Lec 2 Tube Controls

Question 1

Flow of electrons from the cathode to the anode.

Answer 1

Current

Question 2

This is regulated by the milliampere control.

Answer 2

Tube current

Question 3

It regulates the number of electrons produced by the filament.

Answer 3

Tube current

Question 4

The mA setting is fixed, typically at ?

Answer 4

7-10 mA

Question 5

Adjusts the high-voltage transformer to boost the peak voltage of the incoming line current (110 or 220 V).

Answer 5

Kilovolt peak (kVp) selector

Question 6

Intraoral, panoramic, and cephalometric machines operate between?

Answer 6

50 and 90 kVp (50,000 to 90,000 V)

Question 7

Computed tomographic machines operate at?

Answer 7

90 to 120 kVp, and higher

Question 8

• Generates the high potential difference (kV) to accelerate the electrons across the X-ray tube via the step-up transformer .
• Provides the low-voltage current to heat the tube filament via the step-down transformer.

Answer 8

Tube voltage

Question 9

What are the 2 types of X-ray current generators?

Answer 9

1. Alternating current X-ray Generators
2. Constant Potential (Direct Current) X-ray Generators

(AC/DC)

Question 10

• Half the cycle is positive, and the other half is negative.
• For X-ray production, only the positive half of the cycle can be used to ensure that the electrons from the filament are always drawn towards the target.
• X-ray tube needs to be rectified in order to eliminate the negative phase

Answer 10

Alternating current x-ray generator

Question 11

4 Types of Rectified Circuits used?

Answer 11

1) Half-wave rectified
2) Single-phase, full-wave rectified
3) Three-phase, full-wave rectified
4) Constant Potential (DC units)

Question 12

This provides constant potential between the anode and the cathode.

Answer 12

Constant potential (direct current) x-ray generator

Question 13

• X-ray production per unit time is more efficient
• More high-energy, diagnostically useful photons are produced per exposure
• Fewer low-energy, harmful photons are produced
• Shorter exposure times are possible

Answer 13

Constant potential (direct current) x-ray generator

Question 14

If using a DC unit, it may be advantageous to select _____ rather than 70 kV to ensure adequate radiographic contrast is maintained.

Answer 14

60 kV

Question 15

Controls the length of time that high voltage is applied to the tube and thus the time during which x-rays are produced.

Answer 15

Timer

Question 16

It is built in the high-voltage circuit to control the duration of exposure.

Answer 16

Timer