Principles of Radiography Flashcards
How is an X-ray made?
Fast electrons colliding with atom’s of heavy metal (such as tungsten) produces X-rays.
What are the basic components of an X-ray tube?
Filament attached to low voltage (produces electrons), Copper with tungsten attached to high voltage (target), a vacuum to contain these.
What 3 things affect the x-ray absorption in the body?
Density of tissue, thickness of tissue, and atomic no. of elements in tissue.
What are the two important positive contrast mediums that can be used? Where are they most likely to be used? Why are they suitable for this job?
Barium and Iodine. Barium often used in GI problems, Iodide often in aqueous contrast media. They are suitable for this job as they have high atomic numbers.
Give an example of a negative contrast medium.
Gases e.g. air, carbon dioxide.
What is Bremsstrahlung radiation used to explain?
It is used to explain how X-rays are emitted. The nucleus of tungsten attracted moving electron and slows it down and puts it on a different path. The difference in kinetic energy is emitted as X-rays.
On radiographs, what is constituted as “soft tissue”?
Parenchymal organs, muscle, fluids e.g. blood, bile, urine.
What are mA’s? If you increase the number of mA’s what happens?
Milliamperes: The current (no. of electrons) passing across the X-ray tube. Increasing the mA’s increases the number of X-rays, but does not effect the energy.
When would it be preferable to use a higher mA setting?
Minimise exposure time and avoid motion blur.
What is kVp? What does increasing the kVp do?
Kilovoltage peak: The voltage applied across the X-ray tube. Increasing the kVp increases the no. of X-rays as well as increasing the X-ray beam energy (which increases the penetrating power of the X-ray.
When would you adjust the kVp settings?
Often adjusted for thickeness of tissue. e.g. Low kVp (45-60) used for smaller body parts e.g. extremeties. High kVp (>80) used for thicker body parts e.g. thorax.
