Digital Imaging

Digital Imaging
MohamedAbdulHaleem(INTERNI)
BapujiDentalCollege&Hospital,
Davangere.

CONTENTS
 Introduction
 Formation of digital images
 CHARGE-COUPLED DEVICE (CCD)
 COMPLEMENTARY METAL OXIDE
SEMICONDUCTORS (CMOS)
 Digital Subtraction Radiography (DSR)
 PHOTOSTIMULABLE PHOSPHOR PLATES
(PSP)

Introduction
Digital Imaging refers to the numeric
format of the image in terms of pixels
with its different shades.
• Pixel = picture + element
• A digital image consists of a
large collection of individual
pixels that are organised in a
matrix consisting of rows and
columns.

Formation of digital
images
• The formation of digital images involves several steps,
beginning with analog processing.
• Each pixel ---consists of individual electronic detector ---
absorb x-ray --- generate small voltage proportional to
the amount of x-ray absorbed by each individual pixels
within the detector.
• The voltage fluctuation at each pixel is therefore known
as “analog signal”
• Conversion of the analog signal into an usefull digital
image is done through a process called “Analog to
Digital Conversion (ADC)”

ADC --- SAMPLING --- QUANTIZISING
• In order to view the image, the computer
organizes the pixels in their proper location and
gives them a grey shade that corresponds to
the number that was assinged during
quantization step.

• Various receptors that are used to absorbs the
x-ray from the source were developed over the
period times which includes…
• Each has their own credits and limitations in
producing the final digital images
 DSR  PSP
 CMOS CCD

CHARGE-COUPLED DEVICE
(CCD)
• Made up of thin layer of silicon.
• When exposed to radiation--- covalent
bonds between the silicon atoms are
broken--- prduce electron-hole pairs which
are proportional to amount of exposure.
• Electrons are then attracted towards the
positive site in the device creating a “charge
packets”

• The image is read by
transferring each
rows of pixel charges
in a “bucket brigade”
fashion.
• Each packet corresponds to one pixel.
• As the charge reaches the end of its
row--- transferred to the amplifier---
then transmitted as a voltage to ADC

COMPLEMENTARY METAL OXIDE
SEMICONDUCTORS (CMOS)
• As same as that of CCD with few difference
such as…
• It is made of silicon based semi-
conductor
• Unlike CCD, each pixels are
connected individually to a
transistor.
• These are less expensive than CCD

Digital Subtraction
Radiography (DSR)
Two images( base line and follow up
image) of the same object registered ---
image intensities of corresponding pixels
are subtracted --- a uniform difference
image is produced.
 Projection geometry of both two images should be same to
avoid errors in distinguishing the actual changes.
Brighter area --- changes represent gain
Darker are --- changes represent loss.

PHOTOSTIMULABLE
PHOSPHOR PLATES
(PSP)
• Made of…. barium + iodine + chlorine/bromine….
Which forms a crystal lattice.
• Europium (Eu+2) when added forms imperfection in the
lattice.
• Eu+2 --- when exposed to sufficient radiation ---
valence electron in Eu+2 absorbs energy --- move into
the near by halogen vacancies (F-Centers) --- trapped
there in a metastatic state --- which represents the
latent image.

• Number of electrons trapped is proportional to the amount
of exposure.
PSP IMAGE PROSESSING:
 When stimulated by red
light(600 nm)--- barium
fluorohalide releases the
trapped electron --- electron
returns to Eu+3 ion ---
energy is released in green
spectrum (300-500nm)
 Lights from PSP --- conducted by fiberoptics to a
photomultiplier tube

Digital image
obtained
Lights from PSP --- conducted by fiberoptics --- to a
photomultiplier tube
Quantified by
ADC
Converts light into electrical
energy
Is inbuilt with red filter that
selectively remove the
stimulating red light.
Prevent distortion in the final
image

Specialized Radiographic
Techniques
 COMPUTED TOMOGRAPHY
(CT)
 CONE-BEAM COMPUTED
TOMOGRAPHY (CBCT)
 MAGNETIC RESONANCE
IMAGING (MRI)

