Radiology in orthodontics /certified fixed orthodontic courses by Indian dental academy

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Radiology in orthodontics /certified fixed orthodontic courses by Indian dental academy

  1. 1. RADIOLOGY IN ORTHODONTICS INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2.  Introduction  Radiation physics  Radiation biology  Radiographic techniques  Specialized radiographic techniques  Diagnostic imaging of TMJ  Maxillary canine projections  Conclusion www.indiandentalacademy.com
  3. 3. INTRODUCTION The use of X Rays in an integral part of clinical dentistry with some form of radiographic examination necessary on the majority of patients. As a result, radiographs are often referred to as the clinician’s main DIAGNOSTIC AID. www.indiandentalacademy.com
  4. 4. RADIATION PHYSICS www.indiandentalacademy.com
  5. 5. XRAY   Discovery by Roentgen in 1895. X Rays are form of high energy electromagnetic radiation & part of electromagnetic spectrum, which also includes low energy radio waves, television & visible light. PRODUCTION OF X RAYS X Rays are produced when energetic (high speed) electrons bombard a target material & are brought suddenly in to rest. This happens inside a small evacuated glass envelope called X Ray tube. www.indiandentalacademy.com
  6. 6. X RAY MACHINE   l. X Ray tube 2. Power supply I.X Ray tube     1) Cathode 2) Anode When electrons from the cathode strike the target in the anode, they produce X Rays. Cathode -- Consists of Filament ( electron production) Focusing Cup. (Mb) Anode -- Consists of tungsten target embedded in copper stem. (electron’s kinetic energy is converted in to X Ray Photon) www.indiandentalacademy.com
  7. 7. II. Power Supply Functions 1. Provide low – voltage current to heat the X Ray tube Filament by use of step down transformer. 2. Generate a high potential difference between the anode and cathode by use of high voltage transformer. www.indiandentalacademy.com
  8. 8. PRODUCTION OF X RAYS I. BREMSSTRAHLUNG RADIATION.   If High speed electrons hits the nuclei of a target atom, all its kinetic energy is transformed in to single X Ray Photon. The energy of the resultant photon is numerically equal to the energy of the electron. II. CHARACTERISTIC RADIATON.  It occurs when an electron from a filament displaces an electron from a shell of a tungsten target atom. When the displaced electron is replaced by the outer-shell electron, a PHOTON is emitted with an energy equivalent to the difference in the two orbital binding www.indiandentalacademy.com energies.
  9. 9. PROPERTIES OF X RAYS     They are wave packets of energy of electromagnetic radiation that originate at the atomic level. Each wave packet is equivalent to a quantum of energy and is called as PHOTON. Velocity is 3 x 10 8m/s. Shorter wavelength X - Ray posses Increase energy and penetrate greater distance. www.indiandentalacademy.com
  10. 10. FACTORS CONTROLLING X RAY BEAM.    i) Exposure time ET = No of photons generated (energy is unchanged) only quantity control. ii) Tube current TC = No of photon. iii) Tube voltage TV = NO of photons. Mean energy Maximal energy. Bramsstrahlung photons. Quality control. www.indiandentalacademy.com
  11. 11. FILTRATION To reduce the patient dose, the less penetrating photons should be removed. This can be accomplished by placing a Aluminium filter in the path of the beam. COLLIMATION It is a Metallic barrier with an aperture in the middle. Used to reduce the size of the X Ray beam, and therefore the volume of irradiated tissue with in the patient. Types 1. Round 2.rectanqular 3.circle www.indiandentalacademy.com
  12. 12. DOSIMETRY  Determining the quantity of radiation exposure (or) dose. UNITS OF MEASUREMENT:Quantity SI Unit Traditional Unit (a) Exposure (b) Absorbed Dose (c) Equivalent (or) effective dose (d) Radioactivity C/Kg Gray Roentgen Rad Sievert Becquerel (Bg) Rem Curie www.indiandentalacademy.com
  13. 13. IMAGE RECEPTORS (FILM) Composition:(i) Emulsion (ii) Base Emulsion - It is sensitive to X Rays & visible light, records the radiographic Image. Base it is a plastic supporting material on to which the emulsion is coated. Types  direct actions or non screen film ex- IOPA  indirect actions or screen film ex- extra oral film ( it is used in combination with intensifying screen) www.indiandentalacademy.com
  14. 14. INTENSIFYING SCREEN It transfers X-Ray energy into visible light and this in turn exposes the screen films. So less radiation exposure and less radiation time is required. Base These are made up of polyester plastic measures . 25mmthickness. It provides mechanical support for the screen. Reflecting layer It is a white layer of titanium dioxide coated on the base lies beneath the phosphor layer. It reflects any light emitted from the phosphor layer back to the X-Ray film. Phosphor layer It consists of light sensitive phosphor crystals suspended in a plastic material. When phosphors are struck by photons, they fluorescence i.e they emit visible light photons that www.indiandentalacademy.com exposes X-ray film. 
