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CT-Volumenrekonstruktion
mit dem
MUSCOT-Algorithmus
und
TCOT-Algorithmus
(MUltiSlice COnebeam Tomographie)
(True COnebeam Tomographie)
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Einzelschicht- Helical CT
r
Focus β
Axial
y
x
Saggital
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Coronal
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Conebeam- Geometrie
Kegelwinkel
Fächerwinkel
Röntgenstrahler
Kegelwinkel
Z- Richtung
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Outline
Step-and-shoot (non-helical) scan
fan-beam reconstruction
Cone-beam reconstruction (Feldkamp)
Helical scan
Review of single-slice and 4-slice CT
HFK (TCOT): Cone-beam
ASSR (AMPR & SMPR): Quasi cone-beam
HFI+ (MUSCOT): Fan-beam
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Cone-beam
geometry
Quasi cone-beam
geometry
Fan-beam
geometry
HFK
ASSR
HFI+
w
w
w
z
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MUSCOT- Rekonstruktion
Rotationsachse
(z- Achse)
Primärprojektionen
mit verschiedenen Kegelwinkel
Rekonstruktionsebenen
Schichtdicke
Filterprozess für z- Richtung
mit variabler Filterweite
(FW)
Sekundärprojektionsdaten
ohne Kegelwinkeleffekt
1.
2.
3.
4. Schicht
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MUSCOT- Rekonstruktion
1.
0
2.
3. Rot.
Pitch 4.5:1
(1.125:1)
1 2 3 4 Schicht
180
360
Zusätzliche Projektionen für
die gewichtete Interpolation
Rekonstruktionsebene
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MUSCOT- Rekonstruktion
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MUSCOT- Rekonstruktion
HP=2.5
Ergebnis:
Dosiseinsparung ≈ 30- 40%
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Problem
für Cone-beam
Helical
Problem
in cone-beam
helical scan
Scan
-Verstärkter Kegelwinkel
-Kleine Messintervalle in z-Richtung
-Tischgeschwindigkeiten (Bewegung)
Problem wird stärker
Z
8 x 1 mm
Z
16 x 1 mm
Z
8 x 2 mm
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HFK (TCOT)
Datenbeitrag zur Bildebene
Bildebene
HFI
>> w
HFK
(TCOT)
z
w
Gut im Zentrum
hp = 7
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Gut im
Zentrum und
am Bildrand
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Feldkamp Algorithmus
für Conebeam Geometry
Schichtprofil
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Feldkamp Algorithmus
für Conebeam Geometry
Schichtprofil
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Relative evaluation
[A > B > C]
Algorithm
HFK ASSR
Cone-angle problem
accurate partial
1. Artifact
A
B
2. Z resolution (SSP) @ center
B
C
@ off-center
A
B
3. Practical maximum helical pitch
A
A
4. Required computation power
C
B
5. Easy to implement
C
B
HFK
ASSR
HFI+
neglect
C
A
C
C
A
A
HFI+
Amount of error or
z resolution
z
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HFK (TCOT)
Accurate 3-D backprojection along x-ray path
Weighting data considering cone-angle and
view angle
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Kopf- Scans
Scanschichtdicke [mm]
10
9
8
7
6
5
4 4-Schicht- CT
(hp = 6)
3
2
1
0
5
10
15
8 x 4 mm
4 x 5 mm
8-Schicht- CT
(hp = 10)
8 x 3 mm
4 x 4 mm
16 x 2 mm
16-Schicht- CT
(hp = 20)
20 25
30
35 40 45 50
Tischgeschw. [mm/Rot.]
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Abdomen-Scans
Scanschichtdicke [mm]
10
9
8
7
6
5
4-Schicht- CT
4
(hp = 6)
3
2
1
0
5
10
15
8- Schicht- CT
(hp = 10)
4 x 5 mm
8 x 4 mm
4 x 4 mm
8 x 3 mm
16 x 2 mm
16- Schicht- CT
(hp = 20)
20 25
30
35 40 45 50
Tischgeschw. [mm/Rot.]
