dual energy ct - technology and scan modes energy ct - technology and... · dual energy ct (dect)...
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Dual Energy CT (DECT) Dual Energy CT (DECT)
––
Technology Approaches and Technology Approaches and
Scan ModesScan Modes
MarcMarc KachelrieKachelrießß
Institute ofInstitute of MedicalMedical PhysicsPhysics (IMP) (IMP)
FriedrichFriedrich--AlexanderAlexander--UniversityUniversityErlangenErlangen--NNüürnbergrnberg
SCCT 2010
www.imp.uniwww.imp.uni--erlangen.deerlangen.de
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DisclosuresDisclosures
• I have the following financial relationships to disclose
– Consultant to CT Imaging GmbH
– Managing director of RayConStruct GmbH
– Grant supports from AiF, DFG, Intel, Siemens, Varian, Ziehm
• I will discuss the following off-label use in my presentation
– Exact Material Decomposition from Inconsistent Rays
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Standard CT image
Calcium density image Soft tissue density image
Kalender WA et al. Radiology 164:419-423, 1987
1980ies: The First Clinical DECT 1980ies: The First Clinical DECT Product ImplementationProduct Implementation
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DECT (ImageDECT (Image––based)based)
C/W=0/500 HU
2500 HU
1700 HU
E0
High energyspectrum 140 kV
Low energy spectrum 80 kV
80 keV 140 keV
wj
µ–images
Aluminum densityWater density 70 keV image
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DECT ApplicationsDECT Applications• Selective display of body substances with high atomic number:
Quantification of calcium, iron or iodine concentrations, bone mineral density etc.
• Separate displays of bones and soft tissue: Material-selective projection radiography of the chest, the skeleton etc., and image segmentation
• Distinction between iodine and calcium: Differentiation between contrast medium in blood and calcified plaque or bone for CT angiography
• Selective display of contrast media and other injected tracers:Concentration measurement of injected substances such as iodine or gadolinium
• Exact quantification of contrast media: Perfusion measurement
• CT numbers for hypothetical monoenergetic sources: Attenuation correction for PET/CT (at 511 keV) and for SPECT/CT
• Electron density: Planning of radiation therapy with protons, electrons or high-energy x-rays
• …
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Dual Energy whole body CTA: 100/140 Sn kV @ 0.6mm
Courtesy of Friedrich-Alexander University Erlangen-Nuremberg - Institute of Medical Physics / Erlangen, Germany
Single DECT
Scan
DE bone removal
Virtual non-contrastand Iodine image
Examples(Slide Courtesy of Siemens Healthcare)
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Technology ApproachesTechnology Approaches• Multiple scans at different spectra
• Dual source CT
• Fast tube voltage switching
• Slow tube voltage modulation
• Dual layer detectors (sandwich detectors)
• Split detector (different prefiltration)
• Photon counting detectors (two or more energy bins)
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DemandsDemands
• Simultaneous acquisition to avoid motion artifacts
• Independent tube current curves for both spectra– Select tube currents
– Select anatomy-dependent tube current curves1
• Free and application-dependent choice of spectra– Select prefiltration
– Select tube voltages
• Achieve good angular sampling
• Avoid scatter and cone-beam artifacts
• Acquire consistent rays– Each ray should be measured twice
– or reconstruction should correctly handle inconsistencies2
1 Stenner, Kachelrieß. Dual energy exposure control (DEEC) for computed tomography. Med. Phys. 35(11):5054-5060, November 2008. 2 Maaß, Meyer, Kachelrieß. Exact dual energy material decomposition from inconsistent rays (MDIR). Med. Phys 37:under consideration, 2010.
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U0= 120 kV, U1= 80 kV, U2= 140 kV, (C=0 HU / W=200 HU)
Optimal TubeOptimal Tube CurrentCurrent ModulationModulation
Stenner, Kachelrieß. Dual energy exposure control (DEEC) for computed tomography. Med. Phys. 35(11):5054-5060, November 2008.
