Dental Imaging by Dina Osman

Dr Mohammad Fitri Bin Khalil 850620-13-5127 Nuclear Medicine P-IPM 0022/16

2016-10-11 06:22:24 UTC

Components:
Dental x-ray vary in size and appearance. typical dental x ray machine consist of 3 parts:
1. control panel - contains regulating devices
2. extension arm or bracket - enable the tube to be positioned
3. tube head - contains x ray tube from which x rays are generated

Technique:
Two basic technique are employed in intraoral radiography.
1. Bisecting technique -
principle is applied when the film packet is not, or cannot be placed parallel to the long axes of the teeth. To cast a shadow of a tooth onto a film, the angle form by the long axis of the tooth and the plane of the film must be bisected. Need to identify the long axis of the tooth and find the long axis of the packet as it is placed next to the tooth. After visualising these two planes, an imaginary line called the bisector which bisect the angle where the long axis of the tooth and the long axis of the film meet. Radiation beam is directed perpendicular to the imaginary bisector and not to the long axis of the tooth or the film plane.
2. Paralleling technique -
The film is placed parallel to the long axes of the teeth being radiographed.
The central ray is directed at the right angles to both teeth and film.
The paralleling technique achieve parallelism by placing the film away from the crowns of the teeth. Paralleling is accomplished by using a film folder specifically designed to allow the patient to stabilise the film packet in this position away from the crowns of the teeth.

Image formation:
X-ray tube:
After machine is switch on, the currents enter the filaments circuit of the x ray machine. Transformer (step down) reduces the voltage before it enters the filament circuit and heats the filament of the cathode to incandescent, separating electrons from their atoms. The degree of the filament heated depends on the milliamperage that is selected:
-the higher the mA, the more electrons in the electron clouds.
When electrons are in excited state, they hover around the filament wire recessed in the focusing cup. After a time delay of less than 1/2 seconds, the line current enters the cathode-anode high voltage circuit. A step up transformer then increases the voltage to impart sufficient force to propel the free electron to the focal spot on the target anode. These high velocity electrons are stopped by the tungsten atoms in the target resulting in the production of general radiation (Bremsstrahlung) and characteristic radiation. This kinetic energy is converted into 99% heat and 1% x rays.
A window is located at a point where the emission of x rays is most intense and aligned with an opening in the tube housing called the port that is covered by a permanent seal of glass or beryllium or aluminium. After the beam escape through the port, the lead collimator further restricts the x ray beam to the desired size.
X ray beam is cone shaped. The primary beam is the original useful beam that originates at the focal spot and emerge through the port of the tube head. The x ray beam formed at the focal spot is polychromatic consisting of x rays of various wavelength. Only x ray with sufficient energy to penetrate oral structures are useful for diagnostic radiology. X ray of low penetrating power (long wavelength) add dose to patient but not information. To reduce this, a thin sheet of aluminium called filter is placed in the path of x ray.
Intensity of x ray beam refers to quantity and quality of x rays (product of number of x ray and energy of x ray per unit of area per unit of time). Quantity refers to number of x ray in the beam. Quality refers to energy or penetrating power of the the x ray beam.

Composition of dental x ray films:
1. Film base - to provide support for the fragile emulsion and to provide strength of handling.
2. Adhesive - each emulsion is attached to the base by thin layer of adhesive.
3. Emulsion - composed of gelatine and function to keep silver halide crystal evenly suspended over the base.
4. Silver halide crystal - sensitive to radiation and when exposed to x ray will retain the latent image.
5. Protective layer - to protect the emulsion from scratch and rough handling.

Latent image formation:
X ray radiation strike and ionise some but not all the silver halide crystal resulting the formation of latent image (invincible image). Not all radiation will reach the film emulsion. Enamel and bone will absorb or stop the x ray from reaching the film than the less dense structures such as the dentin or pulp chambers of the teeth. The varying thickness of the objects in the path of the beam will allow more or less radiation to pass through and reach the film emulsion. When radiation does reach the emulsion, the silver halide crystal are ionised or separated into silver and bromide ions that stores this energy as a latent image.

Manual film processing:
1. Developing - The film hanger with the attached films should be immersed into the developer tank first.
2. Rinsing - Purpose is to remove as much of the alkaline developer as possible before placing the film to fixer
3. Fixing - the film hanger with the attached films should be immersed into the fixer insert tank next, gently agitating the hanger to keep air bubbles from clinging to the film. Recommended fixing time is 10 minutes.
4. Washing - Removes all chemicals left. Films should be placed in the circulating water for 20 minutes.
5. Drying - The film hanger should be lifted above the water tank and allowed to dry. Use a fan or blower to expedite the drying process.

Automatic film processing:
Requires the use of an automatic processor unit. The automatic processor uses a roller transport system to move the film through the processing cycle. It consist of three compartments: developing, fixing and water, and drying chamber. Unwrapped film is fed into the film feed support slot on the outside of the processor. The roller transport system moves the film through an opening on the outside of the processor called the film recovery slot.

