national guidance on standards for pacs image display devices dr rhidian bramley pacs &...

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– AAPM TG18 (USA)– DIN V 6868-57 (Germany)– IPEM 91 (UK)– RCR (UK)– Connecting for Health (England)

• International– 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


• 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?


How often How bad Total

Radiology

Fracture clinic

A&E

ITU

Chest clinic

Theatres

Wards



Radiology 5

Fracture clinic 3

A&E 4

ITU 2

Chest clinic 2

Theatres 1

Wards 2



Radiology 5 5

Fracture clinic 3 5

A&E 4 3

ITU 2 4

Chest clinic 2 3

Theatres 1 3

Wards 2 1



Radiology 5 5 25

Fracture clinic 3 5 15

A&E 4 3 12

ITU 2 4 8

Chest clinic 2 3 6

Theatres 1 3 6

Wards 2 1 6


• 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 RadiographsRadiology 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.


• 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.


• ROC Analysis for Diagnostic Accuracy of Fracture by Using Different MonitorsJournal 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.”

• 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 grey-scale 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 on how to view images

RCR Guidance Minimum [1]

Recommended [1]

Screen Resolution [2] (Native Pixel Array)

>= 1280 x 1024 [3] (~ 1.3 megapixels)

>= 1500 x 2000 [4] (~ 3 megapixels)

Screen Size (Viewable Diagonal)

>= 42 cm (~17”) >= 50 cm (~ 20”)

Maximum Luminance[5]

> 170 cd/m2 [6] >= 500 cd/m2 [7]

Luminance Contrast Ratio (Max/Min)

>= 250:1 [6] [8] >= 500:1

Grey-scale Calibration

Within 10% GSDF [8] Calibrated to GSDF [5]

Grey-scale bit depth 8 bit grey-scale (24 bit colour) [9]

>= 10 bit grey-scale

Video Display Interface Digital-analogue Digital video interface (DVI)

Pixel Defects [10] ISO 13406-2 class

Class 2 (2 per million)

Class 1 (0 defects)

IPEM 91 GUIDANCEPhysical 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 AngleCalibration

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 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

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