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Dual Energy Imagingwith Dual Source CT Systems

Rainer Raupach, PhDSiemens Healthcare

rainer.raupach@siemens.com

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

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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!