DR GOURI KUMAR DAS770419145876 PIPM0011/16

2016-10-13 13:56:37 UTC

DENTAL IMAGING
- OVERVIEW
There are two main types of dental x-rays: intraoral (the x-ray film is inside the mouth) and extraoral (the x-ray film is outside the mouth).

Intraoral x-rays are the most common type of x-ray. There are several types of intraoral x-rays. Each shows different aspects of teeth.

Bite-wing x-rays show details of the upper and lower teeth in one area of the mouth. Each bite-wing shows a tooth from its crown (the exposed surface) to the level of the supporting bone. Bite-wing x-rays detect decay between teeth and changes in the thickness of bone caused by gum disease. Bite wing x-rays can also help determine the proper fit of a crown (a cap that completely encircles a tooth) or other restorations (eg, bridges). It can also see any wear or breakdown of dental fillings.
Periapical x-rays show the whole tooth — from the crown, to beyond the root where the tooth attaches into the jaw. Each periapical x-ray shows all teeth in one portion of either the upper or lower jaw. Periapical x-rays detect any unusual changes in the root and surrounding bone structures.
Occlusal x-rays track the development and placement of an entire arch of teeth in either the upper or lower jaw.

Extraoral x-rays are used to detect dental problems in the jaw and skull. There are several types of extraoral x-rays.

Panoramic x-rays show the entire mouth area -- all the teeth in both the upper and lower jaws -- on a single x-ray. This x-ray detects the position of fully emerged as well as emerging teeth, can see impacted teeth, and help diagnosis tumors.
Tomograms show a particular layer or “slice” of the mouth and blur out other layers. This x-ray examines structures that are difficult to clearly see because other nearby structures are blocking the view.
Cephalometric projections show an entire side of the head. This x-ray looks at the teeth in relation to the jaw and profile of the individual. Orthodontists use this x-ray to develop each patient’s specific teeth realignment approach.
Another test that uses x-rays is called a sialogram. This test uses a dye, which is injected into the salivary glands so they can be seen on x-ray film (Salivary glands are a soft tissue that would not be seen with an x-ray.) Dentists might order this test to look for salivary gland problems, such as blockages, or Sjogren’s syndrome (a disorder with symptoms including dry mouth and eyes; this disorder can play a role in tooth decay).
Dental computed tomography (CT) is a type of imaging that looks at interior structures in 3-D (three dimensions). This type of imaging is used to find problems in the bones of the face such as cysts, tumors, and fractures.
Cone Beam CT is a type of x-ray that creates 3-D images of dental structures, soft tissue, nerves, and bone. It helps guide tooth implant placement and evaluates cysts and tumors in the mouth and face. It also can detect problems in the gums, roots of teeth, and jaws. Cone beam CT is similar to regular dental CT in some ways. They both produce accurate and high quality images. However, the way images are taken is different. The cone-beam CT machine rotates around the patient’s head, capturing all data in one single rotation. The traditional CT scan collects “flat slices” as the machine makes several revolutions around the patient’s head. This method also exposes patients to higher level of radiation. A unique advantage of cone beam CT is that it can be used in a dentist’s office. Dental computed CT equipment is only available in hospitals or imaging centers.
Digital imaging is a 2-D type of dental imaging that allows images to be sent directly to a computer. The images can be viewed on screen, stored, or printed out in a matter of seconds. Digital imaging has several other advantages compared with traditional x-rays. The image taken of a tooth, for example, can be enhanced and enlarged. This makes it easier for your dentist to see the tiniest changes that can’t be seen in an oral exam. Also, if necessary, images can be sent electronically to another dentist or specialist for a second opinion or to a new dentist (eg, if you move). Digital imaging also uses less radiation than x-rays.
MRI imaging is an imaging method that takes a 3-D view of the oral cavity including jaw and teeth. (This is ideal for soft tissue evaluation.)
Another test that uses x-rays is called a sialogram. This test uses a dye, which is injected into the salivary glands so they can be seen on x-ray film (Salivary glands are a soft tissue that would not be seen with an x-ray.) Dentists might order this test to look for salivary gland problems, such as blockages, or Sjogren’s syndrome (a disorder with symptoms including dry mouth and eyes; this disorder can play a role in tooth decay).

INTRA ORAL RADIOGRAPHIC TECHNIQUES :

- INTRA ORAL PERIAPICAL RADIOGRAPHY

- BITEWING RADIOGRAPHIC TECHNIQUE

- OCCLUSAL VIEW RADIOGRAPHIC TECHNIQUE

- LOCALIZATION TECHNIQUE

X-RAY FILM • COMPOSITION • It has 4 principal components.

