Beam restricted device and filter used in x ray

BEAM RESTRICTION DEVICE AND VARIOUS FILTER USED IN THE XRAY DEPARTMENT

1. BY RADIOGRAPHER SUSHIL PATTAR BEAM RESTRICTING DEVICES AND RADIOGRAPHIC FILTERS

2. Introduction Beam restricting Devices Filter and types Grid Conclusion CONTENTS

3. The X-Ray beam emerging from tube head is composed of large numbers of photons that travels in straight line in all direction. It is important to limit the size of the primary beam and prevent exposure of body region which are not required in image production. Large X-Ray fields result in unnecessary exposure, thus scatter radiation is increased and image contrast is decreased. Beam restricting devices limit the field size to reduce scatter and primary radiation . INTRODUCTION

4. X-Ray tube are designed so that the projectile electrons interact with the target. Some of the electrons bounce off the focal spot and interact with other areas of target, causing X-Ray production outside of the focal spot. OFF FOCUS RADIATION

5. The scatter radiation arises from an object after interaction of primary beam. In diagnostic radiology scatter radiation leads to Fog in the X-Ray image. SCATTER RADIATION

6. Diaphragm apertures Cones and cylinders X-ray collimators BEAM RESTRICTIVE DEVICES

7. It is a simplest device. A sheet of lead with a hole in the centre. Determination of size and shape of X-Ray beam. DIAPHRAGM APERTURE

8. DISADVANTAGE The size and shape is fixed. It produced large penumbra. Reduce Sharpness and resolution.

9. Modification of the aperture. Heavy Metal Base like Lead. Copper Lined Barrel. CONES AND CYLINDERS cylinder cone base barrel

10. Advantage Better restriction to the x-ray field. Produce less penumbra than aperture diaphragm. Round image on a rectangular film. Reduce scatter Radiation. CONES AND CYLINDERS

11. Most effective beam restricting device. Two stage of shutters to control the Beam. The shutters are made up of lead . COLLIMATOR

12. The first stage entrance shutter and two independently acting adjustable shutter permit infinite variety of square or rectangular fields A light bulb is fitted in the Collimator to provide the light beam in the desired X-Ray field. COLLIMATOR

13. The light beam is deflected by a mirror mounted in the path of an X-ray beam at an angle of 45 degree. The distance from the centre of the mirror to target of the X-ray tube and light bulb should be the same otherwise the size of beam will be changed . COLLIMATOR

14. Fieldenter indicator To identify the centre of the x-ray field a thin plastic sheet having a painted cross line is mounted at end of the collimator. COLLIMATOR

15. OR . Four TYPE OF COLLIMATOR Manually operated collimator Electrical collimator Automatic collimator CT collimator

16. AUTOMATIC COLLIMATOR ( positive beam limiting device ) Motor driven shutters are limit the beam also called positive beam limiting devices. Three basic mechanism are Cassette size detector. Motorized X-Ray collimator . Focal spot-to- Bucky plane distance compensating unit .

17. AUTOMATIC COLLIMATOR HOW TO WORK AUTOMATIC COLLIMATOR When a cassette is loaded in to the film holder (Bucky tray ) sensors in the tray identify the size of the cassette. These sensors relay this information to the collimator motor which aligned the shutters to automatically collimate the image to film size .

18. CT COLLIMATOR Pre patient Collimator It is mounted on the tube housing or adjacent to it . It consists of several section. So that a nearly parallel X-Ray beam results. This collimator limits the area of patient that intercepts the useful beam and determine FOV on the patient & reduce the patient dose. CT Tube CT Tube collimator object Detector Collimator

19. CT COLLIMATOR Post patient Collimator This collimator restrict the X-Ray field viewed by detector array. It defined the slice thickness when coupled with pre patient collimator. It reduce scatter radiation that reaches to the detector array & enhance the contrast but does not influence patient dose .

20. COLLIMATION RULES Collimation required, at least three borders of collimation to be seen on the film . Collimation must be slightly less than film size or to the area of clinical interest , whichever is smaller. Any exposure beyond the film is unnecessary patient exposure.

