DICOM INTERNATIONAL CONFERENCE SEMINAR Oct 9 11 2010

DICOM INTERNATIONAL CONFERENCE & SEMINAR Oct 9 -11, 2010 Rio de Janeiro, Brazil Managing Display Quality & Consistency Lawrence Tarbox, Ph. D. Washington University in St. Louis

Overview • Review of Grayscale Standard Display Function • Review of Grayscale Presentation State • Color Presentation States – Color Consistency – Presentation States applied to Color Images – Color Blending - CT-PET fusion • Hanging Protocols

Problems of Inconsistency • VOI chosen on one display device • Rendered on another with different display • Mass expected to be seen is no longer seen mass visible mass invisible Slide Provided by David Clunie, Quintiles Intelligent Imaging

Problems of Inconsistency 0. 5 1. 0 • Not all display levels are perceivable on all devices 1. 5 3. 0 Slide Provided by David Clunie, Quintiles Intelligent Imaging

Problems of Inconsistency Digital Modality Printed images does not look like displayed images Laser Printer Slide Provided by David Clunie, Quintiles Intelligent Imaging

Grayscale Standard Display Function • Defines a standardize output ‘unit’ for monochromatic DICOM images called ‘P-Values’ (Presentation Values) • Based on a model of human vision described by Barton, et al • A mathematical derivation that takes into account lighting conditions • Follows a curve that is roughly perceptually linear

Grayscale Standard Display Function 1000 Despite different change in absolute luminance 100 10 1 0 200 400 600 800 1000 . 1 . 01 JND Index Same number of Just Noticeable Difference == Same perceived contrast Slide Provided by David Clunie, Quintiles Intelligent Imaging

Calibrate the Monitor! • First set up monitor/graphics subsystem as optimally as possible • Measure the ambient light • Measure the current response of the monitor • Calculate a calibration LUT that converts Pvalues into digital driving levels for the monitor • Most high end medical imaging monitors can auto-calibrate

Display Calibration Tools (Photometer) Slide Provided by Jerry Gaskill, Image Smiths Inc.

Monitor Characteristic Curve Luminance 100 10 0. 1 Ambient Light 0. 01 0 50 100 150 Digital Driving Level 200 250 300 Slide Provided by David Clunie, Quintiles Intelligent Imaging

Perceptual linear device - LUT Mapping P-Values to Input of Characteristic Curve (DDL’s) 300 250 DDL 200 150 100 50 0 0 50 100 150 200 250 300 P-Values Slide Provided by David Clunie, Quintiles Intelligent Imaging

Grayscale Standard Display Function 1000 Despite different change in absolute luminance 100 10 1 0 200 400 600 800 1000 . 1 . 01 JND Index Same number of Just Noticeable Difference == Same perceived contrast Slide Provided by David Clunie, Quintiles Intelligent Imaging

Distributed Image Consistency Laser Printer Digital Modality Identical perceived contrast Workstation

DICOM Grayscale Presentation State • Separate object from the image objects • Specifies how the referenced image is to be displayed – Grayscale transformation – Graphics and text overlays – Spatial transformations

DICOM Grayscale Image Transformation Model Rescale Slope/Intercept or Modality LUT Original Image Modality LUT Transformation Window/Level or VOI LUT Mask (Subtraction) VOI LUT Transformation Presentation LUT Transformation Grayscale Transformations P-Values Shutter Transformation Image Annotation Spatial Transformation Disp. Area Annotation Shutter, Annotation and Spatial Transformations Display

Spatial Transformations Entire Image Selected Flip Horizontal Original Image Scale To Fit Transformed Image

Spatial Transformations Part of Image Selected Flip Horizontal Original Image Scale To Fit Transformed Image

Transformation & Annotation Part of Image Selected Flip Horizontal Scale To Fit Mass behind heart Original Image Transformed Image In this example, - text annotation is specified by image relative visible anchor point - the circle is a separate image relative graphic annotation

Limitations of Grayscale Presentation States • Apply to grayscale images – no means to specify spatial transformations or graphic annotations for color images • Only grayscale consistency – standard display function defined only for luminance • No pseudo-color capability • No blending or fusion capability

Distributed Color Image Consistency Printer Digital Modality Different perceived color Workstation

Distributed Image Consistency Printer Digital Modality Identical perceived color Workstation

True and Pseudo-Color

Goals for Color • Color consistency – standard function – defined for image output space of existing color images • Transformation and annotation pipeline • Pseudo-color for grayscale images • Blending of grayscale images – alpha blending function – colorizing superimposed image

Standard Color Space • • GSDF filled a void Color consistency already standardized ICC - International Color Consortium Graphics and pre-press industry CIE Colorimetry Profiles of input and output devices Commercial Off-The-Shelf color management software handles conversion • Perceptual rendering intent

Three New SOP Classes • Color Presentation State • Pseudo-Color Presentation State • Blending Presentation State • ICC Profile – Defines output of all color presentation states – Optionally present in all color images • PCS-Values (analogous to grayscale PValues) – Profile Connection Space (CIELAB or CIEXYZ)