1.Film base

2.Adhesive layer

3.Film emulsion

4.Protective layer

X RAY FILM SIZE •

SIZE-0 : 22X35mm in children •

SIZE-1 :24x40mm for anteriors in adults •

SIZE-2 :31X41mm standard size

INTRAORAL FILM SPEED •

Film speed refers to amount of radiation required to produce a radiograph of standard density • An alphabetical classification system is used to identify film speed

Speed ratings ranging from A speed [slowest] to F speed [fastest]

Only D speed and E speed film is used for intra oral radiograph.

INTRA ORAL PERIAPICAL RADIOLOGY •

Periapical radiography describes intra oral techniques designed to show individual teeth and the tissues around the apices .

Each film shows two to four teeth and provides detailed information about the teeth and surrounding alveolar bone

INDICATIONS :

- Detection of infection and pathoses

- Assessment of periodontal status , state of periodontal membrane space and lamina dura

- After trauma to the teeth and associated alveolar bone

- Assessment of presence and position of unerupted teeth

- Assessment of root morphology , before extractions

- During endodontics

- Preoperative assessment and post operative appraisal of apical surgery

- Detailed evaluation of apical cysts and other lesions with in alveolar bone

- Assessment of position and prognosis of implants

PERIAPICAL RADIOGRAPHY :

TECHNIQUES :

There are two basic techniques for obtaining periapical radiographs:

- Paralleling technique.

- Bisection of the angle technique.

The American Academy of Oral and Maxillofacial Radiology and the American Association of Dental Schools recommended the use of the paralleling technique because it provides the most accurate image. <

The paralleling technique of intraoral radiography was developed by Gordon M. Fitzgerald, and is so named because the tooth, receptor, and end of the position indicating device (PID) are all kept on
parallel planes. Its basis lies in the principle that image sharpness is primarily affected by focalreceptor distance (distance from the focal spot within the tube head and the receptor), object receptor distance, motion, and the effective size of the focal spot of the tube
The paralleling technique is the most accurate intraoral radiographic technique, meeting four of the five principles of accurate image projection. The paralleling technique does not allow for as short as possible object-to-receptor distance (Principle Three) as desired. In order to achieve parallelism, it is necessary to place the receptor more lingual to the structures. The use of receptor-holding devices helps to standardize and execute this technique.

The paralleling technique is accomplished by placing the receptor parallel to the long axis of the tooth. After this parallel relationship has been established, the central ray must be directed perpendicular to both the tooth and receptor. Because the receptor cannot always be placed as close as possible to the tooth due to the receptor-holding device or anatomical obstacles, image magnification may occur. However, this can be compensated for by using an increased source-object distance, which decreases magnification and unsharpness. The paralleling technique, when performed correctly, is superior to the bisecting angle technique by producing an image with both linear and dimensional accuracy.

Bisecting Angle Technique
Bisection of the angle technique
The bisecting-the-angle or bisecting angle technique is based on the principle of aiming the central ray of the x-ray beam at right angles to an imaginary line which bisects the angle formed by
the longitudinal axis of the tooth and the plane of the receptor. To bisect is to divide a line or angle into two equal portions. A bisector is a plane or line that divides a line or angle into two equal
portions.

The bisecting angle technique is accomplished by placing the receptor as close to the tooth as possible. The central ray of the x-ray beam should be directed perpendicular to an imaginary line that bisects or divides the angle formed by the long axis of the tooth and the plane of the receptor. Principle Three of accurate image projection is met by using this technique.

Images produced by the bisecting angle method are in true linear relationship. However, this technique does not follow several of the principles of accurate image projection and also requires accurate visualization of the bisected angle in order to accomplish it properly. Bisecting angle images are not anatomically accurate and are prone to shape distortion. However, the bisecting angle provides an alternative technique when parallel placement cannot be achieved or occlusal techniques are employed

Bitewing Technique

The bitewing radiographic image is used to examine the interproximal surfaces of the teeth and is particularly useful for the detection of dental caries and alveolar bone levels. The receptor is placed into the mouth parallel to the crowns of the maxillary and mandibular posterior teeth. The patient stabilizes the receptor by biting on a tab or bitewing holder. The central ray of the x-ray beam is then directed through the contacts of the posterior teeth and at a +5º to +10º vertical angle.

Receptor-holding devices or bitewing tabs may be used to stabilize the receptor in the mouth. Receptors may be positioned in the horizontal or vertical dimension with this technique, depending upon the area to be examined. Bitewings may be taken in the anterior segments of the dentition as well. Some dentists, particularly periodontists, may prescribe a 7 image bitewing survey consisting of 4 vertical bitewings in the posterior with size 2 receptors and 3 vertical bitewings in the anterior using size 1 receptors. This permits evaluation for both alveolar bone loss and caries detection.