  15. 15. Most common phosphor used are    Calcium tungstate that fluorescence in blue portion of spectrum phosphor used by rare earth intensifying screen. Terbium activated gadolinium oxysulfide. Thulium activated lanthanum oxybromide that fluorescence in green position of spectrum. Advantage  They respond to a shorter exposure to X Rays, enabling a lower dose of radiation to be given to the pt. Disadvantage  Inferior image quality www.indiandentalacademy.com
  16. 16. RADIOGRAPHIC IMAGE CHARACTERSTICS (i) Radiographic Density (ii) Contrast - atomic no) (iii) Radiographic Speed Fast film requires Slow (iv) Image Quality ∞ Exposure time (x) ∞ Subject Thickness ∞ Subject Density Subject contrast (Subject’s thickness, density and Film contrast (Intensity of the remnant beam) Scattered radiation. - exposure exposure by using Grid. (Reduces the amount of scattered radiation). www.indiandentalacademy.com
  17. 17. RELATIVE RADIATION EXPLOSURE www.indiandentalacademy.com
  18. 18. RADIATION BIOLOGY www.indiandentalacademy.com
  19. 19. Radiation effects at the tissue and organ level     The radio sensitivity of a tissue or organ is measured by its response to radiation. Short term effects Of radiation on a tissue is determined primarily by the sensitivity of its parenchymal cells. Cells are lost primarily by mitosis linked death. Extent of cell loss depends on – damage to the stem cell pools & proliferative rate of cell population. Long term effects The long term deterministic effects of radiation on tissues and organs depend primarily on the extent of damage to the fine vasculature. www.indiandentalacademy.com
  20. 20. Radiation effects of oral tissues Oral mucous membrane • mucositis • secondary candida albicans infection • long term – atrophic changes due to progressive obliteration of fine vasculature and fibrosis Taste buds Extensive degeneration. Salivary glands • Xerostomia • Ph ↓ to 5.5 • Progressive fibrosis, adiposis, loss of fine vasculature and parenchymal degeneration Teeth • radiation caries. Bone • Normal marrow may be replaced with fatty marrow and fibrous connective tissue • Osteoradionecrosis Late somatic effects • Carcinogenesis and leukemia www.indiandentalacademy.com
  21. 21. ALARA The most recent recommendations involving the establishment of permissible doses and dose limits to occupational and nonoccupational groups can be summarized in the principle of ALARA (As low as reasonably achievable). This means that every available method for reducing exposure to ionizing radiation will be implemented to minimize potential risks and adverse consequences www.indiandentalacademy.com
  22. 22. Protective measures that aim to minimize the radiation exposure to the patient are: •Utilization a high sped film and intensifying screens to reduce the dose of radiation and the exposure time. •Filtration of secondary radiation or scatter radiation produced by low energy x-ray photons by an aluminum filter. •Collimation by a diaphragm made of lead in order to achieve optimal beam size www.indiandentalacademy.com
  23. 23. •Proper exposure technique and processing in order to avoid unnecessary repetition of the procedure. •The patient’s wearing a lead apron in order to absorb scatter radiation. •In order to avoid scatter radiation the operator must stand at least 6 feet behind the tube head or should stand behind a lead protective barrier while making the x-ray exposure. www.indiandentalacademy.com
  24. 24. TYPES OF RADIOGRAPIC TECHNIQUES I II Intra oral Extra Oral - IOPA, Bitewing, Occlusal. Oblique lateral, various skull projections OPG. INTRA ORAL PERIAPICAL RADIOGRAPH:It shows 2 to 4 teeth & provides detailed information about the teeth and surrounding alveolar bone.       Indications:Detection of apical Infection / Inflammation. Periodontal status detection. Assessment of pressure & position of unerupted teeth. Evaluation of implants post operatively. Techniques:Paralleling tech www.indiandentalacademy.com Bisected angle tech
  25. 25. PARALLELING TECH ( Right angle intra oral tech ) (or) (Long cone tech.) Procedure:- X Ray film in supported to the long axis of the teeth by film holder & the central beam in directed at right angle to the teeth & the film – To further reduce geometric distortion X Ray source be located relatively distant from the teeth. www.indiandentalacademy.com
