Dual Energy CT - Technology and Scan Modes Energy CT - Technology and... · Dual Energy CT (DECT)...
Transcript of Dual Energy CT - Technology and Scan Modes Energy CT - Technology and... · Dual Energy CT (DECT)...
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
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
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
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
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
• …
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)
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)
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.
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.
80 kV / 140 kV80 kV / 140 kV
80 kV / 140 kV + Prefilter80 kV / 140 kV + Prefilter
100 kV / 140 kV + Prefilter100 kV / 140 kV + Prefilter
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
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)
Consistent RawdataConsistent Rawdata
• two subsequent circle scans + no object motion
• special detectors (sandwich, energy resolving)
140 kV 80 kV
Almost Consistent RawdataAlmost Consistent Rawdata
• dual source circle scan(source misalignment)
• tube voltage switching
140 kV
80 kV
Inconsistent RawdataInconsistent Rawdata
• spiral scans(subsequent or dual source)
• two orthogonal circular source trajectories
140 kV
80 kV
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.
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
SimulationSimulation
• Forbild head phantom– inconsistent rays
(two orthogonal circles)
– 80 kV and 140 kV
– 3 iterations
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
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
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
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