Recent advances in imaging techniques/ /certified fixed orthodontic courses by Indian dental academy

Recent Advances In
Imaging Techniques
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

Oral
Radiology
Lectures

Recent
Advances
In Imaging
Techniques

Contents
•

Introduction

•

Importance of radiography in endodontics

•

Conventional techniques
Recent advances in imaging techniques
- Digital radiography
- Xerioradiography
- Computed tomography
- TACT

•


•
•
•
•
•

MRI
Cone beam computed tomography
Digital substraction radiography
Conclusion
References


INTRODUCTION
We are sick of the roentgen ray ... you can see other people's bones with the
naked eye, and also see through eight inches of solid wood. On the revolting
indecency of this there is no need to dwell. But what we seriously put before
the attention of the Government... that it will call for legislative restriction
of the severest kind. Perhaps the best thing would be for all civilized nations
to combine to burn all works on the roentgen rays, to execute all the
discoverers, and to corner all the tungstate in the world and whelm it in the
middle of the ocean.

EDITORIAL IN PALL MALL GAZETTE LONDON, 1896



X-rays has brought dentists
“out of the dark”, allowing
them to visualize areas not
accessible
by
other
diagnostic means.


•

The advent of the first oral radiography equipment
permitted visualization for the first time of the changes
that occur in the bone surrounding the apices of non-vital
teeth, as well as the results of endodontic therapy.


Importance of Radiography in Restorative
and Endodontics
The three general areas of application are :
i. Diagnosis
ii. Treatment
iii. Recall



Application of radiography in
endodontics
DIAGNOSIS
• Identifying caries

TREATMENT
•Determining
length

RECALL

working • Identifying new pathosis

•Identifying pathosis

superimposed
•Moving
•Determining root and pulp structures
anatomy
•Locating canals
normal
•Characterizing
structures
•Differentiating canals and
periodontal ligament spaces

•Evaluate healing

•Evaluating obturation


Basics






Technology systems
- Traditional
- Digital
Traditional machines
- Long cone
- Short cone
Films
- Ultraspeed film
- Ektaspeed film (E –film)
- F speed (faster film)

Bisecting Angle Technique




This technique, described at the turn of the century by
Price and Cieszynski.
Principle:


Film holders or finger holding method


A. The Rinn bisected
angle instrument (BAI).



B. The Emmenix® film
holder.



C. The Rinn Greene
Stabe bite block.



D.The Rinn Greene Stabe
bite block reduced in size
for easier positioning and
for use in children




Horizontal angulation : CR directed
perpendicular throgh the curvature of the
arch and through the contact areas of the
teeth.



Vertical angulation : CR perpendicular to
the imaginary bisector .

Improper vertical angulation


ADVANTAGES




Positioning of the film packet is reasonably comfortable
for the patient in all areas of the mouth.
Positioning is relatively simple and quick.



If all angulations are assessed correctly, the image of the
tooth will be the same length as the tooth itself and should
be adequate (but not ideal) for most diagnostic purposes.



Decreased exposure time (short PID)

DISADVANTAGES


The many variables involved in the technique often result in the image
being badly distorted.



Incorrect vertical angulation will result in foreshortening or elongation of
the image.



The periodontal bone levels are poorly shown.



The shadow of the zygomatic buttress frequently overlies the roots of the
upper molars.



The horizontal and vertical angles have to be assessed for every patient
and considerable skill is required.



It is not possible to obtain reproducible views.



Coning off or cone cutting may result if the central ray is not aimed at the
centre of the film, particularly if using rectangular collimation.



Incorrect horizontal angulation will result in overlapping of the crowns and
roots.



The crowns of the teeth are often distorted, thus preventing the detection of
approximal caries.



The buccal roots of the maxillary premolars and molars are foreshortened.

