Transcript Slide 1

National Guidance on Standards
for PACS Image Display Devices
Dr Rhidian Bramley
PACS & Teleradiology SIG
Hillingdon, London 22 Nov 2006
FAQ
• Is the LSP PACS web client suitable for
diagnostic use?
• Are there different recommendations for
diagnostic and review workstations?
• Are there different recommendations for different
modality workstations?
• How do you decide what specification is
appropriate for A&E, clinics, wards, theatres etc.
• Should we deploy 2, 3 or 5 MP display devices
on reporting workstations?
Display Device QA Guidance
• National
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AAPM TG18 (USA)
DIN V 6868-57 (Germany)
IPEM 91 (UK)
RCR (UK)
Connecting for Health (England)
• International
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SMPTE
VESA FPDM
ISO 9241 and 13406
DICOM GSDF and GSPS
IEC 61223-3-6
UK Guidance Drivers & Objectives
• Assist UK PACS deployments
• Guidance on purchase and QA of display devices
for PACS projects & business cases
• Promote clinical safety
• Set minimum standards
• Achieve benefits of PACS
• Support clinical workflow
• Provide realistic achievable targets
UK Guidance Scope
• All PACS display devices used for ‘clinical image
interpretation’
– because by definition there is an associated clinical
risk
• Specify QA tests and minimum standards for a
display device to reproduce a DICOM test image
– Assess whole imaging chain from PACS server to
workstation display (including effect of room lighting)
• Provide guidance on how to view images
– To optimise spatial and contrast resolution
Classification of Display Devices
• Are there different recommendations for
diagnostic and review workstations?
• If so, what constitutes a review
workstation?
AAPM TG18 Classification
• Primary display systems
– those used for the interpretation of medical
images. They are typically used in radiology
and in certain medical specialties such as
orthopedics.
• Secondary display systems
– those used for viewing medical images by
medical staff or specialists other than
radiologists after an interpretive report is
rendered.
IEC Classification
• Primary Usage
– use of an image display system or its
components for the interpretation of medical
images toward rendering clinical diagnosis
• Secondary Usage
– use of an image display system or its
components for viewing medical images for
medical purposes other than primary usage
RCR/CfH Guidance
• This guidance deals with the QA of primary
diagnostic display devices used for clinical
image interpretation. Where images are
reviewed without a requirement for clinical
interpretation, the image quality is considered to
be of secondary importance. The quality of
display in these circumstances should be
considered locally, depending on the purpose of
the review.
Classification of Display Devices
• Are there different recommendations for
different modality workstations?
– Mammography
– Plain Radiography
– CT, MR
Classification by Image Modality
• DIN V 6868-57
– Class 1 (projection radiography)
– Class 2 (cross sectional imaging)
• IEC 61223-3-6
– Mammography
– Radiography, Fluoroscopy
– CT, MRI
– US, NM
Classification by Area?
• How do you decide what specification is
appropriate for Radiology, A&E, clinics,
wards, theatres etc?
• Should everyone have the same display
devices?
• How do you justify one clinical area having
a better workstation that another?
Clinical Risk Assessment
• What can go wrong
– Patient may be harmed as a result of
inadequate quality of the PACS display device
• How often
• How bad
• Need for action?
Clinical Risk Assessment
How often
Radiology
Fracture clinic
A&E
ITU
Chest clinic
Theatres
Wards
How bad
Total
Clinical Risk Assessment
Radiology
Fracture clinic
A&E
ITU
Chest clinic
Theatres
Wards
How often
5
3
4
2
2
1
2
How bad
Total
Clinical Risk Assessment
Radiology
Fracture clinic
A&E
ITU
Chest clinic
Theatres
Wards
How often
5
3
4
2
2
1
2
How bad
5
5
3
4
3
3
1
Total
Clinical Risk Assessment
Radiology
Fracture clinic
A&E
ITU
Chest clinic
Theatres
Wards
How often
5
3
4
2
2
1
2
How bad
5
5
3
4
3
3
1
Total
25
15
12
8
6
6
6
Clinical Risk Assessment
• What can go wrong
– Patient may be harmed as a result of
inadequate specification and QA of the PACS
workstation
• How often
• How bad
• Need for action?
Evidence base examples 1
• Effect of Monitor Luminance and Ambient
Light on Observer Performance in Soft-Copy
Reading of Digital Chest Radiographs
Radiology 2004;232:762-766
• When adequate window width and level are
applied to soft-copy images, the primary
diagnosis with chest radiographs on the monitor
is unlikely to be affected under low ambient light
and a monitor luminance of 25 foot-lamberts or
more.
Evidence base examples 2
• Personal Computer versus Workstation
Display: Observer Performance in Detection
of Wrist Fractures on Digital Radiographs
Radiology 2005;237:872-877
• The results of this study showed that there was
no difference in accuracy of observer
performance for detection of wrist fractures with
a PC compared with that with a PACS
workstation.
