Tăng cường ảnh chụp với hệ thống CT

Dual Energy Radiography

Dual Energy Imaging
with Dual Source CT Systems
Rainer Raupach, PhD
Siemens Healthcare

Radiograph

Bone image
2 energies

Tissue image

2 materials

Armato SG III. Experimental Lung Research. 2004;30 (suppl 1):72-77.

kV Switching with SOMATOM DRH – in the 80s
Calculation of material selective images:
Calcium and soft tissue

Principle of Dual Energy CT
Data acquisition with different X-ray spectra: 80 kV / 140 kV

Standard image

Rapid kVp switching

Mean Energy:
Calcium image

56 kV

76 kV

Basis material
decomposition

Low kVp

Tube 1
Soft tissue image

Tube 2

High kVp

Attenuation profiles

Different mean energies of the X-ray quanta

W. Kalender: Vertebral Bone Mineral Analysis, Radiology 164:419-423 (1987)

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SOMATOM Definition
The World’s First Dual Source CT

Principle of Dual Energy CT

Many materials show different attenuation at different mean energies

Faster than Every Beating Heart
1.0E+02

gated mode / same kV
high temporal resolution (80ms)
Cardiac imaging

Iodine
Bone

Attenuation

56 kV 76 kV
1.0E+01
Large increase

One-Stop Diagnosis in Acute Care
non gated mode / same kV
low temporal resolution
Obese patients, low kV scanning

1.0E+00
Small increase
1.0E-01
10

30

50

70
90
Energy / keV

110

130

Beyond Visualization with Dual Energy

150

different kV (gated and non-gated)

Reason: different attenuation mechanisms (Compton vs photo effect)

“Contrast Enhanced Viewing” using Dual Energy
Information in Addition to Simple Image Mixing

Spectra of Dual Energy Applications

Basic application: Enhanced viewing, contrast optimization
Contrast enhanced studies: Iodine has much higher contrast at 80 kV
Non-linear, attenuation-dependent blending of the images
combines benefits of 80 kV (high contrast) and mixed data (low noise)
Direct Angio

Lung PBV

Virtual Unenhanced

Lung Vessels

140 kV

Hardplaque Display

Heart PBV

Musculoskeletal

Gout

Calculi Characterization

Lung Nodules*
*510(k) approved

80 kV

Blending

Brain Hemorrhage

Xenon*
Courtesy of CIC Mayo Clinic Rochester, MN, USA

2

syngo Dual Energy
Direct subtraction of bone

syngo Dual Energy
Direct subtraction of bone
Modified 2-material decomposition: Separation of two materials
Assume mixture of blood + iodine (unknown density)
and bone marrow + bone (unknown density)
Separation line
600

Iodine pixels

Bone
550 HU

HU at 80 kV

500
400

Automatic bone removal without user interaction
Clinical benefits in complicated anatomical situations:
Base of the skull
Carotid arteries
Vertebral arteries
Peripheral runoffs

Bone pixels

Blood+iodine

80kV

Marrow+bone

300

Iodine
425 HU

Modified 2-material decomposition: Separation of bone and Iodine

200
100

Soft
tissue

0
-100
-100

Bone
400 HU

Blood
Marrow

Iodine
250 HU

140kV
0

100

200
300
HU at 140 kV

400

500

600

syngoDualEnergy
Differentiation between hard plaques and contrast agent

Courtesy of Prof. Pasovic,
University Hospital of Krakow,
Poland

Image Based Methods
Modified 2-material decomposition: Characterization of kidney stones
Urine + calcified stones / uric acid stones

HU at 80 kV

high Z

low Z

HU at 140 kV

Courtesy of CCM Monaco, Monaco

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syngo Dual Energy Musculoskeletal
Visualization of tendons

syngo Dual Energy
Visualization of Tendons: Tibialis posterior tendon rupture
SOMATOM
Definition
World’s first DSCT
Spatial Res. 0.33 mm
Rotation 0.5 sec
Scan time: 4 s
Scan length: 133 mm
140/80 kV
Eff mAs 80/150
Spiral Dual Energy

