RAD 354 Chapt. 25 Fluoroscopy

• Fluoro’s primary function is to enable one to view the patient in “real time” with dynamic motion

Fluoro was first invented by Thomas Edison in 1896

• Utilized a conventional x-ray unit with a fluorescent screen that would convert the x-rays exiting the patient to low level light the radiologist could view

Image Intensified Fluoro

II

II Tube Parts

• Input phosphor• Photocathode (photo emission)• Evacuated glass envelope• Electrostatic focusing lens (neg. charged!!!)• Anode• Output phosphor

II Fluoro

• Increased image brightness with II over “direct” fluoro is the biggest advantage of II– Maintains OD by “automatic brightness control”

(ABC) that the radiologist can preset and control

Eyes use rods and cones

• Photopic vision – daylight vision uses the CONES

• Scotopic vision - night time vision and uses the RODS

Fluoro Techniques

• Fluoro usually is operated at 5 mA and uses highest optimum kVp

• Back up timer = 5 minutes• Protective Fluoro measures– Bucky slot cover– Lead curtain– Lead gloves and aprons (secondary barriers)– Distance

Gain

• Minification gain (ratio of input to output sizes)

• Flux gain – ratio of # of inpupt PHOTONS to output LIGHT PHOTONS

• Brightness gain (total brightness gain) = minification gain X flux gain

Fluoro Magnification

• Most fluoro II units have DUAL input phosphor sizes (9” and 6” {27/17cm})– Some have TRI sizes input (trifield tubes

27/17/12cm)• The crossover of the electron stream distance from the

output phosphor determines the amount of magnification• Mag mode = BETTER SPATIAL RESOLUTION, better

contrast, HIGHER pt. dose!

TV Monitoring

• Must “couple” the output phosphor to a TV camera tube or photomultiplier tube– Vidicon is the MOST frequently used tube –

plubicon and image orthocon are also tube types– Fiber optics and beam splitters are used to help

direct the digitized image to the various destinations (TV monitor, photo spot film, VCR/CD recorder, cine camera)

Vidicon Camera (tube)