Paralleling technique


Described by Fitzgerald toward the end of
the 1940s


Film holders
 A.
Hawe–Neos Superbite
posterior holder (colour coded
red).
 B.
Hawe–Neos Superbite
anterior holder (colour coded
green).
 C. Rinn XCP posterior holder
(colour coded yellow).
 D . Rinn XCP anterior holder
(colour coded blue) with film
packet inserted.
 E . Unibite posterior holder.














Advantages
Greater geometric accuracy.
Reproducibility.
Less radiation dose (beam is not directed towards body trunk,
finger not holding film).
Superior images of upper molar roots,bone margins
,interproximal margins.
A number of commercial devices can hold the film at varying
distances from the teeth.
Drawbacks
Reduced sharpness and resolution.
Image size distortion-magnification.


Differences b/n bisecting and parallel angle
technique
Bisecting Angle Technique

Parallel Ray Technique

1) Details obscured by large penumbra
2) Superimposition of zygomatic process
3) Image shape distortion

1) Sharp details because of small penumbra
2) Control of the shadow of the zygomatic process
3) Slight image size distortion

4) Distortion greater in apical zone
5) Anatomical relationships altered

4) Distortion equal throughout the entire image
5) Correct anatomical relationships

6) Crown-root ratio not preserved

6) Crown-root ratio preserved

7) Poor image standardization and reproducibility

7) High image standardization and reproducibility


Localization technique


Is a method to locate the position of a tooth or object in the
jaws



Purpose: To depict the B-L relationship or depth of an
object .



Two methods :



Buccal object rule



Right angle technique

Buccal object rule


Described by Clark in 1910 and refined and amplified by
Richards in 1952 and 1980.



According to this rule, when a radiograph is performed at a
certain angle, the object closer to the radiographic source – the
buccal object – is displaced in the radiograph in the same
direction as the X-ray beam.



Stated more simply as INGLES RULE(MBD)-always shoot
from mesial and buccal root will be to the distal.



With an orthoradial projection
(A) the two objects appear
superimposed.



With an oblique projection (B,
C), the two objects cease to be
superimposed and easily become
recognizable
when
the
angulation of the X-ray machine
is known.



The buccal object (the one
closest to the radiographic
source) is displaced in the same
direction as the X-rays

Central (x-ray) beam passing directly through a root containing two canals
will superimpose the canals on the film. When the cone is shifted to the
mesial or distal aspect, the lingual object will move in the same direction as
the cone; the buccal object will move in the opposite direction (SLOB rule)


buccal root during endodontic treatment of a first
upper premolar with two roots

With the standard projection, the roots
appear superimposed.

Angling the X-ray machine in a
mesiodistal direction, the buccal root
appears close to the second premolar,
while the palatal root appears close to
the canine.




If this technique is standardized so that the upper
premolars are always radiographed at a slight mesiodistal
angle, the buccal roots will always appear to be distal,
while the palatal roots will be mesial.



Obviously, if the angle of the X-ray beam was reversed in
a distomesial direction, the buccal root would appear close
to the canine in the radiograph, while the palatal would
appear close to the second premolar.




DIGITAL RADIOGRAPHY



A digital radiograph consists of a number of pixels(picture elements)
and each pixel is the smallest picture element of the image.



DIRECT DIGITAL IMAGING -a digital sensor is used.
CCD
CMOS
STORAGE PSP



INDIRECT DIGITAL IMAGING -imaging plates of various sizes are used
in place of x ray film.

INPUT

IMAGE
PROCESSING

OUTPUT



Indirect system



Uses film like photo phosphor plates that are activated using X-rays,
then scanned in special devices that read the image from the plate.



These imaging plates which replace conventional screen film system
are a polyester base sprayed and coated with a crystalline halide
composed of Europium activated Barium fluorhalide compounds.
(BaF Br : Eu2+).




Principle:



When X-ray beams are irradiated onto Imaging Plate (IP), the X-ray
energy is temporarily stored within the crystals.



Next, a He-Ne laser beam is irradiated onto IP, and the X-ray energy
stored in the crystals is emitted as fluoroscent blue light.




