Download A COMPARISON OF IMAGE QUALITY AND RADIATION DOSE

Ensuring safety in transition to
digital radiography in practice
Kwan-Hoong Ng, PhD
President, AFOMP
University of Malaya, Kuala Lumpur,
Malaysia
KH Ng
1. Introduction
2. Advantages of going digital
3. Issues in going digital
4. Strategies in monitoring dose
5. Strategies in dose management
6. Summary
KH Ng
1.
Introduction
KH Ng
“ While digital techniques have the
potential to reduce patient doses,
they also have the potential to
significantly increase them.”
- ICRP 93 Editorial
KH Ng
“This is a technology that is advancing rapidly
and which will soon affect hundreds of
millions of patients.
If careful attention is not paid to the
radiation protection issues of digital radiology,
medical exposure of patients will increase
significantly and without concurrent benefit.”
- ICRP 93 Editorial
KH Ng
• Most principles for dose reduction for
screen-film radiography, especially
justification, are relevant to digital systems
• However, in digital systems different
scenarios apply for dose reduction and
optimisation compared with screen-film
radiography
KH Ng
2. Advantages of going digital
KH Ng
Screen-Film
Radiography
Digital
Radiography
Recording
Digital
detector
Displaying
Display
Monitor
Archiving
PACS server
Major limitation is ‘film’
Optimize each component
independently
KH Ng
• The diagnostic information provided by
modern digital detectors can be equal or
superior to conventional screen-film
systems, with comparable patient doses.
• Digital imaging has practical technical
advantages compared with film
techniques, e.g. wide contrast dynamic
range, post-processing functions, multiple
image viewing options, and electronic
transfer and archiving possibilities.
KH Ng
3. Issues in going digital
KH Ng
“This is a technology that is advancing rapidly
and which will soon affect hundreds of
millions of patients.
If careful attention is not paid to the radiation
protection issues of digital radiology, medical
exposure of patients will increase significantly
and without concurrent benefit.”
[We are witnessing the consequences now]
- ICRP 93 Editorial
KH Ng
KH Ng
Digital imaging brings benefits but also
demands changes in ways of working
Digital x ray imaging involves issues
cost and productivity,
 need to acquire new skills,
 radiation doses,
 overuse,
 image quality.

It is easy to delete digital images,
and repeat exposures normally go undetected.
Ng BMJ 2006
Different imaging tasks require different
levels of image quality.
e.g. the follow-up examination
for a fracture does not require the
same image quality as that required for
its diagnosis.
Ng BMJ 2006
Current safety issues with clinical
digital radiography:
Technology Factors
• Automatic Exposure Control (AEC)
• Exposure (sensitivity) index
KH Ng
AEC
The wide exposure dynamic range of such
systems may have the disadvantage that, if
the X-ray generator AEC develops a fault or
the output calibration drifts, the dose
increase/decrease may not be identified
readily.
Also, the wide exposure dynamic range
means there is significant potential for the
initial set-up of such systems not to be
optimised.
KH Ng
AEC

Digital radiography systems may have different
X-ray energy responses to screen-film systems.
Therefore the generator's AEC compensation
characteristics should be different from that used
for screen-film systems.

For existing systems which have been upgraded
to CR or DR, the existing AEC compensation
characteristics will need reprogramming. X-ray
equipment manufacturers should work with
physicists on this.
Exposure (sensitivity) Index
Each image should ideally have an
associated number to indicate the level
of exposure to the detector. Currently all
digital systems have a exposure
(sensitivity) index which is related to
detector exposure.
Once digital radiography systems are in
use, the constancy of applied exposure
factors should be monitored on a regular
basis.
List of terms for exposure indices for various digital systems
and their relationship to traditional dose measure (in µGy). In
the 2nd column the proposal for an international standardisation
is detailed (courtesy of Ulrich Neitzel, Philips Medical Systems,
Hamburg).
Uffmann et al E J Radiol 72 (2009) 202–208
Am J Roentgenol. 2012 Dec;199(6):1337-41
Both the IEC (IEC standard 62494-1) and the
AAPM (AAPM Task Group 116) have developed
similar standards for monitoring exposure in
digital radiography to eliminate proprietary and
confusing terminology.
Radiologists and technologists will need to learn
three new terms - exposure index, target
exposure index, and deviation index - to
understand the new standards.
Current safety issues with clinical
digital radiography:
Human Factors
•
•
•
•
Inappropriate exposure
Increase in number of examinations
No (inadequate) collimation
Image quality is not compatible with
imaging task
KH Ng
Inappropriate exposure
• With digital systems, an overexposure can
occur without an adverse impact on image
quality.
• Overexposure may not be recognised by the
radiologist or radiographer. In conventional
radiography, excessive exposure produces a
“black” film and inadequate exposure
produces a “white” film, both with reduced
contrast. In digital systems, image brightness
can be adjusted post processing independent
of exposure level.
