-
Off focus error
SID is wrong. Ok in the middle
-
Lead content is high with what frequency and ratio?
Lowfrequency but high ratio
-
What is grid cutoff?
Undesirable absorption of primary radiation
-
Two types of moving grids
Reciprocating and oscillating
-
Intersection at top of grid radius?
Convergence line
-
Decrease in distance between strips results in
Increased grid ratio
-
Grid ratio is
Height divided by interspace distance
-
Order of tissue density?
Air fat water muscle bone
-
Densities of tissues?
Air 1.29. Fat 916. Water 1000. Muscle 1040. Bone 1650.
-
Decrease in atomic number causes
Increase in scatter
-
A 10 inch air gap is same as what grid?
15:1
-
Density is measured as
Kg per meter cubed
-
Automatic collimation is called
PBL- positive beam limitation.
-
Four Advantages of collimators
Light field, central ray. Less penumbra. Infinite field sizes.
-
T/F. Scatter helps create the image
False, it causes fog
-
When the beam restrictor is close to the tube, this is created
Penumbra
-
At 120 kvp, interactions are what percent PE absorption and what percent Compton?
25 and 75
-
Examples of beam restrictors include
Cones. Cylinders aperture diaphragms and collimators
-
Off focus radiation comes from
Somewhere other than the focal spot, such as the tube
-
Lead content of a grid is determined by
G over cm 2
-
Clavicle test
- Center lock tube
- Crosswise small IR
- Right marker, in light field
- Turn head to side
- Central ray at mid clavicle
-
Muscle atomic number
7.64
-
-
-
-
Atrophy osteoporosis, emphysema and acute osteomyelitis are (destructive or additive) conditions?
Destructive
-
For additive conditions, increase the
Kvp
-
For destructive conditions, decrease the
MAs
-
The three main things that happen with the primary photons are
Transmission, pe absorption, and compton interaction
-
Primary radiation that interacts with outer shell electrons and change direction is
Compton interaction
-
When kvp increases, scatter (increases or decreases) and contrast (increases or decreases)
Increases, decreases
-
Greater sharpness is from more or less OID?
Less
-
Grid conversion factor equals
MAs with the grid divided by mAs without the grid.
-
Grid conversion equation is:
- Mas 1 over mas 2
- equals gcf 1 over gcf 2
-
Off level error happens when
Tube is angled against grid strips
-
if lead strips are 3mm high and interspace is .25 mm, what is the grid ratio?
- 3.0
- ------
- 0.25. Equals 12:1
-
A short sid has a ( more or less) divergent beam than a long sid
More
-
The incident photon knocks out an outer electron and changes direction with less
Energy
-
At 50 kvp, interactions are --- percent kvp and ---percent Compton
50/50
-
At 120 kvp, interactions are what percent PE and Compton?
25/75
-
Kg per m3 is the unit of
Density
-
Ion chambers ionize the air inside in proportion to what?
In proportion to the radiation striking the chamber during the exposure.
-
what happens to the ionized air in the ionization chamber after it is exposed to radiation?
It completes an electrical circuit, the current is amplified, and termination of the exposure is signaled.
-
What metal is used inside the ionization chambers of the AEC?
Aluminum strips.
-
AEC devices provide diagnostic quality exposure for structures positioned how?
Directly over the ionization chambers.
-
What are the most critical guidelines for using ionization chambers of AEC?
Positioning the patient properly, and selecting the correct chambers
-
What does a phototimer use to regulate exposure?
A thyratron
-
What is an older term for an AEC device?
A phototimer
|
|
