X-Ray Image Characteristics, Bisecting, Paralleling, Bitewing Techniques, Errors PDF

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Summary

Professor Sherry Frey ...

Description

Dental X- Ray Image Characteristics

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visual image characteristics include density and contrast as well as geometric image characteristics include sharpness, magnification, or distortion dental images appear black and white with varying grey shades black areas are radiolucent white areas are radiopaque deal image is not too dark and not too light diagnostic images have lots of info, proper density, contrast, same shape / size as object, sharp outlines density is the overall darkness or blackness of a dental image

Influencing Factors

- milliamperage (mA) and kilovoltage (kV) directly influence density - exposure time and milliamperage has the greatest impact on density Visual Characteristics

Influencing Factors

Effect of Influencing Factors

Density

mA

↑ mA= ↑ density ↓ mA= ↓ density ↑ kV= ↑ density ↓ kV= ↓ density ↑ Time= ↑ density ↓ Time= ↓ density ↑ Thickness= ↑ density ↓ Thickness= ↓ density

kV Time Subject Thickness

Contrast

kV

↑ kV= long scale, low contrast ↓ kV= short scale, high contrast

Subject Thickness

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subject thickness is what the picture is being taken of subject thickness for a small patient is less thick, density is increased and darker) if patient is small, ↓ kV, mA, and time subject thickness for a big patient is more thick, density decreased and lighter if patient is big, ↑ kV, mA, and time

Contrast

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difference in adjacent areas high contrast and low contrast compromise is preferred film contrast is influenced by development time or temp of the developer solution

Subject Contrast

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determined by the size and thickness of patent tissue can be altered by increasing of decreasing kV (affected by it)… high kV results in low contrast and many shades of grey low kV results in high contrast and black to white shades

Step Wedge - aluminum steps that demonstrate short and long scale contrast - used for quality assurance of developing solutions - used to monitor quality of film, film processing, sensors, and calibration Geometric Characteristics Sharpness

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distinct outline of an object lack of sharpness is present in every dental image the fuzzy unclear area that surrounds a structure is called a penumbra penumbra is the unsharpness or blurring of edges because of the diverging x-ray path there will always be penumbra determined by (1) focal spot size (2) film composition (3) movement a small focal spot made by the tungsten target makes things sharp C speed film is slower with a better picture F is faster with a worse picture crystals and their size determined sharpness movement creates blurred images (child) x-rays cant be focused to a point

Characteristic

Influencing Factors

Effects

Sharpness

Focal Spot Size

↑ focal spot size= ↑ sharpness ↓ focal spot size= ↓ sharpness

Film Composition

↑ film composition= ↑ sharpness ↓ film composition= ↓ sharpness

Movement

↑movement = ↑ sharpness ↓ movement= ↓ sharpness

Shadow Casting Principles (SCP) 1. 2. 3. 4. 5. 6.

Focal Spot as Small as Possible Focal Film Distance as Big as Possible (Long PID and TRD Results in Less Image Magnification) Object (Tooth) to Receptor Distance Must be as Close as Possible Tooth and Receptor Should be Parallel (foreshorten=angle of rays too short, elongation=stretched ) Central Ray (CR) Must be Perpendicular to the Tooth and Film CR Must be Directed Between Teeth

FFD- focal film distance TFD- target film distance ! TRD and FRD- FRD- target and film receptor distance OFD and ORD- object film and receptor distance Intraoral Imaging

- intra oral receptors are placed inside the mouth - bitewings are the most important picture (shows bone levels and cavities between teeth) - anterior bitewings (premolars) and posterior (molars) x4 for both sides 1. Periapical Examination - involves 14 pictures - used to take images for the roots (bone around apex) - paralleling technique and bisecting technique (#2 film everywhere) are used 2. Interproximal (Bitewing) Exam- examining adjacent tooth surfaces and crestal bone 3. Occlusal Exam- #3 or #4 film for maxilla or mandible Complete Mouth Series (CMS) - also called Full Mouth Series / Exam (FMS or FMX) - a range of 14 to 20 images may be included - 18 on a test and in Canada (16 with a small mouth) Panoramic - extra oral film receptor outside the mouth Paralleling Technique - one method can be used to expose periapical, bitewing, and occlusal - film parallel to long axis of the tooth - place the film far from the tooth (breaking shadow casting rule) - central ray is perpendicular to the long axis of the tooth and receptor - beam alignment device is used to keep receptor parallel to long axis - patient cant hold receptor - TRD is increased to 16” (required) fixed broken rule - current x-ray machines manufactured with recessed focal spot

1. Receptor placed to cover prescribed area

2. 3. 4. 5.

