Lec 2 Production of X-rays, Factors Controlling X-ray Beam

Question 1

2 types of radiation produced during x-ray production?

Answer 1

Bremsstrahlung Radiation
Characteristic Radiation

Question 2

The X-ray photons emitted by the rapid deceleration of the bombarding electrons passing close to the nucleus of the tungsten atom.

Answer 2

Bremsstrahlung or braking radiation

Question 3

The amount of deceleration and degree of deflection determine the amount of energy lost by the bombarding electron and hence the energy of the resultant emitted photon. A wide range or spectrum of photon energies is therefore possible and is termed _________?

Answer 3

Continuous spectrum

Question 4

Small deflections of the bombarding electrons are the most common, producing many __________?

Answer 4

Low-energy photons

Question 5

• Have little penetrating power and most will not exit from the X-ray tube itself.
• They will not contribute to the useful X-ray beam

Answer 5

Low-energy photons

Question 6

Removal of low-energy photons from the beam is known as?

Answer 6

Filtration

Question 7

Large deflections are less likely to happen so there are relatively few ________?

Answer 7

High-energy photons

Question 8

The ______________ is directly elated to the size of the potential difference (kV) across the Xray tube.

Answer 8

Maximum photon energy possible (E max)

Question 9

This involves electron ‘jumps’ from one energy level (shell) to another, and results in the emission of X-ray photons with specific energies.

Answer 9

Characteristic radiation

Question 10

Contributes only a small fraction of the photons in an x-ray beam.

Answer 10

Characteristic radiation

Question 11

The production of this radiation has no practical implications for dentomaxillofacial radiography.

Answer 11

Characteristic radiation

Question 12

What are the 6 factors controlling the x-ray beam?

Answer 12

1. Exposure Time (s)
2. Exposure Rate/ Milliamperage (mA) Setting
3. Tube Voltage Peak (kVp)
4. Filtration
5. Collimation (shape)
6. Inverse Square Law (distance)

Question 13

It is desirable to keep the exposure time as _______ as possible to minimize _______ from patient motion.

Answer 13

• Short
• Minimize blurring from px motion

Question 14

Also known as exposure rate.

Answer 14

Milliamperage setting

Question 15

Affects the quantity of radiation produced by the X-ray tube

Answer 15

Milliamperage setting (exposure rate)

Question 16

Affects image density or darkness

Answer 16

Milliamperage setting (exposure rate)

Question 17

Refers to the number of photons in an x-ray beam.

Answer 17

Beam quantity

Question 18

Increases the kinetic energy of the electrons to the target

Answer 18

Tube voltage peak (kVp)

Question 19

Increasing the kVp of an X-Ray machine increases:
a. The _______ of photons generated.
b. The __________ of the photons.
c. The _________ of the photons
d. Affects __________ and differences in ________.

Answer 19

• number of photons
• mean energy
• maximal energy
• image contrast and differences in density

Question 20

Refers to the mean energy of an x-ray beam.

Answer 20

Beam quality

Question 21

Beam quantity =
Beam quality =

Answer 21

Beam quantity = milliamperage setting
Beam quality = tube voltage peak

Question 22

A metal disk (aluminum) filters harmful low-energy (soft) X-rays.

Answer 22

Filtration

Question 23

• Consists of the materials that x-ray photons encounter as they travel from the focal spot on the target to form the usable beam outside the tube enclosure. - - - E.g. x-ray tube glass wall, insulating oil

Answer 23

Inherent filtration

Question 24

May be supplied in the form of aluminum disks placed over the port in the head of the x-ray machine.

Answer 24

Added filtration

Question 25

• It is the sum of the inherent and added filtration.
• Is to be equal to the equivalent of 1.5 mm of aluminum for a machine operating at up to 70 kVp and 2.5 mm of aluminum for machines operating at higher voltages.

Answer 25

Total filtration

Question 26

• It is a metallic barrier with an aperture in the middle used to shape and restrict the size of the x-ray beam and the volume of tissue irradiated.
• Rectangular or round

Answer 26

Collimator

Question 27

• Improve image quality
• Reduces the exposed volume and thereby the number of scattered photons reaching the image receptor, resulting in reduced patient exposure and improved images.

Answer 27

Collimator

Question 28

The intensity of an x-ray beam (the number of photons per cross-sectional area per unit of exposure time) varies with distance from the focal spot.

Answer 28

Inverse square law

Question 29

Changing the distance between the x-ray tube and the patient, such as by switching from a machine with a short aiming tube to one with a long aiming tube, has a marked effect on beam intensity. Such a change requires a corresponding modification of the kVp or mA to maintain the same intensity at the image receptor.

Answer 29

Inverse square law