1. Challenges with Digital Imaging
Rad T 265
Challenges with Digital Imaging
I would like to thank ACERT for the opporunity to share our expereicnes in acquiring digital imaging with you and particularly Bette Schans for adjusting the program so that I can make it home to see my daughters lsat high school soccer game.

2. Digital Lab Experiments
Issues that affect the ‘S’ number
This has been discussed in the literature ……..
We feel it is important that students do labs that generate false ‘S’ number is order to reaffirm some of the causes.

3. ‘S’ Number
Fifteen percent rule does not effect ‘S’ number.

4. ‘S’ Number
LUT affects the ‘S’ number and may prevent getting an acceptable image.
We have found that when the wrong LUT is used it is impossible to adequately adjust the width and level
‘S’ = 470
‘S’ = 290
Also notice how using the correct LUT affects image size

5. ‘S’ Number This image was done as part of
a distance affects density and
‘S’ number experiment.
The ‘S’ number is 1740.

6. ‘S’ number issues Some things we have found
Low ‘s’ numbers, < 100, consistently indicate overexposure.
High ‘S’ numbers, >1000, do not necessarily indicate under exposure

7. Activities Affecting ‘S’ Number
Centering
Dennis Bowman has produced a series of seminars on various digital radiography issues and has demonstrated this issue well.
Collimation
We have certainly seen this occur

8. As film size changed S number changed with same technique

9. ‘S’ number affected by positioning
Same technique ‘S’ number affected by positioning

10. ‘S’ number 80
‘S’ number 159

11. Acceptable Positioning Options for Fuji CR

12. The Professionals weight in The ‘S’ number is just a reference

13. Other Basic Digital Labs
We try to replicate various digital artifacts
Lightbulb
Moire
Quantum mottle

14. Light bulb Artifact Excessive kVp
By Paul Keough | December 8, 2009

15. We were unable to replicate the light bulb artifact, due to phantom size.
113 kVp
125 kVp
150 kVp

16. Moire Artifact
As you know, Moire is a function of grid frequency and reader direction in CR imaging.
Using our old grids we are able to demonstrate the artifact.
We have also demonstrated the artifact occurs when the grid lines are both parallel and perpendicular to the reader orientation.

17. Moire
Image courtesy of Barry Burns, University of North Carolina

18. 10 x lines
10 x lines

19. Same grid
8 x 10
10 x 12

20. 10 x lines
10 x lines

21. Rad T 110 kVp Intro to the lab
This lab is a two-parter; this week, we will look at the effect kVp changes have on image density. Next week, we will learn how to compensate for changes to kVp so that image density can be maintained (15 percent rule).

22. Week 1 data
Technique
Density
DAP value
Exposure
‘S’ number 20
484
124.7
217
241 20
499
91.6
157
711 20
491
162.1
274
124 20
199.9
347 73
Density is only possible
from film or PACs
These columns were added
for digital imaging

23. 75 at 20; ‘S’ 241
64 at 20; ‘S’ 711

24. 85 at 20; ‘S’ 124
96 at 20; ‘S’ 73

25. Week 2 data
Corrected Technique
Density
DAP value
Exposure
‘S’ number 20
484
124.7
217
241 40
508
183.4
316
318 10
433
81.4
137
252 5
488
50.4 86
303
The analysis includes a discussion of the results and reasons for the results.

26. 75 at 20; ‘S’ 241
64 at 40; ‘S’ 318

27. 85 at 10; ‘S’ 252
96 at 5; ‘S’ 303

28. The effects of kVp and penetration

29. Rad T 180 mAs lab Demonstrate the effects mAs has on the image.
Perform a series of exposures at different mAs values and record the results.

30. mAs DAP value Dose ‘S’ number Density 6.5 25 100
 6.5
37.3 63
1129
734
 25
148
253
252
746
 100
592
1020 70
728
These columns were added
for digital imaging

31. 73 at 25; ‘S’ number of 252
73 at 100; ‘S’ number is 70
73 at 6.5; ‘S’ number is 1129

32. Rad T 110 Density Maintenance
This week we are again going to make a series of exposures. You will use either the pelvis phantom or a shoulder phantom
Before making these exposures you will need to change the mAs according to the density maintenance formula  
The first exposure will be at 40” using the above techniques.
Make another exposure at 30” SID.
Move the phantom to the upright and take another exposure at 50”.

