Advances Image acquisition- unit 1 Chapter 22 DR-Flat panels, CCD, CMOS

what are the 2 types of radiography systems?

CR and DR

what does CR stand for and what does it use?

computed radiography- photostimulable phosphor imaging plates

what does DR stand for and what does it use?

flat panel detecors, charged coupled devices and complementary metal oxide semiconductors

what is detector element abbreviated as?

del (or dexel)

what is the typical size for detector elements?

100 microns (0.100 milimeters)

what are the detector elements aranged in?

active matrix array AMA

what is an active matrix array?

a flat layer of elements in a matrix

what does each layer of AMA contain?

its own thin film transistor

what do these thin AMAs lead to?

flat panel technology

what is a del?

a hardware device for detecing radiation

what is a voxel?

a volume element within the patient

what is a pixel?

a picture element in the final image or on a monitor

how to form a DR image?

info from different voxels within the patient is collected by the dels of the imaging machine, and computer processed to become pixels of the final image

what are the 3 components of a del?

capacitor, thin film transistor, semiconductor detection surface

what does a capacitor do in a del?

stores charge

what is the TFT thin film transistor in a del?

acts as a switch, allows capacitor to relase charge

what is the semiconductor detction surface sensitive to?

xrays or light

what will the semiconductor detection surface be sensitive to if it is made of selenium?

xrays

what will the semiconductor detection surface be sensitive to if made od silicon?

light

what is the efficiency factor?

a dels efficiency which is a physicist measurment, DQE (detective quantum efficiency)

what is the fill factor?

the percentage of a dels square area devoted to the semiconductor detection surface

what does a higger fill factor provide?

higher contrast resolution and better spatial resolution

what are the 2 types of flat panel detectors?

indirect and direct conversion

what fill factor does a smaller del have?

less fill factor for the detector surface

what happens with a smaller percentafe of detection surface area?

an increase in radiographics technique would be necessary

what is the first step of direct conversion of DR flat panel upon exposure?

1. xrays ionize molecules of amorphus selenium (amorphus-lacking shape)

what is the 2nd step of direct conversion of Dr flat panel upon exposure?

top and bottom electrodes have opposite charges

what is the 3rd step of direct conversion of DR flat panel upon exposure?

since selenium is ionized, freed electrons are attracted to one electrode, and positively charges particles are attracted to the other

what is the 4th step of direct conversion of DR flat panel upon exposure?

electrons from an electrode accumulate in the capacitor, the amount of charge stored will eventually be represented as the pixel value for each pixel

what is the 5th step of direct conversion of DR flat panel upon exposure?

TFT acts as a switching gate to release the charge when the del is ready to be read by the computer

what are the main differences between indirect and direct conversion systems?

indirect uses amorphus silicon not selenium

indirect absorbs light

indrect- entire AMA of dels is overlaid with scintillation layer made of cesium iodide

what is a scintillation layer?

gives of light when exposed to xrays

what is the 1st step of indirect conversion of DR flat panel upon exposure?

the phosphor screen scintillates of fluresces when exposed to xrays

what is the 2nd step of indirect conversion of DR flat panel upon exposure?

emitted light of scintillator will strike the AMA of detectors directly below

what is the 3rd step of indirect conversion of DR flat panel upon exposure?

light ionizes molecules of amporphus silicon

what is the 4th step of indirect conversion of DR flat panel upon exposure?

top and bottom electrodes have opposite charges

what is the 5th step of indirect conversion of DR flat panel upon exposure?

Since silicon is ionized freed electrons are attracted to one electrode and positively charges particles are attracted to each other

what is the 6th step of indirect conversion of DR flat panel upon exposure?

electrons from an electrode accumulate in the capacitor, the amount of charge stores will eventually be represented as the pixel value for each pixel

what is the 7th step of indirect conversion of DR flat panel upon exposure?

TFT acts as a switching gate to release the charge when the del is ready to be read by the computer

in the AMA what is the array of dels?

criss-crossed by wires calles gate lines and data lines

what are gate lines controlled by?

address driver, which controls the order in which the dels are read out

what happens when voltage is applied to the gate line?

the TFT gates open in sequence and dump their charge into a data line

what does this surge of charge allow?

flow to an amplifier then to the computer through an anaolg digital converter ADC

what does direct conversion of flat panel systems produce better than indirect?

higher spatial resolution

why do direct conversion panels create higher spatial resolution?

because there is no spreading of light

what do0es indrect conversion do better than direct conversion?

results in less patient does

what does indirect conversion create less patient dose than direct conversion?

because of the amplifying effect of converting xrays into light

what does the glowing light of the scintillator get channeled through?

fiber optic cables to CCD array

what is a fiber optic cable?

uses glass thread to transmit light

what des CCD convert the light into?

electrical signal, which is converted into a digital signal

what is different about a CMOS compared to CCD?

each pixel has its own sensor

what is the image production with CMOS?

1. screen scintillator glows when xrays absorbed

2. the glowing loght of the scintillator is channeled through fiber optic cables

3. each pixel has its own CMOS sensor

4. CMOS converts the light into an electrical signal, which is converted into a digital signal

what creates superior image CCD or CMOS?

CCD

which is cheaper CCD or CMOS?

CMOS

what does CCD do in reading image compared to CMOS?

CCD reads all eletrical charges in order

CMOS has sensors for each indivicual del

what happens when the DQE is more efficient?

lower dose and lower techniques

what happens when its not efficient?

higher dose higher techniques

what is most ideal in the semi conductor detection surface area?

high fill factor with small dels pixels