INTRAORAL IMAGE RECEPTORS
Intraoral radiographic images can be acquired with digital receptors or radiographic film. Digital image receptors include rigid sensors and phosphor plate receptors. Intraoral digital receptors are available in sizes comparable to traditional dental film. Rigid digital receptors are typically available in sizes 0, 1, and 2 while the plate receptors are available in sizes 0, 1, 2, 3, and 4. The range of available sizes is dependent on the specific product manufacturer. Digital receptors cannot be sterilized. Therefore, it is important to utilize proper infection control techniques to prepare and cover digital receptors for placement inside the mouth. Refer to manufacturer recommendations for proper infection control procedures for digital receptors.

Rigid digital receptors are categorized as direct digital receptors and are available in both wired and wireless formats. These rigid receptors are usually either a charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) sensors. The same receptor can be used for each projection by repositioning the receptor for the next view after exposure. These direct digital receptors convert the x-ray beam into an electronic signal, which is then converted into a digital signal displayed as a grayscale image and stored in a computer. The digital image is displayed on the computer monitor almost immediately.

Indirect digital receptors known as storage phosphor plates (SPP) or photostimulable phosphor plates (PSP) are also available. These plates have a europium-activated barium fluorohalide emulsion which stores the latent image after exposure. Phosphor plates require careful handling to avoid abrasion of the emulsion and resultant image artifacts.1 A separate plate is needed for each projection and the plates must be erased with white light before reuse. After the plate is exposed, the receptor is laser scanned and the image is digitized and displayed on the computer monitor. In newer scanner models, plate erasure occurs after the scanning step but before exit of the plate from the device.

Digital images can be adjusted to view the information in different ways. Software enhancement features include changes in density, contrast, colorization, zoom or magnification of particular areas of interest, measurement, image reversal and the application of filters for noise reduction or edge sharpening. Image enhancement tends to be subjective and is dependent on the visual preferences of the clinician interpreting the image.2 Subtraction can also be performed using digital images. This is the process used to compare an area before and subsequent to treatment to assess progress or change. The computer subtracts the two images and the image that remains represents the difference or change between pre- and post-treatment. The challenge with digital subtraction is the need to register the images prior to subtraction. The images are seldom identical in their placement or projection geometry and must be matched structurally in order to determine the actual change that occurred between the two images taken at different points in time.3

After the image has been obtained, it can be stored in the computer, printed or sent electronically in instances of referral or insurance claims. Digital radiography facilitates storage and easy access for image viewing, duplication, printing or electronic transfer. Digital imaging is an integral part of a complete electronic record without the need for physical storage space and fear that the images will be damaged or destroyed. However, it is important to back-up patient records daily to avoid lost data. There are a variety of media that can be used for back-up storage such external hard drives, CDs, DVD or cloud technology.

Digital imaging like film radiography utilizes x-ray beam collimators to reduce the area of exposure at the skin surface with a preference for rectangular collimation and receptor holding devices to reduce retakes. Rectangular collimation more so than round reduces both primary and scatter radiation which not only benefits the patient but also improves image quality.4 Because digital receptors are more sensitive to scatter radiation than film, rectangular collimation is recommended for use with digital imaging systems. There are a number of commercially available devices that the clinician can utilize to achieve rectangular collimation and reduce exposure.5 Current digital receptors offer equal or greater dose reduction than F-speed film and comparable diagnostic utility.2

The majority of technique and exposure errors can be produced with digital receptors as with conventional film with a few exceptions. The greatest advantage of digital imaging is elimination of processing errors which are the most common causes of retakes in film-based radiography. Digital imaging also eliminates the darkroom, processor and chemical maintenance which requires additional time and effort when done properly, and lengthy processing time. Regardless of the imaging system employed, the clinician should take all necessary steps to reduce the amount of radiation the patient receives in compliance with the ALARA Principle (As Low As Reasonably Achievable). Primary to dose reduction is the application of selection criteria in the determination of necessary radiographs.4

DR GOURI KUMAR DAS

2016-10-13 15:23:20 UTC

Dental Imaging Homework by MUHAMMAD ADIB ABDUL ONNY - 870201146145 - PIPM0013/16

2016-10-13 15:40:54 UTC

Component of dental x-ray

Dental X-ray machine can be divided into 3 areas (parts);

1. Component parts

2. X-ray tube

3. X-ray generating apparatus

The component parts consist of 3 visible component parts;

a) control panel

- contains on and off switch

- exposure button

- control devices for time, kilovoltage and miliamperage selectors to regulate x-ray beam.

b) extension arm

- wall mounted

- suspend the x-ray tube head

- allow movement and positioning

c) tubehead

- tightly sealed, heavy metal housing that contains the x-ray tube that produces dental x-ray.

- Component of tubehead includes:

ü Metal housing – filled with oil and protects the x-ray tube and grounds the high voltage components.

ü Insulating oil – prevents overheating by absorbing the heat created by the production of x-ray.

ü Tubehead seal – aluminium or leaded-glass covering the tubehead that permits the exit of x-rays from the tubehead. Seals oil in the tubehead and acts as filter to the x-ray beam.