Fluoroscent optic signals converted to time serial electric signals.
A very small amount of stored X-ray energy remains in IP even after
the latent image has been converted to light.



This residual energy can easily be eliminated by exposing IP to
sunlight. Consequently IP can be used repeatedly.



Merits:



No chemicals are required for processing.



No film and chemical waste disposal problem.



One of the main advantages is their similarity to film. They are thin or
often thinner than film plates.



Elimination of problems that can be caused through processing faults.

•

Images can be stored together with patient records thus moving the
practice towards a truly paperless environment.

•

The plates are more flexible and thinner than direct type sensors.




Ease of positioning the plates as compared to wired sensors used in
direct systems which are difficult to position especially when
assessing posterior teeth.



Unlike direct sensors, plates are relatively inexpensive, which is wise
since they typically must be replaced after 500-700 uses.



Demerits:



The plates get easily scratched and while they theoretically can last through
500 uses, damage normally requires their replacement frequently.



Phosphor plates have less resolution in line pairs / mm than sensors.




Also because of the steps needed to obtain an image, the time needed to take
phosphor plate image is very close to the time needed for film.



Examples :- GENDEX DENOPTIX and SOREDEX DIGORA.

Direct digital sensor systems


Direct systems use a wire based sensor that contains a computer chip inside
a protective casing, the sensor being further connected to the computer.




Principle:



The computer chip which is a Charged Couple Device (CCD)
captures light information that is emitted by a phosphor plate in the
sensor, when it is hit by X-rays.



The information is then directly transmitted into the computer,
digitized, then displayed as an X-ray image on the computer.



-

Examples of leading manufacturers of direct systems are
Schick CDR, Trex.
Trophy RVG, New Image Ni-Dx, Siemens.
Sirona Sidexis, Dexis Digital X-ray
Cygnus Ray 2
Sens-A-Ray


Advantages of digital radiography
over conventional radiography :


Working time from image exposure to image display is reduced .



Chemical processing is avoided, so there are fewer hazards to the
environment and no image errors because of processing.



Exposure to radiation is reduced . Greater dynamic range is available
compared with film; overexposure and underexposure are less apt to occur,
contrast and density can be enhanced, size can be changed, and colors added.



Cephalometric measurements and analyses can be more easily performed with
the aid of task dependent software.



Storage and communication are electronic, so copies of an image can be sent
to others without losing the original.


Radiovisiography


Introduced by Moyer et al in 1989.



Radio part- sensor – Exchangeable scintillation screen,
A fiber optic,
miniature CCD device.



Visio part- stores & converts point by point into one of 256
discrete gray scales.



Graphy part

Digital Radiograph (RVG)
sensor head

object

x-ray
source
scintillator

CCD

fibre optic
layer

transmitter
converter
amplifier


PC

quantizer
amplifier
receiver

Radiovisiography


RVG comprises of four basic components:



An X-ray set with electronic time; an intra-oral sensor; a display processing
unit (DPU); and a printer.



Features of RVG:



1) Image Enhancement
A) A smoothing (low-pass) filter eliminates ‘noise/scatter’ that may be
present within the image;



B) Edge enhancement (high-pass filter) enhances the ‘edges’ between
adjacent regions of different grey-level values, but increases the electronic
noise level (this feature can be further improved by use of the next method
of enhancement)




C) Edge detection (Laplacian)- enhances the edges within image but
eliminates detail from the rest of the time.



2) Radiation dose - The specific radiation dose required is
dependent on the area of the mouth to be irradiated, for example the
dose required is greater in the maxillary molar region than the lower
incisor region.



3) Resolution

- The introduction of the ZHR function increased the

resolution to 11 line pairs/ mm in this mode. This measurement has
been confirmed by Benz and Mouyen. The authors found a resolution
of 7 line pairs/ mm in standard mode.




4) Collimation -

Incorporating rectangular collimation to the

RVG sensor would therefore permit a further decrease in radiation
dose.

Merits:


The image processing time is very short being about 5 seconds.



