Beam restriction technique and devices.pptx

IT REVIEWS Introduction and definition INTRODUCTION
BEAM-RESTRICTING DEVICES
ADVANTAGES AND DISADVANTAGES
TECHNIQUE
FILTERS
AND PHYSICS BEHIND IT AND LIGHT AND MIRROR ARRANGMENT CLEARLY EXPLAINED WELL.IT ALSO INCLUES THE FLITERS CLASSIFICATION AND COLLIMATORS CLASSIFICATION.
COLLIMATIORS ARE NOTHING BUT BEAM ALINERS

1. BEAM LIMITING TECHNIQUE AND DEVICES Precentor: Vani pushpa M.Sc 1 st year RIT

2. Contents Introduction Beam-Restricting Devices Advantages and disadvantages Technique Filters

3. Beam restriction: The beam restriction and collimation  are refer to decrease in the size and shape of the projected radiation field .  Collimation decreases the risk of radiation and minimizes scattered radiation with better contrast.

4. The Unrestricted Beam. Unrestricted primary beam

5. Beam-Restricting Devices An x-ray beam restrictor is a device that is attached to the opening in the x-ray tube housing to regulate the size and shape of an x-ray beam.

6. Importance of beam limiting devices :   Beam restriction serves fo r three purposes: L imiting patient exposure Reducing the amount of scatter radiation Focus on the correct anatomy . Limitation: R educe   intensity  by blocking incoming radiation .

7. The relationship between collimation (field size) and quantity of scatter radiation  Increasing   collimation means  decreasing  field size ,  and  decreasing  collimation means   increasing  field size . Collimation and scatter radiation are Inversely proportional.

8. Material used as collimator? Composed of high density (atomic number) materials which is required to "collimate" the incoming photons Lead is the most common element and the least expensive However, collimators can also be made of tungsten , gold, depleted uranium, all of which are better attenuator when compared to lead . Cost is another significant factor

9. Types : All beam-restricting devices are made of metal or a combination of metals that readily absorb x-rays. Classified into 3 categories: Aperture Diaphragms Cones and Cylinders Collimators

10. Aperture Diaphragms An   aperture diaphragm  is a thin sheet of lead (diaphragm) with a hole (aperture) in center. Aperture diaphragms are easy to use. They are placed directly below the x-ray tube window . An aperture diaphragm can be made by cutting rubberized lead to the size needed. Application : 😊 Used in dental radiography with rectangular collimation. 😊 In addition, it is used in trauma and chest radiography.  😊 angio 😊

11. Aperture Diaphragms contd.. Advantages Lead is soft, so the aperture can be easily altered to any desired size or shape. Disadvantages: Large penumbra—can be reduced by keeping Aperture Diaphragm far away from target.

12. Cones and Cylinders Cones and cylinders are shaped differently. Both have extended metal structures ( 10-20inch) that restrict the useful circular beam to require size. Positioning and size of the distal end determines the field size. Cone is a ideal beam restrictor, but the flare of cone is greater than the flare of x ray beam. If the x ray source, film and cone are not aligned properly, then one side of the film may not be exposed, which is called cone cutting . Advantage : Reduces the penumbra (as they placed far ) Disadvantage: These systems provide only limited number of field sizes.

13.   CYLINDER CONE.

14. Application: Designed to operate most effectively at a designed SID Sinuses Dental x ray and treatment

15. Collimators The most useful, and accepted beam-restricting device is the collimator. The terms  collimation  and  beam restriction  are used interchangeably . It has two advantages over the other types: it provides an infinite variety of rectangular x-ray fields a light beam shows the center and exact configuration of the x-ray field.

16. Structure of the collimator: 2 sets of shutters control the dimensions. Each shutter contains 4 or more lead plates of 3mm thickness, which move in independent pairs. When the shutters are closed, they meet at the center. Collimator also has a light and mirror arrangement to create radiation and optical coincidence.

17. The light beam is deflected by a mirror mounted in the path of x ray beam at an angle of 45 degree. The target of x ray tube and the light bulb should be the exactly same distance from the center of the mirror. The light field and radiation field should match exactly with each other .

18. Quality assurance : Do collimator –beam alignment check at least every six months Do check of alignment of center of x ray beam at least every six months.

19. X RAY FILTERS When the X ray beam is produced many energies of photons exit (polychromatic). Many are of such low energies that they were offered nothing to production of that radiograph. So, removal of low energy x rays from beam spectrum is called filtration. Metals such as aluminum will absorb the soft low energy rays. This reduces the patient exposure

20. why we use filters in the diagnostic radiology? In diagnostic radiology, if the filters are not used , The patient acts as a filter, W hich will result in absorption of X rays by the tissues. Unnecessary dosage of radiation to the patient . To Increase the tube age

21. Types of rays: The radiation emitted by the X ray tube consists of heterogeneous beam of various wavelengths that are (longer and shorter wavelengths both soft and hard rays respectively). As the soft rays (long wave lengths) are harmful to skin and other tissues these rays shall be filtered off to get better penetrated X ray and to avoid damage to skin. If not filtered the patient may get skin burns during fluoroscopic examination.

22. Preferred metal: Copper (Z= 29 ) Aluminum (Z=13) most commonly preferred in diagnostic radiology low atomic number therefore excellent material for absorbing soft rays. low energy X ray photons low in weight therefore make the extra tube lighter in weight and easily handling

23. Types

24. Inherent filtration Absorption of X rays as they pass through The window in the Glass envelope (thin beryllium 1mm) The insulating oil with in the shield thickness 0.5mm aluminum equivalent About three together added up to a filter which is able to remove the longest wavelength in the this is called inherent filtration of x ray tube.

25. Added filtration Filters are used to remove unwanted bremsstrahlung x rays outside the X ray tube housing is called added filters Copper Aluminum Combination of cu+Al Rhodium Molybdenum Silver

26. Applications: Copper- 0.1-0.9mm- general radiography x ray tubes- in pediatric applications Aluminum-0.1mm-general radiography x ray tubes Rhodium - 0.025mm- mammo with Rh anode Molybdenum - 0.03mm- Mammography Silver –used in mammo with tungsten anode

27. Filter X ray beam = decrease photon intensity + increase X ray beam energy. Total filtration : Combination of inherent and added Minimum total filtration of 2.5mm of Al eq is required for x ray tube operating above 70 kVp

28. Disadvantages Reduction in the intensity of X ray photons but not no. of photons. Lengthen the time required to make an exposure May absorb primary X ray beam during excessive filtration Increase tube loading (due to more mAs )

29. Reference : The Physics of Radiology and imaging by K.Thayalan radiologykey.com Christensen’s Physics of Diagnostic Radiology Handbook of medical radiography C R amamohan

30. Queries Difference between collimation and filtration? Why can’t we use lead as a filter material ?

31. Thank you for your attention