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Dual Energy Imagingwith Dual Source CT Systems
Rainer Raupach, PhDSiemens Healthcare
Dual Energy Radiography
Armato SG III. Experimental Lung Research. 2004;30 (suppl 1):72-77.
Radiograph Tissue imageBone image
2 energies 2 materials
kV Switching with SOMATOM DRH – in the 80s
� Calculation of material selective images: � Calcium and soft tissue
W. Kalender: Vertebral Bone Mineral Analysis, Radiology 164:419-423 (1987)
Rapid kVp switching Standard image
Calcium image
Low kVp Soft tissue image
Basis material
decomposition
High kVp
Attenuation profiles
Principle of Dual Energy CT
Tube 2
Tube 1
Mean Energy:
56 kV 76 kV
� Data acquisition with different X-ray spectra: 80 kV / 140 kV
� Different mean energies of the X-ray quanta
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Principle of Dual Energy CT
� Many materials show different attenuation at different mean energies
� Reason: different attenuation mechanisms (Compton vs photo effect)
1.0E-01
1.0E+00
1.0E+01
1.0E+02
10 30 50 70 90 110 130 150Energy / keV
Att
enu
atio
n
IodineBone
56 kV 76 kV
Large increase
Small increase
SOMATOM DefinitionThe World’s First Dual Source CT
Faster than Every Beating Heart
� gated mode / same kV� high temporal resolution (80ms)� Cardiac imaging
One-Stop Diagnosis in Acute Care
� non gated mode / same kV� low temporal resolution� Obese patients, low kV scanning
Beyond Visualization with Dual Energy
� different kV (gated and non-gated)
Spectra of Dual Energy Applications
Direct Angio Lung PBV Virtual Unenhanced Lung Vessels
Hardplaque Display Heart PBV Calculi Characterization Brain Hemorrhage
Musculoskeletal Gout
*510(k) approved
Lung Nodules* Xenon*
Spectra of Dual Energy Applications
� Basic application: Enhanced viewing, contrast optimization
� Contrast enhanced studies: Iodine has much higher contrast at 80 kV
140 kV 80 kV
� Non-linear, attenuation-dependent blending of the imagescombines benefits of 80 kV (high contrast) and mixed data (low noise)
Blending
Courtesy of CIC Mayo Clinic Rochester, MN, USA
“Contrast Enhanced Viewing” using Dual Energy Information in Addition to Simple Image Mixing
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� Modified 2-material decomposition: Separation of two materials���� Assume mixture of blood + iodine (unknown density)
and bone marrow + bone (unknown density)
-100-100 0 100 200 300 400 500 600
HU at 140 kV
HU
at
80 k
V
0
100
200
300
400
500
600
Blood+iodine
Marrow+bone
BloodMarrow
Separation line
Softtissue
Iodine pixels
Bone pixels
syngo Dual Energy Direct subtraction of bone
140kV
Bone400 HU Iodine
250 HU
80kV
Bone550 HU Iodine
425 HU
� Modified 2-material decomposition: Separation of bone and Iodine
� Automatic bone removal without user interaction���� Clinical benefits in complicated anatomical situations:
� Base of the skull � Carotid arteries� Vertebral arteries� Peripheral runoffs
Courtesy of Prof. Pasovic,University Hospital of Krakow,
Poland
syngo Dual Energy Direct subtraction of bone
syngoDualEnergyDifferentiation between hard plaques and contrast agent
Courtesy of CCM Monaco, Monaco
� Modified 2-material decomposition: Characterization of kidney stones���� Urine + calcified stones / uric acid stones
Image Based Methods
HU at 140 kV
HU at 80 kV
high Z
low Z
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syngo Dual Energy MusculoskeletalVisualization of tendons
Courtesy of University Medical Center Grosshadern / Munich, Germany
SOMATOM Definition
World’s first DSCT
Spatial Res. 0.33 mmRotation 0.5 secScan time: 4 sScan length: 133 mm140/80 kVEff mAs 80/150
Spiral Dual Energy
syngo Dual Energy Visualization of Tendons: Tibialis posterior tendon rupture
Courtesy of University Medical Center Grosshadern / Munich, Germany
Gout: Application
Vancouver General Hospital, Canada
Applications of Dual Energy CT
� Three material decomposition: quantification of iodine – iodine image
