To study the basics of fluoroscopy

Reference book:Stewart C.bushong

By Huzaifa AtiqueSir Syed University of Engineering & Technology

Fluoroscopy:

The primary function of a fluoroscope is to perform dynamic studies; that is, the fluoroscope is used to visualize the motion of internal structures and fluids.

The purpose of this technique is to get real-time and moving images of the insides of a person by way of the fluoroscope.

If something is observed that the radiologist would like to preserve for later study, a radiograph can be made with little interruption of fluoroscopic examination. Such a radiograph is known as spot film.

Visualization of vessels is called Angiography.

The two main areas of angiography are: Neuroradiology Vascular Radiology.

And with all this procedure spot films are obtained.

During fluoroscopy the x-Ray tube is operated at less than 5mA. Normally 2 to 4mA.

Components of Fluoroscopex-ray generator x-ray tube collimator filters patient table grid image intensifier optical couplingtelevision systemimage recording

Image intensifier The image intensifier is a complex electronic device

that receives the remnant X-Ray beam, converts it into light, and increases the light intensity.

Image Intensifier TubeComponents: Glass envelope Input phosphor Photocathode Electrostatic focusing lenses Output phosphor

Glass envelope:Maintains tube vacuum to allow control of e flow, has no functional part in image formation.

Input phosphor:X-Rays that exit the patient and are incident on the image intensifier tube are transmitted through the glass envelope and interact with the input phosphor, which is cesium iodide.

When X-Rays interacts with the input phosphor, its energy is converted into a burst of visible light photons as occur on the intensifying screen.

Input phosphor Materials: 1st Generation Image Intensifiers Input phosphor - Zinc Cadmium Sulfide Output phosphor - Zinc Cadmium Sulfide. 2nd Generation Image Intensifiers

Input phosphor- Cesium Iodide (smallercrystals with greater packing density - manmade)Output phosphor - Zinc Cadmium Sulfide.

Photocathode:

It is bonded directly to the input phosphor with a thin, transparent, adhesive layer.

The photocathode is a thin metal layer, usually composed of cesium and antimony compounds, that respond to stimulation by light with the emission of electron. This process is known as photoemission.

EIectrostatic focusing lenses Located along length of the tube,

responsible for focusing the electrons across the tube from input to output phosphor. Image is reversed from input to output phosphor (right becomes left, superior to inferior). The concave input screen reduces distortion by keeping the same distance between all points on the input & output screens.

Anode

Anode is usually charged with 25 kV and is used to accelerate e across the tube (not a target) to > kinetic energy & > light produced. Collects stray e as well.

Output phosphor:The output phosphor is usually made up of zinc

cadmium sulfide crystals. Each photoelectron that arrives at the output phosphor results in approximately 50-70times

Schematic image intensifier:

The principal advantage of image-intensified fluoroscopy over earlier types of fluoroscopy is increased image brightness.

Image monitoring: Two methods are used to electronically

convert the visible image on the output phosphor of the image intensifier into an electronic signal.

1. Thermionic television camera tube2. The solid state charge-coupled device

(CCD).

CAMERA ATTACHED TO THE OUTPUT POSPHOR:

Camera: The television camera consists of

cylindrical housing, approximately 15 mm in diameter by 25 cm in length, that contains the heart of the camera, TV camera tube.

It also contains electromagnetic coils that are used to properly steer the electron beam inside the tube.

A number of such television camera tubes are available for television fluoroscopy, but the vidicon and its modified version, the Plumbicon, are used most often.

Two methods are commonly used to couple the television camera tube to the image-intensifier tube. Fiber optics. Lens system.

The simplest method is to use a bundle of fiber optics.

One advantage of this type of coupling is its compact assembly, which makes it easy to move the image-intensifier tower. This coupling is rugged and can withstand relatively rough handling.

The principal disadvantage is that it cannot accommodate the additional optics required for devices such as cine or photospot cameras.

Lens coupling: To accept a cine or photospot camera, lens

coupling is required. This type of coupling results in a much larger assembly that should be handled with care.

Working: The objective lens accepts light from the

output phosphor and converts it into a parallel beam.

When an image is recorded on film, this beam is interrupted by a beam-splitting mirror so that only a portion is transmitted to the television camera; the remainder is reflected to a film camera. Such a system allows the fluoroscopist to view the image while it is being recorded.

The video signal is amplified and is transmitted by cable to the television monitor, where it is transformed back into a visible image.