01, 02 Principles and biology Flashcards
How are x-rays produced?
- pyrex glass tube
- two electrodes in a vacuum: Cathode (negative filament) and Anode (positive)
- generation of electrons,
- accelerate electrons
- abrupt stoppage of electrons
Cathode
-Negative electrode and source of e-s
-tungsten filament wound in molybdenum focusing cup
-strong when thin
-high melting point (6098 degrees)
this is heated and e-s “boil off”
Anode
- positive electrode
- copper to conduct heat with tungsten target
- interacts with electrons to produce radiation
- 99% kinetic energy generates heat, 1% radiation
types of x-ray interactions with patient
- scattered
- absorbed/attenuated
- transmitted
What is the source of “fog” on film
scatter
what does the kilovoltage determine?
x-ray wavelength, ie the penetrating power
What do mAs control?
the amount
inverse square law
- intensity of radiation varies inversely with the square of the source-film distance (SFD)
- I=1/d^2
- i.e. increase d by 2 =decreased intensity by 4X
what are the most attenuating natural tissues of the body?
cortical bone and enamel
what is present in the film to protect the patent from back scatter radiation?
lead foil at the back of the film
what type of film would you use for a periapical radiograph?
No 1, 2
what No. of film for a bitewing?
No. 2 with a bite-tab
what type of film for an occlusal rad?
No. 4
Do fast speed films require more or less radiation exposure than slow speed films?
-less
What is the alphabetical classification of the fastest film available?
F speed (Insight)
What is the primary controlling factor for density?
Milliamperage Seconds (mAs)
if you increase the mAs, what does that increase?
-and when you increase them, what’s the general rule?
the quantity of x-rays produced
-change the mAs by a factor of 2
How do you change the radiographic contrast?
- kVp,
- kilovoltage determines the relative strength of the x-ray photons or penetrating ability
- increasing the kilovoltage produces x-rays which penetrate tissues more deeply
Penumbra
(edge gradient), fuzzy, unsharp margin around a structure on a radiograph
what gives rise to magnification?
-x-rays traveling in diverging straight lines
which cusp tips would have greater magnification, B or L?
Buccal, more magnification and more unsharpness
what are the five keys to accurate image formation?
- small focal spot
- source to object distance as long as possible
- object to film distance as short as possible
- long axis of object parallel to film
- central x-ray perpendicular to film
who discovered x-rays?
Wilhelm conrad roentgen, 1895
x-ray of bertha’s hand
what are the effects of radiation on atoms and molecules?
- excitation (from low energy photons)
- ionization (from high energy photons)
- breakage of molecular bonds
Radiolysis of water:
X-ray photons strip electrons from water molecules creating ion pairs
- Electron + free radical, and these free radicals are extremely reactive and can cause damage to DNA, RNA and ATP
- produces H+ and OH-
- which can make H2O2 or HO2
Indirect efect
- photons and radiolysis of water
- depending on the degree the cell may be able to repair
The time between the irradiation and the development of the observed biologic effect is called…?
The latent period
What factors influence radiobiologic effects?
- type of radiation
- LINEAR ENERGY TRANSFER
- total dose
- penetrating ability of radiation
- acute vs. chronic exposure
- local area vs whole body
Linear Energy Transfer
relates to the amount of energy imparted to a tissue as the ionizing species passes through
- Alpha particles are high LET (more damaging) imparting all their energy in a short distance with events close together
- X-rays have low LET, imparting their energy over a deeper area with more widely separated individual events
Host factors of radiobiologic effects
Species of animal, intrinsic resistance, type of tissue,
- rate of cell division (rapid turnover=more sensitive_
- somatic tissues: radiation damage not inherited
- genetic (reproductive) tissues (ova and sperm): involved in transmission of genetic info to next generation, radiation damage is inherited
what types of radiation damage is inherited?
Genetic (reproductive) tissues (ova and sperm)
-somatic damage is not inherited
Threshold Dose
the point at which there seems to be a biological effect from radiation
-NON-LINEAR dose-response curve
effects of radiation on skin
basal cell layer of epidermis sensitive to radiation
-squamous cell carcinomas
Total body irradiation syndromes
- CNS
- GI
- bone marrow
CNS doses >50 Gy
- GI 10-50 GY
- Bone marrow 2-10 Gy
- no human survival at doses >10 Gy
What is the biggest source of Radiation exposure?
- Radon 54%
- Medical x-ray=11%
What are the old and new radiation measurement (units)?
- old system: roentgen (R), rad, rem
- “new” system: Gray (Gy), and sievert (Sv)
how much radiation in in a panoramic radiograph?
7 micro Sv
- average US background radiation, one year 3000 micro Sv
what is the difference between exposure and dose?
exposure (R) refers to the amount of radiation coming out of the machine, and DOSE (Gy) is the amount of radiation absorbed by a unit mass (total weight) of tissue- this is the indicator of potential harm
ALARA
“As Low as reasonably achievable”
What does a filter do on a x-ray unit? What is the filter made of and what size is it?
filtration removes soft, low wavelength x-rays that don’t contribute to the image.
-aluminum and it is 2.5 mm thick
what is collimation?
collimation limits the beam by restricting the cross-sectional area
what is a collimator made of?
Lead, and rectangular is best
according to the law, how big can the diameter of the beam be?
7 cm
does a long BID increase or decrease radiation to the patient?
reduces, like a long rifle compared to a sawed off shot-gun
where should you stand while taking a radiograph?
90-135 degrees and 6 feet from the primary beam
