Chapter 33: Fluoroscopy Flashcards
Dynamic movement of an image?
Fluoro
KUB is considered what type of image?
static image
Active diagnosis in fluoro is in control of who?
domain of radiologist
What can the radiologist see when doing fluoro?
Visibly watching barium go through the esophagus to the stomach
who was the fluoroscope invented by and when?
Invented by Thomas Edison in 1896
When Thomas Edison invented fluoro how were the machines back then?
Consisted of x-ray tube and hand-held fluoroscopic screen that was very high exposure directly into eyes, neck and hands
Who was the first person to introduce radiation protection and was also a dentist?
William Rollins
Where is the x-ray tube and image intensifier located in fluoro?
x-ray tube is below and image intensifier is on top
dynamic imaging modality designed to observe moving structures in the body
Fluoroscopy
When was the image intensification (ii) developed?
in 1948
Fluoro is considered what two types?
CR in the OR + Fluoro with barium
Digital fluoro deals with what?
-predominated by 2005
-TFT matrices
-Post processing capabilities
What are the different pieces of equipment involved with fluoro?
-Fluoroscopic screen
-mirrors for viewing (obsolete)
-image intensification (video camera and monitor)
Electronic devise mounted above the table and patient and permantely attached to the x-ray tube
Image Intensifier
Purpose of the image intensification?
increase brightness of fluoroscopic images by thousands (8,000 times)
What did mirror optics for viewing replaced with?
replaced with closed circuit TV systems
What is the last image hold for?
- a type of radiation protection for the patient
- decrease dose
- the last image is up on the monitor
fluoroscopic uses for functional studies:
o Gastrointestinal (GI) tract studies
o Angiograms
o Line placements
o Orthopedic surgeries
o IVU
Audible timer, radiation protection that beeps saying patient has been in fluoro for 5 minutes?
5 minute timer
In order to active fluoro what must you do?
You have to apply pressure whether is up on the tower or the paddle
When applying pressure is considered what?
dead man switch
A dead man switch is also considered
another type of radiation protection
Should fluoro be used to preview patient’s radiographic position?
NO!!!
Where should the patient be shielded for fluoro?
from behind the patient since the x-ray tube is below
Since you are using a high time in fluoro what happens to your mA?
you are using a low mA
-reciprocity law
In what directions can the image intesnifier move?
It can move up and down, side to side
-moves in all directions
Why does the image intensifier only go down a certain amount?
Is another type of radiation protection
Your beam in fluoro is still what?
the beam is geometry
What is the mA range for the fluoroscopic x-ray tube
0.5 to 5.0 mA
What is SOD?
Source to object distance
What is the source for SOD for fluoro?
The source is the x-ray tube
What is the object for SOD in fluoro?
the object is the patient
What is the minimum SOD in fixed fluoroscopic equipment (fluoro room)?
15 inches or 38 cm
What is 15 inches converted to centimeters?
38 cm
What is the minimum SOD in mobile fluoro examination (C-arm)
12 inches or 30 cm
What is 12 inches in cm?
30 cm
What is known as the foot switch
deadman switch
Can you collimate for fluoro?
Yes is known as your shutters also your patient protection
components of the image intensifier: correct order
-output phospher
-anode
-electrostatic lenses
-photocathode
-input phospher
How do your eyes adjust in fluoro?
-cones
-rods
Help you see in bright lights, photopic
Cones
Helps you see in low lights, scotopic
Rods
Supports the patient and can be changed from a horizontal position to a vertical position
- Equipped with a movable footboard
X-ray table
What is the function of input phosphor?
Collecting x-ray photons and converting it to light because there is cesium iodide
Image intnsifier starts off from the x-ray table to patient by:
Incoming photons are coming up (exit radiation) to the input phosphor
Input phospher is coated with what?
Cesium iodide
*concave surface
*approx. 10-35 cm in diameter
*coated with cesium iodide
* converts xray photons to light photons
input phosphor
What two things are concave in shape?
Input phosphor and photocathode meaning they could fit on top of each other
converts light photons to electrons ; called photoemission
Photocathode
Mimics the pattern of light demonstrating the anatomy of the patient emitted by the input phosphor (latent image)
Photocathode
made of cesium antimony
Photocathode
Narrowing of electrons
- has a negative charge
-slight kvp applied to help keep moving the beam
-acceleration of electrons
Electrostatic lenses
-located along the inside of the image intensifier
-charged with a low voltage of 25-35 kvp
-function: accelerate and focus the electrons towards the output phosphor
-focal point: location where the electrons cross as they travel from the photocathode to the anode; changes position when intensifier is operated in normal vs. magnification mode
Electrostatic lenses
Electrons pass through the hole in
Anode
Do the electrons interact with the anode?
No!!
Why is the anode there?
to capture the attraction of negative to positive
*positively charged end of the image intensifier
*attracts the photoelectrons due to electrostatic charge
*contains the output phosphor at end
Anode
When electrons pass through the anode where are they going?
to the output phosphor
After electron passes through the anode it is then converted to light in?
Output phosphor
The after the electrons is converted to light in the output phospher what happens next?
Is then converted to your analog-digital-converter which goes on the monitor your manifest image
Made of zinc cadmium sulfide
Output phosphor
-Made of zinc cadmium sulfide
-approximately 2.5-5.0 cm in diameter
-Function: converts photoelectrons to visible light
Output phosphor
The output phospher is coated with a thin aluminum coating because?
To help prevent light leaking back into the intensifier
How much lead is in the bucky slot cover?
0.25 mm of lead
How much lead in the curtain (lead curtain) (lead drape)?
0.25 mm of lead
How much does a regular lead apron have? recommend lead for an apron
0.25 mm of lead
What is the recommend lead for a lead apron for fluoro?