Evidence base examples 3
• ROC Analysis for Diagnostic Accuracy of
Fracture by Using Different Monitors
Journal of Digital Imaging 2006;19: 276
• A significant difference was observed in the
results obtained by using two kinds of monitors.
Color monitors cannot serve as substitutes for
monochromatic monitors in the process of
interpreting computed radiography (CR) images
with fractures.
Options to Mitigate Risk
• Install higher spec display device
• Optimise QA - ensure workstation is
configured correctly (+ ambient lighting)
• Training - ensure workstation is used
correctly
• Implement ‘hot reporting’ service
• Disallow clinical image interpretation on
the workstation
Importance of Clinical Workflow
• Workflow should dictate where ‘diagnostic’
quality display devices are positioned
– Providing it does not render then non-diagnostic!
• May use workflow to justify a higher spec display
device in some areas
– Where viewing conditions can not be optimised fully –
e.g. operating theatres, angiography rooms
– Where large numbers of plain radiographs reported to
reduce requirements for systematic magnification
(spatial resolution) and windowing (contrast
resolution).
RCR guidance on how to view images
• To optimise spatial resolution
– View image fully in maximum available screen area to optimise
pattern recognition of non-spatially limited abnormalities
– Systematically magnify image to acquisition resolution or greater
(100%, 200% etc) to reveal spatial detail
• zoom and pan image around screen
• use magnifying glass tool
– “Studies suggest that there is little reduction in the diagnostic
power of using these techniques when compared to displaying
the whole image at 1:1 on higher resolution screens, but there is
an increase in the time taken to make a report.”
– “High fidelity dual screen displays (>= 3 MP) are recommended
in radiology and other areas where large numbers of
radiographic images are reported, to reduce reporting times and
thereby optimise department workflow.”
RCR guidance on how to view images
• To optimise contrast resolution
– View image at different window level and window width presets
to optimise demonstration of different structures
• e.g. soft tissue, lung, bone windows
– “.By changing the centre (level) and range (width) of the greyscale values presented, it should be possible to demonstrate all
the grey-scale data represented in the image. The minimum
specification of a display device in terms of contrast resolution
parameters is therefore somewhat arbitrary, and depends on
how the windowing tools are used during normal workflow.”
– “High fidelity display devices are recommended in radiology and
other areas where large numbers of images are reported to
reduce requirements for windowing images, and thus assist in
reporting workflow.”
RCR Guidance
Minimum [1]
Recommended [1]
Screen Resolution [2]
(Native Pixel Array)
Screen Size
(Viewable Diagonal)
Maximum Luminance[5]
>= 1280 x 1024 [3]
(~ 1.3 megapixels)
>= 42 cm (~17”)
>= 1500 x 2000 [4]
(~ 3 megapixels)
>= 50 cm (~ 20”)
> 170 cd/m2 [6]
>= 500 cd/m2 [7]
Luminance Contrast
Ratio (Max/Min)
Grey-scale Calibration
>= 250:1 [6] [8]
>= 500:1
Within 10% GSDF [8]
Calibrated to GSDF [5]
Grey-scale bit depth
8 bit grey-scale
(24 bit colour) [9]
Video Display Interface Digital-analogue
>= 10 bit grey-scale
Pixel Defects [10]
ISO 13406-2 class
Digital video interface
(DVI)
Class 1
(0 defects)
Class 2
(2 per million)
IPEM 91 GUIDANCE
Physical parameter
Frequency
Remedial level
Image display monitor
condition
Daily to weekly
Image display monitors should be clean, and the
perceived contrast of the test pattern should
be consistent between monitors connected
to the same workstation. Verify that the 5%
and 95% patches are visible.
Greyscale contrast
luminance ratio
3 monthly
Ratio white to black < 250
Distance and Angle
Calibration
3 monthly
± 5 mm
± 3
Resolution
3 monthly
Grade AAPM TG18-QC resolution patterns
according to the reference score (CX > 4)
Greyscale drift
6 to 12 monthly
Black baseline ± 25%
White baseline ± 20%
DICOM greyscale
calibration
6 to 12 monthly
GSDF ± 10%
Uniformity
6 to 12 monthly
U% > 30%
Variation between
monitors
6 to 12 monthly
Black baseline > 30%
White baseline > 30%
Room illumination
6 to 12 monthly
> 15 lux
FAQ
• Is the LSP PACS web client suitable for
diagnostic use?
• Are there different recommendations for
diagnostic and review workstations?
• Are there different recommendations for different
modality workstations?
• How do you decide what specification is
appropriate for A&E, clinics, wards, theatres etc.
• Should we deploy 2, 3 or 5 MP display devices
on reporting workstations?
Summary RCR Guidance
• Set ‘achievable’ minimum standard for all
workstations used for clinical image
interpretation
– Number and locations of clinical ‘diagnostic’
workstations determined by and workflow analysis
and QA programme
• Recommended higher standard for some
workstations to optimise clinical safety and
workflow
– Where large numbers of plain radiography images
reported
– Where viewing conditions can not be optimised fully
Which is the PACS workstation?
A
B