Dual Energy Physik for linear accelerator.ppt

its all about dual ebergy physics stating double energy or two edge sword. physics means double the energy means doing what we know to give double and twice a output that we might expect about that

1. Copyright © Siemens AG 2007. All rights reserved.
syngoDual Energy
Physical Background

2. Page 2 CTM CASiemens AG
Data Acquisition with the SOMATOM Definition
tube voltages 140kV / 80kV
tube currents approx. 1:4
dose approx. 1:1
collimations: 64×0.6mm,
20×0.6mm, 14×1.2mm
CareDose / CareDose4D
protocols optimized for each
application
with or without contrast agent
3 images series from scanner:
80kV / 140kV / mixed
post processing on CTWP or
MMWP

3. Page 3 CTM CASiemens AG
The following slide illustrates the unique behaviour of iodine
contrast agent which doubles the HU-valuesfrom the 140kV
to the 80kVdataset.
Other structures inside the human body e.g. bones & metal
increase the HU-values but do not double the value.
Data Acquisition with the SOMATOM Definition

4. Page 4 CTM CASiemens AG
Data Acquisition with the SOMATOM Definition
140kV
Bone
450 HU Iodine
144 HU
80kV
Bone
670 HU Iodine
296 HU

5. Page 5 CTM CASiemens AG
The Dual Energy Spectrum
X-ray spectra of the Definition (80kV...140kV)
broad distributions; average energy increases with kV

6. Page 6 CTM CASiemens AG
X-ray Absorption of Typical Materials
similar absorption for low and
high energy (red & blue)
much stronger absorbtion for low
energy (red)
Patient
(Absorber)
Source

7. Page 7 CTM CASiemens AG
Spectral Behaviour and Atomic Number
Dual Energy Index: characterizes spectral behavior of materialHUxx
xx
DEI
2000
14080
14080



Oxygen
Iodine
Calcium
(x: HU-value)

8. Page 8 CTM CASiemens AG
Which Information is Accessible
X-ray absorption depends on the inner electron shells:
DECT is sensitive to atomic number and density
DECT is not sensitive to chemical binding
For the relevant photon energies there are only 2
dominant absorption processes; each absorption curve
alone is very similar for different atoms:
DECT provides all possible information (Triple Energy
makes no sense)
it is not possible to distinguish between more than 2
materials of arbitrary density

9. Page 9 CTM CASiemens AG
HU-Values of Typical Materials
Higher CT-value at 80kV: iodine, bone, metal ...
Higher CT-value at 140kV: fat, plastic, uric acid ...
(almost) same CT-value: water, soft tissue, blood ...
bright iodine dark fat
80kV 140kV100kV 120kV
iodine
bone
fat
plastic

10. Copyright © Siemens AG 2007. All rights reserved.
syngoDual Energy
Physical Background
Dual Energy Index

11. Page 11 CTM CASiemens AG
Dose Efficiency of Mixed Image
at same dose DE Mixed Imagehas better contrast/noisethan 120kV
for same noise 10% more dose (head), 30% more dose (body)
0 1
(noise/contrast
(mixed)) /
(noise/contrast
(120kV)
1
Dual Energy Composition = image weight (80kV image)
Iodine Contrast Agent
DE better than
120kV

12. Page 12 CTM CASiemens AG
Pre-Reconstruction / Post-Reconstruction
Analysis
Pre-Reconstruction:
decompose into 2 materials of
arbitrary density; reconstruct
material images
very sensitive to motion
artifacts
material images difficult to
interpret
remove beam hardening
insensitive to beam hardening
Post-Reconstruction:
reconstruct images at
80kV/140k; analyse images
sensitive to large beam
hardening
works well inside central ~90%
of object
does not require matching
projections

13. Page 13 CTM CASiemens AG
Post Reconstruction Analysis and 3 Material
Decomposition
ideal case: very high dose, round patient, fixed diameter
one material, fixed density
HU (140kV)
HU (80kV)
fat

