dual -energy x -ray ct with fast -kvp switch · 2009. 8. 3. · 2 dual -energy ct physics energy,...
TRANSCRIPT
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Dual-energy X-ray CT with Fast-kVp Switch
Jiang Hsieh, Naveen Chandra, David Langan, Mary-sue Kulpins, Xiaoye Wu, Paul Licato
GE Healthcare Technologies
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Dual-energy CT Physics
energy, keV
% in
tera
ctio
n
photoelectric
Compton
)()()( EfEfE ccpp ααρµ +=
)()()( EEEB
B
A
A
+
=
ρµβ
ρµβ
ρµ
• Concept proposed in the 70’s.
• Two x-ray / matter interaction: photoelectric & Compton.
• Mass attenuation coefficient is composed of the Photoelectric effect component, ααααp, and the Compton scatter component, ααααc.
• Also be expressed as a linear combination of the mass attenuation coefficient of two materials.
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Material Basis
0.1
1
10
100
1000
10000
100000
0 30 60 90 120 150
energy (keV)
atte
nu
atio
n c
oef
fici
ent
iodine
bone
soft tissue
• For CT, we can select water-iodine pair or soft-tissue-bone pair.
iodinewaterbone µµµ 18.088.0 +=
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Equivalent-density Images• Non-basis materials are mapped to both.
• Equivalent-density images are not in HU, but in g/cm3
80kVp
140kVp Iodine
Water
Non-linear mapping
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Monochromatic Imaging
80 kVp 140 kVp
A hybrid image optimizing image qualities of 80/140 kVp
Monochromatic
•More contrast•More noise
•Less contrast•Less noise
∫∫∫
+
= dsEdsEdsE B
B
A
A
)()()()(),( 000 rrr ψρµψ
ρµµ
• The material basis pair can be mapped to produce a synthesized monochromatic project.
• The reconstructed mono-images are in HU.
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Image Quality Optimization
40 keV 75 keV 140 keV
• Mass attenuation coefficient decreases with energy.• Low-contrast decreases with increased energy.• Optimal LCD and Noise performance at certain keV.
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Fast kV Switching
• Change kVp setting on a view by view basis.• High- and low-kV are toggled
every view• Little patient motion• Allow projection space
processing
• Require fast generator response.
• Require fast scintillator response.
140kV80kV
140kV
High Power Tube Fast Generator
Fast Scintillator High-speed DAS
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Detector Requirement
3 µµµµsXYZ
0.03µµµµsGemstone
Primary speedScintillator
0
0.25
0.5
0.75
1
0 5 10 15
Time (microsec)
Inte
nsity
Pulsed x-ray 30kvp, 0.5A, ~1ns pulse
• Key Performance Parameters of Gemstone Spectral Imaging• Primary speed and afterglow
• Stability
4.5cm
Stable in boiling water
high-precision molding
Gemstone
XYZ
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Projection Based Material DecompositionInterleaved High- andLow-kVp ProjectionsGSI Data Acquisition
split
Low kVp Projections
High kVp Projections
....)()()()()()()()()( 12
12
1111 +++++= iPiPiPiPiPiiPiiP highlowhighlowhighlow εδχβα
....)()()()()()()()()( 22
22
2222 +++++= iPiPiPiPiPiiPiiP highlowhighlowhighlow εδχβα
iodine
water
Attenuation-to-material density transformation
Iodine Projections Water Projections
140kVp QC Image
Image reconstruction
MD Iodine MD Water
Image Reconstruction
70 keV
Monochromatic Generation
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Beam Hardening Effect on Lesion ROI ValuesSingle Energy Imaging Not Consistently Accurate
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80 kVp Source Image Spectral 80keV image
Gemstone Spectral Imaging’s ability to reduce beam hardening artifact due to dense bone in the posterior fossa is demonstrated in the Spectral image.
Beam hardening reduction
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Low Density, Hypo-Enhancing Hepatic Masses
MD Iodine MD Water140 kVp
Kno
wn
Mal
igna
nt (
ME
T)
Kno
wn
Ben
ign
(Cys
t)
Hypo-Enhanced (with structure)
Close to Normal Liver
Hypo-Enhanced Black like Background
Mayo Clinic: Dr. Amy Hara, MD
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Linear Discriminate Analysis
Normal Liver (Enhanced by Iodine)
(Un-enhanced)
• Tissue is Characterized by Combining Water and Iodine Basis Density• Require accurate density measurement
LDA
Proj
ectio
n Li
ne
(Enhanced)
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original
Renal Cyst with Calcification
Images Courtesy of Dr. Amy Hara, Mayo Clinic, Scottsdale, AZ
Mayo Clinic: Dr. Amy Hara, MD
MD Water MD Iodine
cyst
calcification
• Enhanced lesion indicates potential malignancy. • Calcification appearance: bright on water density image.
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Kidney Stone Identification
Low kVp High kVp 75 keV
Kidney stone can be easily identified in the water-density image.
Mayo Clinic: Dr. Amy Hara, MD
MD IodineMD Water
kidney stone
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Kidney Stone Experiment
• Kidney stones placed inside. potato phantom
• Potential differentiation with GSI
• Data-base to set up
• Similar approaches to other applications such as cardiac
Ca Oxolate
Brushite
Cystine
Uric acidPotato
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Dynamic Heart Phantom…Pavlicek, Mayo Clinic
Fast Switching Dual KVP Cardiac
Recent Research: Cardiac Spectral Imaging*• Cardiac motion phantom study
• Delineation of different material in the moving vessels• No motion artifacts
• Applications• Re-stenosis• Complex calcification
*Technology-in-development 18
regular scout soft-tissue scout bone scout
Recent Research: Spectral Projection Imaging*• Separation of bone and soft-tissue• No mis-registration due to motion• Same time and orientation
Fast-kV Acquisition
*Technology-in-development
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Conclusion
• Gemstone spectral imaging provides an advanced platform to move CT beyond the pure anatomical modality.
• Provides additional information for aiding in tumor characterization, material differentiation,
• Artifact reduction
• Current research on GSI for cardiac imaging and super low-dose spectral projection imaging.
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