advanced imaging techniques - umm.uni-heidelberg.de · 14.11.2018 1 advanced imaging techniques...
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Advanced Imaging TechniquesDual Energy Computed Tomography
Prof. Dr. Frank G. Zöllner
(Today: Dominik Bauer)
Computer Assisted Clinical Medicine
Medical Faculty Mannheim
Heidelberg University
Theodor-Kutzer-Ufer 1-3
D-68167 Mannheim, Germany
www.ma.uni-heidelberg.de/inst/cbtm/ckm
Prof. Dr. Zöllner I Slide 2I 11/14/2018
Learning Goals
� introduction to CT imaging
� basic CT principles -> Physics of Imaging Techniques
� Goals:
1. How does the technique work?
2. What kind of images do we receive?
3. Where is this applied to?
� Slides of the lectures at
https://www.umm.uni-heidelberg.de/inst/cbtm/ckm/lehre/index.html
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Prof. Dr. Zöllner I Slide 3I 11/14/2018
References
� Johnson, “Dual-Energy CT: General Principles”, 2012.
� K. Cranley et al., “Catalogue of diagnostic x-ray spectra and other data”, 1998.
� Schlegel, Bille, “Medizinische Physik II”, 2002.
� McCollough et al., “Dual- and Multi-Energy CT: Principles, Technical Approaches, and Clinical Applications”, 2015.
� Hansmann et al., “Correlation analysis of dual-energy CT iodine maps with quantitative pulmonary perfusion MRI”, 2013.
� Goo and Goo, “Dual-Energy CT: New Horizon in Medical Imaging”, 2017.
� NISTIR 5632: “X-Ray Mass Attenuation Coefficients”, https://www.nist.gov/pml/x-ray-mass-attenuation-coefficients, July 2017.
� Slavic et al, Technology White Paper, GSI Xtream on RevolutionTM CT, 2017
� Ravi et al, Dual-Energy CT with Single- and Dual-Source Scanners: Current Applications in Evaluating the Genitourinary, RadioGraphics2012 32:2, 353-369
Prof. Dr. Zöllner I Slide 4I 11/14/2018
Motivation
80 kVp
140 kVp
Max. contrast
Dual-Energy CT
Iodine map
Dual-Energy CT
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Prof. Dr. Zöllner I Slide 5I 11/14/2018
X-Ray Properties: Attenuation
X-ray source Attenuation Projection
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Prof. Dr. Zöllner I Slide 6I 11/14/2018
X-Ray Properties: Attenuation
X-ray source Attenuation Projection
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Prof. Dr. Zöllner I Slide 7I 11/14/2018
Photon Attenuation Effects
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Photoelectric effect Compton effect
Prof. Dr. Zöllner I Slide 8I 11/14/2018
Photoelectric Effect
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Prof. Dr. Zöllner I Slide 9I 11/14/2018
Photon Attenuation Cross-Section
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Cortical Bone Iodine
Prof. Dr. Zöllner I Slide 10I 11/14/2018
Photon Attenuation Cross-Section
Cortical Bone Iodine
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Prof. Dr. Zöllner I Slide 11I 11/14/2018
Photon Attenuation Ambiguity
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Prof. Dr. Zöllner I Slide 12I 11/14/2018
Photon Attenuation Ambiguity
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Prof. Dr. Zöllner I Slide 13I 11/14/2018
Physics
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Prof. Dr. Zöllner I Slide 14I 11/14/2018
Dual-Energy CT
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Prof. Dr. Zöllner I Slide 15I 11/14/2018
DECT: Components
Detector:
�Spectral sensitivity
X-ray tube:
�Voltage
�Current
Image quality
Filter/Collimation:
�Hardening
�Filtering
bandwidth energy throughput
efficiency
Spectral separation
attenuation
Dose
E resolution
Prof. Dr. Zöllner I Slide 16I 11/14/2018
DECT: Implementations
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Prof. Dr. Zöllner I Slide 17I 11/14/2018
DECT: Sequential Scanning
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Prof. Dr. Zöllner I Slide 18I 11/14/2018
DECT: Rapid Voltage Switching
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Prof. Dr. Zöllner I Slide 19I 11/14/2018
DECT: Rapid Voltage Switching
Slavic et al, 2017
Prof. Dr. Zöllner I Slide 20I 11/14/2018
DECT: Rapid Voltage Switching
Slavic et al, 2017
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Prof. Dr. Zöllner I Slide 21I 11/14/2018
DECT: Dual Source
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Prof. Dr. Zöllner I Slide 22I 11/14/2018
Dual Source CT
courtesy: Siemens Medical Solution, Erlangen
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Prof. Dr. Zöllner I Slide 23I 11/14/2018
Comparison of Dual Energy CT Imaging Devices
Ravi et al, RadioGraphics 2012
Prof. Dr. Zöllner I Slide 24I 11/14/2018
Dual-Energy CT
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Prof. Dr. Zöllner I Slide 25I 11/14/2018
DECT: Image Processing
� Dual energy CT offers two image informations of the same material
� allows for material decomposition
� blended images
� virtual unenhanced images
� monocromatic images
� Processing of DE images in
� projection space
� image space
Prof. Dr. Zöllner I Slide 26I 11/14/2018
DECT: Image Processing in Projection Space
� conventional X-ray source have a broad energy spectrum
� separate the attenuation coefficient into the contributions
� from photoelectric effect and Compton scattering
� can be approximately modeled using
� a material’s effective atomic number ( Zeff)
� effective mass density (reff )
� knowledge of the X-ray energy spectra ( E )
� Alternative: attenuation coefficient, @A , can be expressed with sufficient
