Oral Radiology Flashcards
Position-Indicating Device
Line up tube head
What is an X-ray?
High energy and High Frequency Wave
* between UV rays and Gamma rays
Attenuation
How the X-ray beam weaknes as it passes through matter on its way to receptor
Filtration
Involves aluminum
Collimation
Involves Lead
* Rectangular=best method to decrease pt exposure
What are the 2 types of Ionizing Radiation?
Electromagnetic
Particulate
Electromagnetic Ionizing Radiation
Energy Movement= Electrical Fiel + Magnetic Field
Shorter Wavelength= Increased Energy
Particulate Ionizing Radiation
Atomic nuclei or subatomic particles moving at high velocity
What are the 2 types of X-ray Production?
Bremsstrahlung
Characteristic
X-ray Production: Bremsstrahlung
Primary Source of X-ray Photons
* generates a continuous spectrum of energy
X-ray Production: Characteristic
Secondary Source of X-ray Photons
* emits a photon of specific energy when it moves orbitals
Intensity
Quantity of electrons & photons
Effects: Density
* Darkness of the image
Energy
Quality of electrons and Energy of photos
Effects: Contract
* difference among Gray values
Exposure Time
Changes the NUMBER of photons
* most frequently altered setting
Affects: Intensity (Density)
What if the exposure time is too long?
To Dark, overexposed
What if the exposure time is too short?
Noisy and light, underexposed
Tube Current (mA)
Not adjusted easily
Affects: Intensity (Density)
What if the tube current is too much?
Too dark, underexposed
What if the tube current is too little?
Noisy, underexposed
Tube Potential
Acceleratioin of e- from cathode to anode
* affects the number and energy of photons
Affects: Density & intensity
What if the Tube Potential is too high?
Too gray (not enough contrast)
mostly compton scattering
What if tube potential is too low?
Too light (Very high contrast)
mostly photoelectric absorption
Distance: Inverse Square Law
Inverse Square Law: Further from the source, Decrease photons per unit area
Intensity =1/distance
* short distance=Increase intensity=Increase Density=Dark
Ideal Distance
Incrase Source Object= Decrease Intensity (Density), Increase Quality
Decrease Object-Image Distance=Increase Quality, Decrease Magnification
Size depends on:
Focal Spot Szie
Source-to-Object Distance
Object to image distance
Ideal Size:
Decrease Focal Spot Size
Decrease Object to image distance
Increase Source-to-Object distance
Coherent Scattering
Incident Photon contacts outer electron
Effect: Decrease contrast
Photoelectric Absorption
Incident Photon contacts & ejects an inner electron
forms an ion pair
Effect: Increase Contrast
What happens to photoelectric absorption when kVp is too low?
Increase Photoelectric absorption
Compton Scattering
Incident Photon contacts an outer electron
Form ion pair
Effect: Decrease Contrast
Deterministic Effects:
Hair loss, Cataracts, Skin Damage, Oral Mucositis
Threshold needs to be reached:
* Less than=no effects
Stochastic Effects
Cancer, Leukemia, Hertiable Effects
No threshold: Dose builds up over years
Direct Radiation
Direct alteration of biologic molecules
Indirect Radiation
Ionizing radiation converts H2O into free radicals
* alter biologic molecules
Cells that are mitoticallys active are more radiosensitive
* Most Sensitive: Hematopoietic cells, epithelial cells, sperm cells
* Least sensitive: Nerve cells, Muscles Cells
Film vs Digital Imaging: General
Film:
* Requires chemicals to process
* quires time to develop
* Superior image quality
* More radiation dose to patient
Digital:
* No chemicals
* Instant viewing
* Image
Film composition
Base: Flexible Plastic
Emulsion: Silver halide crystals in gelatiin material
Intensifying Screens:
* coated w/fluorescent phosphor
* Decrease amount of exposure needed
* decrease resolution
Film Speed
A<B< C < D < E < F
Film Speed is determined by:
Large Crystals: Faster films
Double Emulsion: Faster Film
Radiosensitive Dyes in emulsion=faster film
Film Imaging: Chemical Processing steps:
- Developing
- Fixing: wash away unexposed silver halide crystals
- Washing: Wash away residual chemics
- Drying
Chemical Procesing: Developing
Converts exposed crystals into metallic silver grains
If final image is light: Developer is porbably old
Chemical Processing: Fixing
Wash away unexposed silver halide crystals
* Ammonium Thiosulphate: removes undeveloped silver halide crystals
* Aluminum slats: preserves emulsion
Detector: Contrast resolution
Distinguish shades of gray
Film>Digital
Spatial Resolution
Distinguish 2 close points
Film> CCD/CMOS> PSP
Detector Latitude
Exposure range
* provide useful image
PSP> CCD/CMOS> FIlm
Detector Sensitivity
Dose required to achieve standard gray level
CCD/CMOS is 1/2 the speed of F speed film=way less radation
What could cause an image to be underexposed?
Inadequate exposure time
inadequate development time
old development solution
Temp too low
What could cause an overexposed image?
Exposed too long
Exposed to light
What are the types of intraoral x-rays?
Periapical
Bitewing
Occlusal
What are the different type of extraoral x-ray?
Pan
Cephaolmetric
CBCT
Occlusal
Receptor flat on occlusal plane
* canine to canine
assesses: Trauma, Impacted teeth, SUpernumery
Panoramic
Used for:
screening
pathology
3rd molar location
CBCT
Cone Bean Computed Tomography
3d image:
* axial view (top bottom)
* Sagittal (Side-side view)
* Coronal (Front back)
* 3D volumetric render
CBCT is useful for
Implant planning
CBCT (Strange anatomy)
Ortho
TMJ
Pahtology
Waters View
PA ceph at 45 degrees to obrito medial line
Best for:
* Paranasal sinus
* Midface
* Orbits
Townes View
PA ceph at 30 degree from orbito medial line
Best for: Condyle
* eliminates superimposition of amstoid and zygoma
Submentovertex View
Base projection of the skull
Best for:
* basilar skull fractures
* Zygomatic fractures
Bisecting Angle Technique
Central ray of x-ray is aime perpendicular to bisecting line b/w:
long axis of the tooth
long axis of receptor
Paralleling Technique
Receptor parallel to long axis of tooth
* Beam center perpendicular to long axis of tooth and receptor
Less distortion
Increase Image quality
Elongation
Most common error
could be:
* angulation issue
* bending film
Cone cut
X-ray beam & receptor not line up
Underexposed
Grainy or too light
* too short exposure time
* Decrease mA and kVP
Overexposed
image to dark
* Increase mA
* Increase kVp
Double exposure
2 images exposed on same plate
Pan: Motion Error
Wavy & irregular borders
* pt swallows or moves
Corticated Unilocular
One Compartment
Radiopaque Border
