Dual -energy X -ray CT with Fast -kVp Switch · 2009. 8. 3. · 2 Dual -energy CT Physics energy,...

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1/ GE / 1 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 2 Dual-energy CT Physics energy, keV % interaction photoelectric Compton ) ( ) ( ) ( E f E f E c c p p α α ρ μ + = ) ( ) ( ) ( E E E B B A A + = ρ μ β ρ μ β ρ μ Concept proposed in the 70’s. Two x-ray / matter interaction: photoelectric & Compton. Mass attenuation coefficient is composed of the Photoelectric effect component, α p , and the Compton scatter component, α c . Also be expressed as a linear combination of the mass attenuation coefficient of two materials. 3 Material Basis 0.1 1 10 100 1000 10000 100000 0 30 60 90 120 150 energy (keV) attenuation coefficient iodine bone soft tissue For CT, we can select water-iodine pair or soft- tissue-bone pair. iodine water bone μ μ μ 18 . 0 88 . 0 + = 4 Equivalent-density Images Non-basis materials are mapped to both. Equivalent-density images are not in HU, but in g/cm 3 80kVp 140kVp Iodine Water Non-linear mapping

Transcript of Dual -energy X -ray CT with Fast -kVp Switch · 2009. 8. 3. · 2 Dual -energy CT Physics energy,...

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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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