RT212 FINALS

Film-Based Radiography

- It has been the workhorse of radiology since the

discovery of x-rays by Wilhelm Conrad Roentgen in

1895

− It uses film and intensifying screens in the image

formation process

− It is considered obsolete and has been replaced by

digital radiography

1. Poor image quality

2. Increased radiation exposure

3. Limitation in contrast resolution

4. Limited optical range and fixed film contrast

5. Manual handling for archiving and retrieval in large rooms

Limitations of Film-Screen Radiography (5)

Digital Radiography

It is any imaging acquisition process that produces

an electronic image that can be viewed and

manipulated on a computer, and can be sent

through a computer network to various locations

Computed radiography and digital radiography

Digital radiography systems are divided into two types generally known ... and ...

Albert Jutras, Canada

The concept of moving images digitally was

introduced by __________ in _________ during his

experimentation with teleradiology (moving images

via telephone lines to and from remote locations) in

the 1950

Godfrey Hounsfield

One of the first uses of digital imaging was with the

introduction of the CT scanner by ____________ in the 1970s

National Aeronautics and Space Administration (NASA)

_______ used digital image processing to

process images beamed back to Earth from

the Ranger spacecraft

Paul Lauterbur

MRI was introduced commercially for healthcare

use in the early 1980s. Several companies began

pioneering efforts in the mid- to late-1970s after the

publication of an article by. ____________ in 1973

1. Data Acquisition

2. Computer Data Processing

3. Image Display and Post-processing

4. Image Storage

5. Image and Data Communications

6. Image and Information Management

Major Components of a Digital Radiography Imaging

System:

Data Acquisition

− It refers to the collection of x-rays transmitted

through the patient

− It is the first step in the production of the image

− Digital detectors used are of several types to

convert x-rays to electrical signals (analog-to-digital signals), and then converted into digital data for processing by a computer with the use of ADC

Computer Data Processing

- The ADC sends digital data for processing by a

digital computer with the use of a special

software to create or build up digital images

using the binary

Image Display and Post-processing

− The output digital image must be converted

into an analog signal before it can be displayed

on a monitor for viewing with the use of digital-

to-analog converter (DAC)

− The image displayed for initial viewing can be

processed using a set of operations and

techniques (post-processing techniques) to

transform the input image into an output image

to enhance diagnosis

Image Storage

- Various kinds of storage devices and systems

are used for this purpose, such as magnetic

tapes, disks, and laser optical disks, for long-

term storage

− In a PACS environment, a storage system such

as a RAID (redundant array of independent

disks) is not uncommon

− Image compression reduces storage space

and decreases the image transmission time

Lossless or Reversible Compression and Lossy or Irreversible Compression

Two popular compression methods are:

Lossless or Reversible Compression

There is no loss of information when the image is decompressed

Lossy or Irreversible Compression

It will result in some loss of information

Image and Data Communications

Are concerned with the use of computer

communication networks to transmit images

from the acquisition phase to the

display/viewing and storage phase

Picture Archiving and Communication System (PACS)

are being used for storing/archiving

and communicating images in the digital

radiology department

Image and Information Management

Refers to the use of PACS and information systems to

manage the vast number of images and text

data produced in a digital radiology department

RIS and HIS

Image and Information Management: handle textual information

PACS

Image and Information Management: handle image generated by various digital imaging modalities

Kenneth R. Castleman

Uses set theory to classify images based on their form and method used to produce them

Kenneth R. Castleman

He conceptualizes images as a subset of all

objects and that the image set contain

subsets

Analog images and Digital images

In medical imaging, there are two types of images:

Analog Images

- It refers to a device or system that

captures or measures a continuously

changing signal

− The light intensity generated from the

light source and a photomultiplier tube

(PMT) would generate an output signal

where its intensity various continuously

depending on the location of the light on

the image (analog signal)

Digital Images

Are formed through

multiple samplings of signal rather than

the one single exposure of an analog

image

Spatial Location Domain, Spatial Frequency Domain

Image Domains:

Spatial Location Domain

- All images use a right-handed X-Y coordinate

system, to identify the location of any number

that makes up the image

− It is usually described as the pixel location

Spatial Frequency Domain

- Images are based on the number of cycles per

unit length

− It is usually described as the resolution (object

size) and the contrast

Small

_______ structures produce high frequency and high contrast

Large

______ structures produce low frequency and low contrast

Fourier transformation

Is the mathematical algorithm that is applied to change an image from the spatial location domain to the spatial

frequency domain, and an inverse FT can be

used to return an image back to the spatial

location domain

Fourier transformation

One of the primary goals for doing this is

to facilitate image processing that can

enhance or suppress certain features of

the image

receptor exposure, subject contrast noise,

sharpness, geometric magnification and shape

distortion

The primary influences on the signal image are

Standardized radiation exposure (KSTD)

- It is a standard exposure typical of that

imaging receptor system

− The exposure is made with additional

filtration that hardens the beam to

simulate patient tissue

− These standard conditions for the

exposure are used to ensure that the

equipment is functioning appropriately

Indicated equivalent air kerma (KIND)

− It is the measurement of the radiation

that was the incident exposure on the

imaging plate for that particular

exposure, derived from the reading the

pixel values (for-processing pixel values

[Q]) produced by the exposure on an IR

− This value will help determine whether

the IR has been overexposed or

underexposed for that particular body

part

Target equivalent air kerma value (KTGT)

a set of values, established by either the system manufacturer or the system user, that represents an optimal exposure for each specific body part and view.

Deviation Index (DI)

− It is simply the difference between the

actual exposure (KIND) and the target

exposure (KTGT) except that it is

expressed in a logarithmic fashion

𝐷𝐼 = 10 × log 10 [𝐾𝐼𝑁𝐷 ÷ 𝐾𝑇𝐺𝑇(𝑏, 𝑣)]

Deviation Index formula

0

A perfect image according to the

deviation index has a DI value of __

Increase technique by 25%

If DI is negative

Underexposed

If the DI is negative, the image has been ______

Decrease technique by 20%

If DI is positive

Overexposed

If the DI is positive, the image has been _______

Matrix

It is a square arrangement of numbers

laid out in rows and columns that gives

form to the image.

Inversely proportional

Matrix size and pixel size(for the same FOV) relationship

Inversely proportional

Pixel size and spatial resolution relationship

Pixel

It is the smallest element in a digital image

Pixel size

is directly related to the amount of spatial resolution or detail in the image

Pixel size = FOV/matrix size

The pixel size can be

calculated using the

relationship:

Bits

- These are referred

to as binary digits;

these are discrete

units

− The binary consists

of information

recorded as either a

0 or 1

Byte

An 8-bit word

Voxel

It is a third-dimension data point, creating

a volume data point along the z-axis

Field of View

The overall dimension of the image matrix

Exposure Indicators

It refers to the amount of exposure received by the IR, not by the patient

Spatial resolution

- It is the ability of the imaging system to demonstrate small details of an object

- It is a critical image quality factor that is determined by pixel size

line pairs per millimeter (lp/mm)

Spatial resolution is measured in:

1. Brightness

2. Contrast and Grayscale

3. Noise

4. Sharpness

5. Geometric Magnification

6. Display Magnification

7. Shape Distortion

Primary Influences on the Final Displayed Image:

Brightness

It refers to its appearance on the display

monitor of the computer and is a function

of the monitor's ability to emit light

through the surface of the display

(luminance)

Contrast Resolution

− It refers to the ability of the digital system

to display subtle changes in the shade of

gray

Magnification

Digital systems allow the operator to

selectively magnify an area or anatomy

or to zoom the entire image without

significant loss of resolution (operator

controlled)

Noise

It refers to any interruption of the image signal by the patient or the equipment

Shape Distortion

− It occurs because of an angle of the part,

receptor or tube

− It will not be subject to manipulation by

the operator and must be handled prior to

exposing the patient

Sharpness

It is the abruptness with which the edges

of a bone or soft tissue transitions to an

adjacent tissue or background density

Scanning

The image is divided into an array of small

square regions (pixels)