accuracy as a linear combination of the photoelectric and Compton
attenuation coefficients
B C � � DEF)1D�GH9 C ( @
A IDJGKHI C
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Prof. Dr. Zöllner I Slide 27I 11/14/2018
DECT: Image Processing in Projection Space
� DE signal can be written
with L9 � ��MH9 DCG and LI � ��MHI DCG represent the attenuation
density line integrals for the two basis materials
Prof. Dr. Zöllner I Slide 28I 11/14/2018
DECT: Image Based Processing
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Prof. Dr. Zöllner I Slide 29I 11/14/2018
DECT: Image Based Processing
� simplest way to process dual-energy data
� Perform a weighted subtraction or addition for the separately
reconstructed images at different beam energies (i.e., image
blending)
� low-voltage images (typically 80 kV) are multiplied by a weighting
factor and subtracted from or added to the high-voltage images (140
kV) to obtain material-specific information
Prof. Dr. Zöllner I Slide 30I 11/14/2018
DECT: Image Based Processing
� simplest way to process dual-energy data
� Perform a weighted subtraction or addition for the separately
reconstructed images at different beam energies (i.e., image
blending)
� low-voltage images (typically 80 kV) are multiplied by a weighting
factor and subtracted from or added to the high-voltage images (140
kV) to obtain material-specific information
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Prof. Dr. Zöllner I Slide 31I 11/14/2018
DECT: Image based processing – Types of Images
� Blended Image
� nonmaterial-specific images generated from the dualenergy data
to provide images for the purpose of routine diagnostic
interpretation
� Material-Selective Image
� differentiation between different atomic elements and therefore
chemical compositions
� Energy-Selective Image
� a pseudo monoenergetic image created at any desired energy
Prof. Dr. Zöllner I Slide 32I 11/14/2018
Blended Image
� combining the low- and high energy images, mixed images utilize all
of the radiation doses delivered by the dual-energy scan
� better image quality
� Generating the highest iodine contrast to noise ratio (CNR)
� two types of image blending methods
� linear and nonlinear
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Prof. Dr. Zöllner I Slide 33I 11/14/2018
Blended Image
� Linear blending
with wL + wH = 1.
� Increasing the blending ratio more toward the 80 kV image
� Iodine contrast enhancement but more noise
� Increase towards high energy image
� higher CNR and less noise
� Optimal settings for best settings exist
Prof. Dr. Zöllner I Slide 34I 11/14/2018
Blended Image
� Non linear blending
� combine images by
various weighting
functions
� e.g. modified sigmoidal
blending
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Prof. Dr. Zöllner I Slide 35I 11/14/2018
Blended Image
Prof. Dr. Zöllner I Slide 36I 11/14/2018
Material Decomposition / material selective image
� DE CT offers decomposition into two materials
� total mass attenuation coefficient of an object containing two
constituent elements is the weighted summation of the two element’s
mass attenuation coefficients
� assume the dual-energy measurements are made with two
monochromatic X-ray beams of high energy EH and low energy EL
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Prof. Dr. Zöllner I Slide 37I 11/14/2018
DECT: Image Based Processing
� effective linear attenuation coefficients µeff can be obtained from the
dual-energy CT image data:
� perform chemical identification (i.e., material decomposition) based on
previous equations using the reconstructed dual-energy images
Prof. Dr. Zöllner I Slide 38I 11/14/2018
DECT: Two Material Decomposition
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Prof. Dr. Zöllner I Slide 39I 11/14/2018
DECT: Three “Material” Decomposition
� DE CT can quantify 2 mass fraction -> 2 independent measurements
� for 3 materials and 2 spectral measurements one need additional
condition
� assume sum of volumes of the 3 materials is equivalent to the mass of
ist mixture
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Prof. Dr. Zöllner I Slide 40I 11/14/2018
DECT: Three “Material” Decomposition
Iodine slope Virtually Un-enhanced
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Prof. Dr. Zöllner I Slide 41I 11/14/2018
Application - Angiogram Bone-Removal
Two material decomposition
+
Contrast material map
Prof. Dr. Zöllner I Slide 42I 11/14/2018
Application - Pulmonary Perfusion
Contrast Agent Map(Iodine based)
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Prof. Dr. Zöllner I Slide 43I 11/14/2018
Application - Gout Diagnosis
calcium pyrophosphate crystal
uric acid
Prof. Dr. Zöllner I Slide 44I 11/14/2018
Virtual noncontrast- enhanced Images
Axial CE DE scan, mixed images shows subcapsular menatoma (*)
and low attenuation lesions (arrow)
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Prof. Dr. Zöllner I Slide 45I 11/14/2018
Iodine overlay demonstrate idodine within one lesion
indicating a metastasis, the other a hematoma
Virtual noncontrast- enhanced Images
Prof. Dr. Zöllner I Slide 46I 11/14/2018
Atherosclerotic Plaque Removal
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Prof. Dr. Zöllner I Slide 47I 11/14/2018
Dual-Energy CT Summary
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Prof. Dr. Zöllner I Slide 48I 11/14/2018
Outlook/Honorable Mentions
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