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.
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.
‘S’ Number Fifteen percent rule does not effect ‘S’ number.
‘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
‘S’ Number This image was done as part of a distance affects density and ‘S’ number experiment. The ‘S’ number is 1740.
‘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
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
As film size changed S number changed with same technique
‘S’ number affected by positioning Same technique ‘S’ number affected by positioning
‘S’ number 80 ‘S’ number 159
Acceptable Positioning Options for Fuji CR
The Professionals weight in The ‘S’ number is just a reference
Other Basic Digital Labs We try to replicate various digital artifacts Lightbulb Moire Quantum mottle
Light bulb Artifact Excessive kVp By Paul Keough | December 8, 2009
We were unable to replicate the light bulb artifact, due to phantom size. 113 kVp 125 kVp 150 kVp
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.
Moire Image courtesy of Barry Burns, University of North Carolina
10 x 12 60 lines 10 x 12 85 lines
Same grid 8 x 10 10 x 12
10 x 12 85 lines 10 x 12 178 lines
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).
Week 1 data Technique Density DAP value Exposure ‘S’ number 75 @ 20 484 124.7 217 241 64 @ 20 499 91.6 157 711 85 @ 20 491 162.1 274 124 96 @ 20 199.9 347 73 Density is only possible from film or PACs These columns were added for digital imaging
75 at 20; ‘S’ 241 64 at 20; ‘S’ 711
85 at 20; ‘S’ 124 96 at 20; ‘S’ 73
Week 2 data Corrected Technique Density DAP value Exposure ‘S’ number 75 @ 20 484 124.7 217 241 64 @ 40 508 183.4 316 318 85 @ 10 433 81.4 137 252 96 @ 5 488 50.4 86 303 The analysis includes a discussion of the results and reasons for the results.
75 at 20; ‘S’ 241 64 at 40; ‘S’ 318
85 at 10; ‘S’ 252 96 at 5; ‘S’ 303
The effects of kVp and penetration
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.
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
73 at 25; ‘S’ number of 252 73 at 100; ‘S’ number is 70 73 at 6.5; ‘S’ number is 1129
Rad T 110 Density Maintenance This week we are again going to make a series of exposures. You will use either the pelvis phantom (75@20) or a shoulder phantom (66@11). 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”.
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
75 at 20, 30 inches ‘S’ 196 75 at 12, 30 inches ‘S’ 310
75 at 20, 50 inches ‘S’ 382 75 at 32, 50 inches ‘S’ 236
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.
Also, contrast did not significantly change.
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.
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
CR plate size and resolution 14 x 17
8 x 10
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.
Focused grid; Wrong focal distance
Angled grid
Upside down focused grid
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.
Sensitivity of CR plates to scatter
Grid v. Non Grid Bowman, 2009
without with
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.
73 at 5; ‘S’ 592 73 at 10; ‘S’ 297
73 at 20; ‘S’ 142 73 at 40; ‘S’ 88
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
EDR (Exposure Data Recognizer) Fixed at 200
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
EDR (Exposure Data Recognizer) Fixed at 200
95 at 5 63 at 40
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
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.
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
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
Other Problems we have had This image was given to a faculty member and the student denied doing anything wrong.
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 70@20 technique. So the determination was he changed the technique after the first exposure.
Verification
Dirty Reader Picked up initially on the diagnostic monitor
Artifact had been there unseen
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
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.