Digital Radiography Flat-Panel Systems (Ch. 22)

Flat panel digital radiography (DR) eliminates having a ______, therefore reducing the steps for the radiographer

Cassette

DR systems use either a:

1. Direct detector with a photoconductor (one type)

2. Indirect detector with a scintillator (three types)

Direct detectors convert incoming x-ray photons to an ___________

Electronic digital signal

A direct detector uses ________ being the active layer (photoconductor) and a _________

Amorphous selenium (a-Se), thin film transistor (TFT)

_____ are used in flat panel technology for both amorphous silicon and selenium plates

TFT’s

TFT’s containing _________ are the last step of the x-ray conversion which collects the electric charge to produce an electronic readout

Detector elements (DELs)

TFT’s are set up like an array or matrix with pixel-size ______

DELs

_______ sense/collect and store image signal information and contain a switch

DELs

When DELs are filled with information, they become a ______

Dexel

Each pixel contains a “____________”, while other electronics which are not sensitive to charge

Sensing area

Fill factor

Refers to the sensing area compared to the non-sensing area (expressed as a percentage)

The fill factor has a _______ relationship with spatial resolution and contrast resolution

Direct

The ______ the fill factor, the ______ the spatial resolution and contrast resolution, compared to detectors with a lower fill factor

Higher

______ is a semiconductor with excellent x-ray photon detection ability

a-Se

The process of direct conversion contains three steps:

1. High voltage is applied to the top surface of a-Se

2. Ionization from the exposure frees the atoms from a-Se for the collection by electrodes at the bottom of an a-Se layer

3. Charges are collected by the TFT and are then read line by line to the computer for processing

Indirect detectors _______ directly convert x-rays into an electric signal

Cannot

Indirect detectors all use a ________

Scintillator

The three types of indirect detectors are:

1. Amorphous silicon (a-SI:H) with a flat panel TFT detector

2. Charged coupled device (CCD)

3. Complementary metal oxide semiconductor (CMOS)

All indirect detector systems need the ________ to change x-ray photons to light

Scintillator

All indirect detector systems must have a _______ or _______ to change light to an electronic signal

Photocathode or photodetector

The process of the indirect conversion when using amorphous silicon with a TFT contains three steps:

1. The scintillator emits light isotropically

2. Amorphous silicon (a-Si:H) acts as a light detector (photodiode)

3. Flat panel TFT detector read line by line to computer for processing

When the scintillator emits light isotropically is will be made of either two things:

1. Cesium iodide (Csl)

2. Rare-earth intensifying screen composed of gadolinium oxysulfide (Gd2O2S)

Amorphous silicon will need a relatively _____ layer to provide adequate sensitivity to photons and must be paired with a scintillator

Thicker

Amorphous silicon capture fluorescent light, and then converts that light into ____________ which are then gathered by the TFT within DELs

Electrical charges

The three disadvantages of using CMOS chips with the indirect conversion is:

1. Less stable over time

2. Yield lower quality images

3. More susceptible to noise

The DR images are processed with an algorithm selected that will use exposure field recognition, histogram analysis, and applying the ________

LUT

Flat field detectors can have bad ______, which creates artifacts

DELs

One major difference with DR processing (compared to CR) is that only exposed ______ are read and use for image data

DELs

DR panels range from $_____ to $_______

$30,000 to $80,000

The routine use of DR panels requires cleansing to prevent the spread of ________

Infection

Some DR panels can handle _____ lbs of direct weight, but only around 500 lbs if the DR panel is bending

800

Detector bag

Protects the DR panel from blood urine, discharge, scrub fluid, saline, etc