statistical reconstruction for soft tissue imaging with...

A. Wang et al (Johns Hopkins University) www.jhu.edu/istar

06/18/2013

Presented at Fully 3D Image Reconstruction in Radiology and Nuclear Medicine 2013, Lake Tahoe 1

CT CBCT

Johns Hopkins University Schools of Medicine and Engineering

Statistical Reconstruction for Soft Tissue Imaging

with Low Dose C-arm

Cone-Beam CT

Adam S. Wang,1 J. Webster Stayman,1 Yoshito Otake,1 Gerhard Kleinszig,2 Sebastian Vogt,2

A. Jay Khanna,3 Ziya L. Gokaslan,4 and Jeffrey H. Siewerdsen1

1Biomedical Engineering, Johns Hopkins University

2XP Division, Siemens Healthcare 3Orthopaedic Surgery, Johns Hopkins University

4Neurosurgery and Oncology, Johns Hopkins University

CT CBCT

Acknowledgments

The I-STAR Laboratory Imaging for Surgery, Therapy, and Radiology

www.jhu.edu/istar

Hopkins Collaborators School of Medicine

G. Gallia, D. Reh

School of Engineering R. Taylor, G. Hager, J. Prince

Siemens XP R. Graumann

Funding Support Siemens Healthcare (XP Division)

National Institutes of Health

Johns Hopkins University Schools of Medicine and Engineering


06/18/2013


Mobile C-arm

Intraoperative C-arm CBCT High-precision surgical guidance Detection of complications OR quality assurance Challenges Higher noise, artifact than diagnostic CT Conventionally limited to high contrast (bone, contrast enhanced vessels) Need for lower dose (patient and staff) Opportunities Statistical reconstruction Extend low-dose CBCT to soft-tissue surgeries

Motivation

Faster acquisition If acquisition limited by frame/source rate Reduce patient motion

Gated acquisition Novel geometries and trajectories … Lower dose (?) (a) Lower mAs per projection: better sampling (b) Undersample: avoid electronic noise floor Impact on image quality?

Sparse Sampling in Image-

Guided Surgery


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Soft Tissue Imaging Large (>10 mm), low contrast (< 100 HU) tasks Image quality assessment: Compare to FBP Emphasis on fair comparison (noise and resolution) Abdomen Anthropomorphic Abdomen Phantom Cadaver Abdomen Low-Dose CBCT Protocols 100 kVp, (15 – 120) mAs CBCT: 100 kVp, 120 mAs (3.1 mGy)† (c.f., MDCT: ~10 – 25 mGy)‡

Sparse Acquisitions Compare {100%, 50%, 25%} projections at equal dose

Overall Approach

30 cm

†Schafer et al, Med Phys 2011 ‡Sagara et al, Am J Roentgen 2010

Experimental Methods Image Acquisition Motorized orbit: angular range 178° 200 projections FOV: 15×15×15 cm3 768×768 pixels (0.6 mm isotropic voxels) PaxScan 3030+ FP detector Dual-gain mode 2×2 binning: 0.388 mm Image Reconstruction Penalized likelihood (PL) † Separable quadratic surrogates (SQS) Allows all voxels to be updated simultaneously Requires 1 forward-, 1 back-projection per iteration Ordered subsets allows speedup ~# subsets Separable footprints (SF-TT) projector‡

CUDA implementation on Nvidia GTX 680 † Erdogan and Fessler PMB 1999 ‡ Long et al IEEE TMI 2010 ‡ Wu and Fessler Fully3D 2011


06/18/2013


Image Reconstruction Penalized likelihood (PL) † Separable quadratic surrogates (SQS) Allows all voxels to be updated simultaneously Requires 1 forward-, 1 back-projection per iteration Ordered subsets allows speedup ~# subsets Separable footprints (SF-TT) projector‡

CUDA implementation on Nvidia GTX 680

Experimental Methods Image Acquisition Motorized orbit: angular range 178° 200 projections FOV: 15×15×15 cm3 768×768 pixels (0.6 mm isotropic voxels) PaxScan 3030+ FP detector Dual-gain mode 2×2 binning: 0.388 mm

