Chapter 5 and 6 Study Guide (old questions and clover)

What is a thin-film transistor?

a photosensitive array of small DELs that can convert photons into electric charges

What is pixel fill factor?

the percentage of the pixel face that is made of the sensing component

What are the 2 sensing components?

amorphosilicon and amorphoselenium

What is another name fro gain callibration?

flat fielding

What is tiling?

how the DEL’s come together to form a matrix

Which modality is most closely linked to digital tomosynthesis

Mammo

When were direct and indirect capture systems introduced?

1995

What is the bucket brigade scheme?

Is a readout system used by CCD to move electrons down by row

What is the blooming effect?

Occurs when the detector element overfills and electrons spill into adjacent detector elements

What are built into the CCD system to reduce the blooming effect?

Overflow drains

Which scintillator is generally considered the most rugged?

Gadolinium Oxysulfide

In CCD systems, dropping the temperature by __________ can reduce dark noise by a factor of 100

40 degrees F

What are photoconductors?

Convert x-rays into electrical signal

What photoconductor do we use today?

amorphoselenium

What material produces light when it absorbs x-rays?

scintillators

What two types are commonly used?

Gadolinium Oxysulfide and Thallium-doped Cesium Iodide

Which scintillator is unstructured, or turbid?

Gadolinium

In a structured scintillator, phosphor crystals are grown in what pattern?

needle-like columns

Which scintillator has very little light spread, in turn, increasing resolution and efficiency?

Cesium Iodide

What may cause dead pixels in a flat-panel detector?

Dust, scratches, static, chemical erosion, and age

How can dead pixels be masked?

by computer programs

What is the standard that manufacturers must meet regarding dead pixels?

0.1% to 0.2%

What are some factors that may lead to image lag?

rapid succession of images, overexposure of certain areas, and limited beam attenuation

T/F: underexposure leads to image lag

False

T/F: Dead pixels at the edge of the detector are easily identified.

False

What is the purpose of gain calibration or flat-fielding?

To remove inherent detector artifacts

What is the purpose of offset correction?

To remove the inherent signal that remains in the detector (reduces image lag)

What is the purpose of fiberoptics in CCD?

Focuses the signal from the scintillator to the CCD chip

What are the three most common types of noise in CCD systems?

Statistical (quantum mottle), amplification, and dark/current

What do lenses help with?

focusing the light and deliver it to the chip

T/F: detector elements contain voltage gates that open and close at readouts to allow the flow of electrons

True

What is the most common noise in ay digital system?

electronic noise

What are the primary uses of CCD today?

FLUORO, mammo, and digital

Which indirect capture system, CCD or CMOS, uses the most energy?

CCD (about 110 times more than CMOS)

Which semi-conductor is the most frequently used for integrated circuits?

Silicon

Where is the CCD attached in fluoro?

to the output phosphor

What did CCD replace?

TV tube

Reducing the phosphor output image to the size of the active area of the CCD is known as __________

demagnification

T/F: CCD’s have a lower fill factor than CMOS

False, they have a higher fill factor

Which indirect system utilizes the concept of demagnification?

CCD

Who developed CMOSs?

NASA

A measurement of the amount of electrons produced relative to the incident light from the scintillator is known as _____

Quantum efficiency

Will quantum efficiency affect detective quantum efficiency?

Yes

What are advantages of CCD?

cheap, simple.modular, easy to repair/replace

What is a disadvantage of CCD?

demagnification - reduces DQE

What is the purpose of applying a dopant to a semi-conductor?

To turn a semiconductor into a full conductor to be able to convert electric charges

In CCD systems, the number of __________ produced is relative to the amount of light absorbed.

electron-hole pairs

Does kVp affect DQE, if so, in what way?

Yes (increasing kVp means you must decrease mAs which will decrease signal)

• Increased kVp = decreased DQE

• Decreased kVp = increased DQE

Does spatial frequency affect the modulation transfer function?

Yes, a lower frequency will increase MTF

Loss of detail in a digitally process image

• is extremely minimal compared with film

• has almost no impact on the image

• occurs because of the number of conversions

• is equal to film

occurs because of the number of conversions

Raw data used to form the image histogram is compared with

• the last histogram of that anatomic part

• a normal histogram referenced by the computer

• all histograms stored for that anatomic part

• none of these options

a normal histogram referenced by the computer

An archive query retrieves images from the PACS based on any of the following except:

• patient name

• technologists employee number

• anatomical area

• exam date

technologists employee number

T/F: the shape of a histogram is anatomy specific

True

Dynamic range in radiographic imaging is defined as the:

• number of x-ray photons striking the IR

• Range of exposures that produces quality images at an appropriate patient dose

• Sharpness of structural lines recorded in the image

• Range of exposures that can be captured by an IR

Range of exposures that can be captured by an IR

Exposure latitude is defined as the:

• number of x-ray photons striking the IR

• Range of exposures that produces quality images at an appropriate patient dose

• Sharpness of structural lines recorded in the image

• Range of exposures that can be captured by an IR

Range of exposures that produces quality images at an appropriate patient dose

The specification for an x-ray imaging system indicate the detector can capture exposure values from 0.1 microgray to 1,000 microgray. This quality of the x-ray system is called

• spatial resolution

• exposure latitude

• quantum mottle

• dynamic range

dynamic range

What is another name for MTF?

