of glass fibers that connect to a camera tube/CCD

Charged-Couple Device (CCD) 

In indirect DR, light sensitive semiconductor with fiber optics mounted to II or FPD with a high DQE and SNR, increased resolution

Complementary Metal-Oxide Semiconductor (CMOS)

In indirect DR, two stacked together to create electron hole pairs

Automatic brightness system (control)

Monitors the electrical current between the photocathode and anode of the II, or by measuring output intensity  

Continuous fluoroscopy

30 frames a second, typically 0.5-4 mA

Low dose continuous fluoroscopy

Halves the mA value as selected by AERC; saves patient dose with minimal visualization of noise

High dose continuous fluoroscopy

Can be used for increased penetration of the patient; increased patient dose

Pulse width

Exposure length of each pulse (measured in msec)

Pulse interval

Beam off time

Pulse height

Determined by mA

Frame rate

Number of images obtained per second

Most fluoroscopic acquisition systems have what spatial resolution?

4-6 lp/mm

What is size distortion primarily caused by?

OID

Shape distortion

Geometric problems in the shape of the II tube

Pincushion distortion (shape distortion)

Borders of fluoro image are inherently magnified

Vignetting (shape distortion)

Reduction of the brightness at the edges of a fluoro image

Vignetting can affect how much of the image?

8-10%

Spot image

A static image recorded at diagnostic mA levels; image is captured from radiation before it reaches the intensifier

Photospot camera

Records a series of static images; requires the beam-splitting mirror to record light leaving the output phosphor

Cine run

Capable of 15, 30, 60, and 90 acquisitions per second

Digital subtraction

First image is saved by the computer as a reference; cine run is started, the software program subtracts most of the pixel values from the saved image

Road mapping

Starts with digital subtraction acquisition; a cine run is performed during an injection of contrast  

Frame averaging

The computer averages multiple frames together; reduces visibility of noise allowing for lower mA settings

Image Gently says pulse width should be less than ____ ms for pediatrics

6

Image Gently says pulse width should be less than ____ ms for adults

10

Tabletop dose rate for fluoro should not exceed ____ mGy/min

88

Tabletop high level fluoro should not exceed ____ mGy/min

176

How do you determine DAP?

Air kerma x field size

What measures patient dose?

Air kerma

What affects DAP?

Beam restriction, technique, and total volume of irradiated tissue

What is SSD for stationary fluoro units?

15 in (38 cm)

What is SSD for mobile fluoro units?

12 in (30 cm)

Last image hold  

Displays the last image on the monitor after fluoro stopped; allows viewer to study the image without continued exposure  

Last sequence display

Dynamic storing of the last sequence of fluoro images for instant replay, editing and storage

II should be on _____ and angled towards _______

Top, operator

Lead apron lead equivalent

.5 mm

Lead curtain and bucky slot cover lead equivalent

.25 mm