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Information Signal ProcessingInformation Signal Processing
Joseph A. OJoseph A. O’’SullivanSullivan
Electronic Systems and Signals Research Laboratory
Center for Security TechnologiesDepartment of Electrical and Systems Engineering
Washington [email protected]
http://essrl.wustl.edu/~jaoSupported by: ONR, NSF, NIH, Boeing Foundation, DARPASpecial thanks to Naveen Singla
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CollaboratorsCollaborators
Jasenka BenacMichael D. DeVoreAndrew (Lichun) LiClayton MillerLee MontagninoRyan Murphy Natalia SchmidNaveen SinglaBrandon WestoverShenyu Yan
G. James BlaineRoger ChamberlainMark FranklinDaniel R. FuhrmannRonald S. IndeckChenyang LuPierre Moulin, UIUCMarcel MullerRobert PlessDavid G. PolitteChrysanthe PrezaAndrew Singer, UIUC Donald L. SnyderBruce R. WhitingJeffrey F. Williamson, VCULihao Xu
Faculty Current and Former Students
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OutlineOutline
• DSP ISP
- Data models, computational models,
algorithms
- Central role of information
• Graphical Data Models- X-ray CT imaging
- Iterative decoding
• Message Passing EM
Algorithms
• Applications Revisited
• Speculation on Trends• Conclusions
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Signal Processing
Information TheoryComputation and
Communication
FFTFFT
MultiresolutionMultiresolutionanalysisanalysis
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X(0)
X(1)
X(2)
X(3)
X(4)
X(5)
X(6)
X(7)
x(0)
x(4)
x(2)
x(6)
x(1)
x(5)
x(3)
x(7)
FFT
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Signal Processing
Information Theory
Numerical analysisNumerical analysis
Processors: parallel, Processors: parallel, ASIC, etc.ASIC, etc.
Systolic architecturesSystolic architectures
FFTWFFTW
Computation and
Communication
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Signal Processing
Information Theory
Numerical analysisNumerical analysis
Processors and Processors and architecturesarchitectures
FFT, FFTWFFT, FFTW
Transversal filtersTransversal filters
MRAMRA
Complexity theoryComplexity theory
Graphical modelsGraphical models
KalmanKalman filtersfilters
CompressionCompression
Computation and
Communication
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Computation and
Communication
Information Signal ProcessingInformation Signal Processing
Signal Processing
Information Theory
ComplexityComplexity--constrained processingconstrained processing
Signal processing on graphsSignal processing on graphs
Distributed signal processingDistributed signal processing
Distributed information theoryDistributed information theory
Distributed computation and Distributed computation and communicationcommunication
Optimal information extraction, Optimal information extraction, communication, computationcommunication, computation
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Distributed sensing,
communication, computation““The architecture for a The architecture for a
fully netted maritime forcefully netted maritime force””
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Wireless Sensor NetworksWireless Sensor Networks
http://www.greatduckisland.net/index.php
Great Duck Island Habitat
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OutlineOutline
• DSP ISP
- Data models, computational models,
algorithms
- Central role of information
• Graphical Data Models- X-ray CT imaging
- Iterative decoding
• Message Passing EM
Algorithms
• Applications Revisited
• Speculation on Trends• Conclusions
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Graphical Data ModelsGraphical Data Models
•• Model 1:Model 1: y = Hsy = Hs– y is n × 1, s is m × 1,
and H is n × m
– yj depends on sk if hjk 0
– Defines a graphical model
•• Model 2:Model 2:
– Neighborhood structure
– Bipartite graph model
•• Model 3:Model 3:– RVs on edges of graph
k
j
j
kj jksypp ))(,|()|( sy
k kj
kjk sxpp)(
)|()|( sx
j
jkj jkxypp ))(,|()|( xy
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Tomography
S
D
Nonrandom Graphs
Line integrals through patient
Quantization point spread function
weights on edges of graph
Helps organize computations
Siemens Somotom Emotion
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Computational ModelsComputational Models
System model accounts for:
• Information extraction
problem definition
• Compression of sensor data
• Network throughput
• Processor cycles per
instruction
• Size of processor local
memory
• Communication bandwidth
of each link
• etc.