Courtesy of University Medical Center Grosshadern / Munich, Germany

Courtesy of University Medical Center Grosshadern / Munich, Germany

Applications of Dual Energy CT

Gout: Application

Three material decomposition: quantification of iodine – iodine image

HU at 80 kV

Iodine

Iodine content

65

Tissue

0

-100

Fat
-90

0

60

HU at 140 kV

Vancouver General Hospital, Canada

Removal of iodine from the image: virtual non-contrast image

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Image Based Methods

Applications of Dual Energy CT

Most promising application: 3-material decomposition
Calculation of a virtual non-contrast image, Iodine quantification

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
Mixed image

Mixed image 80kV+140kV

Virtual unenhanced image

VNC image

Iodine image

Iodine overlay image

+

Courtesy of University Hospital of Munich - Grosshadern / Munich, Germany

SOMATOM Definition Flash
Latest Generation of Dual Energy CT

Applications of Dual Energy CT
Quantification of iodine to visualize perfusion defects in the lung
Avoids registration problems of non-dual energy subtraction methods
80/140kV Mixed Image

Iodine Image

Mixed image + iodine overlay

System Design
Two X-ray tubes at 95°,
each with 100 kW

33 cm

Two 128-slice detectors,
each with 64x0.6mm collimation
and z-flying focal spot
Embolus

SFOV A/B-detector:
50/33 cm
0.28 s gantry rotation time
75 ms temporal resolution

Courtesy of Prof. J and M Remy, Hopital Calmette, Lille, France

5


Dual Energy Imaging with Tin Filtration
‘Definition’ vs. ‘Definition Flash’: Improved DE Signal

SOMATOM Definition Flash
Single dose Dual Energy

Mixed Images

80 kV
140 kV
overlap

VNC

Iodine

DE Images

Definition

Conventional DE

DSCT
Dual Energy
DE with
Selective
Photon Shield

80 kV
140 kV with SPS
overlap

Tissue characterization
Improved DE contrast
Dose-neutral compared to a
single 120 kV scan

Definition Flash

DE with Selective Photon Shield

SD and dose: equal

SD: -25%

Images acquired and processed in collaboration with CIC Mayo Clinic Rochester, USA

SOMATOM Definition Flash
Impact of the Selective Photon Shield

SOMATOM Definition Flash
Image
Dual
Energy Whole Body CTA: 100/140Sn kV @ 0.6mm

Dose neutral DE: comparison of 120 kV and 100 kV/140 kV+0.4 mm Sn
Single DE CT Scan

120kV, 500mA

100/140Sn kV, 500mA

noise: 14.1 HU

noise: 13.9 HU

iodine: 329.0 HU

iodine: 330.0 HU

bone: 334.8 HU

bone: 335.3 HU

Courtesy of Friedrich-Alexander University Erlangen-Nuremberg - Institute of Medical Physics / Erlangen, Germany

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Dual Energy CT

New Application Classes

Are there alternative approaches?
40 keV

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
Measurement of
Lung Nodule
enhancement
courtesy of ASAN Medical
Center, Seoul, Korea

Measurement of
Xenon Concentration

190 keV

Spectral sensitive „sandwich“ detectors
Inferior spectral separation

courtesy of ASAN Medical
Center, Seoul, Korea

Mono-energetic

imaging
courtesy of Klinikum Großhadern,
Munich, Germany

Dual Energy CT
Evaluation of alternative approaches

Quantum counting
Paralysis at high flux rate
Spectral overlap by fluorescence and pile-up

Dual Energy CT
Evaluation of alternative approaches

dual−source (tin filter)
dual−source (std. filter)
sequential kVp
dual−layer (GOS)
dual−layer (CsI)
dual−layer (ZnSe)
quantum counting (CZT)

1.6
1.4

DE Performance
@ equal dose

relative DEC²

1.2
1
0.8
0.6
0.4

Dose

0.2
0
15

20

25
30
35
phantom diameter [cm]

40

45

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)

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Thank you!

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