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80 kV / 140 kV80 kV / 140 kV
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80 kV / 140 kV + Prefilter80 kV / 140 kV + Prefilter
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100 kV / 140 kV + Prefilter100 kV / 140 kV + Prefilter
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ImageImage––based DECTbased DECT
C/W=0/500 HU
2500 HU
1700 HU
µ–images
Aluminum densityWater density 70 keV image
E0
High energyspectrum 140 kV
Low energy spectrum 80 kV
80 keV 140 keV
wj
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Aluminum densityWater density
RawdataRawdata––based DECTbased DECT
70 keV image
E0
High energyspectrum 140 kV
Low energy spectrum 80 kV
80 keV 140 keV
wjq1
q2
pAl =DAl(q1,q2)
pH2O=DH2O(q1,q2)
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Consistent RawdataConsistent Rawdata
• two subsequent circle scans + no object motion
• special detectors (sandwich, energy resolving)
140 kV 80 kV
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Almost Consistent RawdataAlmost Consistent Rawdata
• dual source circle scan(source misalignment)
• tube voltage switching
140 kV
80 kV
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Inconsistent RawdataInconsistent Rawdata
• spiral scans(subsequent or dual source)
• two orthogonal circular source trajectories
140 kV
80 kV
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MDIR MethodMDIR MethodMaterial Decomposition with Inconsistent RaysMaterial Decomposition with Inconsistent Rays
Init image–based
Estimate error
New estimate
� conventional image–based DECT
� use current material images toestimate the error that would appearif this was the true object
� correct for that error
� repeat with a more accurate material image estimation
Maaß, Meyer, Kachelrieß. Exact dual energy material decomposition from inconsistent rays (MDIR). Med. Phys. 37:under consideration, 2010.
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start image
current error estimate
measurementsimulation
current imageestimate
f (k+1) = BP(q) + f (k) – BP(FP(f (k)))
MDIR Update Formula MDIR Update Formula –– First IterationFirst Iteration
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SimulationSimulation
• Forbild head phantom– inconsistent rays
(two orthogonal circles)
– 80 kV and 140 kV
– 3 iterations
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MDIR ResultsMDIR Results
70 k
eV
µ–
ima
ge
(C/W
=50
/50 H
U)
Bo
ne
de
nsit
y(C
/W=
0%
/10
%)
Wa
ter
den
sit
y(C
/W=
10
5%
/10
%)
Phantom Image–based MDIR
MDIR –Phantom
MDIR –Image–based
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Clinical Phantom MeasurementClinical Phantom Measurement
– Siemens Somatom Definition Flash DSCT scanner
– 20 cm diameter PE disc with HA400 inserts
– 80 kV and 140 kV
– 1 iteration
HA400
80 kV 140 kV
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Measurement ResultsMeasurement Results
Bone material density(C/W=100%/10%)
Soft material density(C/W=100%/10%)
Bone material density(C/W=0%/10%)
70 keV µ–image (C/W=0/50 HU)
Imag
e-b
ased
MD
IR
Somatom Definition Flash operating at 80 kV and 140 kVSiemens Healthcare, Forchheim, Germany
y
x
140 kV
80 kV
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Thank You!
Please also visit:
Low-Dose Phase-Correlated Micro-CT of the Mouse Heart, breakout room 4, Saturday morning, 11:00-11:15
Single and Dual Source Temporal Resolution Improvement, poster session XII, Saturday afternoon, 13:00-13:45
The Near Future in Cardiac CT Image Reconstruction, main room, Sunday morning, 10:30-10:45
Please also visit:
Low-Dose Phase-Correlated Micro-CT of the Mouse Heart, breakout room 4, Saturday morning, 11:00-11:15
Single and Dual Source Temporal Resolution Improvement, poster session XII, Saturday afternoon, 13:00-13:45
The Near Future in Cardiac CT Image Reconstruction, main room, Sunday morning, 10:30-10:45