Radiation Biology Chapter 11

Inherent filtration

the glass envelope encasing the x ray tube, the insulating oil surrounding the tube, and the glass window in the tube housing

Half value layer (HVL)

The thickness of a designated absorber (customarily a metal such as aluminum) required to decrease the intensity of the primary beam by 50% of its initial value

Diagnostic type protective tube housing 

Require to safeguard the patient and imaging personnel from off focus, or leakage radiation by restricting the emission of x rays to the area of the useful, or primary beam 

Spacer bars 

devices that project downward from the x ray tube housing of some collimators to prevent the collimator from being closer than 15cm to the patient 

Added filtration

thin sheets of aluminum of a millimeter r sub- millimeter thickness generally located outside the glass window of the x ray tube housing above the collimator shutters

Control panel or console

Where technical exposure factors such as mA and kVp are selected and seen on indicators by the operator

Scatter radiation 

All the non useful image formation radiation that arises from the interaction of an x ray beam with the atoms of a patient or any other object in the path of the beam 

Positive beam limitation (PBL)

Purpose is to restrict the size and shape of the x ray beam so it does not exceed the size and shape of the selected image receptor

Computed Radiography (CR)

Term used for x ray systems that generate images using the process of photostimulable luminescence (PSL)

Radiographic beam defining system 

consists of two sets of adjustable lead shutters mounted within the collimator at different levels, a light source to illuminate the x ray field and permit it to be centered over the area of clinical interest and mirror to deflect the light beam toward the patient to be imaged 

High level control fluoroscopy (HLCF)

An operating mode for for state of the art fluoroscopic equipment in which entrance radiation levels are substantially higher than those normally employed in routine procedure. this higher exposure rate or entrance dose rates allow the examination of smaller and lower contrast objects that are not ordinarily discerned during standard fluoroscopy

carbon fiber

material commonly used in radiographic/fluoroscopic x ray room tabletop that helps reduce patient dose

Nit

a simple term for candelas per square meter 

luminance

brightness of a surface

Amorphous selenium

A photoconductor used to convert x ray energy directly into electrical signals

Mobile (portable) x ray unit 

equipment that should be used to perform radiographic procedures only on patients that cannot be transported to a fixed radiographic installation

Off focus radiation

x rays emitted from parts of the tube other than the focal spot

Last image hold feature for dose reduction

Allows the fluoroscopist to see the most recent image without exposing the patient to another pulse of radiation

DR

The process of recording an electronic image on a flat panel detector in a digital form that may be transferred directly to a computer without further processing or scanning

Source too image receptor distance (SID)

the distance from the anode focal spot to the radiographic IR

Desquamation

sloughing off of skin cells

Radiographic grid 

device that improves radiographic contrast and visibility of detail by selectively removing scattered x rays, although increases patient dose 

Useful or primary x ray beam

x rays emitted through the x ray tube window or port

Aluminum

metal most widely selected as a filter material for general purpose radiography

Digital image 

image produced by computer representation of anatomic information and displayed on a monitor