14. Page 14 CTM CASiemens AG
Post Reconstruction Analysis and 3 Material
Decomposition
two materials of fixed density
most soft tissues look very similar (same atomic
abundances)
HU (140kV)
HU (80kV)
fat
soft tissue

15. Page 15 CTM CASiemens AG
Post Reconstruction Analysis and 3 Material
Decomposition
voxels that contain both materials are on straight line
good model for kidney, liver
HU (140kV)
HU (80kV)
fat
soft tissue

16. Page 16 CTM CASiemens AG
Post Reconstruction Analysis and 3 Material
Decomposition
if contrast agent is added to soft tissue, the CT-value
increases
HU (140kV)
HU (80kV)
fat
soft tissue
soft tissue and CA,
concentration 1
soft tissue and CA,
concentration 2

17. Page 17 CTM CASiemens AG
Post Reconstruction Analysis and 3 Material
Decomposition
each voxel is decomposed into contrast agent and body tissues
measured point is projected on line of body tissues
mathematically a linear equation is solved
HU (140kV)
HU (80kV)
fat
soft tissue
soft tissue, fat and
CA
Body Tissue only
(Virtual Non-
Contrast)
Contrast agent
only

18. Page 18 CTM CASiemens AG
Cross scatter
0 100 200 300 400 500 600 700
channel
Signal
Cross scatter correction
Cross Scatter is charac-
terized by tangent rays

19. Page 19 CTM CASiemens AG
0 100 200 300 400 500 600 700
channel
Signal
Cross scatter
table
Scatter Correction:
Measure cross scatter
for every projection for
several phantoms.
Store distribution in
cross scatter tables
Cross scatter correction

20. Page 20 CTM CASiemens AG
0 100 200 300 400 500 600 700
channel
Signal
Cross scatter
table
Scatter Correction:
Compare patient tangent
rays with phantom data.
Use corresponding
stored cross scatter
distribution
Scatter corresponds
to object tangents
Cross scatter radiation does not depend on the
inner structure of the object
Cross scatter correction

21. Page 21 CTM CASiemens AG
Dual Source CT without
scatter correction
Dual Source CT with
Siemens scatter correction
Cross scatter radiation can be efficiently corrected
Cross scatter correction

22. Page 22 CTM CASiemens AG
Dual Energy Kernels
Specific Dual Energy Kernels were developed and have the prefix „D“
B30 D30

23. Page 23 CTM CASiemens AG
Dual Energy Kernels
Dual Energy kernels have less overshootcompared to usual body
kernels
B30 D30

24. Page 24 CTM CASiemens AG
Dual Energy Protocols: Properties
kV:A:140kV; B: 80kV best dose efficiency
mAs:ratio 1:4 good dose efficiency; low artifacts from cross-
scattering
Pitch:< 0.9 (1.2 for 14×1.2mm) low artifacts from cross-
scattering
reduced collimation:14×1.2mm instead of 24×1.2mm 
reduce artifacts from cross-scattering

25. Page 25 CTM CASiemens AG
Dual Energy Protocols: Properties
DE composition:weight of 80kV image is ≤0.3 (body) and ≥0.3
(head) optimum noise for typical patient
Dose increase for same image noise:10% (head), 30% (body),
larger for large patients ...
Contrast / noise ratio at same dose betterthan for 120kV!
CareDose4D available

26. Page 26 CTM CASiemens AG
Dual Energy Protocols: DEcomposition
default: 0.3 (head and body)
best noise performance:
head, extremities: 0.4...0.5
body (less than 30cm): 0.4
body (more than 30cm): <0.3
best contrast/noise ratio:
head & body: 0.6
same iodine contrast as at 120kV:
head: 0.25
body: 0.1
Best setting depends on patient diameter and ratio of tube
currents

