Key Terms - Fauber, Chapter 4: Digital Imaging, Chapter 4 Digital Imaging

Latent image

Image that is stored as digital data and must be processed by a computer for viewing on a display monitor

laser beam

A

Brightness and contrast

When displayed on a computer monitor, there is tremendous flexibility in terms of altering these two aspects of a digital image

optical scanner

B

Matrix

Image displayed as a combination of rows and columns (array)

photomultiplier tube

c

Pixel

Smallest component of a matrix; size measured in microns

light guide

d

amplifier

e

Bit

Each 0 and 1 of a computer's binary system; refers to the computer's basic unit of information

Byte

8 bits combined

analog to digital converter

f

Bit depth

Number of bits that determines the amount of precision in digitizing the analog signal and therefore the number of shades of gray that can be displayed in the image

motor

g

Pixel density

Number of pixels per unit area

imaging plate

h

Spatial frequency

The unit of line pairs per millimeter (lp/mm)

Improved spatial resolution

for a fixed matrix size CR system using a smaller IP for a given FOV results in?

Modulation Transfer Function

Measure of the imaging system's ability to display the contrast of anatomic objects varying in size; value will be between 0 (no difference in brightness levels) and 1.0 (maximum difference in brightness levels)

decreased spatial resolution

increasing the size of the IP for a given FOV results in?

Cassette

Part of a digital image receptor that houses the imaging plate

1: x-ray converter

2: houses the thin film transistor (TFT)

3: glass substrate

Layers of the flat panel detectors

Imaging plate (IP)

Part of a digital image receptor that radiation interacts with, where the photon intensities are absorbed by the phosphor and stored to produce a latent image

square detector elements (DEL)

TFT is divided into?

Luminescence

The emission of light when stimulated by radiation

a capacitor to store electrical charges and a switching transistor for readout

DEL have what 2 things?

T

The pixel is smaller then the DEL (T/F) and can only capture a percentage of the x-rays reaching the detector.

Photostimulable phosphor (PSP) in CR

The phosphor layer composed of barium fluorohalide crystals doped with europium

Photostimulable luminescence

The phenomenon in which a photostimulable phosphor emits visible light when stimulated by a high-intensity laser beam

~80% and fill factor

what is the percentage of x-ray capture called in DR flat panel systems and what is it known as

Sampling frequency

Characteristic of an analog-to-digital converter that determines how often the analog signal is reproduced in its discrete digitized form

determined by the DEL, fixed

the size and pitch of the pixel in flat panel detectors are _________ and are _________

Sampling pitch

Distance between the sampling points

limited to the DEL

spatial resolution for flat panel detector IR's is ______

Pixel pitch

Distance between the midpoint of one pixel to the midpoint of an adjacent pixel

smaller

a system that uses _______ DEL size has improved spatial resolution

Flat-panel detectors

Solid-state IRs employing a large-area active matrix array of electronic components ranging in size from 43 x 35 cm to 43 x 43 cm (17 x 14 in to 17 x 17 in)

Scintillation phosphor

A

Fill factor

The percentage of x-ray capture by a flat-panel detector

amplifiers/ multiplexer

b

Scintillator

Used by indirect conversion detectors to convert exit radiation into visible light; phosphor-type material such as cesium iodide or gadolinium oxysulfide

A/D converter

c

Dynamic range

Ability of a digital imaging detector to accurately capture the range of photon intensities that exit the patient

computer

e

glass substrate

f

Detective quantum efficiency (DQE)

Measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image

Signal-to-noise ratio (SNR)

Method of describing the strength of the radiation exposure compared with the amount of noise apparent in a digital image

address drives

G

Quantum noise

Result when too few x-ray photons are captured by the IR to create a latent image

a-Si (amorphous silicon)

H

Contrast-to-noise ratio (CNR)

Method of describing the contrast resolution compared with the amount of noise apparent in a digital image

indirect

what conversion detectors use a scintillator to convert the exit radiation into visible light?

Direct Conversion Detector

what conversion detector uses an Amorphous selenium-coated detector converts exit radiation directly into electrical charges.

higher

structured scintillator phosphors produce images with ______ spatial resolution.

Scintillator type detector converts exit radiation into visible light.

Photodetector converts visible light to proportional electrical charges.

Indirect conversion detector is a two stage process that includes what?

Exposure indicator

Provides a numeric value indicating the level of radiation exposure to the digital IR

Deviation Index (DI)

A value that reflects the difference between the desired or target exposure to the IR and the actual exposure to the IR

Ambient lighting

The level of light in the room while viewing images

Luminance

Measurement of the light intensity emitted from the surface of the monitor and is expressed in units of candela per square meter (cd/m^2)

Electronic masking

Altering, or shuttering, regions of the image after it has been processed

Window level

Sets the midpoint of the range of brightness visible in the image

Grayscale

The number of different shades of gray that can be stored and displayed by a computer system

Contrast resolution

The ability of the imaging system to distinguish between objects that exhibit similar densities because they attenuate the x-ray beam similarly

Window width

A control that adjusts the radiographic contrast

Equalization

Postprocessing function whereby underexposed areas (light areas) are made darker and overexposed areas (dark areas) are made lighter

Picture archival and communication system (PACS)

A computer system designed for digital imaging that can receive, store, distribute, and display digital images

Digital Imaging and Communications in Medicine (DICOM)

A communication standard for information sharing between PACS and imaging modalities

Scintillation layer

The phosphor layer is also known as

Scintillation is made of

Cesium iodide or gadolinium

Cesium iodide is more preferred

Creates a smaller exposure and improves spatial.

What aspect of a cassette-less image receptor system creates bursts of light?

Scintillation layer

Steps to converting a latent image in CR

The reader is scanned with a helium neon laser or diode to release the stored energy

Releases that energy and returns to a low state

Excess emitted is visible light

Which is sent to the PMT to be quantitlzdc

PMT function

Collects amplifes and converts light into an electric single

sampling frequency

how often the analog signal is reproduced in its discrete digitized form

sampling pitch

distance between the sampling points

Increasing the sampling frequency results in

Smaller sampling and pixel pitch better spatial image

Decreasing sampling frequency results in a

Larger sampling and pixel pitch decreased spatial

Flat-panel detectors that use indirect conversion technology convert

X-rays to visible light

the layers of a flat-panel indirect capture detector include the following:

scintillator phosphor, photodiode, TFT array

Smaller DELs =

higher resolution

Indirect Conversion Detectors

Use scintillators such as cesium iodide to convert exit radiation into light

direct conversion detectors

Use amorphous selienium to convert edit radiation into a electrical charge

single to noise ratio (SNR)

Strength or ratio exposure

Contrast to Noise Ratio (CNR)

a method of describing the contrast resolution with the amount of noise apparent in a digital image