Sensors can be easily moved from operatory to operatory, allowing the
operators to work with a minimum number of sensors and within a computer
network environment.



The problems that can be caused through processing faults are eliminated.



It gives opportunity to enhance the images for more precise viewing.




Demerits:



They are thicker than films and have cables running off the sensors which
some patients don’t tolerate well.



The high cost of sensor is another drawback.



There is greater difficulty in placing the sensor with a small percentage of
patients due to its rigidity.


DIRECT DIGITAL SENSORS





CHARGE-COUPLED DEVICE (CCD)
COMPLEMENTARY METAL OXIDE SEMICONDUCTOR
ACTIVE PIXEL SENSOR (CMOS-APS).
Photo stimulable phosphor plates (PSP)

CHARGE-COUPLED DEVICE (CCD)


The CCD is a solid-state detector composed of an array of X-ray or light
sensitive pixels on a pure silicon chip.



A pixel or picture element consists of a small electron well into which the Xray or light energy is deposited upon exposure.



The individual CCD pixel size is approximately 40µ with the latest versions in
the 20µ range. The rows of pixels are arranged in a matrix of 512 x 512 pixels.



There are two types of digital sensor array designs: AREA AND
LINEAR.



Area arrays are used for intra oral radiography,



Linear arrays are used in extraoral imaging.



Area arrays are available in sizes comparable to size 0, size 1, and
size 2 film, but the sensors are rigid and area for image acquisition.


X-RAY IMAGING WITH CCD
SCINTILLATOR
- converts x-radiation to photons
(light)
FIBRE OPTIC LAYER
- conducts photons to CCD
- stops x-radiation
CCD
- converts photons to electrons
(charge)
ELECTRONIC CIRCUIT
- amplifies the signal
- converts the analog signal to digital

Xeroradiography.


Records images without film.



Consists of image receptor plates –selenium particles.



Latent image is converted to a positive image –process called development in
processor unit.



Advantages :



Reduced radiation dose.



Image can be produced in 20 seconds.



Edge enhancement effect .



Ability to have both positive and negative prints.



Improves visualization of files and canals.



Two times more sensitive than conventional D-speed films.



Disadvantages:



Exposure time varies according to the thickness of plate.


DIGITAL SUBSTRACTION RADIOGRAPHY.


This is a technique by which stuctured noise is reduced in order to
increase the detectability of changes in the radiographic pattern.



The structured noises are the images which are not of diagnostic
value and which interfere in routine interpretation of radiographs,i,e,
required areas are enlarged against a background.-



“Image-enhancement method”-area under focus displayed against a
neutral background




Standard radiographs-are produced with identical exposure geometry.



Reference/baseline image.



Follow up image-for comparison.



The difference between original and subsequent images shows up as
dark/bright areas.






Bright area-when the change represents-gain
Dark area-when the change represents-loss.

The strength of digital substraction radiograph is that it cancels out the
complex anatomical background against which this change occurs.

Comparing baseline to follow up images made at 3,6,12 months following endodontic
therapy,
Column 3 indicates substracted of follow up images from baseline radiographprogressive remineralisation of distal root of first molar is seen




Applications



Useful in detecting progess of remineralisation and demineralisation
pattern of dentinal caries, diagnosis of incipient caries.



Assess success of root canal treatment detecting periapical lesions.



90% accurate in detecting as little as 5%mineral loss as compared to
conventional radiograph(30-60%loss)


Computed tomography


Computed tomography (CT) has evolved into an indispensable
imaging method in clinical routine.



It was the first method to non-invasively acquire images inside the
human body that were not biased by superposition of distinct
anatomical structures.



CT yields images of much higher contrast compared with
conventional radiography.



During the1970s, this was an enormous step toward the advance of
diagnostic possibilities in medicine.



PRINCIPLE OF COMPUTED TOMOGRAPHY



In conventional CT, the X-ray tube and detector rotate around the
patient with the table stationary.