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Computational ModelsComputational Models
• Local resources plus remote
• Communicate observation as well as classification- Human in the loop
- Remote contribution to classification when available
• Dynamic resource availability
• Sequence of partial classifications (an, n)
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Progress: Computational Graph Progress: Computational Graph Same as Data Model GraphSame as Data Model Graph
•• Message passing algorithmsMessage passing algorithms– Pearl’s belief propagation
– Iterative decoding
» Turbo-codes, parallel concatenated codes
» Low density parity check codes
» Repeat-accumulate codes, serial concatenated codes
– Iterative equalization and decoding
•• ExpectationExpectation--Maximization (EM) AlgorithmsMaximization (EM) Algorithms– Graphical models
– General problem
– Gaussian, Poisson (emission tomography, transmission tomography)
– Abstract examples on random graphs
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10011010101000
01010101010001
10100001010101
01100110010100
10010101001010
00101000101011
01001010100110
H Regular (3,6) n=14
Random Graphs
Comment: LDPC parity check matrix
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001010100000
100100000010
010001001000
000100010001
100000001100
001000100010
010001010000
000010000101
H Regular (2,3) n=12
Random Graphs
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10011010101000
01010101010001
10100001010101
10101010010100
10010101001010
00101000101101
01001001010110
H Irregular n=14
Random Graphs
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k
j
jk
jk
),(
),(
)1(
'
)1(
)(
'
)1(
stateg
statef
m
kjk
m
jk
m
jkj
m
jk
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Iterative Decoding Message PassingIterative Decoding Message Passing
kjk
m
jk
m
jk
\)('
)(
'
)1(
jkj
m
kjz
m
jk k
\)('
)1(
'
)1(
2tanh)1(
2tanh
Codeword Bit Nodes
zk
xj
Check Nodes
jk
jk
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Iterative Decoding Message PassingIterative Decoding Message Passing
-6
-5
-4
-3
-2
-1
0
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
SNR [dB]
Bit e
rro
r ra
te,
Lo
g B
ase
10
ISI-free
BIAWGN Capacity
[10000,5000] regular (3,6) matrix[10000,5000] regular (3,6) matrix
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OutlineOutline
• DSP ISP
- Data models, computational models,
algorithms
- Central role of information
• Graphical Data Models- X-ray CT imaging
- Iterative decoding
• Message Passing EM
Algorithms
• Applications Revisited
• Speculation on Trends• Conclusions
J. A. O’Sullivan. 11/21/2003Information Signal Processing
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ML Problem: xsxxys
dpp )|()|(lnmax
EM Algorithm: )|()|(
),|(ln),|(minmin
sxxy
syxsyx
s pp
EM AlgorithmEM Algorithm
sk
yj
Hidden Data
Incomplete Data
xjk
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VariationalVariational RepresentationsRepresentations
•• Convex Decomposition LemmaConvex Decomposition Lemma. Let f be convex. Then
• Special Case: f is ln
• Basis for EM; see also De Pierro, Lange, Fessler
i
ii
i i
ii
rii
rr
xfrxf
0,1
)()(1
i
ii
i i
ii
i
iq
q
1,0:
lnminln
P
P
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EM AlgorithmEM Algorithm
')|'()'|(
)|()|(),|(
)(
)()()1(
xsxxy
sxxysyx
dpp
ppm
mmm
xsxsyxss
dp, mmm )|(ln)|(argmax )()1()1(
Assume the factorizations:
k kj
kjk sxpp)(
)|()|( sx
j
jkj jkxypp ))(,|()|( xy
These computations become local and thus message passing
In general, these are global computations
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Message Passing EM AlgorithmMessage Passing EM Algorithm
)('
'
)('
)(
'''
'),('
'
)('
)(
'''
1(
)|())(',|(
)|())(',|(
),|(
jk
jk
jk
m
kjkjkj
kkjk
jk
jk
m
kjkjkj
(m)
jjk
)m
dxsxpjkxyp
dxsxpjkxyp
yx
KK
KK
K
K
s
jkkjk
m
jjk
m
s
m
k dxsxp,yxsk
)|(ln)|(argmax )()1()1(s
sk
yj
Input Data
Measured Data
xjk
)( jkx
ks