Receptor positioned parallel to one axis of the tooth Vertical angulation of central ray (perpendicular to long axis) Horizontal angulation of central ray through contact areas Film receptor exposure centred on receptors expose all areas

Bisecting Angle Technique

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when 2 lines diverge from a common point, you get an angle bisector divides an angle into equal angles congruent triangles are identical hypotenuse is the side opposite the right angle rule of isometry states that 2 triangles are equal if triangles have 2 equal angles with a common side

1. 2. 3. 4.

Receptor must be placed along lingual surface of tooth Form an angle Visualize a plane that bisects the angle from the receptor an long axis (called imaginary bisector) Direct the central ray of x ray beam perpendicular to imaginary bisector

Bitewing Technique Crestal Bone- coronal portion of alveolar bone found between teeth Contact Areas- are of a tooth that touches adjacent tooth (where adjacent teeth contact) Open Contacts- thin radiolucent lines between teeth Horizontal Bitewing- receptor placed in mouth with long portion of receptor in horizontal direction Overlapped Contacts- contact area of 1 tooth overlaps contact area of another Bitewing Technique Principals 1. Receptor placed in mouth parallel to crowns of max and mand teeth 2. Patient bites bitewing tab 3. Central ray of x-ray beam directed through contacts of teeth using vertical angulation of +10°

Exposure and Technique Errors

- only diagnostic images are used - errors in any area may cause makes to be non diagnostic Unexposed Receptor - may occur with digital sensors - image appears clear (blank, white) - emulsion didn't come in contact with x-rays (never exposed) - FIX by turn the machine on, and take a new one Film Exposed to Light - image appears black - all crystals were energized and cooked - exposed to white light - FIX by not unwrapping film until you are in the darkroom with no lights Overexposed Image - dark or high density image - to much radiation exposure - too much time, high kV, high temp, high mA - FIX by setting it up properly Light in Density - image too light - not enough radiation exposure - not enough time, low kV, low temp, low mA, backwards film - FIX by setting up control factors properly Receptor Placement Problems - periodicals show entire tooth including apex and surrounding structures - most be positioned to show specific teeth and related structures Absence of Apical Structures - receptor not positioned properly - apical structures not visible - make sure no more than 1/8th’ of the receptor edge above the crowns of teeth Dropped Receptor Corner - edge of receptor not parallel to the inscisal or occlusal surfaces - FIX by making sure edge is parallel and level Angulation Problems - horizontal angulation is side to side, while vertical is up and down - incorrect vertical angulation results in image not being same length as tooth - these are called foreshorten is too small, and elongated is too long - incorrect horizontal placement causes overlapped contacts

- fix by directing central ray through contacts of teeth - use beam alignment device to help - if vertical angulation is too steep, image is shorter than the actual tooth Elongated Images - long and distorted on the image - vertical angulation too flat - use beam alignment device PID Alignment Problems - when the PID is not properly aligned with periodical beam alignment device - called a cone cut - FIX by making sure they're aligned Cone Cut WITHOUT Beam Alignment Device - clear unexposed area - Readjust PID to cover film Bitewing Issues

- distal or mesial sides may be cut off - extra teeth may be in the image (molar shot shouldn't have premolars) - FIX by positioning the receptor in the proper spot Miscellanous Errors - stretching and distorted from bending - creasing the film results in a radiolucent black line - debris accumulation can scratch sensors or film - phalangioma results from client holding the film - double imagine results from using the same film twice (separate film) - PSP double image from previous film not completely erased - motion blurs the image - backwards film is light with tire tracks

Digital Imaging - anlog images - an electronic charge is produced on the surface of the sensor - electronic signal is digitized and converted to digital form - digital imagine systems aren't limited to intraoral images - can also do panoramics, extra oral, cephalometric, cone beams… - digital imaging requires 50-90% less radiation - this supports the ALARA principle - impulses are 1/60 of a second (60 impulses per second) - wired refers to the fact that its linked by fiberoptic cables to a computer - wireless isn't linked by a cable - sensors put in sleeves before putting in someones mouth Direct Digital Imaging- x-rays hit the sensor and go directly to the computer Indirect Digital Imaging- x-rays go to a PSP, laser reader, and then stored on a computer * PSP (phosphor plate) technology is indirect digital imaging Pros - good viewing - less exposure - increased speed of viewing - lower equipment and film cost - increased efficiency - enhancement of diagnostic imaging - eco friendly - effective patient education Cons - high costs - less quality - sensors are thick for the mouth - infection control can be an issue - wear and tear Anatomy Canals- radiolucent Incisive Foramen- radiolucent Suture- dark narrow slot (radiolucent line) Fossa- slightly radiolucent Nasal Fossa- radiolucent Nasal Septum- radiopaque...