ü Transformer – alter voltage of incoming electricitiy

ü Aluminium disks or sheet – 0.55mm thick aluminium placed in the path of x-ray beam to filter out the non-penetrating, longer wavelength x-ray.

ü Lead collimator – with central hole that fits at metal housing opening which restrict the size of x-ray beam.

ü Position-indicating device (PID) – extends from opening of metal housing and aims and shapes the x-ray beam. Referred to as cone.

ü X-ray tube – produce x-ray beam via beaming electron at cathode to anode (tungsten target). Principle similar to x-ray production of x-ray machine.

Other important component

Other component in dental x-ray machine includes:

1. Film Holders

2. Beam alignment devices

Film Holders

- Device used to hold and align intraoral dental x-ray films in the mouth.

- Eliminate the need for patient to stabilize the film.

Beam alignment devices

- Used to help dental radiographer position the PID in relation to the tooth and the films.

- Can be used with collimating devices, which is a metal plate to restrict size of beam.

Principle of radiographic examinations

May involved two type of technique:

1. Intraoral projections (placed inside the mouth)

2. Extraoral projections (placed outside the mouth)

Intraoral Radiographic Examinations

- Radiographic inspection of the teeth and intraoral adjacent structures.

- Requires used of intraoral image receptors.

- Placed inside the mouth.

- Types:

I. Periapical examination

II. Interproximal examination

III. Occlusal examination

a) Periapical examination

- To examine the entire tooth (crown and root) and supporting bone

- Periapical receptor is used in periapical examination.

- 2 techniques:

-> Paralleling technique

-> Bisecting technique

b) Interproximal examination

- To examine the crowns of both maxillary and mandibular teeth on a single image.

- Useful in examining adjacent tooth surfaces and crestal bone.

- Bite-wing receptor used

- Technique used is the bite-wing technique.

c) Occlusal examination

- To examine large areas of the maxilla or the mandible on one image.

- Occlusal receptor is used

Complete mouth radiographic series / Full mouth series

- CMRS/FMS/FMX

- Series of intraoral dental radiographs that show all the tooth bearing areas of both jaws.

- These are the regions of the maxilla and mandible where the 32 teeth of the human dentition are normally located.

- This include dentulous (areas that exhibit teeth) and endentulous (no teeth present)

- Consist of periapical alone or periapical + bite-wing radiographs.

Extraoral Rdiographic Examinations

- A radiographic inspection of large areas of the skull or jaws requiring use of extraoral imaging receptors.

- Example of common extraoral radiographics examinations:

ü Lateral jaw

ü Lateral cephalometric

ü Panoramic radiograph

ü Posteroanterior

ü Submentovertex

Techniques:

1) Paralleling Technique

2) Bisecting Technique

3) Bite-wing Technique

4) Occlusal Technique

5) Localization Technique

6) Panoramic Imaging

Paralleling Technique

- Method to expose periapical and bite wing image receptors.

- Receptor is placed in the mouth parallel to the long axis of the tooth being radiographed with the central ray of x-ray beam is directed perpendicular to the receptor and the long axis of the tooth. A beam alignment must be used to keep the receptor parallel with the long axis of the tooth.

Bisecting Technique

- Can be used to exposed periapical images.

- Rule of isometry states that 2 triangles are equal if they have 2 equal angles and share common side.

- The receptor must be placed along the lingual surface of the tooth. At the point where the receptor contacts the tooth, the plane of the receptor and the long axis of the tooth form an angle. Visualization of imaginary bisector (plane that divides in half the angle formed by the receptor and the long axis of the tooth). Central x-ray beam is directed perpendicular to the imaginary bisector resulting in 2 imaginary equal triangles.

Bite-Wing Technique

- Method used to examine the interproximal surfaces of the teeth.

- The receptor is placed in the mouth parallel to the crowns of both maxillary and mandibular teeth. Receptor is stabilized when patient bites on bite-wing alignment device. Central of x-ray beam directed through the contacts of teeth using a vertical angulation of +10 degrees.

Occlusal Technique

- Used to examine large areas of the maxilla and mandible.

- Supplementary radiographic techniques that is used in conjunction with periapical or bite-wing images.

- When using film, it is positioned with the white side facing the arch that is being exposed and the receptor is placed in the mouth between the occlusal surface of maxillary and mandible.

Localization Technique

- Method to locate the position of a tooth or an object in the jaws.

- Can be used to obtained 3D information when buccal-lingual position of a structure need to be established.

Panoramic Imaging

- Wide view of the maxilla and mandible.

- An extraoral technique that is used to examine the maxilla and mandible on a single projections.

- Both receptor and tubehead rotate around patient, producing a series of individual images. When images are combined, an overall view of maxilla and mandible is created.

- The x-ray tube and receptor rotates around the patient in opposite direction producing a tomography image.