COMPUTED TOMOGRAPHY (CT)
Invented by Godfrey Hounsfield
and Allan Cormack
(Noble Price in medicine = 1979)
Tomography --- which means
thin layer radiography

X-ray beams are collected in a grid like
pattern called “Matrix”
Made of array of pixels
Each pixel represent a calculation that denote the
actual attenuation of the X-ray beam by the
constituents of the body
A number (CT number / Hounsfield unit) is
designated for each pixel corresponding to the
degree of attenuation to the x-ray beam

• Calibration of the Hounsfield units are inbuilt
within the CT machine which differs
according to the manufacturer’s.
• Most moniter may display only 256 gray-
scales to which the human eyes can
percieve only 64 shades of gray.

ADVANTAGES OF CT
• Multiplanar imaging
• Greater geometric precision
• Manipulation of the acquired image (able to change
contrast and brightness)
• Soft tissue imaging
• Ability to distinguish objects of different density (such
as air, fat, water, CSF, muscle and cortical bones)

DISADVANTAGES OF CT
• Expensive
• High radiation dosage to patient
• Chances of artifacts
ENDODONTIC USES OF CT
• Evaluate the presence and extent of the lesion
• Detection in displacement of the fracture segments

CONE-BEAM COMPUTED
TOMOGRAPHY (CBCT)
Since CT scanners are expensive and offers a high
dosage of radiation, CBCT were invented as it costs
lesser as well as offers lower radiation exposure to the
patient than that of CT scanners.

FUNDAMENTALS OF CBCT
Uses cone-shaped X-ray beam
This serious of 2D images are Combined to
generate an accurate 3D images (Projection
Data)
Produces a “serious of 2D images (Basis Projection)” using
2D detectors

ADVANTAGES OF CBCT
• Lower radiation than CT
• Lower scanning time, space and cost than CT
• Greater hard tissue definition than CT
• Interactive display module (zooming is able)
DISADVANTAGES OF CBCT
• Lesser soft tissue discrimination than CT
• Scattering is more than CT
• Chances of artifacts

 Pre, Intra and Post-operative
assessment
 Diagnosis of root resorption
and identification between its
type
 Diagnosis of root
fracture
 Diagnosis of dentoalveolar
fracture

ENDODONTIC USES OF CBCT
 Root canal morphology:
Precisely determine root curvature
Definitely identify accessory canals
 Periapical pathosis:
Uses in cases were the lesions are superimposed
by anatomical structures
Can support diagnosis of ‘lesions of non-endodontic
origin’
Determines the extent of the lesion and its effect on
surrounding structures

MAGNETIC RESONANCE
IMAGING (MRI)
MRI --- uses strong magnetic fields + radio waves
--- form images of the body.

Human body consists of nearly 70%
water (H2O)
Water has hydrogen molecules in it
Hydrogen atom has only a single
proton within its nucleus
Proton has a positive charge and also
spin on its own

Hence has a magnetic property i.e. has
both north and south poles
Now an external magnetic field is
applied
All hapazaradly aligned proton align
them self towards the direction of
external magnetic field
Then a radiofrequency wave is applied

This enforces the protons to turn away
from the direction of the external
magnetic field
Sudden stoppage of the
radiofrequency wave
Protons tends to return back again to
the direction of the external magnetic
field
This results in the release of energy in
the form of photons

Photons detected by the specialized
detectors
“MRI image” constructed on computer
The amount of photons emitted is proportional
to the concentration of the hydrogen atoms
within the tissue
The images can be taken in all the planes by
altering the direction of the external magnetic
field towards the plane of interest

ADVANTAGES OF MRI
• Absolutely no radiation
• Provide information about blood circulation
DISADVANTAGES OF MRI
• Contraindicated in patients with pace maker
support
• This procedure cannot be carried out on patients
with any kind of fixed metals prosthesis
• Creates loud noises during the procedure
• Highly expensive

References
• Textbook of white and pharoah, oral radiology
• Textbook of oral medicine, oral diagnosis and oral
radiology – 2nd
Edition – Ravikumar ongole, Praveen
BN – Pg no: 760 - 779

Digital Imaging

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