0.5 mm of lead
In fluoro what comes into place to keep you safe?
time, distance, and shielding
-jump behind the radiologist
The closer you are
the more scatter you are going to get
If you don’t have a wrap around apron what should you not do?
Never turn your back to the beam
-walk backwards
is input or output bigger
Input is bigger
Accelerate and focus electron pattern across tube
to anode
*primary source of brightness gain (due to acceleration of electron stream and increased kinetic energy)
Electrostatic lenses
what does greater voltage to electrostatic lenses do
-increases acceleration of electrons
-shifts focal point away from anode
made of zinc cadmium
sulfide
-glass fluorescent screen
Output phosphor
Image intensification tube components:
-input screen and photocathode
-electrostatic lenses
-magnification tubes
-anode and output screen
-total brightness gain (minification gain * flux gain)
image intensification was introduced in 1948. What was modified.
-higher visual acuity
-uses photopic vision (cones)
-reduced fluoroscopic dose
hole in center allows electrons to pass through to output screen
Anode
Early fluoroscopes required imaging to be completed in?
-reliance on?
completed in total darkness
-relied on scotopic vision (rod vision)
When you go to magmode what are you increasing?
You are increasing your patient dose
What is your advantage of going into magmode (magnification)?
increase spatial resolution
What is your disadvantge of magmode (magnification)?
increasing patient dose
distortion in fluoro is called?
Vignetting
because of concave shape you get a distortion called
pincushion distortion
When you go to magmode you are only focus where?
You are focus on the center
-getting rid of outer edge distortion
When you go into magmode what happens to your focal point?
It changes
When you go into magmode your focal point goes closer to what?
goes closer to your input phosphor
In the normal mode is closer to what?
closer to output phosphor
Magnification =
input screen diameter
over
diameter of input screen used during magnification
-smaller during magmode (surface area)
You want everything to go forward because if not what happens?
You get backscatter of light which leads to distortion of the image
minification gain x flux gain is known as your?
Total brightness gain
Total brightness gain =
minification gain x flux gain
measurement of increased image intensity achieved by image intensifier tube
total brightness gain
In order to get your total brightness gain you need to get what?
the minification gain and the flux gain
Output light intensity is measured in
candela
Is known as your input screen diameter squared over your output screen diameter squared
minification gain
Results from concentration of large electron volume from input phosphor, being focused down onto small area of output phosphor
Minification gain
helps increase that brightness
minification gain
minification gain =
input screen diameter ^2/output screen diameter^2
Measurement of conversion efficiency of output screen
ex. one electron strikes output screen
-50 light photons emitted per electron striking output phosphor
-flug gain 50
flux gain
efficiency of image intensifier
flux gain
Increased brightness due to same number of light photons being concentrated on a smaller area
Minification gain
flux gain =
output photons over your input photons
electrons to light come into play
flux gain
Maintains density (brightness) and contrast to compensate for different body thickness
Automatic Brightness Control (ABC)
unit for the measurement of light intensity or luminance
candela
Which is better?
Fluoroscopic or static radiography resolution
Static radiography
Edges of image intensifier have lower resolution due to:
Vignetting
Image quality affected by:
-contrast
-resolution
-distortion
-quantum mottle
contrast is affected by:
-scatter radiation
-light scatter (penumbra)
Controlled by amplitude of video signal
contrast
the more scatter you have
the lesser the contrast
contrast uses
window width and filtering algorithm
unsharpness
penumbra
sharpness
umbra
differences in density between different body parts
contrast
Resolution varies depending on geometric Factors:
SID, OID, minification gain
longer sid, smaller oid
blotchy, grainy appearance
-caused by too little exposure
-most commonly remedied by increases mA
Quantum mottle
-affected by same parameters as static radiography (primarily oid)
- geometric problems in shape of image intensifier input screen
-concave shape helps reduce distortion
-vignetting or pincushion effect
-not a problem with TFT matrices
-uniform resolution across flat panel detector array
Size distortion
Improved by increasing total exposure to intensifier input phosphor
-increase mA
-reduce distance between patient and image intensifier
-increase kvp
Quantum mottle
digital fluoroscopic system use
flat panel displays
What is the difference with flat panel fluoroscopy ?
-No intensifier tube
-no vignetting
-no dose increase in mag mode
Most common viewing system:
Video
-video camera attched to output phosphor
-fluoro video camera uses CCD
-display monitor for viewing
Highest energy scatter
-90 degrees angle to incident beam
- same level as radiographer / radiologists gonads
what generator is used for digital fluoroscopy
High power generator
Newer systems are placing ii with
amorphos silicon (indirect)
in digital, Image intensifier output screen coupled to :
TFT (holding your laten image)
what is used in digital fluoroscopy to lower noise
pixel binning
in digital fluoroscopy, what is connected to each pixel
Photodiodes
Use C C D to generate electronic signal
Signal sent to A D C
Allows for post-processing and electronic storage and distribution
Last image hold function
Post-exposure image processing
digital fluoroscopy
populary for surgery, er, orthopedic studies
operates the same as stationary units
-pary particular attention to radiation dose when using mobile fluoroscopy
C-arm units
patient protection for fluoroscopy
-audible alarm at 5 minutes
-same rules for collimation
-last image hold
What is the mR for xray tube and fluoro
-X- ray tube 100 mR
- Fluoro tube 10 mR per min
how often should the fluoro system and lead aprons be checked?
-the fluoro system should be checked every 6 months
-the lead gowns should be checked yearly
how much aluminum for filtration for fluoro
2.5 mm of aluminum
total number of light photons produced by each electron
flux gain
the ratio of light photons at the output phosphor divided by the number of input photons
flux gain
