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Conflict of interest disclosure
Tetrahedron Beam Computed Tomography


Tiezhi Zhang, Ph.D.
William Beaumont Hospital
Royal Oak, Michigan
CBCT Image Quality
Problems of CBCT

Scatter
Detector performance
Approximate cone reconstruction
Data truncation

…



Helical CT
Tiezhi Zhang has financial interest in TetraImaging Inc.
This work is partially supported by NIH grant 1R21CA13033001A.
CBCT
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Scatter is the enemy of CBCT
Cone beam CT situation
Fan beam CT situation
Detector problem


collimator
collimator
Area detector
Narrow detector
Scattered photons are not detected

Lag effect (Image artifact)
Limited detector size (Data truncation)
DQE (Increased exposure)
Scattered photons are detected
Cone vs. tetrahedron geometry
TBCT and CBCT geometries
X-ray source
z
z
2D detector
Linear detector
Linear source
Point source
CBCT
TBCT
X-ray detector
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Advantages of TBCT
Tetrahedron Beam CT (TBCT) for IGRT and IGI
1.
2.
3.
4.
Scatter rejection.
Use high performance diagnostic CT detector.
Slim structure. More mobile and larger clearance.
Lower cost.
TBCT Image reconstruction
TBCT with multiple detectors
Z
Det
ecto
r ar
Det
ecto
ray
r ar
ray
#1
#2
Source array
Source array
z
Detector #1
Detector #2
Reduce source array length.
Reduce cone angle.
Transverse
Coronal
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Advantages of iterative reconstruction



Evaluation of cone reconstruction artifact
using a numerical Disk Phantom
Allows realistic noise, geometry models.
Noise suppression/dose reduction
Mitigation of cone artifact
24 degree cone angle.
FDK
SART
XVI’s maximum cone angle = 11.4 degree.
M Jiang G Wang / Journal of X-Ray Science and Technology 10 (2002) 77-86
Evaluation of cone reconstruction artifact using real
patient data
TBCT benchtop system
Multi-slot collimator
MPFEX tube
Fan Beam geometry
FDK reconstruction
Rotation stage
5 row CT detector
TBCT geometry
SART reconstruction
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Multi-Pixel Field Emission X-ray tube (MPFEX)
- XinRay systems, North Carolina
Tube output
3.5
3
cathode
gate
anode
Current (mA)
2.5
2
1.5
1
0.5
0
1500
1600
1700
1800
1900
Gate Voltage (V)
2000
2100
2200
75 CNT cathode in 4 mm array
We need 100 times higher current for TBCT.
Multi-slot beam collimation
In-house developed CT detector
Film measurements at different positions
Scintillator material CdWO4. 5 rows, pixel size 2.54 x 2.54 mm2, length 70 cm.
Collimator
Rotation center
Detector
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Focus spot size
Beam hardening correction
Detector width 1.27 cm
Focus spot size 2.0 x 0.9 mm2.
Beam penumbra at detector position
TBCT Image quality
Helical CT
Philips Brilliance
TBCT
Beaumont benchtop
Pig head TBCT images
CBCT
Elekta Synergy
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Image quality comparison
Multiple pixel thermionic x-ray tube for TBCT

Fan beam CT
TBCT benchtop
Thermionic cathodes can have extremely high
emission density and can be made very small too.
CBCT
Work in Progress: Open chamber tube
Conclusions


TBCT can produce improved image quality
compared with CBCT.
Clinical TBCT system needs a higher power
multiple pixel tube.
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Acknowledgements




Xiaochao Xu, Ph.D. Derek Schulze, William
Beaumont Research Institute.
Joshua Kim, B.S., Oakland University.
Philips Laganis, XinRay systems.
This work is partially supported by NIH grant
1R21CA130330-01A1 and DOD Prostate Cancer
Research Program W81XWH-07-0083.
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