† Erdogan and Fessler PMB 1999 ‡ Long et al IEEE TMI 2010; Wu and Fessler Fully3D 2011

Voxel

Detector

Source

arg maxˆ log ( ; ) ( )L y R

Data consistency

Roughness penalty

Consider equal-dose scans, same recon time: (a) 100% P projections, 100% mA

N iterations, M ordered subsets

A·C·B·D|A·C·B·D|A·C·B·D|A·C·B·D|···

(b) 50% P projections, 200% mA 2N iterations, ½ M ordered subsets

A·C|A·C|A·C|A·C|A·C|A·C|A·C|A·C|···

(c) 25% P projections, 400% mA 4N iterations, ¼ M ordered subsets

A|A|A|A|A|A|A|A|A|A|A|A|A|A|A|A|···

Sparse Sampling

A B C D

A

C

A


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0.015

0.02

0.025mm-1

-200

-100

0

100

200

300

HU CBCT: PL

Anthropomorphic Abdominal Phantom Projections fully truncated Best-fit elliptic cylinder estimated from projections - Provide support region, initialization for PL reconstruction Low contrast sphere (-80 HU, 12.7 mm diameter) 1000 HU ≈ 0.02 mm-1

C-arm FOV

Ellipse Support

Diagnostic CT

Low Contrast Target (-80 HU)

Soft-Tissue Imaging

Penalty

Difference

jk j kj k N

R w

2

jk j kj k N

R w

21 , | |2( )

| | , | |2

H

x xx

x x

3D Neighborhood

Noise-Resolution Tradeoff PL: Roughness Penalty Penalize the difference between neighboring voxels

Quadratic Penalty Tends to enforce smoothness throughout image

Huber Penalty Relatively less penalty for large pixel differences Attempts to preserve edges

Quadratic

Linear

Huber

Linear Quadratic

-δ δ


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jk j kj k N

R w

3D Neighborhood

Noise-Resolution Tradeoff PL: Roughness Penalty Penalize the difference between neighboring voxels

Filtered Backprojection

Ramp filter applied with apodization window Cutoff frequency fc Fair comparison should also introduce smoothing in z-direction Use 2D apodization window that is applied in u- and v-directions of projection

u

v

fu fu fc -fc

Ramp

Apodization

fv

0.5 0.75 1 1.25 1.50

5

10

15

20

ESF Width (mm)

CN

R

0.5 0.75 1 1.25 1.50

5

10

15

20

ESF Width (mm)

CN

R

Noise-Resolution Analysis

Tradeoff between CNR and ESF Low contrast sphere (-80 HU) Edge Spread Function (ESF) captures lower resolution with increasing regularization strength β

2

0

2erfx tx e dt

( ) erf2 2c xf x a

0 2 4 6 8 10 12-100

-80

-60

-40

-20

0

20

40

60

Distance (mm)

Attenuation (

HU

)

c σ


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0.5 0.75 1 1.25 1.50

10

20

30

40

50

ESF Width (mm)

CN

R

0.5 0.75 1 1.25 1.50

10

20

30

40

50

ESF Width (mm)

CN

R

0.5 0.75 1 1.25 1.50

10

20

30

40

50

ESF Width (mm)

CN

R

0.5 0.75 1 1.25 1.50

10

20

30

40

50

ESF Width (mm)

CN

R

0.5 0.75 1 1.25 1.50

10

20

30

40

50

ESF Width (mm)

CN

R

0.5 0.75 1 1.25 1.50

10

20

30

40

50

ESF Width (mm)

CN

R

0.5 0.75 1 1.25 1.50

10

20

30

40

50

ESF Width (mm)

CN

R

0.5 0.75 1 1.25 1.50

10

20

30

40

50

ESF Width (mm)

CN

R

Abdomen Phantom

Noise-Resolution Tradeoff 100 kVp, 60 mAs Images shown at ESF σ = 1 mm Select δ = 5 HU as balance between CNR and blocky, piecewise-constant