  26. 26. BISECTING ANGLE TECH • Based on the simple geometric theorem (i.e.) (ieszynski’s rule of isometry), which states the 2 angles are equal when they share one complete side & have 2 equal angles. • The plane of the film & long axis of the teeth form an angle with its apex at the point where the film is in contact with the teeth. When this angle is bisected by an imaginary line or plane, 2 congruent angles with a common side (Imaginary bisector) formed. central ray is directed at a right angle to the plane that bisects the angle between the long axis at the tooth & the film. www.indiandentalacademy.com
  27. 27. OBJECT LOCALIZATION TUBE SHIFT TECHNIQUE (Buccal object rule, Clark' rule)    The relative positions of radiographic images of two separate objects change when the projection angle at which the images were is changed. If the object in question appears to move in the same direction with respect to the reference structures as does the X-ray tube, it is on the lingual aspect of the reference object. If it appears to move in the opposite direction of the X-ray tube, it is on the buccal aspect. If it does not move with respect to the reference object ,it lies at the same depth (in the same vertical plane) as the reference object www.indiandentalacademy.com
  28. 28. RIGHT ANGLE TECHNIQUE  Two projections taken at right angles to one another localize an object. In clinical practice the position of an object on each radiograph is noted relative to the anatomical land marks. This allows an observer to determine the position of the object or an area of interest. www.indiandentalacademy.com
  29. 29. Stanley A. Jacobs et al (AJO 2000). A rotational panoramic radiograph with an ant occlusal radiograph is a preferred combination of radiographs to localize unerupted mandibular anterior teeth. This combination uses a tube shift in the vertical plane. The rotational panoramic radiograph is taken at an effective angle of +7°C to the occlusal plane & anterior occlusal radiograph is taken at -55°C. Conor Armstrong (EJO - 2003). States that localization of ectopic maxillary canines was significantly more successful with horizontal parallax than with vertical parallax. But both radiographic techniques were poor at localizing buccal EMC (success rate is only 63%). www.indiandentalacademy.com
  30. 30. BITE WING RADIOGRAPH Film in designed to show the crowns of the premolar & molar teeth on one side of the jaw. Indications:    To detect proximal Dental Caries. Monitoring the progression of Dental Caries. Assessment of existing restoration. Assessment periodontal status. Technique:-   Film in placed between tongue & teeth, close to the lingual surface of the teeth & parallel to the long axis. Film tab should be centered in occlusal line. X Ray is projected to the center of the film through contact areas (angle 5 degree) www.indiandentalacademy.com
  31. 31. OCCLUSAL RADIOGRAPHY Maxillary occlusal (a) Topographical - Ant Maxilla & dentition, ant nasal fossa. (b) Cross Sectional - Palate, Zygomatic Process of Maxilla, nasolacrimal Canal Nasal Septum, 2nd Molar to 2nd Molar. ( c) Lateral Topographical • Half of the ridge of Maxilla, Inferio Lateral aspect of the antrum, tuberosity, teeth from lateral incisor to molar. www.indiandentalacademy.com
  32. 32. MANDIBULAR OCCLUSAL (a ) Cross Sectional Lingual & Buccal Plates of the jaw bone 2nd molar to 2nd molar. (b) Lateral cross section Soft palate, half of the floor of the mouth, buccal & lingual cortical plate (Lateral incisor to 3rd molar). Uses:  To Precisely locate roots, supernumery unerupted & Impacted teeth (canine to 3rd molar) To aid in examining – pt with trismus who can open the mouth only a few mm. www.indiandentalacademy.com
  33. 33. EXTRA ORAL RADIOGRAPHIC TECHNIQUES • • • • Lateral cephalometric projection ( sagital (or) Median) submento Vertex ( Transverse (or) horizontal) Water’s projection Postero anterior ( Frontal view) I. SUBMENTO VERTEX:It reveals the position and orientation of the condyle, curvature of the mandible. II. WATERS PROJECTION:Used to evaluate orbit, nasal cavity and www.indiandentalacademy.com maxillary sinus.
