Physics
What is the conservation of energy law ?
That energy can neither be created or destroyed. It can only be coneverted from one form of energy to another .
What are Isotopes?
Are members of the same element with:
-same number of protons
-different number of neutrons
-different mass numbers
Formula for acceleration
Acceleration = change of velocity over change of time
Velocity formula
Velocity = distance over time
Newtons law's
1- An object will not change its motion unless a force acts upon the object.
2- The force acting on an object is equal to the mass of that object times its acceleration F=ma
3- For every action, there is an equal and opposite force
What kind of wave can be polarised?
Only transverse waves
What is relfection of a wave ?
-when a wave travels from one medium to another, part of the energy is passed on and part is reflected.
The angle of incidence is = to the angle of reflection
What is refraction in waves?
-When a transmitted wave is deviated from the direction of the incident wave
-The change of direction is called refraction
Inverse Square Law
-the intesity of radiation is inversely porportional to the square of the distance
-the more distance is increased, the intesity of the radiation will decrease porportionally to the square of the distance increased.
Wave intensity
The average energy flowing through a unit area per unit time
Electromagnetic waves
-microwave
-infrared radiation
-ultraviolet radiation
-visible light
-x-rays
-Radio waves
-Gamma rays
Photon Energy Formula
E = hf
photon energy = (Planck's constant) x (frequency)
What is ultrasound?
-Sound of frequency above the threshold of human hearing (20kHz)
-Scans density of materials and the speed of sound in that material
Radiation
Energy in transit in the form of high speed particles or electromagnetic waves
Absorbed dose units
Gray (Gy)
Equivalent dose units
Sievert (Sv)
Effects of radiation
-breaks chemical bonds in the body, leading to damage to DNA
Can interact with atoms or molecules in the cell to produce highly reactive free radicals, this diffuses and causes damage to DNA
-can cause mutations in DNA, causing problems later
-daughter cells may reproduce in a uncontrolled way and lead to cancer later in life
Absorbed Dose- Gray (Gy)
Biological effects in any tissue are proportional to the amount of energy absorbed per unit mass of tissue
Equivalent dose -Sievert (Sv)
different radiation have different biological effects for the same amount of energy absorbed
Effective dose
Different organs of the body are assigned tissue weighting factors, to represent the different sensitivity of each organ to radiation damage
Advantages of using a rotating anode ?
-heat disperses over a larger suface area (preserving the x-ray tube)
-higher heat cpacity
-can be used for longer exposure and larger body parts
-larger focal area
Disadvantge of using a rotating anode?
Not suitable for mobile x-rays
-too bulky, not simple or easy to move around
What are grids used for ?
Reducing scatter and enhancing the contrast of the image
What is the air gap technique used for?
It will magnify the image and reduce scattering
3 methods to reduce scattering in a mammogram ?
1. compression
2. air gap techinque
3. grids
Why is the method of compression used for mammograms ?
-reduces the tissue thickness
-reduces patient movement (reduces motion)
-makes tissue more evenly distributed
-evens the brightness of the image
Why is contrast important for mammograms ?
The tissues inside the breast are very similar, adeqaute contrast allows us to distinguish the different tissues.
What is the function of a thermistor?
Thermistors are dependent of temperature. To change resistance with the changes of temperature.
How can we reduce scattering BEFORE it reaches the patient ?
-beam limitation device (collimation)
-air gap techinque
-grids
How can we reduce scattering AFTER it reaches the patient ?
-air gap technique
-grids
Disadvantage of air gap technique ?
-need to increase the exposure (because distance is increased)
- more radiation is emitted
-magnification
-distortion of the image
How does collimation reduce scattering ?
-Limits the area exposed to x-ray photons
-Contains the filter which filters out low energy photons (which has no contribution to the image quality, but will increase patient dose)
Coherent scattering
Interaction between an incident x-ray of energy and an atom in the material
-no energy is lost in the process to an atom
-purely just scattering
-occurs at low energies (below 30kVp)
Probability of coherent scatter occuring ?
The interaction occuring is inversely proportional to the incident energy and proportional to the square of the atomic number
-the likely hood also depends on the energy of the incident x-ray and on the atomic number, Z (dependent on Z).
Compton scattering
-the x-ray changes direction (is scattered) and has less energy than the incident x-ray, hence a longer wavelength.
by the conservation of energy:
the incident energy must be divided between kinetic energy of the recoil electron and the scattered x-ray
(E)incident = (E)scattered + (E) ecoil electron
functions of a capacitor
-removes noise
-stores energy to use later, accumulates on one plate and relases on another plate
-smoothens the variation of the current
-maintains voltage at the same level
How does a capacitor work ?
like a battery it stores energy. Although it can charge up quicker and release energy faster than a battery. Generally a capacitor has two plates, accumulating energy on one plate and releasing energy on another plate.
THREE uses of a capacitor?
-energy storage
-power conditioning
-electronic noise filtering
Bremsstrahlung
When the electron moves extremely close to the nucleus, decelerates and changes direction, converting kinetic energy into electromagnetic radiation.
Characteristic x-rays
when the incident electron stikes a atom bound electron, the bound electron is ejected from the inner shell of the atom. The incident electron is also deflected off an angle. A higher shell electron will replace this vacancy, and energy is released to compensate - this energy is called characteristic radiation.
The energy produced is dependent of the number of protons and the difference between binding energies- so the same atoms will have the same energies.