Sampling

- It involves measuring the brightness level of

each of the pixels using special devices such

as PMT

− The signal from the PMT is an analog signal

(voltage waveform) that must be converted into

a digital image for processing by a digital

compute

Quantization

- The brightness levels obtained from sampling

are assigned an integer (zero, a negative or a

positive number) called a gray level

− The image is now made up of a range of gray

levels (gray scale)

Bit depth

It refers to the number of bits within a pixel

Computed Radiography

- It is a digital radiographic imaging modality that

uses a photostimulable storage phosphor imaging

plate (PSP or IP), typically inside a cassette

- It is similar to conventional radiography systems,

and can be used interchangeably

- It produces a latent image but differs in how the

exposures are recorded

- It is sometimes referred to as filmless cassettes

- first became available in the early 1980s when it

was introduced by Fuji

Imaging Plate

IP

Photodiode

PD

photomultiplier tube

PMT

photostimulable luminescence

PSL

photostimulable phosphor

PSP

Storage Phosphor

SP

Storage Phosphor screen

SPS

photostimulable phosphor Imaging Plate (PSP IP)

- It is a rigid, lightweight plastic sheet that is

designed to record and enhance transmission of

the image

- It is loaded into a cassette that looks similarly to a

film-screen cassette

Protective layer

It insulates the imaging plate from

handling trauma

Phosphor layer/ active layer

It holds or "traps" electrons in the Photostimulable phosphorus during exposure, which is the active component in the plate

Barium fluorohalide bromides and iodides with europium activators

The most common phosphor with characteristics favorable for CR are?

Reflective Layer

a layer that sends light in a forward direction when released in the cassette reader

Support layer/base

It is simply a base on which to coat the other layers, and it gives the imaging sheet some strength

Binder

It is an adhesive layer that holds the phosphor layer to the base

Conductor layer/antistatic layer

It grounds the plate to eliminate

electrostatic problems and absorbs

light to increase sharpness

Light-shielding layer

It prevents light from erasing data on

the imaging plate or leaking through

the backing, decreasing the spatial

resolution

Backing layer

It protects the back of the cassette and

absorbs backscatter x-ray photons,

improving the contrast resolution of

the image receptor

25

The latent image

will lose about ...% of its energy in 8

hours

Fading

is a term that refers to the

time it takes for the latent image

to disappear

Stimulation or Laser Scanning

- Through this process, the latent image

is made visible

- The finely focused beam of infrared

light (laser or light amplification of

stimulated emission of radiation) with

a beam diameter of 50 to 100 µm is

directed at the PSP

Image read-out

Plate erasure

Imaging Plate Reader

- The latent image is processed by loading the

cassette into an imaging plate reader where the

imaging plate is scanned by a laser beam

- These laser beam scans cause the phosphors to

emit the stored latent image in the form of light

photons, which are detected by photosensitive

receptors and converted to an electrical signal,

which is in turn converted to a unique digital value

for that level of luminescence

Point scan and Line scan

There are two types of PSP readers:

Point scan

It moves from side to side, and only a

single laser point radiates the imaging

plate at any point in time

Line scan

simultaneous stimulation of the imaging plate one line at a time

Fast scan

- It is the movement of the laser

across the imaging plate ("scan")

- Deflection devices (rotating

polygon or oscillating mirror)

deflect the laser beam back and

forth across the IP during this

drive mechanism

Slow scan

It is the movement of the

imaging plate through the reader

at a slow yet constant speed

along the long axis of the

imaging plate ("translation" or

"subscan direction")

Laser, beam-shaping optics, light-collecting optics, optical filters, and a photodetector

Components of the optical subsystem include

Computer Processing

The electrical signal is sampled and digitized to

represent a specific location within the matrix

(spatial location) and displays a specific

brightnes

Scanned Projection Radiography (SPR)

− It was developed by CT vendors to facilitate patient

positioning imaging volume remains in use with

virtually all current multislice helical CT imaging

systems

− The patient is positioned on the CT couch and then

is driven through the gantry while the stationary x-

ray tube is energized, resulting in the production of

a digital radiograph