Chapter 33: Fluoroscopy Flashcards
who was the fluoroscope invented by and when
Thomas Edison in 1896
where is the xray tube and image intensifier loacted in fluoro
xray tube is below table and image intensifier is on top
dynamic imaging modality designed to observe moving structures in the body
Fluoroscopy
what should the SSD be for mobile equipment
30 cm (12 inches)
what should the SSD be for fixed fluoroscopic
38 cm (15inches)
What is the mA range for the fluoroscopic xray tube
0.5 to 5 mA
purpose of the image itensification
increase brightness of fluoroscopic images by thousands (8,000 times)
Electronic devise mounted above the table and patient and permantely attched to the xray tube
Image Intensifier
components of the image intensifier
Input phosphor
photocathode
electrostatic lenses
anode
output phosphor
Function of the input phosphor
converts xray photons to light photons
coated with cesium iodide
Input phosphor
*concave surface
*approx. 10-35 cm in diameter
*coated with cesium iodide
* converts xray photons to light photons
input phosphor
made of cesium antimony
photocathode
function of photocathode
converts light photons to electrons ; called photoemission
Mimics the pattern of light demonstrating the anatomy of the patient emitted by the input phosphor (latent image)
Photocathode
narrowing the electron beam
electrostatic lenses
very high exposures directly into :
eyes, neck, hands
*positively charged end of the image intensifier
*attracts the photoelectrons due to elctrostatic charger
*contains the output phosphor at end
Anode
function of the elctrostatic lenses :
accelerate and focus the electrons toward the output phosophor
made of zinc cadmium
sulfide
glass fluorescent screen
Output phosphor
function of the output phosphor
Converts photoelectrons to visible light
what type of diagnosis is fluoroscopy
Active
what type of examination is fluoroscopy
Dynamic
image intensification tubes dveleoped in 1948. there was mirror optics for viewing what was that replaced with
replaced with closed circuit TV systems
fluoroscopic uses for functional studies:
o Gastrointestinal (GI) tract studies
o Angiograms
o Line placements
o Orthopedic surgeries
total brightness gain
minification gain * flux gain
o 0.1–0.2 mm layer of sodium activated cesium iodide (CsI)
o Converts intercepted x-ray beam to light
Input screen
Emits electrons when struck by light emitted by input screen
Photocathode
audible timer, radiation protection
five minute timer
where should the patient be shielded
from behind since the xray tube is below
what is the last image hold for
to decrease dose
pt. protection
measurment of the increase in image brightness due to the conversions of energy in the image intensifier
Total brightness gain
- 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 is increased in magnification mode
increased resolution
increased patient dose
magnification =
input screen diamter/ diamater of input screen used during magnification
distortion in fluoro
vignetting
where is the focal point in magmode
focal point closer to input phosphor in magmode
what size surface area is during magmode
smaller surface area
measurement of increased image intensity achieved by image intensifier
Brightness gain
results from concentration of large electron volume from input phosphor, being focused down onto small area of output phosphor
Minfication gain
input over output
minification gain
measurement of conversion efficiently of output screen
Flug gain
Automatically adjusting the contrast , takes account the thickness
Automatic Brightness control
help to see in bright lights, phototopic
Cones
help to see in low light, scotopic
rods
is input or output bigger
input is bigger vs. output
how much lead is in the bucky slot cover
0.25 mm
how much lead is in the curtain
0.25mm
how much lead is in the lead aprons
0.25mm
how much lead is in the lead aprons in fluoro
0.5mm
image intensification was introduced in 1948. What was modified.
-higher visual acuity
-uses photopic vision (cones)
-reduced fluoroscopic dose
Image intensification tube components:
-input screen and photocathode
-electrostatic lenses
-magnification tubes
-anode and output screen
-total brightness gain (minification gain * flux gain)
what does greater voltage to electrostatic lenses do
-increases acceleration of electrons
-shifts focal point away from anode
hole in center allows electrons to pass through to output screen
Anode
Results from concentration of large electron volume from input phosphor, being focused down onto small area of output phosphor
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
Image quality
Contrast, resolution, distortion, quantum mottle
-controlled by amplitude of video signal
-digital systems use post processing
(window width and filtering algorithm)
Affected by:
-scattered ionizing radiation
-penumbral light scatter
Contrast
Which is better?
Fluoroscopic or static radiography resolution
Static radiography
Resolution varies depending on geometric Factors:
SID, OID, minification gain
longer sid, smaller oid
Edges of image intensifier have lower resolution due to:
Vignetting
Automatically adjusting the contrast
takes account of the thickness
Automatic brightness control
penumbra
unsharpness
numbra
sharpness
What does more scatter do to the contrast
Decrease contrast
Size distortion
-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
blotchy, grainy appearance
-caused by too little exposure
-most commonly remedied by increases mA
Quantum Mottle
Improved by increasing total exposure to intensifier input phosphor
-increase mA
-reduce distance between patient and image intensifier
-increase kvp
Quantum Mottle
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 is the difference with flat panel fluoroscopy ?
-No intensifier tube
-no vignetting
-no dose increase in mag mode
C- arm fluoroscopic units
- populary for surgery, er, orthopedic studies
- operates the same as stationary units
-pary particular attention to radiation dose when using mobile fluoroscopy
what generator is used for digital fluoroscopy
High power generator
in digital, Image intensifier output screen coupled to :
TFT
in digital fluoroscopy, what is connected to each pixel
Photodiodes
what is used in digital fluoroscopy to lower noise
pixel binning
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
patient protection for fluoroscopy
-audible alarm at 5 minutes
-same rules for collimation
-last image hold
how much aluminum for filtration for fluoro
2.5mm
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
What is the mR for xray tube and fluoro
Xray tube = 100mR
fluoro= 10mR
purpose of intensifier tube :
To increase image brightness
-converts xray to photons
-cesium iodide
Input phosphor
-converts light to photons to electrons
-cesium and antimony
Photocathode
-focuses the photoelectrons to the output phosphor
25-35kvp
-located on the inside of the image intensifier
Electrostatic lenses
