Some special imaging process

1- Xeroradiography2- Copying Radiography3- Subtraction

Xerography An image-recoding process in which the

sensitive material is a plate carrying an electrical charge on its surface. When light falls on the surface the charge is released. The plate is dusted with a special powder and image is formed by the powder being attracted and retained in charged area.

1- XeroradographyXeroradiography is not a process requiring

any specialized x-ray equipment; it is only a different method of recording an x-ray image.

It depends upon the photoconductive behaviour of a selenium plate and substitutes a photoelectric process for photochemical one associated with the use of a film.

Photoelectric and photochemical responses

Selenium Plate Is an insulator in the dark, become

conductive when exposed to light or x-ray.If the plate is given a superficial electric

charge, it is capable of remaining of retaining this charge for a period of hours.

In charged condition, expos of the plate to light or x-rays effect conduction in exposed area.

1- conditioner

Two machines are necessary for xergraphy

The main features of the conditionerA – a storage box containing xergraphic plate.B, C- a plate (B) passes form storage box

through a small oven (C) which removes any residual charge; the plate then to storage elevator (D).

E- insertion of an empty cassette initiates the charging process.

F- an ionizing device which charges the surface of the plate after it leaves the storage elevator and before it enters the open cassette.

2- processor

•I – a rotating brush which cleans the plate before H- a third ionizing device which loosens any powder remaining on the plate after transfer.it enters a storage box.

•J – the paper passes through an oven (J) which fuses the power image to the paper

The main features of the processor for xergraphyA- the cassette containing the exposed plate.B- the plate is transported to a development

chamber, where developer powder (toner) is sprayed on its surface.

C- D paper is removed from the paper tray (C) to a position (D) for contact with powder plate.

F- an ion- emitting device, the effect of which is to loosen the powder on the plate, preparatory to its transfer.

G- another ionizing device which gives the reverse side of the paper a charge of opposite polarity.

Xeroradiograph of female breast

Copying RadiographTo copy radiograph is produce a second from

the first;It may be Smaller in size than the first (miniaturized)The same size (facsimiles)large in size (enlargement)

Duplicate film (copy film):

Is single emulsion film that is exposed to ultraviolet light or blue light through existing radiograph to produce a copy.

Duplicate film is direct positive film.

Used in angiography, although with the increasing application of digital fluoroscopy, its use is declining.

Subtraction film single emulsion, and there are generally two types;

(a) One type to prepare the subtraction mask.(b) One to accommodates the superimposed

image of the original radiograph and subtraction mask.

Subtraction film has high contrast to enhance existing subject contrast

Subtraction film

conventional subtraction

The plain film

The subtraction mask.

The angiogram

The subtraction mask

The plain film

The subtraction mask

The angiogram

The subtracted image

Digital subtraction angiography

Coronary artery

Digital imaging technology (cont)

The technique of digital subtraction angiography (DSA), based on digital image processing, allows enhanced visualization of blood vessels by electronically subtracting unwanted parts of the image.

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