Fluoroscopy

Dr. Hussein Ahmed Hassan

OBJECTIVES• After completing this lecture, the student should be able to:• Describe the principle of operation of the image intensifier.• know limitation of the sharpness, and resolution of a image

intensifier. • Explain how design features can be used to improve image

quality.• Name the events that take place when imaging with image

intensifier is performed.•

Fluoroscopy• A technique used to furnish images that reflect near instantaneous changes occurring

in the patient.

It is possible to view directly, with naked eyes, the fluorescent image produce a simple phosphor coated screen.

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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

• In early fluoroscopic techniques, x rays emerging from the patient impinged directly on a fluoroscopic screen.

• Light was emitted from each region of the screen in response to the rate at which energy was deposited by the incident x rays. The light image on

• The fluoroscopic screen was viewed by the radiologist from a distance of 10 or 15 in.

• A thin plate of lead glass on the back of the fluoroscopic screen shielded the radiologist

from x radiation transmitted by the screen.

Using this direct fluoroscopic technique: The radiologist perceived a very dim image

with poor visibility of detail. Radiologists had to “dark adapt” their eyes

by remaining in the dark for extended periods in order to view the images.

CONVENTIONAL FLUOROSCOPY

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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

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• Light hits lens which focuses the light onto the retina where the cones and rods await

• Cones- central• Rods - periphery

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RODSCONES

• 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

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PRESENTLY.…• Fluoro viewed at same level of brightness as

radiographs.• 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

Image Intensifiers

• Increase the brightness of the fluoroscopic image.

• Because of the brighter images, dark adaptation is not required.

Principles components of an image intensifier tube;1. The input phosphor, is 25-57 cm in diameter, exposure of input phosphor to x-ray beam that has been transmitted through the patient causes it to emit light.2. Photocathode layer, which release electrons in number related to intensity of light (electronic image is produced).

Image Intensifiers

Image Intensifiers

3. In the body of the Image Intensifier tube the electron are accelerated through a potential difference of 25-35 kv

and focused electronically onto a circular output phosphors 2.5-3.5 cm in diameter, which is coated of zinc-cadmium sulphite, which fluoresces when bombarded with electrons.

4. The light image so produced may up to 9000 times brighter than the input phosphor image.

FLUOROSCOPIC DATA AQUSITION-IMAGE INTENSIFIED SYSTEM

1. X-RAY TUBE2. PATIENT3. IMAGE INTENSIFIER4. OUTPUT PHOSPHOR5. CAMERA6. MONITOR

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Image intensifier x-ray tube configuration. The overcouch, undercouch intensifier is the more recent development.

General purpose fluoroscopic system

Fluoroscopic Equipment (cont)

Mobile fluoroscopic system for routine procedures during

surgery

Fluoroscopic Equipment (cont)

• Fluoroscopy is used for the dynamic evaluation of functional disorders and guidance during routine surgical procedures, biopsies, etc.

• Fluoroscopy is used during interventional radiology procedures

Fluoroscopic equipment uses electronic image intensifiers to provide real-time (dynamic) imaging;

Fluoroscopic Equipment

Fluoroscopic Equipment (cont)

Direct fluoroscopy should no longer be used.

“Direct” fluoroscopy does not use electronic image amplification. The real-time image is viewed on a fluorescent screen in a completely darkened room and requires the fluoroscopist to dark adapt for

approximately 20 minutes before the examination .

Improper attention to these requirements can significantly increase the radiation dose to patients

and users .

All fluoroscopic units-:

• shall display the instantaneous values of x-ray tube voltage (kV peak), tube current (mA) and accumulated fluoroscopic exposure time at the control or to the user.

The dose rate at the image intensifier input phosphor shall not exceed the relevant IEC recommended values .

should be provided with a Dose-Area Product meter or a measuring system to indicate patient exposure.

Fluoroscopic Equipment (cont)

Fluoroscopy : dynamic (real time) imaging (cont)

Light amplifier tubes, in combination with a television camera, are the most widely used image intensification systems.

Output phosphor image quality

A. Unsharpness; 1. Geometric unsharpness may be minimized by

positioning the intensifier input phosphor as close as possible to the patient.

2. Spreading of light within the input phosphor is minimized by using needle-shaped caesium iodide micromcrystals. Light emitted with each crystal is internally reflected within the crystal and exits only at its end.

3. Due to limitation of electronic focusing, it results in a slight divergence of and the electrons hit output phosphor over a finite area rather than a point.

Output phosphor image quality –con--

B. Noise;1. Quantum mottle, loss of image quality due

quantum effect is minimized by ensuring that the input phosphor has a high quantum detection efficiency.

2. Structures mottle, input phosphor, photocathode and output phosphor display a graininess, which produce grainy appearance on the output phosphor image.

Alignment of caesium iodide crystal on the input phosphor

The light-pipe principle operating in a caesium iodide crystal. Lateral spread of light is minimized by internal reflection.

Imperfect electron focusing in an image intensifier. Focusing tents to deteriorate toward the edges.

Output phosphor image quality –con--

C. Resolution • The output phosphor image is only 2.5-3.5 cm in

diameter and must be magnified before it is displayed to observer.

D. Distortion • The electron image or pattern created as electrons

from the photocathode, should be duplicated in miniature at output phosphor, any deviation from this pattern results distortion of the intensified image.

Thank you