In the Name of God

Digital Radiography

Lecturer : Seyedeh Shokoofeh Mousavi Gazafroudi

05/01/2023 Isfahan University of Medical Sciences 2

05/01/2023 Isfahan University of M

edical Sciences

3 Introduction to digital radiography(DR) Process System classification

Computed Radiography (CR) photostimulable phosphor (PSP) Exposure & readout Imaging plates Charged Couple Device (CCD)

Indirect Digital Radiography (IDR) Structure & function

Direct Digital Radiography (DDR) Structure & function

Table of Content

Introduction to digital radiography(DR)

ProcessSystemclassification

05/01/2023 Isfahan University of M

edical Sciences

5Introduction Historically, digital radiography referred to specialized

modalities that produced digital images

Digital images can be numerically processed This is not possible in conventional radiology.

Digital images can be easily transmitted through networks and archived

Since the early 1990s, Digital Radiography has grown to include Computed Radiography(CR) and ‘true’ Digital Radiography(DR) or Direct Radiography.

05/01/2023Isfahan University of Medical Sciences

What is digital radiology? In conventional radiographic images, spatial position and blackening are

analogue values

Digital radiology uses a matrix to represent an image

A matrix is a square or rectangular area divided into rows and columns. The smallest element of a matrix is called ”pixel”

Each pixel of the matrix is used to store the individual grey levels of an image, which are represented by positive integer numbers

The location of each pixel in a matrix is encoded by its row and column number (x,y)

6

05/01/2023 Isfahan University of M

edical Sciences

Digital Radiology Process

Image acquisition Image processing Image display Image archiving (PACS) Image retrieving

7

05/01/2023 Isfahan University of M

edical Sciences

8Digital Radiography Systems

05/01/2023 Isfahan University of M

edical Sciences

9

Computed Radiography (CR)

photostimulable phosphor (PSP)Exposure & readout Imaging platesCharged Couple Device (CCD)

05/01/2023 Isfahan University of M

edical Sciences

11Computed Radiography (CR)

Uses same radiographic equipment No change in X-ray machine Uses an imaging plate Contains a photo stimulator phosphor Need a cassette reader Images can be sent to a PACS

05/01/2023 Isfahan University of M

edical Sciences

12Computed Radiography Is a marketing term for photostimulable phosphor (PSP) detector systems.

Re-usable metal imaging plates replace film & cassette

Uses conventional bucky & x-ray equipment

When x-rays are absorbed some light is promptly emitted, but much of the absorbed x-ray energy is trapped in the PSP screen and can be readout later.

CR imaging plates are made of barium fluorohalid.

05/01/2023 Isfahan University of M

edical Sciences

13The principle of PSP

Excitation Storage Emission

CB

Trap

ADCPMT

05/01/2023 Isfahan University of M

edical Sciences

14CR readout processing steps

After the cassette is exposed by the x-ray beam, the cassette is loaded into a reader.

The reader removes the phosphor plate and exposes it to a laser, stimulating the phosphors.

The light emitted from the plate is collected, quantified, and digitized.

after read-out, plate erased using a bright light

05/01/2023 Isfahan University of M

edical Sciences

15CR Exposure & Readout

05/01/2023 Isfahan University of M

edical Sciences

16Reading Imaging Plate Reader scans plate with

laser light using rotating mirror

Film pulled through scanner by rollers

Light given off by plate measured by PM tube &recorded by computer

05/01/2023 Isfahan University of M

edical Sciences

17

PMT

Beam deflector

LaserSource

Light channeling guide

Plate translation: Sub-scan direction

Laser beam: Scan direction

Output Signal

Reference detec tor

Beam splitter

Cylindrical m irrorf-thetalens

Amplifier

ADC

To imageprocessor

18Laser & Emitted Light are Different Colors

Phosphor stimulated by laser light

Intensity of emitted light indicates amount of radiation incident on phosphor at each location

