digital image capture

Question 1

What is A Computer?

Answer 1

Data processor according to a set of instructions (a Program)

 What kind of data?
Numbers

 What does Digit/Digital mean?
It comes from Latin digitus which means “finger”

Question 2

Computers in Diagnostic Imaging

Answer 2

• Modern Computers process numbers on a binary base 0 / 1
• Corresponds to off / on of trillions of electronic switches : Transistors
• bit : Binary digit ( base 2 number, from the Latin bini = two)

Question 3

Digital Imaging & Radiography

Answer 3

Computers in Diagnostic Imaging

Painting by Numbers : Digital Image

Pixel (Picture Element) corresponds to tissue Voxel (Volume Element) within the patient’s body

Numerical value displayed as shades of grey proportional to X-ray attenuation

Question 4

A digital image is a matrix of many small elements, or pixels.

Answer 4

Each pixel is represented by a numerical value. In general, the pixel value is related to electrical signal measured in a certain location . The Numerical value define the brightness (shade of grey) of each pixel when the digital image is converted into an analogue image for display and viewing on a Monitor.

Generally, at the time of viewing, the actual relationship between a pixel numerical value and it’s displayed brightness is determined by the adjustments of the window control as discussed in other modules.

Question 5

A digital image is a matrix of many small elements, or pixels.

Answer 5

Shades of grey are assigned to pixel values.

High density tissues (such as bone) are displayed as bright pixels compared to low density tissues (dark pixels)

Question 6

Advantage of Digital Radiographic Systems

Answer 6

Store Images into Digital Archives

Question 7

Advantage of Digital Radiographic Systems

Answer 7

Easy and fast distribution to local and remote viewingworkstations

Question 8

Easy and fast distribution to local and remote viewingworkstations

Answer 8

Post-process images to aid visualization of anatomy and pathology

Less requirement to repeat

Lower Doses

Speedy availability and distribution of final image

Question 9

CR Overview

Answer 9

Does not use films

Store Image on Photostimulable Phosphor Plate (PSP) also known as “cassettes”

Visualization and Acquisition happen at different times

Based on physical process of Photostimulated Luminescence (PSL)

Question 10

image acquisition
cr image reader
image display

Answer 10

image acquisition
- captures and stores radiographic image in reusable imaging plate

cr image reader
- image is developed in a digitiser

image display
- image is displayed on the monitor

Question 11

cross section of cr plate

Answer 11

protective layer
phosphor layer
anti-halo and reflective layer
base
backing layer

Question 12

CR – Computed Radiography

Answer 12

Electron excited by X- Ray trapped in semi stable Higher Energy Level

”X-ray photons are absorbed by the phosphor layer, and the phosphor electrons become ‘excited’ and are raised to a higher energy level, where they can stay trapped in a semi-stable higher-energy state.”

The trapped electrons represent a latent image in the phosphor plate in the form of ‘stored energy’.

Question 13

CR – Computed Radiography

Answer 13

Trapped Electrons form latent image(stored energy) with short life and will spontaneously decay
”X-ray photons are absorbed by the phosphor layer, and the phosphor electrons become ‘excited’ and are raised to a higher energy level, where they can stay trapped in a semi-stable higher-energy state.”

The trapped electrons represent a latent image ( in the phosphor plate in the form of ‘stored energy’. ) development

theinvisiblechangein aradiographicdetector/platethatiscausedbyx-radiationorlightandismadevisiblethrough the acquisition process in computed and digital (direct) radiography modalities.

Question 14

CR – Computed Radiography

Answer 14

LATENT IMAGE:

theinvisiblechangein aradiographicdetector/platethatiscausedbyx-radiationorlightandismadevisiblethrough the acquisition process in computed and digital (direct) radiography modalities.

Question 15

CR – Computed Radiography

Answer 15

Laser stimulate electrons to escape
energy released in form of Light

” The stored energy can be released by adding energy to the trapped electrons. This is done by stimulation with a laser beam.

The trapped electrons then ‘escape’ from the traps to fall back to their equilibrium state. As they fall back, the electrons release energy in the form of light

The emitted light intensity is proportional to the original X-ray intensity.

Question 16

CR – Computed Radiography

Answer 16

Exposure
Latent Image
Readout

” The stored energy can be released by adding energy to the trapped electrons. This is done by stimulation with a laser beam.

The trapped electrons then ‘escape’ from the traps to fall back to their equilibrium state. As they fall back, the electrons release energy in the form of light

The emitted light intensity is proportional to the original X-ray intensity.
” The stored energy can be released by adding energy to the trapped electrons. This is done by stimulation with a laser beam.