The X-ray beam is attenuated by absorption and scatter as it passes
through the patient with the detector measuring transmission



Multiple measurements are taken from different directions as the tube
and detector rotate.



A computer reconstructs the image for this single “slice.” The patient
and table are then moved to the next slice position and the next image
is obtained.

COMPUTED TOMOGRAPHY
Parts of the Equipment;
1.
Scanner ( movable x
ray table + gantry)
2.
Computer system
3.
A display console


Fig. 4: Schematic illustration showing the continuous
relationship for different projection angles and related
apertures existing between transmission radiography at one
extreme and conventional computed tomography at the
other.


RADIATION DOSAGE FOR CT

Radiation dosage

1.536 rad for
a single section
1.8432 rad for

multiple sections
Estimated dose to the centre of the condyle
with CT is 180mR

ADVANTAGES


Eliminates the super-imposition of images of structures outside the
area of interest.



Because of the inherent high-contrast resolution of CT differences
between tissues that differ in physical density by less than 1% can be
distinguished.



Very small amounts and differences

in X-ray absorption can be

detected. This in turn enables:


Detailed imaging of intracranial lesions



Imaging of hard and soft tissues



Excellent differentiation between different types of tissues both
normal and diseased



Images can be manipulated.



Axial tomographic sections are obtainable



Reconstructed images can be obtained from information obtained
in the axial plane.



Images can be enhanced by the use of IV contrast media (so
altering the patient) providing additional information


DISADVANTAGES


Need for contrast media for enhanced soft tissue
contrast.



Tissue non-specificity i.e. it does have ability to
highlight any particular organ/ tissue.



Cost concerns .




The equipment is very expensive.



Very thin contiguous or overlapping slices may result
in a generally high dose investigation.



Metallic objects, such as fillings may produce marked
streak or star artefacts across the CT image.



Inherent risks associated with IV contrast agents .






IMAGE RECONSTRUCTION
In CT a cross- sectional layer of the body is divided in to many
tiny blocks.



Each block is assigned a number proportional to the degree the
block attenuated the x-ray beam.



The individual blocks are called “Voxels and Pixels”.



A voxel is a volume element and the pixel is a picture element.



Their composition & thickness along with the quality of the
beam determines the attenuation coefficient .

Cone-Beam computed tomography


CBCT is an x-ray imaging approach that provides high
resolution 3-dimensional images of the jaws and teeth.



Provide valuable information not contained in conventional 2
dimensional films.



CBCT shoots out a cone-shaped x-ray beam and captures a large
volume of area requiring minimal amounts of generated x-rays.



Within 10 seconds, the machine rotates 360º around the head and
captures 288 static images.



Advantages:



Precise identification and detection of periapical lesions.



Detection of mandibular canal.



Complete 3-d reconstruction and display from any angle.



Patient radiation dose 5 times lower than normal ct..



Accurate 3d imaging,excellent resolution.



Inherent quickness in volumetric data acqusition and potential for
low cost compared to ct



It requires only a single scan to capture the entire object ,with
reduced exposure time.



Micro – CT



Recently, micro-CTs, which essentially comprise a miniaturized
design of the cone beam CTs -typically used for non destructive
three-dimensional microscopy have become commercially
available.



The X-rayed measuring field usually as small as 2 cM3 in
volume.





Micro-CT desk device of Sky-Scan Inc. at the
Institute of Medical Engineering.
The object to be examined is placed on a rotating
specimen holder inside the measurement chamber.
The measurement field is about 2cm3 volume.


TUNED APERTURE COMPUTED TOMOGRAPHY
(TACT)


Improve accuracy in caries diagnosis because of its 3-D or pseudo
3-D capabilities.



Principle of TACT:



TACT slices can be produced from an arbitrary number of X-ray
projections, each exposed from a different angle.



Using the TACT algorithm, it is possible to use one X-ray source and
move it through several points in space or use several fixed sources to
collect multiple X-ray projections which in turn can be processed to
produce TACT slices .