- Rotation centre is the pivotal point or axis around which the receptor and x-ray tubehead rotate and depends on manufacturer.

Image Production

X-ray beam passess through the teeth and adjacent structure to the x-ray film. Film serves as image receptor. Composition of x-ray film are:

- Film base

Ø Flexible piece of polyester plastic (0.2mm) in thickness that is constructed to withstand heat, moisture, and chemical exposure. It is transparent and exhibits a slight blue tint that is used to emphasize contrast and enhance image quality.

- Adhesive layer

Ø A thin layer of adhesive material that covers both sides of film base. Serves to attach the emulsion to the base.

- Film emulsion

Ø Is coating attached to both sides of the film base by adhesive layer to give film greater sensitivity to x-ray. It is a homogenous mixture or gelatin and silver halide crystals.

- Protective layer

Ø Thin, transparent coating placed over the emulsion. Serves to protect the emulsion surface from manipulation as well as mechanical damage.

Latent Image Formation

- Silver halide crystals absorbed x-radiation during x-ray exposure and store energy from the radiation.

- Stored energy in silver halide forms a pattern and creates and invisible image within the emulsion on the exposed film which cannot be seen and hence term latent image.

- X-ray photons hit the surface of the film emulsion, some silver bromide crystals are exposed to x-ray photons and ionized. The atoms of silver and bromide are separated. Irregularities in the lattice structure of the exposed crystals (sensitivity specks) attract the silver atoms. The aggregates of neutral silver atoms are known as latent image centres. Collectively, crystals with aggregates of silver at the latent image centres become the latent image on the film.

- Latent image remains invisible within the emulsion until it undergoes chemical processing procedures. Once processed, visible image is produced.

2016-10-13 15:50:44 UTC

DR GOURI

DR NIMALA BASKARAN Masters of Nuclear Medicine P-IPM0064/15 (831231-4-5504)DENTAL IMAGING

nimala — 2016-10-14 03:50:55 UTC

PARTS AND COMPONENTS OF THE DENTAL X-RAY MACHINE

The standard structural parts of the dental x-ray machine include:

1. a control panel (usually mounted behind a protective shield)

2. a tube head, which houses the dental x-ray tube

3. a flexible extension arm from which the tube head is suspended

The Control Panel:

i. contains on and off switch and indicator light

ii. exposure button and indicator light

iii. control devices for time, kilovoltage and miliamperage selectors to regulate x-ray beam.

- allow movement and positioning

c) tubehead

- tightly sealed, heavy metal housing that contains the x-ray tube that produces dental x-ray.

The Extension Arm:

i. The extension arm suspends the Xray tube head and houses the electricl wires that extend from the control panel to tube head

ii. The tube head is attached to the metal extension arm by means of a yoke that can revolve 360 degrees horizontally where it is connected. The construction of the yoke also provides vertical movement as well. Thereby, horizontal and vertical movement is possible.

The Tube Head:

i. Tightly sealed in a heavy metal housing is the x-ray tube, whereby the dental Xrays are produced.

Component of the Xray tube are :

i. Metal housing

a. Metal body of the tube head, surrounds the xray tube and transformer

b. filled with oil

c. Function : protects the x-ray tube and grounds the high voltage components

ii. Insulating oil

a. prevents overheating by absorbing the heat created by the production of x-ray.

iii. Tubehead seal

a. aluminium or leaded-glass covering the tubehead that permits the exit of x-rays from the tubehead.

b. Function : Seals oil in the tubehead and acts as filter to the x-ray beam.

iv. Aluminium disks

a. 0.55mm thick aluminium placed in the path of x-ray beam to filter out the non-penetrating, longer wavelength x-ray, which is less harmful to the patient ( thereby decreasing the skin dose).

v. Transformer

a. alter voltage of incoming electricitiy

vi. X-ray tube

a. Main Xray generating system

b. produce x-ray beams via beaming electron at cathode to anode (tungsten target). Principle similar to x-ray production of an x-ray machine.

vii. Lead collimator

a. with central hole that fits at metal housing opening which restrict the size of x-ray beam.

viii. Position-indicating device (PID)

a. which is also referred to as the cone, extends from opening of metal housing

b. Function : aims and shapes the x-ray beam.

TECHNIQUES OF DENTAL IMAGING

There are two main types of dental x-rays:

1. intraoral (the x-ray film is inside the mouth)

2. extraoral (the x-ray film is outside the mouth).

Intraoral x-rays are the most common type of x-ray. There are several types of intraoral x-rays. Each shows different aspects of teeth.

Bite-wing x-rays

Ø show details of the upper and lower teeth in one area of the mouth.Each bite-wing shows a tooth from its crown (the exposed surface) to the level of the supporting bone.

Ø Bite-wing x-rays detect decay between teeth and changes in the thickness of bone caused by gum disease. Bite wing x-rays can also help determine the proper fit of a crown (a cap that completely encircles a tooth) or other restorations (eg, bridges). It can also see any wear or breakdown of dental fillings.