δ = 1 δ = 3

δ = 5

δ = 10

δ = 20 PL-Q

FBP

δ = 1 * δ = 3 δ = 5

δ = 10 δ = 20 PL-Q

FBP

20 40 60 80 100 1200

5

10

15

20

25

30

35

mAs

CN

R

15 mAs 30 mAs 60 mAs 120 mAs

FBP

PL

½ Dose

2.2× CNR

PL

FBP

Abdomen Phantom

Low Dose Comparison 100 kVp, {15, 30, 60, 120} mAs Matched resolution Low contrast ESF width σ = 1 mm PL-Huber (δ = 5 HU) vs FBP


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20 40 60 80 100 1200

5

10

15

20

25

30

35

mAs

CN

R

20 40 60 80 100 1200

5

10

15

20

25

30

35

mAs

CN

R

Equal dose, resolution, recon time (PL) Same total dose: {15, 30, 60, 120} mAs Fixed ESF: σ = 1 mm P = 192 projections, N = 100, M = 32 Sparse sampling (50% P) beneficial at

ultra low dose (~40 mAs)

Sparse Sampling 100% P

50% P

25% P

100% P

Sampling

50% P

25% P

15 mAs Total Dose

30 mAs 60 mAs 120 mAs

FBP

FBP

PL

PL

100% P

50% P

25% P

15 mAs Total Dose

30 mAs 60 mAs 120 mAs

Realistic Soft Tissue Imaging Fresh cadaver (non-fixed) Apply abdomen phantom parameters for matched resolution 80 HU contrast ESF width σ = 1 mm PL-Huber (δ = 5 HU) vs FBP 100 kVp, 480 mAs used for reference images

Cadaver Abdomen

164/330351/500

224/350

0.014

0.015

0.016

0.017

0.018

0.019

0.02

0.021

0.022

0.023

0.024

164/330351/500

224/350

0.014

0.015

0.016

0.017

0.018

0.019

0.02

0.021

0.022

0.023

0.024

164/330 351/500

224/350

0.014

0.015

0.016

0.017

0.018

0.019

0.02

0.021

0.022

0.023

0.024


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FBP

PL


20 40 60 80 100 1200

2

4

6

8

10

12

14

16

mAs

CN

R

1.4× CNR

½ Dose Low Dose Comparison Noise calculated from subtraction with respective reference images 100 kVp, {15, 30, 60, 120} mAs PL reduces noise, preserves high contrast structures

Cadaver Abdomen PL

FBP

Sparse Comparison Fully sampled better at higher dose 50% sparsity better at lower dose Suggests two regimes for dose reduction strategy

Cadaver Abdomen


100% P

50% P

25% P

Sampling

20 40 60 80 100 1200

2

4

6

8

10

12

14

16

mAs

CN

R

100% P

50% P

25% P

PL


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Statistical Reconstruction Improvements in CNR by a factor ~1.4-2.2× at ½ dose for soft tissue imaging Fair comparison achieved by matching resolution w.r.t. low-contrast target

Dose Reduction Strategy Lower tube current, then go sparse Sparse advantage in overcoming electronic noise Crossover point function of imaging task, and electronic vs quantum noise levels

Advanced Modeling Scatter correction Polyenergetic spectrum Electronic noise model

Conclusion & Future Work

FBP PL (½ dose)

Phantom

Cadaver

Statistical Reconstruction Improvements in CNR by a factor ~1.4-2.2× at ½ dose for soft tissue imaging Fair comparison achieved by matching resolution w.r.t. low-contrast target

Dose Reduction Strategy Lower tube current, then go sparse Sparse advantage in overcoming electronic noise Crossover point function of imaging task, and electronic vs quantum noise levels

Advanced Modeling Scatter correction Polyenergetic spectrum Electronic noise model

Conclusion & Future Work

20 40 60 80 100 1200

2

4

6

8

10

12

14

16

mAs

CN

R

100% P

50% P

120 mAs 15 mAs

100% P

50% P

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