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GaussianGaussian--MAPMAP
)2
,0(~
),0(~
;
0 Iw
Is
wHsy
NN
PN
)(
)(
0
)1( ˆ
|)(|2|)(|
ˆkj
l
jk
l
k x
j
NkP
Ps
)('
)1(
'
)1()1( ˆ|)(|
1ˆˆ
jk
l
kj
l
k
l
jk syj
sx
sk
yj
Input Data
Measured Data
xjk
jkx
ks
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GaussianGaussian--MAPMAP
[10000,5000] regular (3,6) matrix[10000,5000] regular (3,6) matrix
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Emission TomographyEmission Tomography
y ~ Poisson(H )
: Mean of emitted photons
)(
)()(
)1( ˆ|)(|
ˆˆ
kj
m
j
m
km
k qk
)('
)(
'
)(
ˆˆ
jk
m
k
jm
j
yq
k
yj
Pixels
Measured Data
jq
kˆ
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Emission TomographyEmission Tomography
[10000,5000] regular (3,6) matrix[10000,5000] regular (3,6) matrix
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Emission TomographyEmission Tomography
[50000,1000] regular (3,150) matrix[50000,1000] regular (3,150) matrix
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Transmission TomographyTransmission Tomography
y ~ Poisson(I0exp(-H ))
: photon attenuation )(
)(
)()()1( ln1ˆˆ
kj
m
j
kj
j
m
k
m
kq
y
z
)(
)(
0
)( ˆexpjk
m
k
m
j Iq
k
yj
Pixels
Measured Data
jq
kˆ
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[10000,5000] regular (3,6) matrix[10000,5000] regular (3,6) matrix
Transmission TomographyTransmission Tomography
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Comments on DetailsComments on Details
•• Information geometry basisInformation geometry basis
•• Easily extended to arbitrary Easily extended to arbitrary HH
•• Low density Low density sparsesparse
•• Constraints in iterative decoding vs. forward Constraints in iterative decoding vs. forward modelmodel
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OutlineOutline
• DSP ISP
- Data models, computational models,
algorithms
- Central role of information
• Graphical Data Models- X-ray CT imaging
- Iterative decoding
• Message Passing EM
Algorithms
• Applications Revisited- Iterative decoding
- X-ray CT imaging
• Speculation on Trends• Conclusions
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Science and technologyScience and technologypotentially yield potentially yield
6 Tb/in6 Tb/in22
courtesy R. S. courtesy R. S. IndeckIndeck
Patterned Magnetic Media
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Advanced Recording MediaAdvanced Recording MediaBluBlu--Ray DiscRay Disc
Next-generation Optical Disc Video Recording Format
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2D Intersymbol Interference2D Intersymbol Interference
1111
11
11
11
1111
21
21
11211
kkkk
k
xxx
x
xxx
1111110
110
12
1111110
100100
kkkkkk
kkkkkk
k
kk
k
rrrr
rrrr
r
rrrr
rrrw(i,j)
25.05.0
5.01h
Includes
Guard Band
jijijijijiji wxxxxr ,1,11,,1,, 25.05.05.0
Singla et al., “Iterative decoding and equalization for 2-D recording channels,” IEEE Trans.
Magn., Sept. 2002.
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Full Graph Message PassingFull Graph Message Passing
Measured Data Nodes (r)
Codeword Bit Nodes (x)
Check Nodes (z)
jijijijijiji wxxxxr ,1,11,,1,, 25.05.05.025.05.0
5.01h
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Full Graph Message Passing
-6
-5
-4
-3
-2
-1
0
0 0.5 1 1.5 2 2.5 3
SNR [dB]
Bit e
rro
r ra
te, L
og
Ba
se
10
ISI-free
Full Graph_50
Full Graph Message PassingFull Graph Message Passing
[10000,5000] regular (3,6) matrix[10000,5000] regular (3,6) matrix
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Full Graph AnalysisFull Graph Analysis
Length 4 cycles present which degrade performance Length 4 cycles present which degrade performance of messageof message--passing algorithm passing algorithm
x(i+2,j) x(i+2,j+1)
x(i+1,j) x(i+1,j+1)
x(i,j) x(i,j+1)
x(i+2,j+2)
x(i+1,j+2)
x(i,j+2)
r(i+1,j+1)
r(i,j+1)r(i,j)
r(i+1,j)
From
Check
Nodes
Kschischang et al., “Factor graphs and the sum-product algorithm,” IEEE Trans. Inform.
Theory, Feb. 2001.