The trapped electrons then ‘escape’ from the traps to fall back to their equilibrium state. As they fall back, the electrons release energy in the form of light

The emitted light intensity is proportional to the original X-ray intensity.

Question 17

CR – Computed Radiography

Answer 17

Light detected by Photomultiplier tube
A/D Convertor process data to a file that can be displayed on a monitor
Exposure to Bright Visible light erase plate (reusable)

The light energy is detected and the signal is digitised. These data are processed digitally to produce a visible diagnostic image on a monitor. The phosphor plate is then ‘erased’ with a bright white light to remove any remaining trapped electrons, and the plate is then ready for the next examination

Photomultipliertubes (photomultipliers orPMTsfor short), members of the class of vacuum tubes, and more specifically vacuum phototubes, are extremely sensitive detectors of light.

Question 18

CR – Computed Radiography
Plate Reading

Answer 18

Stimulation (Laser) and Emission lights have different wavelength so they can be filtered

The spectra of the stimulating and released light used in the phosphor screens are chosen for a very specific reason. Because these peaks are separate, they enable the stimulating laser light to be filtered from the phosphor screen luminescence.

Question 19

CR – Computed Radiography

Answer 19

Sampling :
Asampleis adigitalrepresentation of an analog signal

Sampling pitch,or distance between the sampling points

Sample Frequency: How often the analog signal is reproduced in digital format

Question 20

CR – Computed Radiography

Answer 20

Sampling :
Asampleis adigitalrepresentation of an analog signal

Sampling pitch,or distance between the sampling points

Sample Frequency: How often the analog signal is reproduced in digital format

Question 21

DR – Direct Radiography
DR Overview

Answer 21

DR imaging combines image capture and image readout (versus two steps of CR)

Self-scanning readout mechanism via an array detectors that convert the varying-ray intensities into proportional electronic signals

DR images available almost instantly after exposure

Question 22

DR Overview

Answer 22

DR Receptors more fragile and much more expensive than CR

Flat Panel Detectors are constructed in layers to convert X- Rays to Electrical charges

Read-out , Digitalization and storage integrated

Question 23

Direct Radiography

Answer 23

The energy of a photon creates an electron/hole combination (or Charged Couple )within the depletion layer which allows current to flow across the terminals of the Photodiode

Very Fast switch activated by Light

Aphotodiodeis a semiconductor device that converts light into an electrical current. The current is generated when photons are absorbed in thephotodiode.

Question 24

Direct Radiography
Do you remember what is called an array of photo diodes?

Answer 24

CCD (Charged Couple Device) are made up of a two dimensional array of photo diodes that change light into a grid of different amounts of electrical charge.

Each photodiode represent a pixel in the image, the charge created is proportional to the amount andof lightfalling on it.

Question 25

Shift Register

Answer 25

TheShift Registeris a type of sequential logic circuit that can be used for the storage or the transfer of binary data.

Question 26

Shift Register

Answer 26

TheShift Registeris a type of sequential logic circuit that can be used for the storage or the transfer of binary data.

Question 27

DR Technology

Answer 27

INDIRECT CAPTURE DR (Scintillator)
Phosphor (Cesium Iodide) + Charged Couple Device
OR
Phosphor (Cesium Iodide) + Photodiode ASi (Amorphous Silicon) +Thin- Film Transistor TFT

DIRECT CAPTURE DR
Amorphous Selenium + TFT

Question 28

DR Technology- INDIRECT CAPTURE - Scintillator + CCD

Answer 28

LAYERS :
Scintillator Phosphor (Cesium Iodide)
Fiberoptic (Optical Coupling)
CCD (Convert light into electronic signal)
Glass Substrate

Question 29

DR – Direct Radiography

Question 30

DR Technology- INDIRECT CAPTURE - Scintillator + TFT

Answer 30

LAYERS :
Scintillator Phosphor
(Cesium Iodide)
Photodiodes (A-Silicon)

TFT
Glass Substrate

TFT:
Thin Film Transistors array
Captures Charges and transmits them to the ADC

Question 31

DR Technology DIRECT CAPTURE DR Amorphous Selenium + TFT

Answer 31

Layers
Amorphous Selenium (Photoconductor )
TFT

Converts X-Ray into Electrons to create Image

Better Resolution than Indirect (No light Scattering)

Question 32

DR – Direct Radiography

Answer 32

After signal is converted by the Analogue Digital Converter (ADC)

This is passed via cable or wireless connection to the modality computer

The digital data is then stored as a digital image file