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X-Ray Production & Emission

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Presentation on theme: "X-Ray Production & Emission"— Presentation transcript:

1 X-Ray Production & Emission
Bushong Ch. 8 & 9

2 Objectives: Review x-ray production requirements
X-ray tube interactions X-ray emission spectrum

3 PRODUCTION OF X RAYS Requirements: a source of fast moving electrons
must be a sudden stop of the electrons’ motion in stopping the electron motion, kinetic energy (KE) is converted to EMS energies heat & x-ray energies

4 How “X-rays” are created
Power is sent to x-ray tube via cables mA (milliamperage) is sent to filament on cathode side. Filament heats up – electrons “boil off” Negative charge

5 How “X-rays” are created
Positive voltage (kVp) is applied to ANODE Negative electrons = attracted across the tube to the positive ANODE. Electrons “slam into” anode – suddenly stopped. X-RAY PHOTONS ARE CREATED

6 How “X-rays” are created
Electron beam is focused from the cathode to the anode target by the focusing cup Electrons interact with the electrons on the tungsten atoms of target material PHOTONS sent through the window PORT – towards the patient

7 X-ray Tube Construction
D F G C E Radiographic Equipment

8 Principle Parts of the X-ray Imaging System
Operating Console High-voltage generator X-ray tube The system is designed to provide a large number of e- with high kinetic energy focused to a small target

9 E- traveling from cathode to anode
Projectile e- interacts with the orbital e- of the target atom. This interaction results in the conversion of e- _______ energy into ________ energy and ________ energy.

10 Tube Interactions 3 possible tube interactions
Tube interactions are generated from _____ slamming into ________? Heat (99%), EM energy as infrared radiation (heat) & x-rays (1%) X-rays = Characteristic (20%) or Bremsstrahlung (80%)

11 Heat Most kinetic energy of projectile e- is converted into heat – 99%
Projectile e- interact with the outer-shell e- of the target atoms but do not transfer enough energy to the outer-shell e- to ionize

12 Heat is an excitation rather than an ionization

13 Heat production Production of heat in the anode increases directly with increasing x-ray tube current & kVp Doubling the x-ray tube current doubles the heat produced Increasing kVp will also increase heat production

14 Characteristic Radiation – 2 steps
Projectile e- with high enough energy to totally remove an inner-shell electron of the tungsten target Characteristic x-rays are produced when outer-shell e- fills an inner-shell void All tube interactions result in a loss of kinetic energy from the projectile e-

15 It is called characteristic because it is characteristic of the target element in the energy of the photon produced

16 Only K-characteristic x-rays of tungsten are useful for imaging

17 Bremsstrahlung Radiation
Heat & Characteristic produces EM energy by e- interacting with tungsten atoms e- of the target material Bremsstrahlung is produced by e- interacting with the nucleus of a target tungsten atom

18 Bremsstrahlung Radiation
A projectile e- that completely avoids the orbital e- as it passes through a target atom may pass close enough to the nucleus of the atom to convert some of the projectile e- kinetic energy to EM energy Because of the electrostatic force?

19 Bremsstrahlung is a german word meaning slowed-down radiation

20 X-ray energy Characteristic x-rays have very specific energies. K-characteristic x-rays require a tube potential of a least 70 kVp Bremsstrahlung x-rays that are produced can have any energy level up to the set kVp value. Brems can be produced at any projectile e- value

21 Discrete spectrum Contains only specific values

22 Continuous Spectrum Contains all possible values

23 Characteristic X-ray Spectrum
Characteristic has discrete energies based on the e- binding energies of tungsten Characteristic x-ray photons can have 1 of 15 different energies and no others

24 Characteristic x-ray emission spectrum

25 Bremsstrahlung X-ray Spectrum
Brems x-rays have a range of energies and form a continuous emission spectrum

26 Factors Affecting the x-ray emission spectrum
Tube current, Tube voltage, Added filtration, Target material, Voltage waveform The general shape of an emission spectrum is always the same, but the position along the energy axis can change

27 Quality The farther to the right the higher the effective energy or quality

28 Quantity The more values in the curve, the higher the x-ray intensity or quantity

29 mAs A change in mA or s or both results in the amplitude change of the x-ray emission spectrum at all energies The shape of the curve will remain the same

30 mA increase from 200 to 400

31 kVp A change in voltage peak affects both the amplitude and the position of the x-ray emission spectrum

32 Filtration Adding filtration is called hardening the x-ray beam because of the increase in average energy Characteristic spectrum is not affected & the maximum energy of x-ray emission is not affected

33 Filtration Adding filtration to the useful beam reduces the x-ray beam intensity while increasing the average energy Added filtration is an increase in the average energy of the x-ray beam (higher quality) with a reduction in x-ray quantity Lowering the amplitude and shifting to the right

34 What kVp does this graph indicate?

35 Target Material The atomic number of the target affects both the quantity and quality of x-rays Increasing the target atomic number increases the efficiency of x-ray production and the energy of characteristic and bremsstrahlung x-rays

36 Target material

37 Voltage Waveform 5 voltage waveforms: half-wave rectification, full-wave rectification, 3-phase/6-pulse, 3-phase/12-pulse, and high-frequency. Maintaining high voltage potential

38 Voltage generators

39 X-ray Quantity or Intensity
What units of measurement is used for radiation exposure or exposure in air? Milliampere-seconds (mAs) – x-ray quantity is proportional to mAs Kilovolt Peak (kVp) – If kVp were doubled the x-ray intensity would increase by a factor of four or kVp2

40 X-ray Quantity or Intensity
Distance – x-ray intensity varies inversely with the square of the distance from the x-ray target When SID is increased, mAs must be increased by SID2 to maintain constant OD

41 Filtration 1 to 3 mm of aluminum (Al) added to the primary beam to reduce the number of low-energy x-rays that reach the patient, reducing patient dose Filtration reduces the quantity of x-rays in the low-energy range

42 Reducing low-energy photons

43 X-ray Quality or Penetrability
As the energy of an x-ray beam is increased, the penetrability is also increased High-energy photons are able to penetrate tissue farther than low-energy photons High-quality = high-penetrability Low-quality = low-penetrability

44 HVL = Half-Value Layer What is the HVL
HVL is affected by the kVp and added filtration in the useful beam Photon quality is also influenced by kVp & filtration HVL is affected by kVp

45 HVL In radiography, the quality of the x-rays is measured by the HVL
The HVL is a characteristic of the useful x-ray beam A diagnostic x-ray beam usually has an HVL of 3 to 5 mm Al

46 HVL 3 to 5 mm Al = to 3 to 6 cm of soft tissue
HVL is determined experimentally and a design specification of the equipment

47 X-ray Quality Kilovolt Peak (kVp) = increasing the kVp increased photon quality and the HVL

48 Types of Filtration Diagnostic x-ray beams have two filtration components – inherent filtration and added filtration Inherent filtration – The glass enclosure of the tube (the window) – approximately 0.5 mm Al equivalent

49 Added Filtration 1 or 2 mm sheet of aluminum between the tube housing and the collimator The collimator contributes an additional 1mm Al equivalent added filtration


51 Compensating filter A filter usually made of Al, but plastic can be used to maintain OD when patient anatomy varies greatly in thickness Are useful in maintaining image quality. They are not radiation protection devices

52 Wedge filter

53 Compensating Filter What is an aspect of the tube design that works as a compensating filter? What causes this?

54 Questions?

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