  34. 34. POSTERO ANTERIOR VIEW The X ray passes in a posterior anterior direction through the skull. A cassette is positioned vertically in a holding device. A grid is used Head is centered in front of the cassette with the cantho meatal line. Uses     To detect developmental abnormalities like facial asymmetries. Used to examine the skull for presence of disease, trauma, developmental abnormalities. Used to detect progressive change in the mediolateral dimensions of the skull. It offers good visualization of facial structures including frontal, ethmoidal sinus, nasal fossa and orbits. www.indiandentalacademy.com
  35. 35. POSTERO ANTERIOR VIEW www.indiandentalacademy.com
  36. 36. LATERAL CEPHALOMETRY “Cephalometry” the term may mean a simple consideration of anatomic part of the skull in the head plate or the treatment of measurements by the use of analytic geometry. History:     1922 – Pacini Introduced a method for standardized head radiography. 1931 – Broad Bent in the US Hofrath in Germany-introduced modern cephalometry. Pacini – Large fixed distance from the X Ray source to the cassette. The head of the subject is placed adjacent to a stand holding the cassette and war immobilized with a gauge bandage wrapped around both the face and the cassette, after the pt’s midsagittal plane was carefully oriented parallel to the cassette. Broad Bent;- Involves a constant focal spot to object distance (5 feet) &constant object to film distance (9cm) Lucien de coster – was the first to publish an analyses based on proportional relationships in the face conforming to the www.indiandentalacademy.com principles used in antiquity.
  37. 37. RADIOGRAPHIC CEPHALOMETRIC TECHNIQUE Simplest procedure to Simplest procedure to obtain head radiographs in natural head position is to instruct the patients to sit upright and look straight ahead to a point at eye level on the wall in front of them. Patient is positioned within the cephalostat using adjustable bilateral ear rods placed within each auditory meatus, usually while the patient is in the standing position. The midsagital plane of the patient is vertical and perpendicular to the X Ray beam. It is also parallel to the film plane which in turn perpendicular to the X Ray www.indiandentalacademy.com beam.
  38. 38. OREINTATION IN NATURAL HEAD POSITION Orientation of pts in natural head position will result in only a small range of error. Such differences have only minor effect on the interpretation of facial morphologic features & facial disharmony www.indiandentalacademy.com
  39. 39. LATERAL CEPHALOGREM www.indiandentalacademy.com
  40. 40. CLINICAL USES (i) GROSS INSPECTION To observe gross anatomic relations of skeletal & soft tissues in the lateral & frontal films in order to determine major dysplasias. use of 3 ‘p’ s Growth assessment of Physical morphology Search for Pathological Phenomenon The interpretation of Physiologic condition. www.indiandentalacademy.com
  41. 41. (ii) DESCRIPTION gives mathematical measurement & description .4 ‘c’ s Characterization or description comes first. Comparison of one individual to another is made possible Classification of factors. Communication of the problems. (iii) GROWTH AND TREATMENT It is used to record and measure changes. (iv) PLANNING AHEAD Treatment Planning More useful to make a “Cephalometric set up” www.indiandentalacademy.com
  42. 42. TRACING & IDENTIFICATION OF CEPHALOMETRIC LANDMARKS Steps     Soft tissue profile, external cranium, Vertebra. Cranial base, internal border of cranium, frontal sinus & ear rods. Maxilla & related structures including nasal bone & pterygomaxillary fissures. The mandible. www.indiandentalacademy.com
  43. 43. CEPHALOMETRIC SUPERIMPOSITIONS Growth and mechano therapy contribute to the outcome of orthodontic treatment to different degrees. cephalometric superimpositions demonstrate the combined effects of growth and mechanotherapy. Regional cephalometric superimpositions are performed to evaluate three basic components of skeletal and dento alveolar development:-maxillary ,mandibular and overall facial changes. Superimposition of cranial base yields information about the movements of facial bones away from the cranial structures. Superimposition of maxillary structures can be used to evaluate changes in the maxillary dento alveolar complex (PNS-ANS line). Mandibular superimposition on relatively stable www.indiandentalacademy.com anatomical structures can be used to evaluate dento alveolar changes.