33. mAs DAP value Dose ‘S’ number Density 40” 11 or 20 20 30” 12 50” 32
11 or 20 20
124.7
217
241
484
30”
 12
122.5
293
310
536
50”
 32
145.5
196
236
475
These columns were added
for digital imaging

34. 75 at 20, 30 inches
‘S’ 196
75 at 12, 30 inches
‘S’ 310

35. 75 at 20, 50 inches
‘S’ 382
75 at 32, 50 inches
‘S’ 236

36. Rad T 110 kVp and Contrast
In today’s, we will quantify the effect of kVp on radiographic contrast. In order to quantify contrast we will use a step wedge to make several different exposures.  
You will need to make exposures using the following kVp settings; for each kVp setting record the number of shades of gray that you see. Use the 15% rule to adjust the mAs between exposures.
We will make exposures using both film and CR.

37. Also, contrast did not significantly change.

38. Rad T 110 Cassette Size and Resolution
This lab will focus on the fact the larger the CR cassette the smaller the image and the lower the resolution. The effect of cassette size is the same principle as field of view affecting image size; the entire field captured has to fit on the visible image (monitor).
We will use both phantoms and resolution grids for this experiment.
Obviously, this lab is a product of the digital lab. We continue to do traditional resolution experiments involving distance as well.

40. 230.24 3.1 230.79 2.5 229.49 2.2 Cassette size Phantom size
Measured on the PACs
Line pairs visible
8 x 10
230.24
3.1
10 x 12
230.79
2.5
14 x 17
229.49
2.2

41. CR plate size and resolution
14 x 17

42. 8 x 10

43. Rad T 180 Grid Lab; Cut-off
This is a lab that does not change from the analog version.
We have the students generate grid cut-off from the various causes.

44. Focused grid; Wrong focal distance

45. Angled grid

46. Upside down focused grid

47. Rad T 180 Grid Lab; To grid or not to grid
Given that digital receptors are much more sensitive to scatter using a grid is a no-brainer.
We have developed labs to demonstrate the improved image quality a grid provides but as you know getting the clinical sites to do the same can be a challenge.

48. Sensitivity of CR plates to scatter

49. Grid v. Non Grid
Bowman, 2009

50. without
with

51. Rad T 180 Reciprocity
Exam the effects of increased mAs on dose, image quality, and ‘S’ number.
This lab is still done with a film component to demonstrate the effect of excessive mAs.
We also do the lab in the CR environment with the sensitivity fixed at 200.

52. 73 at 5; ‘S’ 592
73 at 10; ‘S’ 297

53. 73 at 20; ‘S’ 142
73 at 40; ‘S’ 88

54. mAs DAP value Dose ‘S’ number Density 5
12.8
49 mR
592
709
 10
25.7
93 mR
297
712
 20
51.4
199 mR
142
702
 40
102.9
401 mR 88
724

55. EDR (Exposure Data Recognizer) Fixed at 200

56. EDR Fixed Data mAs DAP value Dose ‘S’ number Density 10 25.7 93 mR 200
652
 20
51.4
199 mR
777
 40
102.9
401 mR
881

57. EDR (Exposure Data Recognizer) Fixed at 200

58. 95 at 5
63 at 40

59. EDR Fixed Data technique DAP value Dose ‘S’ number Density 63 at 40
75.3
298 mR
200
740
73 at 20
51.4
199 mR
777
83 at 10
32.9
129 mR
753
95 at 5
21.7
84 mR
718

60. EDR
As you can see, using the Fuji EDR function allows use to use the CR or DR system and generate the same responses we have come to expect from film.

61. Rad 110 DAP Uses
Using a combination of the radiation detector and the DAP monitor values to demonstrate the value of collimation in lowering the total exposure to the patient

62. Field Size
Detector
Reading mR
DAP
Reading µGy
% change
field size
% change DAP value
14 x 14 40
43.4
10 x 10
22.7 51 52
8 x8
14.6
32.6
33.6
5 x5
5.7
12.8
13.1

63. Other Problems we have had
This image was given to a faculty member and the student denied doing anything wrong.

64. Several other students did the same lab without the difference in density. So the thought was the student did something unusual.
After looking at the images it was determined the image was the first of the day.
When our system is started it defaults to technique.
So the determination was he changed the technique after the first exposure.

65. Verification

66. Dirty Reader
Picked up initially
on the diagnostic
monitor

67. Artifact had been
there unseen

68. Students and QC Activities
We have students perform a variety of QC experiments as part of their lab experience.
Vendor QC activities
One Shot
One Shot Plus
Fluoro mA and kVp
Collimation and centering
Reciprocity
HVL
Timer check

69. Conclusion
While a fully functional lab is a great experience. A mismatched, cobbled together system is a headache waiting to happen.
As you would expect, the digital lab adds several layers of complexity to the lab experience.
There are multiple sources available to provide a framework to begin the process, the results will be worth it.