Commonality • All presentation states share identical – Spatial transformation pipeline – Graphic and text annotation pipeline • Choice of output space – P-Values for grayscale – PCS-Values for color and pseudo-color and blending

Old Grayscale Pipeline

Grayscale & Color Pipeline

Common Spatial & Annotation Pipeline

Blending Pipeline

Blending for CT-PET select underlying select superimposed

Blending for CT-PET select underlying select superimposed [register]

Blending for CT-PET select underlying select superimposed [register] resample

Blending for CT-PET select underlying select superimposed [register] resample within slices

Blending for CT-PET select underlying select superimposed [register] resample within slices [between slices]

Blending for CT-PET select underlying select superimposed rescale and window [register] resample within slices [between slices]

Blending for CT-PET select underlying select superimposed rescale and window [register] resample within slices [between slices] pseudo-color

Blending for CT-PET select underlying select superimposed rescale and window [register] resample within slices [between slices] blend pseudo-color

Color - Conclusion • Color consistency using industry standard • Transformation/annotation for color images • Exchange of pseudo-color information • Support for specifying sets of images to be blended, and how to blend (but not register or resample) them

Hanging Protocols • • “Default display protocols” A set of instructions How to layout a class of images for display Order, orientation, windowing, processing • Not specific to a particular patient’s images • Hence a protocol, not a presentation state

Hanging Protocols

Hanging Protocols L L Old Lateral F Old Study L New Frontal New Lateral F F New Study L New Townes F

Hanging Protocol Goals • Encode – Applicability of protocol (type of display & images) – Selection of images – Display of selected images • Store centrally, retrieve and exchange – Persistent composite objects – Query, retrieval and media encoding • Vendor neutrality – Interchange between sites, PACS and workstations – Survive upgrades and replacements – “Public” library of “good” hanging protocols ?

Using a Hanging Protocol • Given a current exam (e. g. reading worklist) • Find potentially applicable protocols • Retrieve them from archive • Select one from those available • Select image +/- other studies to which it applies • Display selected images as instructed

Finding a Protocol • Definition Module – Name, description, level, creator, creation datetime – Modality, anatomy, laterality – Procedure, reason for procedure – Number of priors • Environment Module – Number of screens – Size(s) of screens – Color or grayscale bit depth

Selecting Images • Definition of “image sets” • By attribute values – Specific attributes, e. g. Modality, Anatomy – Specific values, e. g, CT, Chest – Supports all VRs, coded sequences, private elements and multi-frame functional groups • By time – Relative time (today, yesterday, within last week) – Abstract priors (last, oldest, pre-operative, etc. )

Successful Selection • All hanging protocols depend on consistent and reliable (and standard) information being present in the images • DICOM Hanging Protocols don’t solve this integration problem • Ideally - modality inserts correct anatomy and procedure and reason and orientation codes, and uses standard technique descriptions • Worst case (typically? ) - modality protocol (or operator) inserts recognizable Series Description

Information for Hanging Anterior L Foot Right Modality: Mammography Anatomic Region: Breast Image Laterality: L View Code: Medio-Lateral Oblique Patient Orientation: AFR

Priors • Concept of the “current” study required • Protocol chooses priors based on – Relative time – Abstract temporal ranges (previous, last, etc. ) – Abstract coded descriptions (“pre-operative”) • Does NOT specify how to find them or get them • May have been pushed, may need a query • May be hard to find by abstract descriptions • Creative use of queries or out-of-band information

Mapping to Image Boxes • Image Sets are mapped to Image Boxes • Image Box types – – – Tiled (e. g. 3 x 4) Stack (single image paged manually) Cine (time-based play back) Processed (e. g. MPR, 3 D) Single (e. g. a place for a report or waveform) • Specify – Scrolling mode – Playback rate

Mapping to Image Boxes • Filtering – By attribute, or abstract, e. g. “category” of “image plane” “axial” • Sorting – By attribute, or abstract, e. g. “along axis” “increasing” • Orientation – E. g. rotate/flip until row left column posterior (LP) • Annotation – Patient demographics, technique and graphics on or off

Processing & Presentation • • • Reformatting, e. g. , MPR, 3 D, slab Thickness, interval View direction, e. g. , axial, sagittal, coronal Type, e. g. , MIP, surface, volume VOI Type (windowing), e. g. , brain, bone Pseudo-color type, e. g. , hot iron Invert grayscale True size Synchronized scrolling (by Display Set number) Navigation and localization

Display of Image Boxes • Entire display environment from 0, 0 to 1, 1 • Individual screens are not distinguished

Display of Image Boxes • Image Sets displayed in Image Boxes • Image Boxes rendered at relative location

Hanging Protocols Conclusion • • Interchangeable Vendor neutral Multi-modality Support selection of priors Full richness of current display modes Flexible Extensible • Non-trivial to implement and retrofit • Dependent on reliable image attributes