Fig. 5: Arbitrary example of generalized TACT projection geometry applied to a simple cylindrical object.




TACT useful in



Detection of caries and recurrent caries ,



Periodontal bone loss,



Periapical lesion localization,



Tmj bone change.


Magnetic Resonance Imaging
Principles:
Magnetism is a dynamic
invisible
phenomenon
consisting of discrete fields of
forces.
Magnetic fields are caused by
moving electrical charges or
rotating electric charges.
Images generated from protons
of the hydrogen nuclei.
Essentially imaging of the water
in the tissue.



The technique is based on the presence of specific magnetic

Magnetic Resonance Imaging

properties found within atomic nuclei containing protons and
neutrons,


Inherent property of rotating about their axis



Causes a small magnetic field to be generated around the
electrically charged nuclei.



When dipoles exposed within a strong electric field



Orientation in response to the field



Depending on density and spatial relation



Signal interpreted and image produced

Equipment;
1.
The Gantry ;houses the
patient. Patient is
surrounded by magnetic
coils
2.
Operating console ;
where the operator
controls the computer
and scanning procedure
3.
Computer room
network.



When images are displayed; intense signals show as white and weak
ones as Black and Intermediate as shades of gray.



Cortical bone and teeth with low presence of hydrogen are poorly
imaged and appear black.


Advantages of MRI
•

It offers the best resolution of tissues of low inherent
contrast.

•

No ionizing radiation is involved with MRI

•

Direct multiplanar image is possible without reorienting the
patient.

Disadvantages:




Long imaging time.
Potential hazard imposed by the presence of ferromagnetic
metals in the vicinity of the imaging magnet.




Complications;



Magnetic forces and radio waves - not know to produce any
biological side effects in man.
Non invasive technique and can be used in most patients.





Contraindications;



Patients with cardiac pacemakers.
Patients with cerebral metallic aneurysm clips. Slight movement
of the clip could produce bleeding
Stainless steel and other metals produce artifacts ; obliterate
image details of the facial area.*


















Indications
Assessing diseases of the TMJ
Cleft lip and palate
Tonsillitis and adenoiditis
Cysts and infections
Tumors

Short comings;
Inability to identify ligament tears or perforations
Dynamics of tissue joint not possible
Cannot be used in patients suffering from claustrophobia.


d) Ultra sound scanning.


Ultra high frequency sound waves are used.



The reflected sound waves are processed to electrical signal

that is

amplified, processed and ultimately displayed on a monitor.


Technique currently in use permit echoes to be processed at a
sufficient rate to allow for the perception of motion it is known as
Real-time imaging.



US waves are generated by a quartz or synthetic ceramic crystal when
it is exposed to an alternating current of 3-10 Mhz. as a result of the
piezoelectric effect, the crystal distributes US waves oscillating at the
same frequency



US image produced - automatic movement of the crystal over the
tissue of interest.



As each movement gives one image of this tissue (depending on its
plane) and there is a frequency of 30-50 images per s, they appear in a
screen as moving images.



Useful adjunct to conventional radiography in the management
of extensive periapical lesions, as it provides specific
information on the size of the lesion


CONCLUSION


New approaches to radiography have been and are being
developed.



These are unique; some will improve existing techniques
in addition to decreasing the radiation dose to patients.



This new technology includes digital radiography, digital
subtraction radiology, and tomography.


References
•

•
•
•

•
•
•

Dental radiography :principles and techniques by Laura
jansen ,Haring.4th edition
Textbook of Endodontics by ingle,6th edition
Principles and practice of endodontics by walton. 4th edition
Radiographic manifestations of periapical inflammatory
lesions How new radiological techniques may improve
endodontic diagnosis and treatment planning.(endodontic
topics 2004)
Textbook of Endodontics by Arnaldo Catelucci.
Oral radiology :white and pharaoh 6th edition
Google n internet sources

Thank you!

Leader in continuing dental education


Recent advances in imaging techniques/ /certified fixed orthodontic courses by Indian dental academy

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