  44. 44. Methods of superimposition 1.Superimposition on S-N at S. 2.Superimposition natural reference structures such as cranial base. 3.Using a subtraction technique where a positive copy is made of one of the radiographs and overlaid on the other. Areas of radiograph where no change has taken place appear uniformly grey. 4.Using a “blink comparator”. Two radiographs are illuminated alternately in rapid succession, giving an impression of the changes that have occurred between the radiographs. 5.Using digital images tracings of cephalometric radiographs can be superimposed either on landmarks or structures that have out lined by the operator. www.indiandentalacademy.com
  45. 45. V. Gavel & L.Dermant (EJO – 2003). To identify position of unerupted canine by using lateral cephalogram, 3 different displacements were stimulated. 10 mm frontally, 10 mm sagitally, 5mm vertically. They concluded that the degree of vertical & sagittal displacement of the incisor point of the impacted canine, angulation, length of the teeth measured on cephalogram appeared to give an accurate representation. www.indiandentalacademy.com
  46. 46. COMPUTERIZED CEPH With introduction of digital imaging, automated and semi-automated landmark identification directly from the digital images can be done. This would avoid the • • need for manual tracing removes operator subjectivity but at present automated systems are unable to match human operators in the accuracy of landmark identification. Yi Jane chen et al (AO 2000), compared the traditional and computer aided digital cephalometric landmarks and concluded that the inter observer error for each landmark in digital images was generally larger than that in the original radiograph. Mostly seen in Po, Ar, ANS, UM. www.indiandentalacademy.com
  47. 47. Automatic computerized radiography identification of cephalometric Landmarks. D J Rudolph et al. This study compared manual identification on a computer monitor and Spatial Spectrometry automatic method for landmark identification on minimum resolution image. Fifteen landmarks were selected on set of 14 test images. The results showed no statistical difference (p>0.05) in mean landmark identification errors between manual identification on a computer display and automatic identification using SS www.indiandentalacademy.com
  48. 48. THREE DIMENSIONAL CEPHALOMETRIC ANALYSIS It is a valuable tool in assessment of skeletal remodeling, contour changes, and changes in proportion that occur with aging. Computed assisting tomographic data can be used in either coronal or axial direction. Advantages:• • • • Precise anatomic data unobtainable by other methods can be acquired from a 3D radiological image. Improved diagnostic accuracy. Contours & surface detail are rendered in fine detail. Ability to correlate soft tissue and hard tissue points directly on the computer. Constrains:Lack of uniformity www.indiandentalacademy.com in viewing the reconstructed image.
  49. 49. Method:   Both axial & coronal slices were obtained. Slice 3mm (or) less is used. CT scans were reconstructed in 3 D by reformatting process. Uses:-   Especially useful in patient with marked dentofacial asymmetries. To improve preoperative diagnostic capabilities including volumetric analysis. www.indiandentalacademy.com
  50. 50. XERORADIOGRAPHY It is the process of recording a latent radiographic image on a selenium coated aluminum plate ,the image is then transferred to a specially treated paper for visualization. The whole process is fully automatic , taking 90 seconds to complete. Advantages 1) Soft tissues, bone, teeth, and air passages are clearly visible because of a large recording latitude , high resolution and the “ edge enhancement phenomenon” 2) more pronounced definition and contrast Davis and associates and Johnson conclude Xeroradiography is superior to conventional radiography www.indiandentalacademy.com
  51. 51. ORTHOPANTOMOGRAPHY  It is a technique for producing a single tomographic image of the facial structures that includes both the maxillary and mandibular arches and their supporting structures. ADVANTAGES        Broad coverage of the facial bones & teeth. Low pt radiation dose. Convenience of the examination for the pt. Ability to be used in pts unable to open their mouth. DISADVANTAGES Unequal magnification. Geometric distortion. www.indiandentalacademy.com
  52. 52. INDICATIONS     Need to know the State of the dentition and the presence / absence of teeth. Unerupted tooth. Periodontal tooth support. Destructive disease of the articular surface of TMJ. PRINCIPLE  Two adjacent disks rotate at the same speed in opposite direction as an X Ray beam passes through their centers of rotation. IMAGE LAYER  It is a 3 – dimensional curved zone (focal trough) in which the structures lying with in the layer are reasonably well defined on final panoramic image. www.indiandentalacademy.com
  53. 53. PATIENT POSITIONING Mid sagital plane must be centered with in the image layer. Patient ‘s chin and occlusal plane is aligned so that it is lower anteriorly, angled 20-30 degrees below the horizontal plane. Line from the tragus of the ear to the outer canthus of the eye is parallel with the floor. POSITIONING ERROR 1) Pt. too far from the film. 2) Pt. too close to the film 3) 4) 5) Ant teeth magnified in width and out of focus. Ant teeth narrowed and out of focus. Pt. Asymmetrically turned Post teeth enlarge on one right or left side and decreased on other side. Pts. Wearing earrings Artefactual shadow. Failure to instruct the pt Vertical (or) horizontal to keep still throughout distortion of the part the cycle of the image being produced www.indiandentalacademy.com at the time of the movement.
