CT Imaging DICOM Working Group 21 Computed Tomography Rationale Multienergy CT MECT uses multiple energies from the XRay beam spectrum conventional CT uses a ID: 783955
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Slide1
Supplement 188:
Multi-energy CT Imaging
DICOM Working Group 21
Computed Tomography
Rationale
Multi-energy CT (MECT) uses multiple energies from the X-Ray beam spectrum (conventional CT uses a single (accumulated) X-Ray spectrum).This enables differentiation, quantification and classification of different types of tissues.Challenges:Existing CT and Enhanced CT IODs do not adequately describe MECT.MECT engineering mechanisms differ significantly across vendors (but fortunately the generated diagnostic images are mostly similar)Goals:Facilitate fast/easy
adoption of
MECT
across modalities and PACS/DisplaysRe-use/mirror existing CT/Enhanced CT IOD content for compatibility Capture essential MECT details in IOD (acquisition, reconstruction and processing)Profile usage of existing CT/Enhanced CT IOD attributes for MECT techniquesMinimize interpretation/measurement risks when legacy displays present MECT images
2
Slide3Virtual Mono-energetic Image (VMI)
Color Overlay ImageColor Blending Image
Effective Atomic Number (Z) Image
Electron Density Image
Color Map Image
Multi Energy Imaging
Material Quantification
Family
Material
Visualization
Family
Standard CT Image
Objective Image
Family
Material-Specific Image
Iodine Map;
Bone Density
Overview
Fractional Map Image
Value based Map
Image
Material-Modified Image
Gout crystals
Highlighted;
Partially-Suppressed
Material-Removed Image
Virt
.
Non-Contrast;
Virt
. Non-Ca;
CT IOD
Other IOD
Slide4X-Ray Source
Generate different energies:KVP SwitchingDetector
Filters
Other Parameters
Discriminate different energies:Multiple LayersPhoton CountingMulti-energy
CT Acquisition
Mechanisms
Mechanisms to separate at least two energies include:
Multiple Scans of the same area with different parameters
Switch KVP during the rotation
Multiple X-Ray Sources
One source with Multi-Layer Detector
One source with Photon Counting Detector
Scanned Object
Slide5Objective Images
Virtual MonochromaticEffective Atomic NumberElectron DensityDescribed in ME CT Characteristics Sequence
Data Acquisition
Decomposition to
Base ComponentsDescribed in ME CT Processing SequenceDescribed in
ME CT Acquisition Sequence
A1
A2
M1
M2
Mn
…
An
…
Generation of Diagnostic images
Datasets
Processing Steps
Slide6Material Images
Data Acquisition A1A2
Described in
ME CT
Processing SequenceDescribed in ME CT Acquisition SequenceDescribed in ME CT Characteristics SequenceMaterial Quantification FamilyM1
M2
Mn
Material Visualization
Family
Decomposition to
(and/or Classification of)
two or more Materials
…
An
…
Generation of Diagnostic images
Datasets
Processing Steps
Slide7Material Images
M1M2Material-Specific Image
May be ignored or not described
M1
M2
Mn
Conventional CT or VMI Image
Material Visualization Image
Remove
Suppress
Highlight
Recalculate
Mn
Fractional Map Image
Material-Removed Image
Examples:
:
Iodine Map
Bone (Ca) Density Map
Example
:
Virtual Non-Contrast or Virtual Non-Calcium : REMOVED
Example
:
Tendon Enhancement: HIGHLIGHTED
Slide8Material Maps Images
Material A = 0-15Material B = 10-20Material C = 18-50Contains 20% of material A
0.2
Fractional Map:
4
Value based Map:
20
0
10
15
Material A
B
C
D
Slide9“Visualization” Images:
Color OverlayThe blended image combines an overlay CT image highlighting a particular material (E.g. Iodine image, Effective Z image) with a monochromatic anatomical structure image. The new Multi-energy image format can be used as blending image together with a Standard CT image in the Blending Presentation States.
Blended Image
Structural Image
Overlay Image
Slide10CT IOD Structure
Multi-energy CT Acquisition attribute (YES/NO) added to CT Image ModuleMulti-energy CT Image Module (new, conditional):Multi-energy CT Acquisition Sequence (Type 1, 1 item)Multi-energy CT Characteristics Sequence (Type 1C, 1 item)Multi-energy CT Processing Sequence (Type 3, 1 item)Multi-energy CT Acquisition SequenceME X-Ray Source Sequence (1-n)ME X-Ray Detector Sequence (1-n)ME Path Sequence (2-n)CT Exposure MacroCT X-Ray Details MacroCT Acquisition Details Macro
CT Geometry
Macro
Multi-energy CT Characteristics MacroMonochromatic Energy Equivalent (for Virtual Monochromatic Image)Other image-specific attributesMulti-energy CT Processing Sequence (Type 3, 1 item)Decomposition Method, AlgorithmDecomposition Material Sequence (2-N items, one for each base material)Other decomposition attributes10
Slide11Organization Structure – Path Scheme
11CT IODCT Image ModuleME CT Acquisition
ME CT X-Ray Source Seq.