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Ordered Subsets Message Passing Ordered Subsets Message Passing
From Imaging From Imaging –– Data set is grouped into subsets to Data set is grouped into subsets to increase rate of convergence of image increase rate of convergence of image reconstruction algorithmsreconstruction algorithms
For Decoding For Decoding –– Measured data is grouped into Measured data is grouped into subsets to eliminate short length cycles in the subsets to eliminate short length cycles in the Channel ISI graphChannel ISI graph
H. M. Hudson, and R. S. Larkin, “Accelerated image reconstruction using ordered subsets
of projection data,” IEEE Trans. Medical Imaging, Dec. 1994
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Labeling of data nodes into 4 subsetsLabeling of data nodes into 4 subsets
For each iteration use data nodes of one label onlyFor each iteration use data nodes of one label only
Labeled ISI GraphLabeled ISI Graph
J. A. O’Sullivan, and N. Singla, “Ordered subsets message-passing,” Int’l Symp. Inform.
Theory, Yokohama, Japan 2003.
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Ordered Subsets Message Passing
-6
-5
-4
-3
-2
-1
0
0 0.5 1 1.5 2 2.5 3
SNR [dB]
Bit e
rror
rate
in log10
ISI-free
Ordered Subsets_200
Full Graph_50
[10000,5000] regular (3,6) matrix[10000,5000] regular (3,6) matrix
Ordered Subsets Message PassingOrdered Subsets Message Passing
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CT Imaging in Presence of High CT Imaging in Presence of High Density Attenuators (J. Williamson, PI)Density Attenuators (J. Williamson, PI)
Brachytherapy applicators
After-loading colpostats
for radiation oncology
Cervical cancer: 50% survival rate
Dose prediction important
Object-Constrained Computed
Tomography (OCCT)
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Filtered Back ProjectionFiltered Back Projection
Truth FBP
FBP: inverse Radon transform
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Transmission TomographyTransmission Tomography• Source-detector pairs indexed by y; pixels indexed by x
• Data d(y) Poisson, means g(y: ), log likelihood function
• Mean unattenuated counts I0, mean background
• Attenuation function (x,E), E energies
• Maximize over or ci; equivalently minimize I-divergence
)(),(),(exp),():(
):():(ln)()):(|(
0 yExxyhEyIyg
ygygydgdl
E x
y
X
Y
I
i
ii ExcEx1
)()(),(
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MaximumMaximum--LikelihoodLikelihoodMinimum IMinimum I--divergencedivergence
• Poisson distribution
• Poisson distributed data loglikelihood function
• Maximization over equivalent to minimization of I-divergence
kk
kkI
kkkNP
ek
kNPk
ln)||(
!lnln)(ln
!)(
)(),(),(exp),():(
):()():(
)(ln)()):(||(
):():(ln)()):(|(
0 yExxyhEyIyg
ygydyg
ydydgdI
ygygydgdl
E x
y
y
X
Y
Y
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Maximum Likelihood Maximum Likelihood Minimum IMinimum I--DivergenceDivergence
Difficulties: log of sum, sums in exponent
)()()(),(exp),():(
):()():(
)(ln)()):(||(
):():(ln)()):(|(
1
0 yExcxyhEyIyg
ygydyg
ydydgdI
ygygydgdl
E x
I
i
ii
y
y
X
Y
Y
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Interpretation: Compare predicted data to measured data
via ratio of backprojections
Update estimate using a normalization constant
Comments: choice for constants; monotonic convergence;
linear convergence; fixed points satisfy Kuhn-
Tucker conditions; constraints easily incorporated
)(~
)(ˆln
)(
1)(ˆ)(ˆ
)(
)()()1(
xb
xb
xZxcxc
li
li
i
li
li
New Alternating Minimization AlgorithmNew Alternating Minimization Algorithmfor Transmission Tomographyfor Transmission Tomography
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60David G. Politte
October 31, 2002
Mini CT, AM Iteration 0000001
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61David G. Politte
October 31, 2002
Mini CT, AM Iteration 0000002
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62David G. Politte
October 31, 2002
Mini CT, AM Iteration 0000005
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63David G. Politte
October 31, 2002
Mini CT, AM Iteration 0000010
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64David G. Politte
October 31, 2002
Mini CT, AM Iteration 0000020
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65David G. Politte
October 31, 2002
Mini CT, AM Iteration 0000050
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66David G. Politte
October 31, 2002
Mini CT, AM Iteration 0000100
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67David G. Politte
October 31, 2002
Mini CT, AM Iteration 0000200
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68David G. Politte
October 31, 2002
Mini CT, AM Iteration 0000500
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69David G. Politte
October 31, 2002
Mini CT, AM Iteration 0001000
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70David G. Politte
October 31, 2002
Mini CT, AM Iteration 0002000
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71David G. Politte
October 31, 2002
Mini CT, AM Iteration 0005000
