Digital imaging

Question 1

What is analogue image

Answer 1

Has a continuously varying density across it

A film image is a type of analogue image

Question 2

Digital image

Answer 2

Has discrete pixels (picture elements) with numerical density values

Question 3

Physical principles of digital radiography

Answer 3

In screen film radiography the film is the detector and storage medium
In digital radiography the detector only generates the image which is then stored on a digital medium

Question 4

Digital imaging series

Answer 4

Generation
Processing
Archiving
Presentation

Question 5

Types of digital radiography

Answer 5

Computed radiography (CR)
Direct radiography (DR)

Question 6

CR

Answer 6

uses imaging plates which need developing in a processor

Question 7

DR

Answer 7

acquires an image directly without using a processor

Question 8

Types of CR detectors

Answer 8

Indirect conversions > storage phosphor

Question 9

Types of direct digital radiogtaphy

Answer 9

Indirect conversion:

• Scintillator tft
• Scintillator-CCD
• Image intensifier

Direct conversion:

• Photoconductor FPD
• Selenium-drum

Question 10

Main digital image detector functions

Answer 10

Capture - absorbing x-rays
Coupling - linkage between the capture element and the converter
Conversion - change of x-ray energy into electrical signal which can be read, can be direct and indirect

Question 11

Direct digital radiography (DDR)

Answer 11

X-ray energy is converted directly into electrical signal

Question 12

Advantages of direct imaging

Answer 12

Saves a lot of time
No spread of light, straight conversion process
Give more attention to patient care because it is a quick process

Question 13

Indirect imaging

Answer 13

X-ray is converted into light which is then converted to electrical signal

Question 14

Advantages of indirect imaging

Answer 14

Light taken part in the process, the light can be amplified and increase sharpness

Question 15

Process of digital radiography

Answer 15

Flat panel receptor fixed in an upright stand or x-ray table
Electrical signal goes straight down the wire to the computer
Image doesn’t need to be processed
Image sent to the workstation via electrical or wifi

Question 16

Amorphous selenium DR system: Selenium drum detector system

Answer 16

X-rays>Photoconductor>analog-to-digital converter

Photoconductor converts x-ray energy to electrical charges

Question 17

Amorphous selenium DR system: Flat panel detector system

Answer 17

x-rays>photoconductor>tft-arrays

Question 18

Process of direct digital radiography

Answer 18

Photoconductor of amorphous selenium absorbs x-rays
Photoconductor generates electrical charges
Charge is held in a storage element on a two dimensional detector array

Question 19

Process of Indirect DR

Answer 19

Each cell in the detector has a layer of scintillation crystals which produces light when hit by x-rays
amorphous silicon photodiode converts the light into an electrical chatge
the pattern of charge stored like in DDR

Question 20

Types of CCD indirect radiography systems

Answer 20

Lens coupled CCD based systems

Slot scan CCD based system

Question 21

Similarities of Direct and indirect DR

Answer 21

2D array of electrodes containing TFT

Question 22

Computed radiography

Answer 22

CR images need to be processed
Image receptor is a plate in a portable cassete
The latent image on a plate is developed in a CR processor

Question 23

Features of digital imaging

Answer 23

wide exposure latitude
very low exposure gives image noise: quantum mottle
wide dynamic range
modern digital images have good res
cr plates sensitive x-ray fogging

Question 24

How can we tell if a digital image was over exposed

Answer 24

Clever automated processing means that an over exposed image looks fine
But all systems record an “exposure index or detector
dose index” (DDI) on each image

Question 25

Radiation dose and CR/DR

Answer 25

Give less patient dose than x-ray films: saves repeats and lost images
Dose depends on technique and exposure factors
over exposures lead to high quality images and avoid image noise

Question 26

Dose creep meaning

Answer 26

A term that is used to describe gradually putting exposures higher

Question 27

Digital image quality

Answer 27

Contrast
spatial res
noise (Signal to noise ratio)

Question 28

Digital image contrast

Answer 28

digital imaging amplifies the range of available contrast in body tissues

Question 29

Effect of pixel size on image quality

Answer 29

small pixels give good res and “detail”

small pixels more vulnerable to image noise

Question 30

Resolution in radiography

Answer 30

image resolution is limited by the ability of the system to resolve 2 small closely adjacent objects within the image

Question 31

spatial res in the display

Answer 31

critical image quality factor seen as the detail and sharpness of the image on the monitor

Question 32

What is image noise

Answer 32

Random fluctuation in signal due to imperfections in the image transfer process
Noise in image does not provide a good representation of body anatomy and can give salt and pepper appearance

Question 33

Sources of noise

Answer 33

random electrical fluctuation in circuits
quantum mottle
background radiation and scatter
pressure on digital plates
detector faults

Question 34

Quantom mottle

Answer 34

refers to the graininess of x-ray images

Question 35

Detective quantum efficiency (DQE)

Answer 35

DQE refers to the efficiency of a detector in converting incident x-ray energy into an image signal

Question 36

postprocessing

Answer 36

Windowing- adjusting contrast and greyscale
Edge enhancement
image reversal
algorithm
image stitching
image filtering
annotation
cropping
magnification

Question 37

Windowing

Answer 37

Centring the window level we can just the central value of the density range of tissues that are seen
Window width adjusts the range of densities that are vibisble