27. Page 27 CTM CASiemens AG
Dual Energy Protocols: DEcomposition
default: 0.3 (head and body)
best noise performance:
head, extremities: 0.4...0.5
body (less than 30cm): 0.4
body (more than 30cm): <0.3
best contrast/noise ratio:
head & body: 0.6
same iodine contrast as at 120kV:
head: 0.25
body: 0.1
Best setting depends on patient diameter and ratio of tube
currents

28. Page 28 CTM CASiemens AG
Decomposition-Example
iodine vs. variable fat content / liquids
kidney tumors
renal stones in contrast scans
diagnostic image DE decomposition
Klinikum Großhadern

29. Page 29 CTM CASiemens AG
Decomposition-Example
virtual non-contrast contrast only
Klinikum Großhadern

30. Page 30 CTM CASiemens AG
Importance of Filtering (Correlations)
Original images:
noise is completely
uncorrelated
information is correlated (e.g.
calcium is dense in both
images)
After Material-Decomposition:
coordinate transform leads to
large anti-correlated errors
sum of both images has again
low error
80 kV
140 kV
iodine
VNC
iodine
VNC
compare: Kalender, Klotz, Kostaridou; IEEE Transactions on Medical Imaging, Vol. 7, No. 3, Sep 1988, 218-224
need low-pass / non-linear filter

31. Page 31 CTM CASiemens AG
soft tissue, blood,
red marrow
various concentrations of
contrast agent
ideal bone
HU (140kV)
HU (80kV)
A
no bone at <130HU,only bone at >1000HU
Dual Energy: iodine and bone separated by straight line
yellow marrow can shift bone above pink line more difficult
ONLY
BONE
NO
BONE
DE: BONE
DE: IODINE
Derived Application: Bone Removal

32. Page 32 CTM CASiemens AG
Head/Carotids: 140/80 kV mit 50:210 eff. mAs; 64x0.6mm
Liver:140/80 kV mit 95:400 eff. mAs; 12x1.6mm
Ankle: 140/80 kV mit 45/190 eff. mAs; 64x0.6mm
Headline
Direct Dual Energy subtraction of bone
even in complicated anatomical regions
Courtesy of University Hospital of Munich -Grosshadern / Munich, Germany
SOMATOM
Definition
World’s first DSCT
Spatial Res. 0.33 mm
Rotation 0.33 sec
140/80 kV
50/210 effective mAs
Spiral Dual Energy
CM Ultravist® by
Bayer Schering
Pharma AG

33. Page 33 CTM CASiemens AG
Image
Direct Dual Energy subtraction of bone
Carotid artery CTA stenosis left
SOMATOM
Definition
World’s first DSCT
Spatial Res. 0.33 mm
Rotation 0.33 sec
Scan time 8 s
Scan length 278 mm
140/80 kV
51/186 effective mAs
Spiral Dual Energy
Courtesy of Röntgendiagn.Zentralinstitut Landeskrankenhaus Klagenfurt / Klagenfurt, Austria

34. Page 34 CTM CASiemens AG
Courtesy of NYU Medical Center / New York, USA
Direct Dual Energy subtraction of bone
speeds up your workflow
SOMATOM
Definition
World’s first DSCT
Spatial Res. 0.33 mm
12 sec for 410 mm
Rotation 0.5 sec
140/80 kV
66/190 effective mAs
Spiral Dual Energy

35. Page 35 CTM CASiemens AG
Direct Dual Energy Plaque Display
Differentiation between hard plaques and contrast media
SOMATOM
Definition
World’s first DSCT
Spatial Res. 0.33 mm
26 sec for 1185 mm
Rotation 0.33 sec
140/80 kV
70/195 effective mAs
Spiral Dual Energy
Courtesy of University Hospital of Munich -Grosshadern / Munich, Germany

36. Page 36 CTM CASiemens AG
Siemens Computed Tomography.
Always Thinking Ahead.
For internal use only / Copyright © Siemens AG 2006. All rights reserved.