Physics Intro - Midterm Material Flashcards
(25 cards)
Name the body planes and what they divide?
Mid-sagittal = left & right
Mid-coronal = anterior & posterior
Horizontal (transverse) = superior & inferior
Define Position
Side of body nearest film; should be marked as such (i.e. RAO)
Define Projection
path of the x-ray beam (AP/PA/oblique/lateral)
Define View
side of anatomy best visualized, usually side nearest film
Which body substance has the least subject density?
Air - least attenuation - looks dark
Which body substance has the greatest subject density?
Metal - greatest attenuation - looks white
Which body substance has the middle subject density?
Bone - very attenuated - looks light
Define Attenuation
a quantity that characterizes how easily a material or medium can be penetrated by a beam of light, sound, particles, or other energy or matter.
Less attenuation = greater radiographic blackness; mAs control it
Air-least attenuation - radiolucent (darker)
Fat - relatively dark
Muscle/water - moderate attenuation
Bone-very attenuated
Metal- greatest attenuation - radiopaque
What will disease processes do to an X-ray?
Disease processes may affect the way tissue attenuates x-rays.
Additive conditions: increased attenuation (blastic) (whiter)
Destructive conditions - decreased attenuation (lytic) (darker)
Define Radiographic density
radiographic blackness = amount of blackness on film. mAs control it
mAs/doubling/halving
milliAmps per second is the primary control of quantity of x-ray, radiographic blackness and is directly related to patient exposure.
Doubling mAs doubles radiographic blackness and patient exposure.
Cutting mAs in half makes half the blackness and halves patient exposure
Greater mAs = greater radiographic blackness, less blur
25-30% change in mAs necessary for visible change in blackness.
What x-ray factor is primarily responsible for controlling contrast?
Radiographic contrast: variety of gray shares from darkest to lightest.
Controlled by kVp; controls penetration
Higher kVp lowers dosage, decreased mAs
What is meant by improving contrast?
Increasing number of shades of gray.
Grids can improve contrast by reducing radiation fog by absorbing scatter radiation as it exits patient’s body.
What is beam restriction?
It reduces scatter, improves image quality and greatly reduces patient exposure. Beam must always be restricted.
Through aperture diaphragm, cones/cylinders, collimators
What is scatter?
Scatter serves no good purpose. Scatter is dependent on kVp, amount and type of irradiated tissue (soft tissue scatters more than bone).
What is the purpose of the radiographic grid?
To absorb scatter radiation as it exits patient’s body. It should be used with larger body parts, or higher kVp. It is placed behind the patient and film. It reduces radiation fog and improves contrast on the film.
What are 2 types of shape distortion?
Elongation: occurs when tube or film improperly aligned.
Foreshortening: occurs when body part is improperly aligned with film.
What is size distortion?
occurs only in form of magnification. objects cant be minified. Magnification results from increased OID. Increased SID may compensate.
Are children more sensitive to radiation than adults?
Young cells are more sensitive because they are more rapidly dividing already.
What are the most sensitive/least sensitive body cells to radiation?
Most sensitive cells are the ones that are simple, have a high mitotic rate and a high metabolic rate.
Highest sensitivity: bone marrow, GI, gonadal, eye lenses
Lowest sensitivity: muscle cells, nerve, and chondrocytes
What lifestyle factors put someone at a greater risk than an x-ray exposure?
Alcohol use, being unmarried, smoking, MVA, pedestrian accident
What lifestyle factors put someone at less of a risk than an x-ray exposure?
Owning a small car, long drive, consuming desert/sod, not fastening seatbelt
What is a ROENTGEN?
R-symbolizes amount of ionization produced by a specific amount of radiation in air only.
What is a RAD?
Radiation absorbed dose: measurement of energy absorbed and can be applied to any absorbing material. SI equivalent is gray (1Gray=100RAD)
