BASIC PRINCIPLES OF DIGITAL RADIOGRAPHY

An image acquisition process that produces an electronic image viewable and manipulable on a computer.

Digital Radiography

Devices used in DR that convert x-rays to charge for digital image processing, using direct or indirect conversion.

Flat Panel Detectors

what type of capture converts x-ray photons to electrical signals

Direct Capture

What type of capture converts the incoming x-ray photons first to light then electrical signal to the final digital image

Indirect Capture

Advantages of DR

Lower patient exposure due to low imaging failure rate

high speed of image acquisition,

excellent image quality, and

high-speed workflow.

Disadvantages of DR

Limited flexibility for difficult views and

high initial investment costs.

A matrix of picture elements or pixel

Digital Image

Box of cells with numeric value arranged in rows and columns

Matrix

Represents the level of brightness or intensity at the location in the image

Numeric value

TRUE or FALSE. An image is formed by a matrix of pixels

True

TRUE or FALSE. The size of the matrix is described by the number of pixels in the rows and columns

True

The basic unit of a digital image, capable of representing various shades of gray in the matrix.

Pixel

Formula for Pixel Size

Pixel Size = FOV/Matrix Size

It refers to the number of pixels present on a digital image

Pixel Density

The distance between the center of one pixel to one adjacent pixels

Pixel Pitch

Relationship of Pixel Pitch and Pixel Density

Inversely Proportional

Relationship of Pixel Density and Pixel Pitch to Spatial Resolution

Direct Proportional for Pixel Density and Spatial Resolution

Inversely Proportional for Pixel Pitch and Spatial Resolution

The number of bits per pixel that determines the shades of gray in an image.

Bit Depth

Most digital radiography systems use an ____ of bit depth

8, 10, or 12 Bit Depth

It is determined by the analog to digital converter

Bit Depth

A square arrangement of numbers in rows and columns.

Matrix

Each box within the matrix corresponds to: (2 answer)

A specific location in the image

A specific area of the patient’s tissue

The extent of the patient imaged in the matrix

Field of View (FOV)

TRUE OR FALSE. Smaller FOV, the greater the amount of body part is included in the image

False

TRUE or FALSE. Changes in either the FOV or the matrix size will change the pixel size

True

TRUE OR FALSE. Matrix Size and the FOV are dependent

False

A measure of how efficiently a digital detector converts x-rays into a useful image.

Detective Quantum Efficiency (DQE)

The DQE for a perfect digital detector is?

1 or 100%; no loss of information

A measure of the amount of exposure on the image receptor

Exposure Index

The ability of the imaging system to allow two adjacent structures to be visualized as being separated or distinctness of an image to the image

Spatial Resolution

Refers to the smallest object that can be detected in an image; term usually used in digital imaging

Spatial resolution

The ability to differentiate shades of gray, indicating the imaging receptor's capability to distinguish similar contrasts.

Contrast Resolution

The principal descriptor for contrast resolution is

Dynamic Range

The number of gray shades an imaging system can produce; the ability of the detector to capture accurately the range of photon intensities that exit the patient

Dynamic Range

Dynamic range of digital imaging system is identified by the?

Bit capacity of each pixel

A method of describing the strength of radiation exposure compared to noise in a digital image.

Signal-to-Noise Ratio (SNR)

TRUE or FALSE. Decreasing the SNR improve quality of the digital image

False

Solid-state image receptors that convert x-ray photons to electrical charges for storage and readout; also called Digital Receptors

Flat Panel Detectors

What integrated into the flat panel device

Signal Storage

Signal readout

Digitizing electronics

Are highly dose-efficient and provide quicker access to images

Flat panel System

Three layers of Thin Flat Panel Detector for Indirect Capture

Scintillation Layer

Photodiode Layer

Thin Flat-Panel Transistors

The layer that converts X-rays into small bursts of light energy, is typically made from Cesium Iodide or Gadolinium Oxysulfides.

Scintillation Layer

The preferred material of the Scintillation Layer; has a needlike structure that produces more focused light beam that increases spatial resolution

Cesium Iodide

A layers that converts incoming light photons into electric charge, usually made of Amorphous Selenium.

Photodiode Layer

Amorphous means

without shape or form

What is the process of making the Photodiode Layer; where the amorphous is liquid that can be painted onto a supporting surface

Plasma-Enhanced chemical vapor deposition

It is the both the capture element and coupling element. Limits diffusion of electrons and maintains excellent spatial resolution

Amorphous Selenium

Thickness of Amorphous Selenium

High approx. 200 um thick; sandwich between charged electrons

Temporarily stores electrical charges by the capacitors before digitization and processing.

Thin Flat Panel Transistor (TFT) Layer

TFT comprised of an array or matrix of

Digital elements (DEL)

Detector elements has three components

TFT

Capacitor

Sensing Area

Temporarily store the electrical charge

Capacitors

Acts to open and close the analog signal leaving each DEL

TFT/Switch

An oldest indirect conversion radiography system to acquire a digital image; it is a silicon-based semiconductor

Charged Couple Device (CCD)

Charged Couple Device developed in what year

1970s; highly sensitive device for military use

CCD Three principal advantage

Sensitivity; respond to low lvls of visible light

Dynamic Range; detects from very dim light to intense light

Size; 1- 2 cm

Thin Flat Panel Detectors for Direct Capture has two layers

Semi-conductor

Thin Film Transistor

Determines Pixel density of digital image

Pixel Pitch