Periapical x-rays

Ø show the whole tooth — from the crown, to beyond the root where the tooth attaches into the jaw.

Ø Each periapical x-ray shows all teeth in one portion of either the upper or lower jaw. Periapical x-rays detect any unusual changes in the root and surrounding bone structures.

Ø Occlusal x-rays track the development and placement of an entire arch of teeth in either the upper or lower jaw.

Ø Extraoral x-rays are used to detect dental problems in the jaw and skull. There are several types of extraoral x-rays.

Panoramic x-rays

Ø show the entire mouth area -- all the teeth in both the upper and lower jaws -- on a single x-ray.

Ø This x-ray detects the position of fully emerged as well as emerging teeth, can see impacted teeth, and help diagnosis tumors.

Tomograms show a particular layer or “slice” of the mouth and blur out other layers. This x-ray examines structures that are difficult to clearly see because other nearby structures are blocking the view.

Cephalometric projections show an entire side of the head. This x-ray looks at the teeth in relation to the jaw and profile of the individual. Orthodontists use this x-ray to develop each patient’s specific teeth realignment approach.

Another test that uses x-rays is called a sialogram. This test uses a dye, which is injected into the salivary glands so they can be seen on x-ray film (Salivary glands are a soft tissue that would not be seen with an x-ray.) Dentists might order this test to look for salivary gland problems, such as blockages, or Sjogren’s syndrome (a disorder with symptoms including dry mouth and eyes; this disorder can play a role in tooth decay).

Dental computed tomography (CT) is looks at the 3D dimension of the interior structures , to detect cysts, tumors, and fractures.

Cone Beam CT is a type of x-ray that creates 3-D images of dental structures, soft tissue, nerves, and bone. It helps guide tooth implant placement and evaluates cysts and tumors in the mouth and face. It also can detect problems in the gums, roots of teeth, and jaws. Cone beam CT is similar to regular dental CT in some ways. They both produce accurate and high quality images. However, the way images are taken is different. The cone-beam CT machine rotates around the patient’s head, capturing all data in one single rotation. The traditional CT scan collects “flat slices” as the machine makes several revolutions around the patient’s head. This method also exposes patients to higher level of radiation.

MRI imaging is an imaging method that takes a 3-D view of the oral cavity including jaw and teeth, better for soft tissue evaluation.

PRODUCTION OF THE DENTAL RADIOGRAPH

When an X-ray film has been exposed, it must be processed in order to produce a
permanent visible radiographic image that can be kept without deterioration for a number of

years. Processing transforms the latent image into a visible image. The term for the

several procedures that collectively produce the visible, permanent image is processing

and consists of developing, rinsing, fixing, washing and drying procedures.

1. Exposure - Latent image created.

2. Development - Converts latent image to black metallic silver.

3. Wash [stop bath] - Removes excess developer.

4. Fixing and Hardening - Dissolves out unexposed silver halide crystals.

5. Washing - Removes products of processing.

6. Dry - Removes water.

LATENT IMAGE FORMATION

Ø The latent (invisible) image formation is the ionization of the exposed silver bromide

crystals (by photon energy that emerges from the patient) occurring in the emulsion layer

before processing occurs.

Ø The primary interaction with the bromide crystals is by Compton and photoelectric interactions, thereby knocking out electrons. Thus, a physical change occurs when the radiograph is exposed.

Ø When X-ray photons [or light photons] strike the silver bromide crystals in the emulsion, minute amounts of silver ions are formed on thesurface of the crystal and bromine is liberated and is absorbed by the gelatin.

Ø Crystals are purposely constructed with electron traps (sensitivity specks) consisting of sulfur impurities but also because of the addition of silver iodide.

Ø Electrons are trapped by the sulfur in the sensitivity specks giving it a negative charge. When this situation is created a latent image is produced in the film emulsion.

AgBr + X-ray photons = Ag+ + Br-

Silver bromide = Silver ions + Bromine ions

Ø The latent image is formed by deposits of free (ionized) silver ions that cannot be seen or

detected by any physical test devised as yet. It remains in the emulsion of the X-ray film

until it is changed into a visible silver image by chemical processing procedures.

nimala — 2016-10-14 03:54:21 UTC

2016-10-14 08:44:53 UTC

Dr.Sathiskumar MMed NM Phase 1

2016-10-14 08:46:21 UTC

Dr. Sathiskumar K Muthusamy PIPM0078/15 Mmed Nuclear Medicine Phase 1 : Physics Assignment on Dental Imaging

2016-10-14 08:47:50 UTC

Structural parts of the dental x-ray machine include:

1. a control panel (usually mounted behind a protective shield)

2. a tube head, which houses the dental x-ray tube

3. a flexible extension arm from which the tube head is suspended

Control Panel:

i. contains on and off switch and indicator light

ii. exposure button and indicator light

iii. control devices for time, kilovoltage and miliamperage selectors to regulate x-ray beam.