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72David G. Politte
October 31, 2002
Mini CT, AM Iteration 0010000
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73David G. Politte
October 31, 2002
Mini CT, AM Iteration 0020000
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74David G. Politte
October 31, 2002
Mini CT, AM Iteration 0050000
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75David G. Politte
October 31, 2002
Mini CT, AM Iteration 0100000
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76David G. Politte
October 31, 2002
Mini CT, AM Iteration 0200000
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77David G. Politte
October 31, 2002
Mini CT, AM Iteration 0500000
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78David G. Politte
October 31, 2002
Mini CT, AM Iteration 1000000
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Our Plans in CT ImagingOur Plans in CT Imaging
•• CTCT MultirowMultirow SinogramSinogram data:data:14081408 ×× 768768 ×× nndd ×× nnzz
– where nd is the number of detector rows and nz is the number of gantry rotations
•• Fully 3Fully 3--D Implementations for D Implementations for Quantitative CTQuantitative CT
•• SpeedSpeed--up: Ordered Subsets, up: Ordered Subsets, MultigridMultigrid Methods, Parallel Methods, Parallel Implementations on Clusters Implementations on Clusters of PCsof PCs
•• Future: PETFuture: PET--CTCT Siemens Somotom Emotion
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Slide and data from R. Laforest and M. Mintun.
PETCT-211
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PETCT-165
Slide and data from R. Laforest and M. Mintun.
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Additional Algorithm/DetectorAdditional Algorithm/DetectorModel DevelopmentModel Development
•• RegularizationRegularization
•• Energy integrating detectors Energy integrating detectors
•• Finite detector size, better source modelFinite detector size, better source model
•• Finite pixel, Finite pixel, voxelvoxel sizesize
•• Average integral or average exponentialAverage integral or average exponential(arithmetic vs. geometric average)(arithmetic vs. geometric average)
•• Partial volume effectsPartial volume effects
•• MotionMotion
•• ScatteringScattering
•• Limited angle tomographyLimited angle tomography
•• Region of interestRegion of interest
•• Scanner implementations: beam hardening Scanner implementations: beam hardening correction, sampling, etc.correction, sampling, etc.
),( EyEdN
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Computation and
Communication
Signal Processing
Information Theory
ComplexityComplexity--constrained processingconstrained processing
Signal processing on graphsSignal processing on graphs
Distributed signal processingDistributed signal processing
Distributed information theoryDistributed information theory
Distributed computation and Distributed computation and communicationcommunication
Optimal information extraction, Optimal information extraction, communication, computationcommunication, computation
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Limits of Information TheoryLimits of Information Theory
•• Information theory provides bounds on performance Information theory provides bounds on performance of communication, compression, and data analysisof communication, compression, and data analysis
– Channel coding theorem (capacity)
– Entropy, rate-distortion theory
– Fisher information
•• Open Problems in Information TheoryOpen Problems in Information Theory
– Broadcast channel p(y1,y2|x) capacity region of achievable (R1,R2)
» Depends only on p(y1|x) and p(y2|x); degraded channel known
– Distributed source compression achievable (R1,R2, D1,D2)
•• Algorithmic information theory (Algorithmic information theory (KolmogorovKolmogorovcomplexity)complexity)
p(x,yp(x,y))
XXnn
YYnn
XXnn
ffyy
ffxx
YYnngg ^
^
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Speculation on FutureSpeculation on Future
•• Distributed compressionDistributed compression– Compression with side information
– Analogies to information embedding
– Reduced communication rates
•• Broadcast channel models Broadcast channel models – Appropriate for motes
– Communication at different rates using a common signal
– Reduced communication rates
•• Tradeoffs in communication and computationTradeoffs in communication and computation
•• Mobile computing: cheap Mobile computing: cheap expensiveexpensive cheapcheap– mobile base station + network mobile
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ConclusionsConclusions
•• Information Signal ProcessingInformation Signal Processing
—— DSP, Information Theory, Computation andDSP, Information Theory, Computation and
CommunicationCommunication
•• Role of Graphical ModelsRole of Graphical Models
•• Message Passing EM AlgorithmsMessage Passing EM Algorithms
•• Iterative Equalization and DecodingIterative Equalization and Decoding
•• XX--Ray CT ImagingRay CT Imaging
J. A. O’Sullivan. 11/21/2003Information Signal Processing
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