WEIHUA ZHOU, LINLIN CONG11/07 /2011

DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING

SOUTHERN ILLINOIS UNIVERSITY CARBONDALE

Various reconstruction algorithms for Tomosnythesis

Current Technology of Breast Cancer Detection

Early detection of breast cancer is viewed as the best hope to decrease breast cancer mortality.

Mammography The most commonly accomplished screening tool for early

detection

Supplemental tools Breast Ultrasound Breast CT Breast MRI Biopsy

X-ray Attenuation Model

xI T

T

I

Voxel j

Pixel i

Projection Image

Reconstructed Volumee

xIT

: incident intensity : transmitted intensity

: attenuation coefficient

: the length of the path where x-ray passes through the voxel

Current Tomosynthesis Imaging Geometry

X-ray tube rotates along an arc path above the breast

Series of low dosage images are acquired at different angles

X-Ray tube

Reconstructed planes

Compression paddle

Breast

Digital detector

Reconstruction Algorithms of Digital Breast Tomosynthesis

Reconstruct 3D object volume based on acquired 2D projection images

Categories Mathematic reconstruction methods (SAA / BP) Filter-based reconstruction methods (FBP / MITS) Statistical reconstruction methods (MLEM, MOSC,

etc) Algebraic reconstruction methods (ART, SART, etc)

Reconstruction Algorithm: SAA (Shift-And-Add)

Z

Plane I

DetectorP i

Compression paddle

X-ray tubes

O

(1)

Note: O is the center of the reconstructed plane I. The shift amount of any pixel on Plane I will be equal to the shift amount of O.

Reconstruction Algorithm: BP (Back-Projection)

Note: O is the center of the reconstructed plane I. The shift amount of any pixel A on Plane I varies with its location.

X-ray tubes

Z

Plane I

DetectorP i

Compression paddle

OA

Reconstruction Algorithm: FBP (Filtered Back Projection)

Take BP as the foundationApply high-freq and low-freq filters to

enhance signals and suppress the noiseFilters

Ramp Filter Hamming Filter

Gaussian Filter

Reconstruction Algorithm:MLEM (Maximum Likelihood Expectation Maximization)

Originally invented by Lange and FesslerML: maximize the likelihood of getting the projection T from the incident X-ray intensity I and attenuation coefficient μ.

EM: one of the methods to solve ML problem.Iterative equation*:

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* Wu, T., et al, “Tomographic mammography using a limited number of low-dose cone-beam projection images,” Med. Phys. 30, 365-380 (2003).

Reconstruction Algorithm: SART (Simultaneous Algebraic Reconstruction Technique)

Originated from ART and was invented by Henderson

Iteratively solves the attenuation equationsIterative equation *:

i ji

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* Zhang, Y., et al.,“A comparative study of limited-angle cone-beam reconstruction methods for breast tomosynthesis,” Med. Phys. 33(10), 3781-3795 (2006).

Image Reconstruction with Breast Phantom

• Standard breast biopsy training phantom with solid masses and two micro-calcification clusters.

• 25 projection images at a total exposure of 100 mAs (4mAs/projection) were obtained. View angle 48 degrees.

Low Dosage Middle Projection

Breast Biopsy Training Phantom

In-plane slice images of FBP and MLEM

Image Reconstruction with Breast Phantom

(a) BP

(b) FBP

(c) MLEM

(d) SART

Reconstructed ROIs of a mass (z=45 mm above the detector).

(a) BP

(b) FBP

(c) MLEM

(d) SART

Reconstructed ROIs of a micro-cluster / micro-calcification (z=45 mm above the detector).

Comparisons of Reconstruction Methods

MITS and FBP are fast-speed reconstruction methods with deblurring algorithms to remove out-of-plane blur

MLEM and SART are iterative methods based on ray-tracing computation; they can provide good image quality, but need a long running time

Acknowledgements

Appreciate our collaborators at The University of North Carolina at Chapel Hill (UNC), North Carolina State University (NCSU), Southern Illinois University (SIU).

o The related work is supported by U.S. National Institutes of Health (NIH/NCI R01 CA134598-01A1).

Thank you