Physics Intro - Midterm Material

Question 1

Name the body planes and what they divide?

Answer 1

Mid-sagittal = left & right
Mid-coronal = anterior & posterior
Horizontal (transverse) = superior & inferior

Question 2

Define Position

Answer 2

Side of body nearest film; should be marked as such (i.e. RAO)

Question 3

Define Projection

Answer 3

path of the x-ray beam (AP/PA/oblique/lateral)

Question 4

Define View

Answer 4

side of anatomy best visualized, usually side nearest film

Question 5

Which body substance has the least subject density?

Answer 5

Air - least attenuation - looks dark

Question 6

Which body substance has the greatest subject density?

Answer 6

Metal - greatest attenuation - looks white

Question 7

Which body substance has the middle subject density?

Answer 7

Bone - very attenuated - looks light

Question 8

Define Attenuation

Answer 8

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

Question 9

What will disease processes do to an X-ray?

Answer 9

Disease processes may affect the way tissue attenuates x-rays.
Additive conditions: increased attenuation (blastic) (whiter)
Destructive conditions - decreased attenuation (lytic) (darker)

Question 10

Define Radiographic density

Answer 10

radiographic blackness = amount of blackness on film. mAs control it

Question 11

mAs/doubling/halving

Answer 11

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.

Question 12

What x-ray factor is primarily responsible for controlling contrast?

Answer 12

Radiographic contrast: variety of gray shares from darkest to lightest.
Controlled by kVp; controls penetration
Higher kVp lowers dosage, decreased mAs

Question 13

What is meant by improving contrast?

Answer 13

Increasing number of shades of gray.

Grids can improve contrast by reducing radiation fog by absorbing scatter radiation as it exits patient’s body.

Question 14

What is beam restriction?

Answer 14

It reduces scatter, improves image quality and greatly reduces patient exposure. Beam must always be restricted.
Through aperture diaphragm, cones/cylinders, collimators

Question 15

What is scatter?

Answer 15

Scatter serves no good purpose. Scatter is dependent on kVp, amount and type of irradiated tissue (soft tissue scatters more than bone).

Question 16

What is the purpose of the radiographic grid?

Answer 16

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.

Question 17

What are 2 types of shape distortion?

Answer 17

Elongation: occurs when tube or film improperly aligned.
Foreshortening: occurs when body part is improperly aligned with film.

Question 18

What is size distortion?

Answer 18

occurs only in form of magnification. objects cant be minified. Magnification results from increased OID. Increased SID may compensate.

Question 19

Are children more sensitive to radiation than adults?

Answer 19

Young cells are more sensitive because they are more rapidly dividing already.

Question 20

What are the most sensitive/least sensitive body cells to radiation?

Answer 20

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

Question 21

What lifestyle factors put someone at a greater risk than an x-ray exposure?

Answer 21

Alcohol use, being unmarried, smoking, MVA, pedestrian accident

Question 22

What lifestyle factors put someone at less of a risk than an x-ray exposure?

Answer 22

Owning a small car, long drive, consuming desert/sod, not fastening seatbelt

Question 23

What is a ROENTGEN?

Answer 23

R-symbolizes amount of ionization produced by a specific amount of radiation in air only.

Question 24

What is a RAD?

Answer 24

Radiation absorbed dose: measurement of energy absorbed and can be applied to any absorbing material. SI equivalent is gray (1Gray=100RAD)

Question 25

What is a REM?

Answer 25

Radiation Equivalent Man: measurement of biological change; this is the reading on monitoring devices. SI equivalent is sievert (1REM=10mSV) (1Sv=100REM)