Ch. 22 Digital Radiography/Flat-Panel Detector Systems

When were DR systems produced?

1995

eliminated cassettes and have reduced numbers of steps required to perform exams

digital radiography

What type of detectors are used in digital radiography?

1. Direct

2. Indirect

uses a photoconductor

direct detector

uses a scintillator

indirect detector

capable of converting light into an electronic signal in direct detector

photoconductor (direct)

converts incoming x-ray photons to light

scintillator (indirect)

converts light photons to an electronic signal in indirect detector

photodetector

Indirect DR systems use either...

charge couple device (CCD)

or

amorphous silicon used with a thin-film transistor (TFT)

capable of directly converting incoming xray photons to an electronic signal

direct detectors

used to describe both amorphous silicon and amorphous selenium

flat panel detector

uses amorphous silicon

indirect

uses amorphous selenium

direct

There are two types of indirect DR detectors. What are they?

charge couple device and amorphous silicon with a TFT

both use a scintillator to convert light photons to an electronic signal

what is a-Si:H?

amorphous silicon

What is the atomic # of silicon?

14

cannot directly convert x-rays into an electric charge but it does work as a light detector to capture fluorescent light

amorphous silicon (a-Si:H)

What can be used as a scintillator?

1. cesium iodide (CsI)

2. rare earth intensifying screen composed of gadolinium oxusulfide (Gd2O2S)

to minimize light spread, _____ is manufactured as structured crystals in the form of needles or columns 10-20 micrometers in diameter

cesium iodide (CsI)

turbid phosphor where crystals are deposited as fine powdered particles

gadolinium oxysulfide

once the light reaches the amorphous silicon, it is converted into electrical charges that are then depositied on a ...

thin film transistor (TFT)

collects the charges by either the selenium or silicon as an array or matrix of pixel size detector elements (DEL)

thin film transistor (TFT)

has a fixed dimension in an x- and y- orientation

detector elements (DEL)

once the DEL receives exposure and collects signal, it then can be references as a _____ due to its bit depth characteristics

dexel

positioned in a matrix that allows the charge pattern to be read out on a pixel-by-pixel and column-by-column basis

DEL

includes the sensing area, the capacitor, and TFT

each pixel

What does each pixel include?

1. sensing area

2. capacitor

3. TFT

refers to the sensing area compared to the non-sensing area and can be expressed as a percentage

fill factor

device that is capable of converting visible light into an electric charge and storing it in a sequential pattern. This stored charge can then be released line by line to the ADC

photodetector

What is an example of a photodetector?

charge couple device (CCD)

What does CMOS stand for?

complementary metal-oxide semiconductor

semiconductor used in direct DR systems, with excellent photon detection ability

amorphous selenium (a-Se)

completed in a line-by-line fashion, and it involves switch lines, data lines, and voltage controls

readout scheme

used to complete the readout process

electronic circuitry

In DR, only the ____ are used for the image data

DEL

Performed during pre processing in DR to correct bad detector elements, so that artifacts aren't showed up

system calibration

For DR, does image display optimization happen during pre or post processing?

post processing

DR detectors have two general classifications. What are they?

1. portable detectors

2. integral detectors

mobile detector and can be carried carried like a film-screen cassette

portable detector

detector built into the design of a radiographic table or upright holder

integral detector

the earliest style of portable DR detectors with a grid weighed as much as ____lbs

13 lbs

earlier versions of flat-panel technology required an electrical connection between the panel and xray system through wires known as _____, from the panel to the xray generator

tethers

what have tethered DR panels been replaced with?

wireless technology and transmission to a local area network (LAN)

works by sensing the presence of radiation during the first 1-2 milliseconds of the xray exposure

auto detection technology

in order to capture an electronic signal from xray exposure, the active electronic layer of the detector must have...

a small electrical potential placed on the surface

this is needed in order to capture the electrons and holes liberated (freed) during exposure

the presence of irradiation triggers the collection of electrons for image acquisition

trigger panel

in some panels, a ______ mechanism is inserted to measure the amount of force a panel has encountered during usage

internal sensor