- allow movement and positioning

c) tubehead

- tightly sealed, heavy metal housing that contains the x-ray tube that produces dental x-ray.

Extension Arm:

i. The extension arm suspends the Xray tube head and houses the electricl wires that extend from the control panel to tube head

Tube Head:

i. Tightly sealed in a heavy metal housing is the x-ray tube, whereby the dental Xrays are produced.

Xray tube component are :

i. Metal housing

a. Metal body of the tube head, surrounds the xray tube and transformer

b. filled with oil

c. Function : protects the x-ray tube and grounds the high voltage components

ii. Insulating oil

a. prevents overheating by absorbing the heat created by the production of x-ray.

iii. Tubehead seal

a. aluminium or leaded-glass covering the tubehead that permits the exit of x-rays from the tubehead.

b. Function : Seals oil in the tubehead and acts as filter to the x-ray beam.

iv. Aluminium disks

a. 0.55mm thick aluminium placed in the path of x-ray beam to filter out the non-penetrating, longer wavelength x-ray, which is less harmful to the patient ( thereby decreasing the skin dose).

v. Transformer

a. alter voltage of incoming electricitiy

vi. X-ray tube

a. Main Xray generating system

b. produce x-ray beams via beaming electron at cathode to anode (tungsten target). Principle similar to x-ray production of an x-ray machine.

vii. Lead collimator

a. with central hole that fits at metal housing opening which restrict the size of x-ray beam.

viii. Position-indicating device (PID)

a. which is also referred to as the cone, extends from opening of metal housing

b. Function : aims and shapes the x-ray beam.

TECHNIQUES OF DENTAL IMAGING

There are two main types of dental x-rays:

1. intraoral (the x-ray film is inside the mouth)

2. extraoral (the x-ray film is outside the mouth).

Intraoral x-rays are the most common type of x-ray. There are several types of intraoral x-rays. Each shows different aspects of teeth.

Bite-wing x-rays

Ø show details of the upper and lower teeth in one area of the mouth.Each bite-wing shows a tooth from its crown (the exposed surface) to the level of the supporting bone.

Periapical x-rays

Ø show the whole tooth — from the crown, to beyond the root where the tooth attaches into the jaw.

Ø Each periapical x-ray shows all teeth in one portion of either the upper or lower jaw. Periapical x-rays detect any unusual changes in the root and surrounding bone structures.

Ø Occlusal x-rays track the development and placement of an entire arch of teeth in either the upper or lower jaw.

Ø Extraoral x-rays are used to detect dental problems in the jaw and skull. There are several types of extraoral x-rays.

Panoramic x-rays

Ø show the entire mouth area -- all the teeth in both the upper and lower jaws -- on a single x-ray.

Ø This x-ray detects the position of fully emerged as well as emerging teeth, can see impacted teeth, and help diagnosis tumors.

Dental computed tomography (CT) is looks at the 3D dimension of the interior structures , to detect cysts, tumors, and fractures.

MRI imaging is an imaging method that takes a 3-D view of the oral cavity including jaw and teeth, better for soft tissue evaluation.

PRODUCTION OF THE DENTAL RADIOGRAPH

When an X-ray film has been exposed, it must be processed in order to produce a
permanent visible radiographic image that can be kept without deterioration for a number of

years. Processing transforms the latent image into a visible image. The term for the

several procedures that collectively produce the visible, permanent image is processing

and consists of developing, rinsing, fixing, washing and drying procedures.

1. Exposure - Latent image created.

2. Development - Converts latent image to black metallic silver.

3. Wash [stop bath] - Removes excess developer.

4. Fixing and Hardening - Dissolves out unexposed silver halide crystals.

5. Washing - Removes products of processing.

6. Dry - Removes water.

LATENT IMAGE FORMATION

Ø The latent (invisible) image formation is the ionization of the exposed silver bromide

crystals (by photon energy that emerges from the patient) occurring in the emulsion layer

before processing occurs.

Ø The primary interaction with the bromide crystals is by Compton and photoelectric interactions, thereby knocking out electrons. Thus, a physical change occurs when the radiograph is exposed.

Ø Crystals are purposely constructed with electron traps (sensitivity specks) consisting of sulfur impurities but also because of the addition of silver iodide.

Ø Electrons are trapped by the sulfur in the sensitivity specks giving it a negative charge. When this situation is created a latent image is produced in the film emulsion.

AgBr + X-ray photons = Ag+ + Br-

Silver bromide = Silver ions + Bromine ions

Ø The latent image is formed by deposits of free (ionized) silver ions that cannot be seen or

detected by any physical test devised as yet. It remains in the emulsion of the X-ray film

until it is changed into a visible silver image by chemical processing procedures.