Lectures 1 and 2 Flashcards
Breifly explain the difference between radiography and radiology:
- Radiography = the use of X-rays to form an image
- Radiology = interpretation of abnormal and normal findings
What are the three main elements of an X-ray machine that can be controlled?
- Kilovoltage (kV or kVp)
- Milliamperage (mA) - control and metre
- Time control (s) - of linked to mA
Briefly explain the differences between the cathode and the anode:
- The cathode consists of a coiled filament wire and focusing cup with small and large focus wires - it is LOW voltage, NEGATIVE electrode
- The anode has a target and focal spot. Stationary and rotating types exist. It is HIGH voltage and POSITIVE electrode
Complete the sentance below:
The pre-exposure button activates ____(1)____ through the filament. __(2) __ setting controls the SIZE of electron cloud. Releasing the pre-exposure button returns electrons to their ___(3)___. Continually pressing the pre-exposure button with no exposure causes __(4)_____ damage.
- current
- mA (mAs also acceptable answer)
- shells
- cathode
Pressing the exposure button causes electrons to travel from cathode to ___(1)___. The potential difference across the tube as resultant kinetic energy is controlled by ____(2)____ setting.
- Anode
- kV
What 2 facotrs determines the NUMBER of electrons travelling across the tube?
- Size e- cloud (mA)
- Time allowed to cross (s)
- Hence, mAs setting
Electrons collide with target atoms and lose energy in several forms. ___(1)___% of electrons collide with outer shell electrons producing ___(2)__ energy. This limits the potential to produce high exposures. ___(3)____ % of electron collisions results in the production of radiation. This radiation comprises of Bremsstrahlung radiation (_(4)__%) a result of colliding with the atoms nucleus and characteristic radiation (_(5)__%) a result of colliding with inner shell electrons.
- 99%
- Heat production
- 1%
- 75-90%
- 10-25%
Increasing the mAs will increase __(1)__ of beam. Increasing mAs increases radiographic __(2)___ only. mAs increases film ____(3)____ if of sufficient energy (or kV) to penetrate tissue being examined.
Increasing the kV results in increased __(4)___ and ___(5)___ of the beam. This means ___(6)_____ penetration and radiographic density and decreased ___(7)____.
- Intensity
- Density
- Blackness
- Energy or intensity
- Energy or intensity
- Increased
- Contrast
What is the cause of the peaks on the BR spectrum of radiation seen below?
The peaks are caused by characteristic radiation (CR) peaks. These corrospond to specific atomic radiation levels.
Breifly explain what is meant by the heel effect and why it is important in taking X-rays:
The heel effect is where greater intensity of the beam occurs at the cathode size. It is significant as it can be utilised with thicker body parts. See the image below.
What three factors determine the X-ray machine capacity?
- The focal spot size
- The heat capacity of the target
- Circuits and power supply
Differentiate between the actual focal spot and effective focal spot (which is larger) and compare the pros and cons of having a large and smaller focal spot:
Actual focal spot versus effective focal spot:
- Actual focal spot = the area of the target bombarded by e-
- Effective focal spot = focal spot as viewed through the tube window
Large versus small focal spot:
- Large focal spot = increased heat dissipation and increased possible exposures
- Smaller effective focal spot = increased detail/edge sharpness, or reduced unsharpness
What is the benefit of a rotating anode?
- Allows smaller focal spot while still allowing for good heat dissipation - meaning increased detail/edge sharpness
What are the two main types of circuits and power supply that are available and which is better?
- Combined circuits - kV and mA dials - these limit the exposure setting that is available
- Independant circuits - mA and kV - hgih ouput is possible - hgih voltage kV circuit and low voltage mA circuit
