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INDIAN DENTAL ACADEMY Leader in continuing dental education

Oral Radiology Lectures

Recent Advances In Imaging Techniques

Contents •


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.


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 ď Ž

Application of radiography in endodontics DIAGNOSIS • Identifying caries

TREATMENT •Determining length


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

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

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Vertical angulation : CR perpendicular to the imaginary bisector .

Improper vertical angulation


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)


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 ď Ž

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.

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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.

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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.

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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.


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


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




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+).


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.


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.


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.


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.


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


x-ray source scintillator


fibre optic layer

transmitter converter amplifier


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.


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.




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.


Exposure time varies according to the thickness of plate.


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


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.


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

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


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


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.


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.

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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.


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.

ď Ž

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

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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.


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.


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


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

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