Formulating Techniques

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Components of a Good Film. Proper positioningAdequate densityGood contrast level. Proper Positioning. Understanding and knowing your evaluation criteria is paramount to positioning success.If you are unable to achieve ideal positioning then you need to record that information for those who see th

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Formulating Techniques

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1. Formulating Techniques Loren Sachs Program Director Orange Coast College

2. Components of a Good Film Proper positioning Adequate density Good contrast level

3. Proper Positioning Understanding and knowing your evaluation criteria is paramount to positioning success. If you are unable to achieve ideal positioning then you need to record that information for those who see the exam later.

4. Factors Effecting Density mAs kVp Distance SID OID

5. Density Factors Continued Collimation/Film size Grid ratio Filtration Screen speed

6. Factors Effecting Contrast kVp Grid ratio Filtration Screen speed OID Collimation

7. Determining the Correct Positioning and Technique Positioning The body part ordered. Pathology or diagnosis Density and Contrast Technique charts Experience

8. Technique Charts Certainly, the preferred method of exposing patients Next best, is technique by body type This is very individualized and makes it harder to share techniques Watch for body habitus and pathology indicators

9. Commercial Guidebooks and Logbooks Generally, I am not a fan of the published technique books. The more you interact with the material the better you will learn it.

10. Experience or Establishing a Baseline Over time you should be able to accurately determine appropriate techniques in your ‘regular’ room. You should maintain a log book with exposures and positioning tips. This is true for any professional experiences you may have.

11. How to record practical information The biggest mistake people make is writing everything down as its done. Tells everybody you don’t know what your doing. Slows down the process. While writing, you miss salient points. After the exam is completed you need to write out the aspects of the exam, ideally in chronological order.

12. Why write later? It allows you to absorb the full import of the exam, the Gestalt. Remembering the events after provides an opportunity to redo the exam in your mind. Your notes are based on your experience, not someone else’s.

13. The next time The next time a same exam comes along you can use your notes to do the exam. If you have problems you will have immediate feedback. After completing the exam make any necessary changes to your notes.

14. Portables versus Rooms Are portables more difficult? Physically yes, radiographically they shouldn’t be. Problems with portables. Wrong distances. Grid cut-off. Using portables.

15. Portables and Distances SID You need to either measure or know what 40 and 72 inches are. Arm span and ‘waist to eye/collimator’ are easy indicators of proper SID. Arm span ranged from ranged from 58 to 70 inches. Waist to eye from 24 to 38 inches. Paying attention during decubitus films. This can be an issue is both rooms and ports.

16. Distance and Grid Cut Off Try to use a parallel or linear grid with a low to medium ratio (nothing over 8:1). If you have to use a focused grid pay attention to the SID. A major advantage of the parallel grid is that you cannot have too great an SID.

17. Additional grid issues Watch the alignment of the grid and CR (they have to be perpendicular). If the patient is heavy or the bed soft, use a CPR compression board to provide a firm surface.

18. Compression boards Along with grid films, compression boards are also useful for portable and room decubitus films. Position the board on the bed and then position the patient on top of the board. The patient is then easily movable and you have a clear delineation between the patient and the bedding.

20. Decubitus Films Another problem is getting the SID right. Often students have a tendency to have the collimator too far from the bed, gurney, or table; thus, creating an increased SID that may not be compensated for.

22. Portables If they use batteries, know when the batteries are properly charged and when to change settings based on the battery charge. If you use a filter make sure when you need it and when you don’t. Techniques should be transferable from rooms to portables.

23. Traction beds Remember, do not remove traction. You are going to have SID issues. Is lower or higher better?

24. Generally, higher is better You have more room to work. If you are vertically challenged, lower may be necessary. Also, patient dose is decreased when the SID increases. Another factor when using short SID is the magnification it causes. Remember your grids.