21. Alignment of x-ray beam and light beam has to be checked periodically. Material required 17x14 inch x-ray film and cassette Four “L” shaped wires Lead letter “R” TESTING X-RAY BEAM AND LIGHT BEAM ALIGNMENT R

22. Place the film on the top of the X-ray table. Open the shutter to a convenient size. (10x10 in) Carefully position the L shaped wire at the corner of the light field. Place the ‘R’ in the right lower corner. Then make an x-ray exposure (100cm, 2-3mAs,40 kVp) and exposed the film. Procedure

23. Procedure R Without touching the film or wires, enlarge the field size to 12x12 in. and expose the film for the second time. The dark centre shows the position of the x-ray beam and the wires indicate the position of the light beam. Light beam film X-ray beam R Correct alignment Incorrect alignment

24. Procedure How to correct alignment R Light beam film X-ray beam

25. Advantages Light beam shows the center & exact configuration of the X-Ray field. Helps to limits penumbra. Provides adjustable rectangular or square field. Reduce scatter radiation that improves image contrast. It reduce patient dose. COLLIMATOR

26. Filtration is the process of increasing the mean energy. Filter A sheet of metal placed in the path of X-ray beam It absorb low energy radiation before it reach to the patients. Reduce skin exposure dose up to 80%. RADIOGRAPHIC FILTER

27. There are two type of filter- Inherent filter Added filter TYPES OF FILTER Inherent filter Added filter

28. Inherent filter Glass envelope window, tube cooling oil and tube housing window are responsible for the inherent filtration it is equivalent of 0.5 to 1 mm Al. Added filter & types Aluminium filter Compound filter Wedge filter Peripheral filter Molybdenum filter INHERENT FILTER Inherent filtration

29. Aluminium filter Aluminium filter is the most commonly use in diagnostic radiology. It is available in different thickness, less than 50 kVp we are use 0.5 mm,50 to 70 kVp use 1.5 mm and above 70 kVp we are use 2 to 2.5 mm Al filter. Compound filter Copper and aluminium use for compound filter, it is useful of high energy X-ray. Copper thickness is 0.1 to 0.9 mm and aluminium filter thickness is 1.0 mm. TYPE OF FILTER

30. Wedge filter To obtaining uniform density of part like we are doing angiography of head, neck and skull lateral radiograph to insert a wedge shape filter. TYPE OF FILTER

31. Peripheral filter Peripheral filter use for lower limb angiography study. Function of peripheral filter is to provide uniform density of part and prevent over exposure. Made up of plastic and putting a thin layer of silicon copper. TYPE OF FILTER

32. Molybdenum filter Molybdenum filter use in mammography, it is work as special k-edge principle. Mo target transmit 17.5 kev K-alpha and 19.6 kev K-beta characteristic radiation to produce good contrast of breast image. TYPE OF FILTER 17.5 6

33. Molybdenum filter Bremsstrahlung radiation is continuous photon energy spectrum with a maximum energy determine by the selected Kvp value. It attenuate the above 20 kev bremsstrahlung radiation and convert into characteristic radiation. Molybdenum filter always use with molybdenum target and thickness of Mo filter is 0.03mm. TYPE OF FILTER

34. Advantage Absorb low energy X-Ray photon. Reduce unnecessary radiation dose to the patient. It increase the quality of radiograph . Disadvantage Decrease some energy of X-ray photon. Increased exposure factor. Higher tube loading required. FILTERS

35. CONCLUSION Ultimately, it is the responsibility of the radiographer to use the proper collimation and under no circumstance should exceed the exposure field the size of the image receptor. T he radiographer should always limit the field to the part being examined thereby improving the image quality and minimizing the patients dose . It is a way to achieves “ALARA”(As Low As Reasonably Achievable) principle by using beam restrictive devices and radiographic filter.

36. REFERENCE All the information provided by this presentation is collected from - X-Ray beam composition and collimation by professor Stelmark DMI50B & kyle Thornton lecture Resident physics lectures – X- ray beam restrictors by Christensen, chapter 7 Textbook of radiology for Residents & Technicians by SK Bhargava & S Bhargava, fifth edition www. slideshare.com https.//radioprotection.wikispace.com

37. THANKS