ME CT Detector Seq.
ME CT Characteristics
ME CT
Processing
ME CT Path Seq.
CT X-Ray Details Seq.
CT Exposure
CT Acquisition Details
CT Geometry
General Image Module
Real-World Value Mapping
Slide12Enhanced CT IOD Structure
Enhanced CT Image IOD Module:Multi-energy CT Acquisition attribute (YES/NO) – new attribute addedEnhanced Multi-energy CT Image Acquisition IOD Module (new, conditional):ME X-Ray Source SequenceME X-Ray Detector SequenceME Path SequenceEnhanced CT Image Functional Group Macros (added, conditional):Multi-energy CT ProcessingMulti-energy CT Characteristics12
Slide13New Image Types
Image Type (Value 4)Recommended Rescale
Type
Description
VMI
HU
a Virtual Monochromatic Image. Each pixel represents CT Hounsfield units and is analogous to a CT image created by a monochromatic (of a specific keV value) X-Ray beam.
MAT_SPECIFIC
HU, MGML
a Material-Specific Image.
Each real-world value mapped pixel value represents a property of a specific material such as attenuation, concentration or density.
MAT_REMOVED
HU, HU_MOD
a Material-Removed Image. Each pixel represents CT Hounsfield units however some pixel values may have been corrected for replacement of one material by another material. Image with one or more materials removed.
MAT_FRACTIONAL
PCT
a
Material-Fractional
Image. Each pixel represents a
fraction of
1 of a material.
EFF_ATOMIC_NUM
Z_EFF
an Effective Atomic Number Image. Each pixel represents Effective Atomic Number
ELECTRON_DENSITY
ED, EDW
an Electron Density Image. Each pixel represents a number of electrons per unit volume (units 1023 /ml) or a relative ED/
EDWater
ratio (N/
Nw
).
MAT_MODIFIED
HU_MOD
a Material-Modified Image. CT Image where pixel values have been modified to highlight a certain target material (either by partially suppressing the background or by enhancing the target material), or to partially suppress the target material.
MAT_VALUE_BASED
US
a
Value-Based Map
Image.
Each pixel represents a values indirectly describing identified material(s).
Slide14Examples for Rescale Type assignments
14Multi-energy Image FamilyRecommended Rescale Type
Image Type Value 4
Intercept
Slope
RWV First & Last Values mapped
RWV Intercept
RWV Slope
RWV LUT Label
RWV Measurement Units
Objective Image Family
Virtual Monoenergetic Image
HU
VMI
-1024
1
0/4095
-1024
1
VMI
hnsf’U
Effective AN (Z)
Image
10^-2 Z_EFF
EFF_ATOMIC_NUM
0
1
0/4000
0
0.01
EFF_ATOMIC_NUM
NewCode2-02
Electron Density Image
10^-2
ED
ELECTRON_DENSITY
0
1
0/4000
0
0.01
ELECTRON_DENSITY
10*23/ml
10^-3
EDW
ELECTRON_DENSITY
0
1
0/4000
0
0.001
ELECTRON_DENSITY
ratio
Material Quantification Family
Material-Specific Image
10^-2
MGML
MAT_SPECIFIC
(0) – (-10)
1
0/4000
-3
0.01
MAT_SPECIFIC
mg/cm3
HU
MAT_SPECIFIC
-1024
1
0/4095
-1024
1
MAT_SPECIFIC
hnsf’U
Material-Removed
Image
HU
MAT_REMOVED
-1024
1
0/4095
-1024
1
MAT_REMOVED
hnsf’U
HU_MOD
MAT_REMOVED
-1024
1
0/4095
-1024
1
MAT_REMOVED
NewCode2-03
Fractional Map Image
10^-1 %
MAT_FRACTIONAL
0
1
0/1000
0
0.1
MAT_FRACTIONAL
%
Value-based Map Image
US
MAT_VALUE_BASED
0
1
0/100
0
1
MAT_ VALUE_BASED
US
Slide15Contacts
Reinhard Ruf Chair WG-21 Siemens Healthineers reinhard.ruf@siemens.comShlomo Gotman Member WG-21 Philips Healthcare shlomo.gotman@philips.com