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 CONES

• Sensitive to low light• Used in night vision

(scotopic vision)• Dims objects seen

better peripherally• Color blind• Do not perceive

detail

• 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 X-RAY 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 x-rays 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 (25/1717) 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 region of input is used

• Spatial resolution is better (think of it as the umbra!)

• Lower noise, higher contrast resolution

• Minification gain is reduced = dimmer image

• To compensate must increase mA

• Increase patient dose

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 437-441• Reference: Chapter 12, Fauber pg

302-303 to include figure 12-6

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