X-Ray Production Flashcards
What are the principles of x-ray production?
-produced when electricity from the mains transformer into a high voltage current, with some of that energy converting to x-rays
-image is produced by computer manipulation of the data
What are the principles of photons?
-travel in straight lines, in the primary beam
-can be absorbed or scattered
-can pass through x-rat and reach x-ray film or by a digital recording system
Describe the energy involved in x-rays?
-it’s directly proportional to the frequency
-it’s indirectly proportional to the wavelength
What is the frequency involved in x-rays?
-the number of waves that pass a certain point in a specified amount of time
What is the wavelength involved in x-rays?
-is the distance between any 2 corresponding points on adjacent waves
Why does penetration occur?
-due to high energy
What are the effects of using photographic film?
-produces latent or hidden images
-revealed by processing
Why is fluorescence used?
-x-rays cause crystals of certain substances to fluoresce
-utilised with digital radiography
What are the properties of atoms?
-contain protons which are positively charged in the nucleus
-contain neutrons which have no charge
-contain electrons which are negatively charged and orbit around the nucleus
How are x-ray photons produced?
-when rapidly moving electrons are slowed down or stopped
What happens when x-ray photons travel at high speeds?
-they collide with other atoms and lose their kinetic energy
What happens to the energy produced by x-ray photons?
-transformed into heat and a very small amount into x-ray energy
What does the tube head contain?
-cathodes which are negatively charged
-anodes which are positively charged
Where are electrons produced?
-at the filament which is a coiled wire made up of tungsten
How are electrons produced?
-a small electrical current is applied to the coiled wire filament which is heated and releases a cloud of electrons
-called thermionic emission
Why is the focusing cup placed around the filament essential?
-to ensure electrons will reach the target in a narrow beam
What is the focusing cup made of and what are its characteristics?
-made of molybdenum
-has a high melting point and is a poor heat conductor
-negatively charged and part of cathode
What does the focusing cup do?
-repels electrons causing them to form a narrow beam due to their concave shape
What happens to the cloud of electrons produced?
-they are accelerated at high speeds across the tube head to the target (anode)
Describe the high electrical potential difference between the filament and the target?
-the negatively charged filament reports the exceptions at the cathode side
-the target becomes positive and attracts electrons to the anode side
What are the characteristics of the tungsten?
-high atomic number
-high melting point
-mechanical properties
What are the characteristics of the copper block
-good heat conducter
-leads heat away form the target to the cooling fins and surrounding oil
What are the characteristics of the target?
-set at an angle of 20 degrees
-allows the area being struck by electrons to be as large as possible
What does angulation mean?
-the x-ray beam appears to originate from a much smaller area
Why is angulation important?
-keeping the smallest area as possible allows very fine radiographic definition
-larger are will reduce radiographic definition substantially leading to a less sharp image
What is the glass envelope?
-a glass vacuum tube that contains the anode and cathode of the x-ray tube
What is the vacuum and its function?
-a space with all air/gases extracted
-allows the x-rays to travel in straight lines, if oxygen were present the x-rays would bounce off the particles and be misdirected
What are soft x-rays?
-they do not have enough power to pass through the patient
-can lead to scatter or absorption
What is the structure and function of the aluminium filter?
-a flat sheet of aluminium
-placed over the window
-absorbs soft x-rays and prevents them from leaving the tube head
How are images formed?
-image is produced when an exposure takes place
-image appears black, white and various shades of grey
What does x-ray absorption depend on?
-in relation to the tissues their;
Atomic number
Specific gravity
Thickness
What is the atomic number in relation to x-rays?
-bone has a higher atomic number than tissues
-absorbs more x-ray photons
-produces paler areas of radiographs
What is specific gravity in relation to x-rays?
-bone has a high specific gravity
-soft tissue has a medium specific gravity
-gas has a low specific gravity
What are the colours of each component seen on images?
Gas is very dark
Fat is dark grey
Soft tissue or fluid is mild grey
Bone is nearly white
Metal is white
When causes a white appearance on images?
Thicker areas which have absorbed more x-ray photons
What causes a grey appearance on images?
Thinner areas which have absorbed less x-ray photons
What is the function of kilovoltage?
Determines the speed and energy of which electrons hit the target (penetrating power)
What is the function of milliamperage?
Measures the quantity of electrons crossing the tube during an exposure
Controls the heating of the filament
What is the function of the timer during exposure?
Controls the amount of time that a high voltage is applied for
What is the focal-film distance?
The distance between the focal spot and the x-rat film/cassette
How would we set kV for patients?
-increased kV for large dog
-decreased kV for small or thin dog
What impact does incorrect kV setting have?
too low means it’s underexposed
too high means it overexposed
What does the milliamperage control?
-controls the electrical current to the cathode and thereby the temp of the tube filament
-controls the amount of x-rays produced
What impact does incorrect milliamperage setting have?
Too low means radiograph will be pale
Too high means radiograph will be dark
What variables affect the radiography image?
X-ray Be including kV mAs collimation and distance
Patient including movement positioning and preparation of the area
What are girds?
A flat plate that is placed between the patient and the cassette
Can be placed underneath x-ray table or built into it
Can be built into the cassette
What is the structure of grids?
-alternating strips
-materials is able to absorb radiation radiologist interspace
-aluminium or carbon plastic fibres scatter will be absorbed by the lead strips
