An Brief Introduction to 4D CT Scanning

An Brief Introduction to 4D CT Scanning

Outline
An Brief Introduction to
4D CT Scanning
Problems with free breathing 3D scanning
What is 4D CT? How does it work?
Steve B. Jiang, Ph.D.
Dept of Radiation Oncology
Univ of California San Diego
Acknowledgements
Paul Keall, George Chen,
Dan Low, Gig Mageras,
Ken Foster
2
Three Types of Motion Artifacts
CT Artifacts in Free Breathing 3D Scan
If CT scanning speed << tumor motion speed,
→ smeared tumor image
If CT scanning speed >> tumor motion speed,
→ tumor position and shape captured at an
arbitrary breathing phase
If CT scanning speed ~ tumor motion speed,
→ tumor position and shape heavily distorted
Tumor
Helical light breathing scan
4DCT – 1 phase
Courtesy of Eike Rietzel and George T.Y. Chen
3
4
1
Interplay: Tumor Motion and Couch Motion
Moving Objects during CT – A Phantom Study
Video courtesy of George T.Y. Chen
Courtesy of Kevin Beaudette and
George T.Y. Chen
Chen, Kung, Beaudette, Artifacts in computed tomography scanning of moving objects, Semin Radiat Oncol. 14(1):19-26, 2004.
5
6
Motion Induced Artifacts
Motion Artifacts
Respiratory organ motion can cause severe
geometrical distortion in free breathing CT
scanning
Distortions along the axis of motion could either
lengthen or shorten the target, kind of random
In addition to shape distortion, the center of the
imaged target can be displaced by as much as
the amplitude of the motion
Photo
Static
Moving / HS mode
Courtesy of George Chen
7
HQ
8
2
Considerations of Organ Motion in CT Sim
Breath-hold CT scan
Basic Idea of 4D CT Scan
Over-sampling images at every
Voluntary breath hold
position of interest along the
Active breathing control
patient’s long axis
Combine inhale and exhale GTVs to get ITV
Slow CT san
Each image is tagged with
breathing signals
4 seconds per slice in axial mode
Images are sorted
Gated CT scan
retrospectively based on the
images at only 1 phase, acquisition times 4-5x longer
corresponding breathing signals
Photo Courtesy of Gig Mageras
Many 3-D CT sets are obtained, each corresponding to a particular
breathing phase
4D CT scan
3D scans at multiple phases
Together, they constitute a 4-D CT set that covers the entire
breathing cycle
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10
Acquisition of 4D CT Images
Resorting 500-1500 CT Slices
Image acquisition can be performed in either
Ciné mode: repeated image acquisition at each couch
position, or
Helical mode: with small pitch
Breathing signals can be obtained using either
A monitor such as RPM, an abdominal belt, or
variation of the patient anterior surface in the CT
images
Courtesy of Eike Rietzel and
George T.Y. Chen
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12
3
4D Image Acquisition in Cine Mode
Sorting of 4D CT Images
X-ray Tube
Retrospective sorting can be done in either
Sinogram space (before reconstruction), or
Image space (after reconstruction)
Table location
00.0 cm
Images can be sorted using either
Breathing phase, or
Amplitude
Acq. Time
0:01
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
13
14
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
00.0 cm
Acq. Time
0:02
Table location
00.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:03
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
15
Courtesy of Ken Foster
16
4
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
00.0 cm
Acq. Time
0:04
Table location
00.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:05
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
Courtesy of Ken Foster
17
18
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
01.0 cm
Acq. Time
0:06
Table location
01.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:07
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
19
Courtesy of Ken Foster
20
5
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
01.0 cm
Acq. Time
0:08
Table location
01.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:09
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
Courtesy of Ken Foster
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22
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
01.0 cm
Acq. Time
0:10
Table location
01.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:11
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
23
Courtesy of Ken Foster
24
6
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
02.0 cm
Acq. Time
0:12
Table location
02.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:13
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
Courtesy of Ken Foster
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26
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
02.0 cm
Acq. Time
0:14
Table location
02.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:15
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
27
Courtesy of Ken Foster
28
7
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
02.0 cm
Acq. Time
0:16
Table location
02.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:17
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
Courtesy of Ken Foster
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30
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
03.0 cm
Acq. Time
0:18
Table location
03.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:19
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
31
Courtesy of Ken Foster
32
8
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
03.0 cm
Acq. Time
0:20
Table location
03.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:21
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
Courtesy of Ken Foster
33
34
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
03.0 cm
Acq. Time
0:22
Table location
03.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:23
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
35
Courtesy of Ken Foster
36
9
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
04.0 cm
Acq. Time
0:24
Table location
04.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:25
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
Courtesy of Ken Foster
37
38
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
04.0 cm
Acq. Time
0:26
Table location
04.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:27
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
39
Courtesy of Ken Foster
40
10
4D Image Acquisition in Cine Mode
4D Image Acquisition in Cine Mode
X-ray Tube
X-ray Tube
Table location
04.0 cm
Acq. Time
0:28
Table location
04.0 cm
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Acq. Time
0:29
4 x 2.5 mm Multi Slice
(10 mm total coverage)
Courtesy of Ken Foster
Courtesy of Ken Foster
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4D Image Acquisition in Cine Mode
Sorted Slices
• Respiratory tracking with Varian RPM
optical monitor
Breathing
Signal
X-ray on Signal
First couch position
Second couch position
Courtesy of Ken
Foster
Third couch position
Courtesy of Gig Mageras
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44
11
4DCT Scan of A Phantom
4DCT Scan of A Lung Tumor
Courtesy of Eike Rietzel and
George T.Y. Chen
Courtesy of Eike Rietzel and George T.Y. Chen
45
4DCT Scan of A Liver Tumor
46
Summary
Respiratory organ motion can cause severe
geometrical distortion in free breathing CT
scanning
Distortions along patient long axis could either
lengthen or shorten the target
The center of the imaged target can be displaced
by as much as the amplitude of the motion
4D CT has been developed to
reduce motion artifacts
give the tumor/organ motion information
Courtesy of Eike Rietzel and George T.Y. Chen
Patient 5618
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What kind of artifacts can be caused by respiratory
motion in free breathing helical CT scanning?
Answer: 5 – All of the above
6%
1.
Lengthen the target along the patient’s long axis
2%
2.
Shorten the target along the patient’s long axis
3.
Displace the target center along the patient’s long
axis by as much as the motion amplitude
4%
4.
None of the above
78%
5.
All of the above
10%
References
Chen G T, Kung J H and Beaudette K P 2004
Artifacts in computed tomography scanning of
moving objects
Semin Radiat Oncol 14(1): 19-26.
49
Answer: 5 – All of the above
4D CT scan can be used to:
2%
1. Reduce motion artifact
0%
2. Estimate motion range
1%
3. Reconstruct tumor motion trajectory
2%
4. Design ITV
96%
5. All of the above
50
References
Keall P 2004
4-dimensional computed tomography imaging and
treatment planning
Semin Radiat Oncol 14(1): 81-90.
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