KH Ng
Increase in number of examinations
In several U.S. hospitals the number of
examinations per in-patient day increased
by 82% after a transition to film-less
operation.
Outpatient utilization (i.e. the number of
examinations per visit) increased by 21%
compared with a net decrease of 19%
nationally at film-based hospitals.
Reiner et al. Radiology. 2000 ;215(1):163-7
KH Ng
No collimation
Post-exam collimation (cropping)
KH Ng
No collimation
Apparently “Perfect” radiographs of the
paranasal sinuses with post exam cropping
Courtesy Dr. Evelyn Ho, SDMC
KH Ng
No collimation
A series of radiographs which were supposed to
be for the paranasal sinuses (yellow collimation
lines) but instead practically the whole head was
x-rayed!
Courtesy Dr. Evelyn Ho, SDMC
KH Ng
No collimation
What happens to collimation?
Lumbar spine radiography - poor collimation
practices after
implementation of digital technology
Zetterberg and Espeland
Brit J Radiol, 84 (2011), 566–569
KH Ng
No collimation
Lumbar spine
radiography - poor
collimation practices after
implementation of digital
technology
Irradiated
field outside
ROI
Total field
size
Digital
Analog
(Film)
61.7%
42.4%
791 cm2 541 cm2
Zetterberg and Espeland Brit J Radiol, 84 (2011), 566–569
KH Ng
No collimation
A survey of 450 technologists by the
American Society of Radiologic
Technologists (ASRT) revealed that
half of the respondents used electronic
cropping after the exposure
Pediatric Radiology, 2011, 41:5, 602-610
KH Ng
No collimation
• Poor collimation
• Large part of the
IAEA
Radiation Protection in Paediatric Radiology
body is irradiated
• Not seen on
digitally cropped
image
L04. Radiation protection in digital radiography
30
4. Strategies in monitoring dose
KH Ng
Nationwide Evaluation of X-ray Trends- NEXT
FDA/ CDRH
KH Ng
National dose monitoring - UK NRPB (HPA) mid 80s
IAEA-TECDOC-1423. Optimization of the radiological protection of patients
undergoing radiography, fluoroscopy and computed tomography.
One of the first online patient dose
monitoring systems (QCONLINE)
was developed for CR auditing
Vano E, et al. Real-time measurement and audit of
radiation dose to patients undergoing computed
radiography. Radiology 2002; 225(1):283-8.
Vano et al Experience on patient dosimetry and quality control on line for diagnostic
Fig. 1
and interventional radiology using DICOM services AJR Oct 2012
Vano et al Experience on patient dosimetry and quality control on line for diagnostic and
Fig. 2
interventional radiology using DICOM services AJR Oct 2012
Fig. 3
DICOM HEADER
Relevant DICOM tags GE Chest flat panel
(0008,0020) : Study Date
: 27/01/03
(0008,0030) : Study Time
: 10:31:12
(0008,0033) : Image Time
: 10:32:43
(0010,0020) : Patient ID
: 795607
(0010,0040) : Patient's Sex
:F
(0010,1010) : Patient's Age
: 085Y
(0018,0015) : Body Part Examined
:
(0018,0060) : KVP
: 125
(0018,1150) : Exposure Time
:5
(0018,1151) : X-ray Tube Current
: 250
(0018,115E) : Image Area Dose Product
: 0.83557
(0018,1190) : Focal Spot(s)
: 0.6
(0018,1405) : Relative X-ray Exposure
: 61
(0018,7060) : Exposure Control Mode
: AUTOMATIC
(0018,7062) : Exposure Control Mode Descript: AEC_left_and_right_cells
(0028,0010) : Rows
(0028,0011) : Columns
(0028,0100) : Bits Allocated
(0028,0101) : Bits Stored
Vano et al AJR Oct 2012
: 2022
: 2022
: 16
: 14
42
Vano et al AJR Oct 2012
Fig. 4
Vano et al AJR Oct 2012
Fig. 5
Vano et al AJR Oct 2012
Fig. 6
Fig. 7
Vano et al AJR Oct 2012
Automated data collection
and evaluation for longitudinal
assessment of dose.
(a) AP lumbar spine
radiographs. Even small
alterations of the automated
exposure control are
indicated (arrow).
(b) Automated assessment of
the kerma-area-product in PA
chest radiographs. The
majority of exposures are
below the DRL level (red line)
(Courtesy of Ulrich Neitzel,
Philips Medical Systems,
Hamburg).
Uffmann et al E J Radiol 72 (2009) 202–208
KH Ng
“I can assure you our x-ray procedures follow
very strict health and safety guidelines”
www.CartoonStock.com
KH Ng
5. Strategies in Dose Management
KH Ng
While digital techniques have the
potential to reduce patient doses,
they also have the potential to
significantly increase them.
Thus we need to manage dose.