  54. 54. SPECIALISED IMAGING TECHNIIQUES  Conventional tomography  Stereoscopy  Scanography  Computed tomography  Magnetic resonance Imaging  Ultrasonography  Arthrography  Digital radiography www.indiandentalacademy.com
  55. 55. COMPUTED TOMOGRAPHY  CT image is a display of a thin slice of the body, developed from multiple X ray absorption measurements made around the periphery. ADVANTAGES:-        Cross Sectional Image Superior contrast resolution Geometric accuracy Tissue Characterization Image windowing Digital image processing Quick and Non invasive www.indiandentalacademy.com
  56. 56. TECHNIQUES  Xenon CT – To study blood flow.  Quantitative CT – Determination of bone mineral content.  Dynamic CT (Rapid sequence CT) - to study physiology.  High Speed resolution CT.         LIMITATIONS High dose of radiation. Geometric (or) Contrast miss. Artifacts. INDICATIONS Bone lesions affecting the TMJ. Implant planning. COMPONENTS Gantry – Consists of a) Detector array b) X Ray source. c) Pt. Support couch. Computer. www.indiandentalacademy.com Control console – This allows the operator to dictate the parameters of the CT scan.
  57. 57. IMAGE ACQUISITION CT images are acquired in the axial, coronal, or sagital planes. These images are taken in succession and are generally referred to as slices. The information form these multiple slices can then be reformatted to produce images in other planes. www.indiandentalacademy.com
  58. 58. CT NUMBERS OR HOUNSFIELD UNITS The numeric data in each pixel is called a CT number. The CT number corresponds to the linear attenuation coefficient of a particular tissue at a designated kilo voltage. Air Fat Water CSF Muscle Bone = = = = = = -1000 -100 -0 +1 +50 +1000 www.indiandentalacademy.com
  59. 59. Gary yip et al (seminar in ortho 2004). Concluded that micro tomography is particularly useful for the technically demanding task of assessing mineral density patterns of bone, supporting titanium implants. The expediency, nondestructive nature, & 3D imagery of this technique used to evaluate quantity, quality & mechanical properties of bone. www.indiandentalacademy.com
  60. 60. MAGNETIC RESONANCE IMAGING (MRI) Discovered by Purcell and Loch in 1946. PRINCIPLE:     MRI uses non-ionizing radiation from the radiofrequency (RF) band of the Electromagnetic spectrum. Unpaired Neutron/Proton  Magnetic Dipoles in biological tissues- H2 atom is the most common. Natural state – Net magnetization is zero. Application of External Magnetic field. • •  Spin-up (Lower energy state). www.indiandentalacademy.com Spin -down (Higher energy state ). MRI reflects the magnetic properties of mobile H2.
  61. 61. IMAGING PROCESS 1)Patient placed in the magnetic field. The protons act like small magnets ,align themselves with in the magnetic field and begin to rotate at a precise frequancy. This is called ‘Precession’ ( Larmor Frequency) Protons align in external magnetic field.a new magnetic vector is induced. That is Net Magnetic vector in Longitudinal Magnetization Superconductive magnet – field strength 0.1 – 2 Telsa. 2)Radio wave sent in. New Magnetic vector excited by RF wave. Tipping of Bulk magnetic vector in space. Duration of RF wave determinates Angle of tip. the tipping of new magnetic vector results in a decrease in its size and a new magnetic vector- Transverse Magnetization appears. 3)Radio wave turned off. Protons calm down/relax www.indiandentalacademy.com to original position. Recovery via T1 & T2 relaxation times.
  62. 62. 4)Patient emits signal ( as T1, T2). Rotation of bulk magnetic vector to pre-excitation state  Induction of electric current in wire coils .Signal received and processed. T1  measures the longitudinal return of protons to align with the external magnet after the RF pulse has stopped. Small water molecules takes long time to transfer energy.leads to long T1- appear black on T1 weighted images. Larger fat molecules-shorter T1- White or Bright. T1 - Shows Anatomy T2  measures the energy transfer between interacting protons after excitation. For water, CSF, saliva – Long T2 – White or bright. For fat – short T2 – bright signal suppressed. T2 - Shows Pathology 5)Reconstruction of picture. Most common –spin echo pulse sequence Application of RF pulses-localization of signals-Fourier transformation-reconstruction of image. www.indiandentalacademy.com
  63. 63. MR CONTRAST AGENT  Injected contrast agents change the signal intensity by altering T 1 and T 2 relaxation times. Paramagnetic GdDTPA-Most popular (Gaddolinium diethylene Triamine pantothenic acid). SAFETY CONSIDERATIONS   Contraindicated in pts with Ferromagnetic materials like Cardiac pacemaker. Safety in Pregnancy not established. www.indiandentalacademy.com
  64. 64.           ADVANTAGES It offers best resolution of tissues of low inherent contrast. No ionizing radiation in involved with MRI. Because e at the region of the body Imaged in MRI in controlled electronically, direct multiplannar imaging is possible without reorienting the patient. DIS ADVAVTAGES Relatively long imaging times and the potential hazard imposed by the presence of ferromagnetic metals in the vicinity of the imaging magnet. Ex – Cardiac pacemakers, cerebral aneurysm clips Some patients suffer from claustrophobia when positioned in a MRI Machine. INDICATIONS It gives excellent soft tissue contrast resolution. Diagnosing a suspected internal derangement of the TMJ and evaluating the treatment of that derangement after surgery. Identifying and Localizing orofacial soft tissue lesions. Gives Images of salivary gland parenchyma. www.indiandentalacademy.com
