CR and DR Information
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10 RESOLUTIONS WHEN GOING DIGITAL
Vol. 21 •Issue 2 • Page 5
Guest Editorial
Resolutions for a Digital Age
By Barbara J. Smith MS, RT(R) (QM), FASRT
While we're still at the beginning of 2008, now is a good time to look over your work practicesCOMPUTER and come up
with a list of changes you can make to improve your department.
I offer you these 10 resolutions I've compiled from topics I covered in my column, "Going Digital," during
2007.
1. Position correctly the first time. It may be easier and faster to repeat digital images, but that's no reason
for sloppy positioning. Repeats contribute to patient dose, and the computer can't correct for that.
2. Use the correct technique. Strive to use a technique that puts the image exposure indicator in the center
of the range for your system. Doing so will keep the image from being under- or over-exposed and limit
patient exposure. Consider using higher kVp and lower mAs based on the 15 percent rule.
3. Collimate instead of crop whenever possible. Limiting field size by collimation achieves several goals: It
reduces patient dose, it limits scatter production and it assists with correct image adjustment by the
algorithms.
4. Use your markers. Place markers before exposure to eliminate any questionable results from image
manipulation. It's better from a legal perspective and less confusing for others who view the images.
5. Limit image receptor exposure to scatter. Digital receptors are very sensitive to scatter. Collimation and
technique affect scatter production, and excessive scatter will lower contrast in CR and DR systems. While
DR is affected by scatter created during exposure, CR can be affected by scatter before or after exams.
Don't leave CR plates propped up in a room during exams.
6. Use the correct algorithm. The algorithms that process digital images are set so that the automatic
rescaling and look-up table will give the appropriate density and contrast for each body part. If your image
does not appear correct due to technique, location or another reason, don't just run it under another
algorithm. Chronically wrong algorithms should be adjusted.
7. Use grids for chest and large body parts. A grid will not affect scatter production, but it will help reduce the
amount that reaches the image receptor. Grids should always be used for chest work, even on portables.
8. Limit image manipulation. Digital images should be manipulated as little as possible before being sent to a
PACS. The more an image is manipulated, the less information, or data, that is sent to PACS, which means
the radiologist has less information with which to work.
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1) If you do multiple images on a single
IP, the computer needs
3 distinct collimated boarders to recognize each data field. My
students want to know why and I can't give them a good enough answer.
Can anybody explain why *3* boarders are required?
The three margin rule is primarily for off
centered single fields, but
could apply to multiple fields also. When you do multiple fields you
need clean collimation margins between the edge of the plate and the
exposure fields and clean collimation margins between the exposure
fields. If the exposure fields extend past he edge of the plate and
if
the exposure fields over lap, the histogram is likely to contain
extraneous data (off focus radiation) and automatic rescaling will
probably produce erratic image appearance (dark or light when the
actual exposure level was correct) . There is some variation in
these
"rules" between vendors because there is no standardization how
vendors
deal with multiple fields. The "three margin rule" most often
applies
to a single field that tis not centered to the plate. If there are
three margins the software is more likely to recognize the exposure
field that if the off centered field only has two margins. The
reasons
why this is true related to the field recognition logic in the
software. Three margins is "stronger" than two and the software does
not have to "estimate" the exposure field location. I have done labs
with these rules and we get failures only part of the time. If the
plate is overexposed and there is an alignment rule violated the
failures occur more consistently. The way I try to describe these
rule
is "if you violate one of the alignment/collimation rules image
quality
will be erratic.
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This document describes a series of tests to assess
CR plate and reader performance. The tests are intended to monitor image
quality and sensitivity.
All the tests described should be performed on all
available reader systems. This document is intended as guidance. For
more specific set-up details the local medical physics department should
be consulted.
*Adapted for local need from IPEM document
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Tape measure
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Adhesive tape
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1 mm Copper filtration (>10 x 10 cm)
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TOR RAD or TOR CDR test object
In all tests described the unique plate
identification code should be recorded, and the same tube and generator
should be used each time the tests are performed.
 TOR
CDR test object
Frequency: 1 - 3 monthly
a)
Place a cassette (e.g. 24cm x 30cm - the same cassette should be
used each time this test is performed) on the couch at 1m from the focus
and centred in the x-ray beam. Set the collimation to cover the entire
cassette.
b)
Place filtration in the beam and set a kVp as indicated in below.
CR
system
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Filtration
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Tube Voltage (kVp)
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Kodak
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1mm
Cu
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80
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c)
Set a manual mAs (this value should be determined in consultation
with medical physics) and expose.
d)
Read the plate immediately using the following parameters
Kodak: Pattern mode.
e) Record the
sensitivity index, i.e.
EI
- Kodak
Tolerance: This sensitivity
index should be compared to a baseline value obtained under the same
conditions (i.e. same x-ray tube, distance, kV, filtration, mAs, plate).
Remedial level:
Kodak: EI should lie between
(Baseline +80) and
(Baseline-100)
Suspension level:
Kodak: EI should lie between
(Baseline+175) and
(Baseline-300)
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