Fluroscopic ImagingImage Intensifier DesignVidicon & CCD Camera

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

patient. Purpose organ motion ingested or injected contrast agents insert stents cathetarize small blood vessels

Fluoroscopic Imaging First generation fluoroscopes consisted of an x-ray

tube, an x-ray table and a fluoroscopic screen. The fluorescent material used in screen was copper

activated zinc cadmium sulfide that emitted light in yellow-green spectrum.

A sheet of lead glass covered the screen, so that radiologist could stare directly into the screen with out having the x-ray beam strike his eyes.

Screen fluoroscence was very faint so, the examination was carried out in a dark room by the radiologist who had to adapt his eyes by wearing red goggles for 20-30 mins prior to the examination technique is now obsolete & gone.

FLUOROSCOPY

Photograph shows an early (1933) fluoroscopic system in use before the development of image intensification. An actual fluoroscopic examination with this device would have occurred in a darkened room.

Fluoroscopic Equipment

Fluoroscpic Equipment Mobile

fluoroscopic system for routine procedures during surgery

IMAGE INTENSIFIER DESIGN Image intensifier was discovered in 1950s-to produce

an image bright enough to allow cone vision without giving the pt an excess radiation exposure.

The components of an x-ray image intensifier The tube itself is an evacuated glass envelope, a

vacuum tube containing- 1.input phosphor and photocathode . 2.electrostatic focusing lens. 3.accelerating anode. 4.out put phosphor.

IMAGE INTENSIFIER DESIGN1. After an x-ray beam passes the pt it enters the image

intensifier tube the input fluorescent screen absorbs x-ray photons and converts their energy into light photons.

2. The light photons strike the photo cathode, causing it to emit photoelectrons these electrons are immediately drawn away from the photocathode by the high potential difference betn it &the accelerating anode.

3. As the electrons flow from the cathode towards the anode, they are focused by an electrostatic lens which guides them to the output fluorescent screen without distorting their geometric configuration.

IMAGE INTENSIFIER DESIGN

4.The electrons strike the output screen, which emits the light photons that carry the fluoroscopic images to the eye of the observer.

5.In intensifier tube, the image is first carried by the x-ray photons, then by the light photons, next by the electrons &finally by the light photons.

Input Phosphor & Photocathode The input fluorescent screen in image

intensifiers is cesium iodide (CsI). (older intensifier- silver activated zinc cadmium sulfide).

CsI is deposited on a thin aluminum substrate by a process called “vapor deposition”. an interesting & useful characteristic of CsI is that during the deposition process the crystals of CsI grow in tiny needles perpendicular to the substrate. There by reducing scattering.

Photocathode The photo cathode is a photoemissive metal

(commonly a combination of antimony & cesium compounds).

When the light from the fluorescent screen strikes the photo cathode, photo electrons are emitted in numbers proportional to the brightness of the screen.

The photoelectrons thus produced has to be moved to the other end of the image intensifier. This can be done using an electrostatic focusing lens and an accelerating anode.

Electrostatic Focusing Lens

The lens is made up of a series positively charged electrodes that are usually plated on to the inside surface of the glass envelope.

These electrodes focus the electron beam as it flows from the photocathode toward the output phosphor.

Electron focusing inverts & reverses the image which is called “point inversion” because all the electrons pass through a common focal point on their way to output phosphor.

The image on the output phosphor is reduced in size ,which is one of the principle reasons why it is brighter.

ACCELERATING ANODEACCELERATING ANODE : :•The anode is located in the neck of the image tube.•Its function is to accelerate electrons emitted from the photocathode towards the output screen. •The anode has a +ve potential of 25 to 35 kv relative to the photocathode, so it accelerates electrons to a tremendous velocity.

OUTPUT PHOSPHOR:OUTPUT PHOSPHOR:•The output fluorescent screen of image intensifiers is silver The output fluorescent screen of image intensifiers is silver activated zn-cd sulfide.activated zn-cd sulfide.•Crystal size and layer thickness are reduced to maintain Crystal size and layer thickness are reduced to maintain resolution in the minified image.resolution in the minified image.•A thin layer of aluminum is plated onto the fluorescent A thin layer of aluminum is plated onto the fluorescent screenscreen prevent light from moving retrograde through the tube prevent light from moving retrograde through the tube & activating the photocathode. & activating the photocathode.

Output Phosphor

The glass tube of the image intensifier is abt 2 to 4mm thick &is enclosed in a lead lined metal container protects the operator from stray radiation.

The output phosphor image is viewed either directly through a series of lenses and mirrors or indirectly through closed circuit TV.