25. 36 inches

26. Density Maintenance Formula New mAs = old mAs(d2/d1)2

27. Applicability to Portables and Traction Beds With a traction bed you are usually going to have an approximately 10 inch difference in SID from normal. This results in a technique change of 40 or 60% from the original technique. For example, of the original mAs was 10 at 40 inches, the new mAs is 16 at 50 inches or 6 at 30 inches.

28. Formula From 40 inches to 50 X= 10(50/40)2 X=10(5/4)2 X=10(25/16) X=250/16 X=16 A 60% increase

30. Formula From 40 inches to 30 inches X=10(30/40)2 X=10(3/4)2 X=10(9/16) X=90/16 X=6 mAs A 40% decrease

32. So you have a math phobia! Try this instead of having to use your math skills. If you go under the bar, cut your mAs in half and add a step. If you go over the bar, add 50% to your mAs plus a step.

33. From 40 to 72 or 72 to 40 inches This is an easy one Either, multiply by 3.25 or divide by 3.25

34. Another Distance Issue Newborns Moving from basinettes and isolettes involves an SID change. Again, measuring or using the known distance indicators is important

36. That’s not a big difference Granted, it is a short distance. But you have to remember, the infants in these devices are small and the techniques are correspondingly low.

37. Know your equipment Do your portables use batteries? What is your grid ratio and focal distance? What speed cassette are you using? Is the room three phase or single? Does your imaging system have a minimum kVp range?

38. What about grids versus no grids? Typically, if an exam calls for a grid you should use a grid. Should a grid not be available, then you need to intelligently adjust your technique. No, closing your eyes and spinning the dials is not a solution. Praying, may be beneficial.

39. Adjusting techniques and grids I think the most common issue is not using a grid for a grid exam. The mistake most people make is to cut the mAs and hope. Given that the most common grid ratio for portables is 8:1 you would decrease the mAs by a factor of 4.

40. Grid Conversions

41. Grid formula New mAs = Old mAs(ngc/ogc) 8:1 grid conversion factor is 4, while no grid is a conversion factor of 1. New mAs = 20(1/4) New mAs = 5

42. The problem If you don’t use a grid and keep your kVp the same you are going to produce a film that has significantly lower contrast (grayer) than what you normally have. The better solution, to the no grid technique, is decreasing both the kVp and mAs.

46. Better solution Decrease the kVp by 15%. Then cut the mAs is half. Combined these changes have the effect of reducing density by a factor of 4. The benefit will be a film that has a level of contrast comparable to a regular film.

49. Cassettes and Techniques The most common mistake involving cassettes is using the wrong screen speed. Again, being aware of your equipment is an important part of solving this problem. Also, changes in density that result from film size changes need to be addressed.

50. Film size corrections When changing cassette sizes you need to change techniques. Smaller films require higher techniques while larger films use less technique.

51. Film Size Conversions

52. Film Size Formula

53. Film Size Rule of Thumb As you decrease film size you increase your technique one mAs step. The reverse is true for increasing film size.

54. Using kVp to your advantage Remember, increasing kVp will provide you with more latitude. Also, when doing portables it provides a means of lowering your exposure time. Decreasing the probability of motion on your films.

55. The Effects of Pathology This cannot be stressed enough You need to consider the presenting diagnosis Additionally, you need to observe the patient

56. Pathology Quiz

57. Computed and Digital Radiography These should not take the place of good techniques. Being able to use any technique you want and then adjusting the film in processing is not new. It used to be called ‘wet tanks’. ALARA mandates that we judiciously use radiation.

58. Making Changes Remember, it takes a 30% change in technique to see a visible difference. If the film is too dark, cut the original mAs in half. Too light, double the mAs. Students are required to repeat films with a technologist present.

59. What about a new facility? Look for a technique chart. This should offer you an idea of what works and you can compare it to what you know. If you can’t find a technique chart, use a phantom or step wedge and try a practice exposure. Lastly, shot one exposure on a patient and then look at the film.

60. Conclusion Learning techniques is not difficult. Establish a baseline and use it. If necessary adjust it. Think about challenging situations, don’t panic. Don’t be afraid to ask questions or for help

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