x-ray image forming

- SOURCE OF ELECTRONS

-ACCELERATION

-DECCELERATION

XRAY PRODUCTION

REQUIREMENTS

Characteristic x-ray

are emitted when outer-shell electrons fill a vacancy in the inner shell of an atom, releasing X-rays in a pattern that is "characteristic" to each element.

Bremsstrahlung

mean "slowed down radiation ". These are x-rays thatresults from braking of projectile electrons by the nucleus. Electrons are slowed and direction is changed by the nuclear force field.

Law of conservation

energy cannot be created or destroyed, but it can be transformed from one form to another

Energy depends :

1. energy of the incoming e kvp ( tube potential) = kEv ( Maximum Bremsstrahlung)

2. depends how close the incoming e- to the nucleus

X-RAY ABSORPTION

THE ENERGY OF THE PRIMARY BEAM IS DEPOSITED WITHIN THE ATOMS COMPRISING THE TISSUE

PHOTO ELECTRIC EFFECT

COMPLETE ABSORPTION OF THE INCOMING PHOTON

Scattering

OCCURS WHEN AN INCOMING PHOTON LOSES SOME BUT NOT ALL OF ITS ENERGY, THEN CHANGES ITS DIRECTION

Type of tissue

Bone, fat, air

The thorax

is an anatomic area of high subject contrast because there is great variation in tissue composition.

Low contrast

FEWER DIFFERENCES IN RADIATION ABSORPTION

High contrast

RESULTS IN GREAT DIFFERENCES IN RADIATION ABSORPTION BETWEEN TISSUES.

Contrast resolution

DESCRIBES THE ABILITY OF AN IMAGING RECEPTOR TO DISTINGUISH BETWEEN OBJECTS HAVING SIMILAR IN SUBJECT CONTRAST.

Subject contrast

IS A RESULT OF THE ABSORPTION CHARACTERISTICSOF THE ANATOMIC TISSUE RADIOGRAPHED AND THE QUALITY OF THE XRAY BEAM (KVP)

Image contrast

THE RADIOGRAPH MUST EXHIBIT DIFFERENCES IN THE BRIGHTNESS LEVELS OR DENSISTIES IN ORDER TO DIFFERENTIATE AMONG THE ANATOMIC TISSUE

Absorbed radiation

CREATES INCREASED BRIGHTNESS OR WHITE

Transmitted radiation

CREATES DECREASED BRIGHTNESS OR BLACK

Tissue thickness

XRAYS ARE ATTENUATED EXPONENTIALLY AND GENERALLY REDUCED BY -50% FOR EACH 4 TO 5 CM