Only color of light emitted by phosphor measured by PMT

05/01/2023

Isfahan University of Medical Sciences

19Reading Imaging Plate

plate is photostimulable phosphor

radiation traps electrons in high energy states

higher statesform latent image

Higher EnergyElectronState

Lower EnergyElectronState

-

--

-

--

-

--

-

--

-

--

-

--

-

--

-

--

-

--

X-RayPhoton

-

Photon pumpselectron tohigher energy state

05/01/2023 Isfahan University of M

edical Sciences

20Reading Imaging Plate

reader scans plate with laser

laser releases electrons trapped in high energy states

electrons fall to low energy states

electrons give up energy as visible light

light intensity is measure of incident radiation

Laser Beam

Higher EnergyElectronState

Lower EnergyElectronState

-

--

-

--

-

--

-

--

-

--

-

--

-

--

-

--

-

--

-

Lower Energy Electron State

05/01/2023 Isfahan University of M

edical Sciences

05/01/2023 Isfahan University of M

edical Sciences

21

05/01/2023 Isfahan University of M

edical Sciences

22CR Throughput Generally slower than film processing CR reader must finish reading one plate

before starting to read the next Film processors can run films back to

back

               

05/01/2023 Isfahan University of M

edical Sciences

23Charged Couple Device (CCD)

Is an integrated circuit made of crystalline silicon

Forms images from visible light

For linear CCD detectors charge pocket at the very bottom of linear array spills onto a transistor, and produce an electronic signal that is digitized. The entire line of pixels and readout in a shift-and-read process.

For 2D CCD detectors , the charges on each column are shifted onto the bottom row of pixels, that entire row is read out horizontally, and then next charges from all columns are shifted down one pixel.

05/01/2023 Isfahan University of M

edical Sciences

24CCD detectors function

05/01/2023Isfahan University of Medical Sciences

25

Indirect & Direct Digital Radiography (IDR & DDR)

27Digital Radiography (DR) Receptor provides direct digital output Potentially lower patient dose than CR High latitude as for CR

No processor / reader required Images available in < 15 seconds Much less work for technologist

05/01/2023

Isfahan University of Medical Sciences

05/01/2023 Isfahan University of M

edical Sciences

28Flat panel detector

05/01/2023 Isfahan University of M

edical Sciences

29Indirect digital radiography

X-ray strike scintillator producing light Photodiode array converts light to electrons The intensifying screen is made up of cesium-iodide crystals and

the photodetector is made up of amorphous silicon.

Light

05/01/2023 Isfahan University of M

edical Sciences

30Indirect digital radiography Electronic sensor are replaces the light sensitive film emulsion

X-rays are absorbed in the screen and the absorbed energy is then relayed to the photodetector by visible light photons

The ratio of the light sensitive area to the entire area of each detector element is called fill factor

Flat Panel Imaging Arrays (indirect conversion)

05/01/2023Isfahan University of Medical Sciences

31

05/01/2023 Isfahan University of M

edical Sciences

32Direct Digital Radiography

Is made from a layer of photoconductor materials on top of a TFT array

The electrons released in the detector layer from x-ray interaction are used to form the image directly

05/01/2023 Isfahan University of M

edical Sciences

33Direct DR

the photoconductor is made up of amorphous selenium. selenium has higher atomic number than silicon, but it is still quit low compared with conventional x-ray intensifying screen phosphorus.

Due to electric field ,selenium direct detectors can be made much thicker.

34Flat Panel Imaging Arrays (direct conversion)

05/01/2023 Isfahan University of M

edical Sciences

05/01/2023 Isfahan University of M

edical Sciences

35Direct Vs. Indirect

05/01/2023 Isfahan University of M

edical Sciences

36

05/01/2023 Isfahan University of M

edical Sciences

37Digital mammography

it uses a mosaic of CCD and CsI scintillator.

As scanning x-ray beam detector move to the right , the charge packet in the CCD array are moving to the left

05/01/2023 Isfahan University of M

edical Sciences

38Patient dose considerations

The exposure necessary to produce good images are directly related to the detective quantum efficiency of the detector (DQE)

CR systems require about twice the exposure of a corresponding 400-speed screen-film detector for comparable image quality

05/01/2023 Isfahan University of M

edical Sciences

39Copy display

Hard copy display refers to displaying image on film, and soft copy display refers using video monitors.

05/01/2023 Isfahan University of M

edical Sciences

40Digital image corrections

Dead pixel correction

Column defect correction

Dark noise correction

05/01/2023 Isfahan University of M

edical Sciences

41Processing

Is performed by altering the relation between digital number in the image and displayed brightness

Windowing, leveling & reversing the contrast are simple procedures performed routinely.

05/01/2023 Isfahan University of M

edical Sciences

42Image Processing based on Convolution

The science of manipulating digital images often involves the mathematical operation called “Convolution”.

05/01/2023 Isfahan University of M

edical Sciences

43DR properties

Adaptive histogram equalization (AHE)

Contrast & spatial resolution

I'm so glad I live in a world where there are

“Autumns”

Thanks for your attention