• Image fidelity

• Image orientation

• Tube potential

• DQE

Image fidelity

An MTF score of ____ indicates a perfect image

1.0

Which of the following was produced using a digital radiography system with the smallest bit depth?

Image C

Which 3 of the following are included in indirect capture systems?

• photodiode

• scintillation layer

• input phosphor

• TFT array

• Photoconductor

Photodiode, Scintillation layer, and TFT array

Which component of an indirect capture converts incident X-ray photons into visible light?

scintillation layer

Which component of an indirect capture flat-panel detector converts visible light into electrons?

• TFT array

• Scintillator

• Photodiode

• Amorphoselenium

photodiode

Flat panel detectors typically use a TFT. This device function to:

• convert x-rays into light

• convert light into electrons

• collect electrical charge

• convert electrical charge into a digital signal

collect electrical charge

Which 2 flat-panel detector components can collect and convert light into an electrical signal

• ADC
  TFT array

• Photodiode

• CCD

Photodiode and CCD

Which element used in the construction of a digital x-ray detector is able to convert x-ray photons directly int a electrical signal?

amorphoselenium

Which device acts as a switch within a detector to release the electric charge collected by the DEL?

TFT

Cesium iodide is the preferred material for the scintillation layer because it can be formed into:

• columns that focus x-ray photons

• squares that focus x-ray photons

• columns that focus light photons

• squares that focus light photons

columns that focus light photons

In a CCD system, the scintillation layer is connected to teh CCD sensor chips by what?

lenses and fiber optics

When compared to CR, DR is:

• faster and produces lower quality images

• slower but produces lower quality images

• faster and produces higher quality images

• slower but produces higher quality images

faster and produces higher quality images

The digital image receptor is comprised of small elements called?

• Pixels

• Voxels

• Display monitor matrix

• DELs

DELs

Which of the following makes up a single DEL?

• capture area, storage capacitor, and TFT gate

• Top electrode, detection layer, and bottom electrode

• TFT gate, detection layer, and storage capacitor

• Top electrode, capture area, and bottom electrode

capture area, storage capacitor, and TFT gate

The capture area of a DEL includes which of the following layers?

• top electrode, detection layer, and bottom electrode

• top electrode, capture area, and bottom electrode

• TFT gate, detection layer, and storage capacitor

• Capture area, storage capacitor, and TFT gate

top electrode, detection layer, and bottom electrode

What part of the DEL detects radiation?

• TFT gate

• storage capacitor

• capture area

• scintillation layer

capture area

The storage capacitor of the DEL stores what type of charges?

positive

What is the percentage of the DEL devoted to the detection layer called?

Fill factor

What is the relationship between fill factor and spatial resolution?

• inversely proportional

• directly proportional

directly proportional

Which of the following is created on an IR by the arrangement of DELs into rows and columns?

Matrix

Which of the following would lead to an increase in patient dose

• increased DEL size

• decreased fill factor

• decreased storage capacitor

• decreased TFT gate

decreased fill factor

Which of the following will produce the highest spatial resolution?

• large matrix and high pitch

• large matrix and low pitch

• small matrix and low pitch

• small matrix and high pitch

large matrix and low pitch

What does ARRT define as a DR system?

• uses only computed radiography

• uses film-screen receptors

• uses detectors that directly capture and read out an electronic image signal

• requires cassette-based imaging

uses detectors that directly capture and read out an electronic image signal

T/F: TFT flat panel detectors require a cassette for image acquisition

False

Which material is used in direct conversion flat panel detectors?

• Gadolinium

• Cesium Iodide

• Amorphosilicon

• Amorphoselenium

amorphoselenium

T/F: indirect conversion is a two-step process involving light production before electrical signal conversions

true

T/F: higher fill factor in a detector leads to improved DQE and reduced patient dose

True

In a TFT array, what determines the shade of gray in a pixel?

• amount of stored electrical charge

• voltage of the control line

• type of scintillator

• number of xrays produced

amount of stores electrical charge

T/F: direct conversion generally has lower spatial resolution than indirect due to light spread

False

T/F: gadolinium improve spatial resolution because they limit light spread

False

In CCD systems, X-ray photons are directly converted into electrical signals without light production

False

T/F: CMOS technology uses very little power compared to CCD

true

T/F: CMOS sensors generally have higher light sensitivity and resolution than CCD sensors

False