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Flashcards in Unit 1 Deck (52)
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1

Parts of a cathode assembly

Filament, Focusing cup, wiring

2

Filament characteristics

coil of thoriated tungsten; high melting point; difficult to vaporize; smaller coils produce best detail

3

Thermonic Emission

heating of the filament causes electrons to be released

4

How to extend tube life

depress exposure switches in one motion, decrease rotor time; excessive rotoring causes tube arching (vaporized tungsten)

5

Components to rotating anode assembly

anode, stator, rotor

6

characteristics of anode targets

high atomic number (enhances production of photons); high melting point; heat conducting ability;

7

Anode layering

backed with molybdenum and graphite to assist with heat loading

8

Target Area

portion of anode that electron stream contacts; point where x-ray photons created

9

Actual focal spot

physical area of the focal track that is impacted by electrons

10

effective focal spot

area of the focal spot that is projected out of the tube

11

Line-focus principle

effective focal spot is controlled by the size of the actual focal spot and anode target angle; when target angle is less than 45 degrees the effective focal spot is smaller than the actual focal spot

12

Anode heel effect

radiation intensity is greater on the cathode side because some rays are absorbed by the anode heel

13

Off focus radiation

composed of photons that were not produced at the focal spot; scatter electrons hit other structures in the tube

14

Stator

induction motor electromagnets send currents to the rotor to turn the anode; located outside the vacuum

15

Rotor

hollow copper cylinder attache to the anode disk; currents from the stator cause it to turn

16

Envelope

constructed around the anode and cathode and sealed tight to maintain vacuum; x-ray beams exit the tube through the window; vacuum allows electrons to flow from cathode to anode without encountering atoms in air

17

Protective housing

controls leakage and scatter radiation; made of lead; isolates high voltages; provides means to cool the tube

18

mA

how many electrons are crossing the tube

19

mAs

how many electrons are crossing the tube per second

20

Reciprocity law

Density exposure should remain unchanged as long as the intensity and duration of the x-ray (mAs) exposure remains unchanged.

21

mAs formula

mAs= mA x seconds

22

kVp

speed of electrons; high kVp = higher x-ray penetrability and quantity

23

15% rule

And increase of kVp by 15% will cause a doubling in exposure, the same effect as doubling the mA or doubling exposure time

24

Distance and x-ray emission

As SID increases, beam intensity decreases

25

Inverse square law

I1/I2 = (D2)^2/(D1)^2

26

Exposure Maintenance Formula

mAs1/mAs2 = (D1)^2/(D2)^2

27

Density/ IR exposure

makes detail visible; degree of blackening

28

Typical optical density range

.25-2.5

29

mAs controlling density

longer exposures increase density; need at least a 30% change in mAs to make a visible change in density

30

kVp controlling density

small changes make a large difference; higher kVp increases scatter radiation