  65. 65. Using Magnetic resonance imaging, temporo mandibular joint Effects of activator treatment are analyzed by Sabine et al , Angle Orthodontist 6; 72, 2002 he concluded the following: During the one year treatment period the sagital dental arch relationship improved .On average, the physiologic position of disc, condyle and fossa was present both present and after one year activator treatment. A pretreatment physiological disc condyle relationship was unaffected by activator therapy. The prevalence of sub clinical capsulitis of the inferior stratum of posterior attachment during activator treatment. Using magnetic resonance imaging and cephalometric investigation , temporo mandibular joint remodeling in adolescent and young adults during Herbst treatment was analyzed by sabine et al The increase in mandibular prognatism accomplished by Herbst therapy is found to be a result of codylar and glenoid fossa remodeling. www.indiandentalacademy.com
  66. 66. ULTRASONOGRAPHY The phenomenon perceived as sound is the result of periodic changes in the pressure of air against the eardrum. Periodicity of these changes lies anywhere between 1500 and 20,000 cycles per second. PRINCIPLE  Electrical impulses generated by the scanner causes the dipoles in the crystal to realign themselves and to the electrical field and thus suddenly change the crystal’s thickness. This abrupt change begins a series of vibrations that produce the sound waves that are transmitted in to the tissues being examined. ADVANTAGES  Does not require special facilities.  Can be used to view the joint in a continuum with out invasion, discomfort. DISADVANTAGES  Noise signal.  Size of the transducer.  Meniscus not seen. www.indiandentalacademy.com
  67. 67. Chien_Lun peng et al (EJO – 2003). To differentiate infantile and mature swallow. He used B +ve mode ultrasonography movements of the tongue tip & submental musculature during swallowing were recorded on video cassette. It provides a noninvasive visualization of tongue movements & no foreign body is required in the oral cavity allowing more natural swallowing behaviour. www.indiandentalacademy.com
  68. 68. DIGITAL RADIOGRAPHY  A digital image is a matrix of square pieces or picture elements (pixels), that form a mosaic pattern from wherein original image can be reconstructed for visual display. Analog Image  1) Conventional radiographic Image  2) Silver halide grain  3) Randomly dispersed  4) Continuous Spectrum Digital Image 1) a) Light sensitive elements to record the image. b) Shades of gray to display the Image 2) Light sensitive elements 3) Regular grid of rows and Columns 4) Numeric and Discrete. www.indiandentalacademy.com
  69. 69. PIXELS AND VOXELS  Pixel 2-D Digital Images – Composed of Picture elements.  Voxel 3-D Digital Images – Composed of volume elements. PRODUCTION OF DIGITAL IMAGE Analog to Digital conversion (ADC).   Sampling - Small range of voltage values grouped together. Quantization - Every sampled signal is assigned a value. Pixels are arranged in proper locations and given a shade of gray corresponding to quantization www.indiandentalacademy.com number.
  70. 70. ADVANTAGES OF DIGITAL RADIOLOGY         Reduces time and effort needed for chemical processing error. Eliminates faulty radiographs due to processing error. Eases image transfer for electronic communication. Eases storage, back up and retrieval. Permits computed optimization at image. Facilities pt communication. Lowers radiation dose to the pt. Ability to manipulate image contrast and density. DISADVANTAGES    Initial expenditure high. X-ray receptor in IO systems –susceptible to rough handling. Risk of system becomes obsolete. www.indiandentalacademy.com
  71. 71. TECHNIQUES  Single step system (CCD/C MOS).  2 step wireless system (PSP Plated). CCD (Charge coupled device)    The CCD uses a thin wafer of silicon as the basis for image recording. Associated read out and amplifying electronics. Scintillating layer-Gadolinium oxybromide or cesium iodide. www.indiandentalacademy.com
  72. 72. IMAGE PRODUCTION IN CCD SENSOR Radiation Breakage of silicon bonds Production of electron hole pairs Creation of Charge pockets Charge pocket in each pixel forms latent image Bucket brigade transfer Read out amplifier ADC www.indiandentalacademy.com IMAGE
  73. 73. ADVANTAGES   It is a part of the direct sensor system. Image is displayed on the monitor in a few seconds. It has the lowest noise. DISADVANTAGES    Bulk of the sensor. Electronic cable is necessary to transfer the data from the senior to the ADC. Detectors are expensive. www.indiandentalacademy.com
  74. 74. C-MOS (Complementary Metal oxide sensors) Semiconductor It is also silicon-based semiconductors. ADANTAGES     “Design Integration”. ADC control functions are built in with in the sensor. Easy manufacturability. Less expensive than CCD. DISADVANTAGES    C-Mos sensors may not perform well in low light conductors. More noise than CCD. www.indiandentalacademy.com Less active area for image acquisition than CCD sensors.
