Transcript FLUOROSCOPY - Montgomery College

FLUOROSCOPY
X-RAYS IN MOTION
“Viewing dynamic studies
of the human body”
HISTORY
• Thomas Edison, 1896
• Screen (zinc-cadmium sulfide)
placed over patient’s body in x-ray
beam
• Radiologist looked directly at screen
• Red goggles-30 minutes before exam
• 1950 image intensifiers developed
PRESENTLY….
• Fluoro viewed at same level of
brightness as radiographs (100-100
lux)
• X-ray tube under table/over table or
in c-arm
• Image intensifier above patient in
carriage
• Carriage also has the power drive
control, spot film selection and tube
shutters
RED GOGGLES?
The eye
• Light passes thru the cornea
• Between the cornea and lens is
iris
• Iris acts as a diaphragm
• Contracts in bright, dilates in
dark
• Light hits lens which focuses
the light onto the retina where
the cones and rods await
• Cones- central
• Rods - periphery
RODS
• Sensitive to low
light
• Used in night vision
(scotopic vision)
• Dims objects seen
better peripherally
• Color blind
• Do not perceive
detail
CONES
• Less sensitive to
light (threshold of
100 lux)
• Will respond to
bright light
• Daylight vision
(phototopic vision)
• Perceive color,
differences in
brightness
• Perceive fine detail
IN FLUOROSCOPY
• The winner is……
• CONES!!
FLUORO X-RAY TUBES
• Operate at .5 to 5mA. Why do they operate
at such low mA stations?
• They are designed to operate for a longer
period of time with higher kVp for longer
scale contrast.
• kVp dependent on body section
• kVp and mA can be controlled to select
image brightness
• Maintaining (automatic) of the brightness
us called ABC or ABS or AGC
(control,stabilization gain control)
Fluoro X-ray Tubes
• Fixed…may be mounted no
closer than 15 inches or 38 cm
to patient
• Mobile may be brought no
closer than 12 inches or 30 cm
to patient
IMAGE INTENSIFIER
RECEIVE REMNANT XRAY BEAM, CONVERT IT
TO LIGHT…INCREASE
THE LIGHT INTENSITY
5000-30,000 TIMES
THE SEQUENCE
• Beam exits the patient
• Hits the input
phosphore(cesium iodide CsI
tightly packed
needles…produce excellent
spatial resolution)
• Converts x-rays to visible light
The sequence cont.
• Hits photocathode (Cesium and
antimony components)
• Emits electrons when struck by
light (photoemission)
The sequence cont
• The potential difference within the
image intensifier tube is a constant
25,000 volts
• Electrons are accelerated to anode
• Anode is a circular plate with hole
for electrons to go thru.
• Hits output phosphor which interact
with electrons and produce light
The Electron Path
• MUST BE FOCUSED FOR ACCURATE
IMAGE PATTERN
• Electrostatic lenses (focusing
devices)
• Accelerate and focus electron beam
• “The engineering aspect of
maintaining proper electron travel is
called electron optics”
Continuing the
sequence
• Electrons hit output phosphor
(zinc cadmium sulfide) with high
kinetic energy producing an
increased amount of light
• Each photoelectron at the
output phosphor has 50-75 more
light photons
FLUX GAIN
• Ratio of number of light
photons at the output
phosphor to the number of xrays at the input phosphor
• Flux gain =
# of output light photon
# of input x-ray photons
MINIFICATION GAIN
• Ratio of the square of
the diameter of the
input phosphor to the
square of the diameter
of the output phosphor
OR
• # of electrons
produces at large input
screen ( 6 inches)
squared, compressed
into the area of small
output screen ( 1 inch)
squared
•
•
•
•
Try the math
6 inches squared = 36
1 inch squared
=1
Minification gain = 36
BRIGHTNESS GAIN
• Minification gain x flux gain
• Increases illumination level of an image
• Ratio of the intensity of the illumination ot
the output phosphor to the radiation
intensity at the input phosphor
• Brightness gain of 5000-30,000
• Maintaining (automatic) of the brightness
us called ABC or ABS or AGC
(control,stabilization gain control)
CONVERSION FACTOR
• Ratio of intensity of illumination
at the output phosphor
(measured in Candela per meter
squared) to the radiation
intensity at the input phosphor
(mR per sec)
• Cd/mr squared
mr/s
MULTIFIELD IMAGE
INTENSIFICATION
Allows focal point change
to reduce field of view and
magnify the image
Some facts about
multifield image
intensifiers
• Standard component on most
machines
• Always built in in digital units
• Most popular is 25/17
• Trifield tubes are 25/17/12 or
23/15/10
MULTIFIELD IMAGE
INTENSIFICATION
• Numeric dimensions refer to the
input phosphor (25/17)
• Smaller dimension (25/17) result
in magnified images
• At 25-all photoelectrons are
accelerated to output phosphor
MULTIFIELD IMAGE
INTENSIFICATION
• Smaller dimension – voltage of
focusing lenses is increased
• Electron focal spot moves away
from the output.
• Only the electrons from the
center of input strike the output
PROS
CONS
• Only central
• Minification gain
region of input is
is reduced =
used
dimmer image
• Spatial
• To compensate
resolution is
must increase
better (think of
mA
it as the umbra!) • Increase patient
• Lower noise,
dose
higher contrast
resolution
VIGNETTING:
REDUCTION OF
PERIPHERAL
BRIGHTNESS
COMING SOON
•
•
•
•
•
•
Coupling (Vidicon, Plumbicon)
Fiber Optics
Lens coupling
Beam splitting
Modulation
Size of the video signal directly
proportion to the light intensity
received by x-ray tube. The signal
received by the TV tube is
modulated
Image recording
• Cassette loaded spot film
• When recording image, the
radiographic mA goes from a low
mA to high mA. Why?
• Photospot camera
• Patient dose increases with size
of film
DIGITAL FLUOROSCOPY
• Bushong, Chapter 27 pgs 437441
• Reference: Chapter 12, Fauber
pg 302-303 to include figure 126
QUESTION
Why is it easy to convert a
conventional fluoro unit to
a digital one?
Facts about digital
fluoro
• Image acquisition is faster
• Can post process
• Similar equipment to a
conventional fluoro room except
• two monitors
• Operates in radiographic mode
DF and radiographic
mode
• Hundreds of mA vs 5 mA
• Due to the high generator
required for DF
• the x-ray beam is pulsed
progressive fluoroscopy
PULSED PROGRESSIVE
FLUOROSCOPY
• Generator can be switched on and
off rapidly
• Interrogation time
• Tube switched on and meets selected
levels of kVp and mA
• Extinction time
• Time required for the tube to be
switched off
• Each must have times of less than
one 1 ms.
CCD
• Instead of a vidicom or
plumbicom (see figure 27-8, pg
440 Bushong)
• Discuss Box 27-1 on pg 441
FPIR (pg 440-442)
• Flat panel Image receptor
• Replacing CCD’s
• Made of cesium Iodide pixel
detectors
• Lighter, smaller than image
intensifiers
• No cassette needed
FPIR CONT.
• Improvement to image as the
spatial resolution is uniform and
distortion free
• High DQE
• Improved contrast
• Rectangular image
• See page 442 Box 27-2