� Removal of iodine from the image: virtual non-contrast image
-100
-90
Fat
0
0
60
65
Tissue
HU at 140 kV
HU
at
80 k
V
Iodine
Iodine content
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� Most promising application: 3-material decomposition� Calculation of a virtual non-contrast image, Iodine quantification
Image Based Methods
Mixed image 80kV+140kV Virtual unenhanced image Iodine overlay image
� Virtual non-contrast image and iodine image:� Characterization of liver / kidney / lung tumors� Solve ambiguity: low fat content or iodine-uptake� Quantify iodine-uptake in the tumor and at the tumor surface
� Differentiation benign - malignant� Monitoring of therapy response
Courtesy of University Hospital of Munich - Grosshadern / Munich, Germany
Applications of Dual Energy CT
Iodine imageVNC imageMixed image
+
� Quantification of iodine to visualize perfusion defects in the lung� Avoids registration problems of non-dual energy subtraction methods
Applications of Dual Energy CT
Courtesy of Prof. J and M Remy, Hopital Calmette, Lille, France
80/140kV Mixed Image Mixed image + iodine overlayIodine Image
Embolus
System Design
� Two X-ray tubes at 95°,each with 100 kW
� Two 128-slice detectors, each with 64x0.6mm collimationand z-flying focal spot
� SFOV A/B-detector: 50/33 cm
� 0.28 s gantry rotation time 75 ms temporal resolution
SOMATOM Definition FlashLatest Generation of Dual Energy CT
33 cm
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� Tissue characterization
DSCT Dual Energy
� Tissue characterization
� Improved DE contrast
� Dose-neutral compared to a single 120 kV scan
DE with Selective Photon Shield
SOMATOM Definition Flash Single dose Dual Energy
Conventional DE80 kV140 kVoverlap
DE with Selective Photon Shield
80 kV140 kV with SPSoverlap
Dual Energy Imaging with Tin Filtration‘Definition’ vs. ‘Definition Flash’: Improved DE Signal
Def
init
ion
Def
init
ion
Fla
sh
Mixed Images
DE
Imag
es
VNC Iodine
SD: -25%SD and dose: equal
Images acquired and processed in collaboration with CIC Mayo Clinic Rochester, USA
noise: 14.1 HU noise: 13.9 HU
iodine: 329.0 HU iodine: 330.0 HU
bone: 334.8 HU bone: 335.3 HU
120kV, 500mA 100/140Sn kV, 500mA
SOMATOM Definition FlashImpact of the Selective Photon Shield
Dose neutral DE: comparison of 120 kV and 100 kV/140 kV+0.4 mm Sn
ImageSOMATOM Definition Flash Dual Energy Whole Body CTA: 100/140Sn kV @ 0.6mm
Friedrich-Alexander University Erlangen-Nuremberg - Institute of Medical Physics / Erlangen, GermanyCourtesy of
Single DE CT Scan
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New Application Classes
Measurement of Lung Nodule enhancement
Measurement ofXenon Concentration
Mono-energetic imaging
courtesy of ASAN Medical Center, Seoul, Korea
courtesy of ASAN Medical Center, Seoul, Korea
courtesy of Klinikum Großhadern, Munich, Germany
40 keV
190 keV
Dual Energy CT
� Sequential acquisition at 80 kV and 140 kV with single source CT� Registration problems (heart/lung motion, varying contrast density)
� Fast kVp-switching during the scan with single source CT� Inadequate power at low kV� Unequal noise for low and high kV data
� Spectral sensitive „sandwich“ detectors� Inferior spectral separation
� Quantum counting� Paralysis at high flux rate� Spectral overlap by fluorescence and pile-up
Are there alternative approaches?
Dual Energy CTEvaluation of alternative approaches
Dose
Dual Energy CTEvaluation of alternative approaches
DE Performance@ equal dose
S. Kappler et al., Dual-energy performance of dual-kVp in comparison to dual-layer and quantum-counting CT system concepts, Proceedings of the SPIE Medical Imaging Conference, Volume 7258, pp. 725842 (2009)
15 20 25 30 35 40 450
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
phantom diameter [cm]
rela
tive
DE
C²
dual−source (tin filter)dual−source (std. filter)sequential kVpdual−layer (GOS)dual−layer (CsI)dual−layer (ZnSe)quantum counting (CZT)
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Thank you!