  75. 75. 2 STEP WIRELESS SYSTEM PSP plates (Phosphostimulable phosphor plates) COMPOSITION Contains “Europium – doped” Barium fluorohalide europium creates imperfections. PRINCIPLES PHOSPHORESENCE  Quantified as a measure of X ray energy absorbed by material www.indiandentalacademy.com
  76. 76.   IMAGE FORMATION Radiation  movement of Valance electron into Conduction band  migration into nearby Halogen vacancies (‘F’ Centers) Formation of Latent images. Stimulation by Red light  Return of electrons into the Valence band  Release of energy in green spectrum  Fibro optics  Photomultiplier tube  Conversion of light into Electrical energy. Removal of stimulatory light by Red filter  conversion of remaining green light into varying voltage— Quantification in ADC  Storage and display. www.indiandentalacademy.com
  77. 77. ADVANTAGES     It can be used indefinitely. Can be used with existing sources. Linear or Logarithmic response to radiation. Wide exposure range. DISADVANTAGES   High Initial cost. Poor spatial resolution. INDICATION     Caries detection. Alveolar bone imaging. To study trabecular Pattern of jaw bones. Cephalometric radiography. www.indiandentalacademy.com
  78. 78. IMAGE QUALITY CONSIDERATIONS • Active area. • Signal to noise ratio. • Contrast resolution. • Spatial resolutions. • Radiation dose. • Detector latitude. • Detector sensitivity. www.indiandentalacademy.com
  79. 79. TMJ PROJECTIONS HARD TISSUE PANORAMIC PROJECTION   Gross osseous changes in the condyle may be identified. Ex – Asymmetries, extensive erosions changes in articular eminance. TRANSCRANIAL PROJECTION  Lateral aspect of the condyle, and temporal component and range of motion. TRANSPHARYNGEAL (PARMA) PROJECTION   Sagital view of the medial pole of the condyle. Erosive changes of the condyle. www.indiandentalacademy.com
  80. 80. SUBMENTOVERTEX VIEW • skull base and condyles superimposed on the condylar necks and mandibular rami • Facial asymmetries, condylar displacement, rotation of the mandible. CONVENTIONAL TOMOGRAPHY • • • erosive changes of the condyle Entire condylar head is visible in the mediolateral plane Depicting true condylar position and revealing osseous changes COMPUTED TOMOGRAPHY • Gives 3 dimensional shape and internal structure of the osseous components of the joint and soft tissue structures www.indiandentalacademy.com
  81. 81. TMJ SOFT TISSUE ARTHROGRAPHY • Information about disk position, function, morphology and integrity of diskal attachments. MRI • demonstrate osseous and diskal tissues. • Inflammation and joint effusion • MEDIAL DISK displacement are best detected. www.indiandentalacademy.com
  82. 82. MAXILLARY CANINE IMPACTION In Radiograph • To determine size and shape of the teeth. • To determine position of the teeth. CANINE LOCALISATION Parallax in horizontal plane. Required Radiography :  2 IOPA  Upper occlusal. Parallax in Vertical Plane.   OPG Upper occlusal. www.indiandentalacademy.com
  83. 83. Vertex occlusal    X-Ray Tube is positioned above the patient , in the mid line, aiming downwards through the vertex of the skull. Buccal or palatal position of an unerupted teeth can be identified. Dis Adv: Radiation to eyes, gonads and pitutarygland. True lateral & PA Jaws. Steroscopic Views. Cross sectional spiral tomography. www.indiandentalacademy.com
  84. 84. CONCLUSION Radiology is one of the rapidly changing field in diagnostic imaging. Systematic approach is necessary to evaluate the complex anatomical relationships displayed on the CT & MRI and other specialized images. For a long time, radiographic film was the most important medium with which to acquire & archive the diagnostic image. In the future conventional radiographs will become obsolete and will be replaced by digital images. www.indiandentalacademy.com
  85. 85. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com

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