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Reference of algorithms
HFK: Helical Feldkamp w/ weighting function = TCOT (True cone-beam tomography)
Aradate H and Nambu K, Japanese Patent No. 2,825,352 (filed in 1990)
Taguchi K, U.S. Patent No. 5,825,842 (Filed in 1995)
ASSR (Advanced single-slice rebinning)
Machida Y, Japanese patent disclosure (KOKAI) H8-187240 (Filed in 1995)
Kachelriess M, Schaller S, Kalender WA, “Advanced single-slice rebinning in cone-beam spiral CT,” Med
Phys 2000; 27: 754-772
à AMPR (Adaptive multiple-plane reconstruction)
Schaller S, et al, “Novel approximate approach for high-quality image reconstruction in helical cone beam
CT at arbitrary pitch,” SPIE 2001; 4322: 113-127.
à SMPR (Segmented multiple-plane reconstruction)
Stierstorfer K, et al, “Segmented multiple plane reconstruction – A novel approximate reconstruction scheme
for multislice spiral CT,” The 6th international meeting of fully 3D image reconstruction in Radiology
and Nuclear Medicine 2001: 95-97.
Flohr TG, et al, “A new cone-beam spiral CT reconstruction approach for a 16-slice scanner with full dose
utilization at arbitrary pitch,” Radiology 2001; 221(P): 543.
HFI+ (Helical filter interpolation with “cross-over correction”)
Taguchi K and Aradate H, “Algorithm for image reconstruction in multi-slice helical CT”, Med Phys 1998;
25: 550-561.
Zmora I, Taguchi K, Silver MD, and Han KS, “Correction of a new type of artifact in helical multi-slice
CT,” Radiology, 1998, 209(P): 434
Hsieh, et al, “A generalized helical reconstruction algorithm for multi-slice CT,” Radiology 2001; 221(P):
217.
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Literatur
1. Fallbeispiele von P. Rogalla, R. Klingebiel
Charitè Berlin Campus Mitte
2. K. Taniguchi et al
Algorithm for image reconstruction in multi-slice spiral CT
Med. Phys. 25 (1998) 550-561
2. Y. Saito
Multislice X-Ray CT Scanner
Medical Review 66 (1999) 1-8
3. M.D. Silver et al
Field-of-view dependent helical pitch in multislice CT
Spie Medical Imaging 2001, paper 4320-103, 2001
4. Dosiskalkulationsprogramm „CT-Expo“
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Vergleich der 16 Schicht- Detektoren
32 mm
24 mm
1mm x 12
20 mm
1mm x 6
1.25mm * 16
0.5mm x 16
0.75mm x 16
1mm x 12
1mm x 6
GE
Siemens/Marconi
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32 mm 40 Elemente
Advanced V-Detektor
1mm x 12 Elemente
0.5mm x
16 Elemente
? Septendicke in µm- Technologie
? StreustrahlenenergieUnterdrückung
1mm x 12 Elemente
35,840 Element
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Combination of proven 0.5
mm technology and detector
system for 32-mm/16-row
acquisition
channel direction
32 mm
slice direction
1 mm x 12 rows
0.5 mm x 16 rows
1 mm x 12 rows
4-row multislice CT
16-row advanced multislice CT
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1mm x 12 row
0.5mm x 16 row
1.25mm x 16
Detector Comparison
1mm x 12 row
4 slice x 0.5/1/2/3/4/5/8mm
8 slice x 0.5/1/2/3/4mm
16 slice x 0.5/1/2mm
Competitor
4 slice x 1.25/2.5/3.75/5mm
8 slice x 1.25/2.5mm
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Adaptive Filterung in z- Richtung
MUSCOT kann die die Schichtbreite und das
Rauschen rekursiv verändern und optimieren.
Parameter : Filter Weite (FW) und Filter Form (FF).
Wt
Wt
z
Wt
z
FW
?
z
FW
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Weighting function in TCOT
(a) OS w
1.0
hp ≤ 8
(b)
NHS w
hp ≥ 9
(c) HS
hp ≈ max
Time reso. = T
0.5
0
π
2π
projection angle: β
1.0
Time reso.
= T/2
0.5
w
0
π
2π
projection angle: β
1.0
Time reso.
= T/2
0.5
0
π
2π
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projection angle: β
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