Osce Radiology Flashcards
The Electro Magnetic Spectrum
Non Ionizing
Radio
Microwave
Infrared
Visible light
Non ionizing medical - Ultrasound, MRI
Ionizing
Ultraviolet
X-ray
Gamma Ray
Ionizing radiation medical - X-ray, CT scans
A type of electromagnetic radiation that doesn’t have enough energy to remove electrons from atoms or molecules, unlike ionizing radiation
Which of these modalities use ionising Radiation?
CT, X-RAY, DEXA
MRI scan uses ionising radiation?
False
Wha are the most radiosensitive tissues and organs?
Bone marrow
Lymphoid tissues
Gonads
The x-ray tube
Converts energy to radiation by: Receiving electrical energy and converts this into X - Radiation and heat
Is a Filament a subcomponent of ?
Cathode
What are the two main components of an X-Ray tube
Cathod and Anode
What are the two types of Anode
Stationary + Rotating anode
XRAY Equipment – Cathode
CATHODE:
- Negatively charged
- Converts an electrical signal into a visual display
- Is a source of electrons that are focused into a beam to generate x-rays
- Is made up of a tungsten filament coiled within a nickel focusing cup
SUBCOMPONENTS
- Filament
- Filament coil sits within a focussing cup, usually made from nickel
- Source of electrons within the tube
- Heated by an electric current to expel electrons from the cathode through thermionic emission (the emission of
electrons from a heated source).
- The size of the filament relates to the size of the focal spot. some cathodes have two filaments for broad and fine focusing. - Focusing Cup
- Negatively charged to focus the electrons towards the anode and stop spatial spreading
XRAY Equipment – Anode
ANODE:
- A metallic bevelled disc made of tungsten where the x-ray beam is produced
- Positively charged
- Body made of molybdenum and graphite – good for heat storage
- Attached to a large copper rotor, allowing it to spin up too 10,000 rpm with a temperature of up to 2000 degrees c
- has two primary functions:
1. converts electronic energy into photons (x-radiation) (the number of x-rays produced depends on the anode material’s atomic number and the energy of the electrons).
- Dissipates heat generated during the process of x-ray production (i.e. spinning of the anode)
CONVERTS ELECTRICAL ENERGY INTO HEAT AND RADIATION
Anode Heel Effect
The variation in x-ray intensity along the longitudinal axis of the tube
Where the photons formed deeper in the anode must first pass through the “heel” of the anode causing that ”side” to lose intensity before reaching the object or image receptor
Used when imaging anatomical parts that are unequal in thickness and densities throughout their respective lengths.
The 3 principle electrical quantities that can be adjusted are
- KVp (kilovoltage peak): the max voltage or electrical potential applied across the x-ray tube
- determines penetration and contrast - MA controls electrical current flowing through the tube and how many electrons produced at the
cathode
- determines image density - s: duration of the exposure or exposure time, generally a fraction of a second
kev (kiloelectron volt): unit of energy of the x-ray photon that determines whether hard or soft x-rays.
What are the 3 principle elctrical quantities that can be adjusted
kvp , MA , s
Imaging Accessories
■ Filters – regular QA
■ Image detectors – CR / DR
■ Lead protection
■ Body measure – TLD badge
■ Stabilisation devices – foam pads, sandbags
■ Body marker
■ Vertical cassette holder
■ X-ray reference ball – 25mm ball diameter
Characteristic Vs Bremsstrahlung Radiation
They both contribute to the production of x-rays, but they differ in several ways:
Characteristic radiation
-Only accounts for small percentage of x-ray photons produced
-Bombarding electron interacts with inner shell electron
-Radiation released due to electron dropping down into lower energy state
-Radiation released is of a specific energy
-X-ray photon energy depends on element of target atoms not tube voltage
Bremsstrahlung
-Accounts for 80% of photons in x- ray beam
-Bombarding electron interacts with whole atom
-Radiation released due to diversion of bombarding electron as a result of the atomic pull
-Radiation released is of a large range of energies
- X-ray photon energy depends on tube voltage
Which type of radiation is represented by the line spectrum
Characteristic radiation
Which one is responsible for most X-rays produced in diagnostic medical X-ray tubes
Bremsstrahlung radiation
Interaction of X-Ray with Matter
When a photon beam interacts with matter, some gets absorbed, some deflected to new direction and rest transmitted to produce a radiographic image. - the beam that’s deflected from its original path to a new direction is known as scatter radiation.
ATTENUATION - Attenuation is the loss of energy of a beam of radiant energy due to absorption, scattering, beam divergence, and other causes as the beam propagates through a medium
There are 5 radiographic densities:
- air, fat, water, bone, metal
each has a different combination of interactions
so each attenuates x-rays to a different degree
■ Three types of interactions occur when radiation is absorbed by matter:
1. Coherent scattering scatter radiation
2. Compton effect
3. Photoelectric effect = secondary radiation
Tissues with high attenuation coefficients
Show up white
Show up black
Show up white
What are the 5 radiographic densities
Air, fat, water, bone, metal
What are the 3 types of interactions that occur when radiation is absorbed by matter?
Coherent scattering , Compton Effect, Photoelectric Effect
Changing KVP
- As KVp increases, number of photoelectric absorption interactions decreases therefore percentage of Compton scatter interactions increases in relation
- this decreases image contrast
INCREASING KVP = INCREASED SCATTER = DECREASED QUALITY
Changing TISSUE VOLUME
The volume of tissue irradiated is determined by the thickness of the subject and the size of the radiation field
- as volume increases, scatter radiation increases
INCREASING THICKNESS= INCREASED SCATTER = DECREASED QUALITY
Changing DENSITY OF MATERIAL
- The density of the material is determined by the number of electrons (density of electrons) present in the outer shell of the atom
- As density of material increases, scatter radiation increases
INCREASING DENSITY OF MATERIAL = INCREASED SCATTER = DECREASED QUALITY