KH Ng
Optimization
Trade-offs
between radiation
dose and image
quality
Dose
Image
quality
KH Ng
Optimization
Optimization does not mean simply
maximizing image quality and minimizing
patient dose, rather it requires radiologists
to determine the level of image quality that is
necessary to make the clinical diagnosis and
then for the dose to be minimized without
compromising this image quality.
KH Ng
Different medical imaging tasks require
different levels of image quality.
The objective is to avoid unnecessary
patient doses; doses which have no
additional benefit for the clinical
purpose intended.
Diagnostic Reference Levels (DRL)
• Useful diagnostic and investigational tool
• Acceptable doses for various exams &
procedures
• Comparison between various facilities
• Local DRLs should be set up and
reviewed when new digital systems are
introduced.
KH Ng
Examples of diagnostic reference levels (DRL)
US 1999 ESAK
[mGy]
UK 2000 ESD Germany 2003
[mGy]
ESD [mGy]
AP/PA skull
-
3
5
Lat skull
-
1.5
3
PA
0.25
0.2
0.3
Lat chest
-
1.0
1.5
AP abdomen
4.5
6
10
AP pelvis
-
4
10
AP C-spine
1.25
-
-
AP L-spine
5
6
10
Lat L-spine
-
14
30
Uffmann et al E J Radiol 72 (2009) 202–208
KH Ng
We need to refine DRL:
• For digital radiography
• Specific for clinical image quality
• Adjust for body weight/ size
KH Ng
“ … finding the appropriate level of
image quality is the most important
objective. Keeping the dose low
should always be secondary.”
- Martin CJ: 20 years of patient dose studies:
Where should we go from here? Brit J Radiol 2005
KH Ng
Based on ICRP 93
KH Ng
Based on ICRP 93
KH Ng
Fluoroscopy
Use correct technique
• intermittent fluoro, image freeze hold
Time, Distance, Shielding
• Duration of exposure (beam on time)
• Distance to source (step back)
• Use of protective device
10 Pearls are
useful in dose
management
KH Ng
KH Ng
L
R
Digital image of lumbar spine.
Fluoroscopy system: 10% dose (left);
100% dose (right) (relative values of dose).
Courtesy of R. Loose.
ICRP 93
KH Ng
Commercial Dose Management
Software
- Dose Alert system
KH Ng
64
DoseWatch Demo
12/11/2012
CAREmonitor
Page 65
Copyright © Siemens AG 2011
Advantages and challenges of
radiographer-performed fluoroscopy
In some countries, radiographers are
performing fluoroscopy
- Role expansion
- Relieve workload of busy radiologists
- Handling routine cases, eg. barium meals
and enema
- May lack clinical knowledge and history of
patient, thus long screening time & repeat
procedure by radiologists
KH Ng
BJR1998 71:399-405
DAP measurements for over 1000 barium enema
performed by radiologists and radiographers were
analysed & compared if there is any stats. sig. in
radiation dose to the patients, depending on the
category of staff performing the examinations.
DAP
KH Ng
Operator group
Mean DAP
(Gycm2)
Radiologists 1994/95
17.8
Radiologists 1996
18.6
Radiographers 1996
22.3
KH Ng
Although radiographers are able to produce
consistent diagnostic results, there is increase
in patient dose due to extra films taken for
reporting, which may be difficult to justify.
KH Ng
WM Thompson et.al. AJR 2006; 187:706–709
No dose information!
We need study on digital fluoroscopy
KH Ng
5. Summary
KH Ng
1. Appropriate training, particularly
in the aspects of patient dose
management, should be undertaken
by radiologists, medical physicists
and radiographers before and
during the clinical use of digital
techniques.
KH Ng
2. National and local diagnostic
reference levels (DRL) should be
reviewed when new digital systems
are introduced in a facility.
KH Ng
3. All imaging procedures should be
audited (evaluated) at least once a
year :
• Clinical practice
• Image quality
• Dose assessment
KH Ng
4. The original (raw) image data
should be made available to the user
not only for objective testing in a
rigorous quality assurance program
but also for other types of
independent tests of the performance
of digital-imaging systems.
KH Ng
5. When a new digital system or
new post-processing software is
introduced, an optimisation
programme and continuing training
should be conducted in parallel.
KH Ng
6. QC in digital radiology requires
new procedures and protocols.
Acceptance and constancy tests
should include aspects concerning
visualization, transmission and
archiving of the images.
KH Ng
7. As digital images are easier to
acquire and to transmit in
communication networks, referring
physicians should be fully conversant
with the justification criteria for
requesting medical x-ray imaging
procedures.
KH Ng
8. Industry should promote tools to
inform radiologists, radiographers and
medical physicists about the exposure
parameters and the resultant patient
doses. The exposure parameters and
the resultant patient doses should be
standardized, displayed and recorded.
KH Ng
9. Making use of radiographic and
dosimetric data contained in DICOM
header for dose management.
KH Ng
10. Educate, Educate, Educate
Train, Retrain, Train RETRAIN
Collimation is urgently needing attention
KH Ng
Radiation is Good for You
Modified from E Hall