1 6 3 1 P r i n c e S t r e e t , A l e x a n d r i a , V A 2 2 3 1 4 | 5 7 1 - 2 9 8 - 1 3 0 0 | w w w . a a p m . o r g

MEASURING SPATIAL RESOLUTION IN DIGITAL BREAST TOMOSYNTHESIS

Update of AAPM Task Group 245DA Scaduto

Stony Brook Medicine, Stony Brook, NY M Goodsitt

University of Michigan, Ann Arbor, MIH-P Chan

University of Michigan, Ann Arbor, MIH Olafsdottir

Image Owl, 105 Reykjavik, IcelandM Das

University of Houston, Houston, TXE Fredenberg

Philips Healthcare, Solna, SwedenW Geiser

UT MD Anderson Cancer Center, Houston, TXD Goodenough

George Washington University, Washington, DCP Heid

ARCADES, Marseille, France

Y-H Hu

Stony Brook Medicine, Stony Brook, NY B Liu

Massachusetts General Hospital, Boston, MAJ Mainprize

Sunnybrook Health Sciences Centre, North York, ONI Reiser

The University of Chicago, Chicago, ILR Van Engen

LRCB, Nijmegen, NetherlandsV Varchena

CIRS Inc., Norfolk, VAS Vecchio

I.M.S., Pontecchio Marconi (BO), ItalyS Glick

U.S. Food and Drug Administration, Silver Spring, MDW Zhao

Stony Brook Medicine, Stony Brook, NY

Detector plane resolution (X/Y-resolution)• Inherent/binned detector resolution• Oblique entry of x-rays• Focal spot size/motion

Depth-direction resolution (Z-resolution)• Limited angular range (9-50°)• Reconstruction algorithms

Aim: Evaluate different spatial resolution measurement techniques

FACTORS AFFECTING SPATIAL RESOLUTION IN TOMOSYNTHESIS

PhantomLab TomoPhan CIRS DBT QC Phantom

QC PHANTOMS

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1 6 3 1 P r i n c e S t r e e t , A l e x a n d r i a , V A 2 2 3 1 4 | 5 7 1 - 2 9 8 - 1 3 0 0 | w w w . a a p m . o r g

SPATIAL RESOLUTION: DETECTOR PLANE

EDGE-SPREAD FUNCTION (ESF)

TomoPhan CIRS Phantom

0 2 4 6 8500

1000

1500

2000

2500

3000Tube Travel Direction

0 2 4 6 8

1000

1500

2000

Tube Travel Direction

0 2 4 6 8

1400

1500

1600

Cross-scan Direction

0 2 4 6 81000

1100

1200

1300Cross-scan Direction

POINT-SPREAD AND MODULATION TRANSFER FUNCTIONS

PSF DEPENDENCE ON OBJECT SIZE

-20 -10 0 10 20-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

PS

F

Distance along profile (mm)

180 µm bead 800 µm bead

-20 -10 0 10 20-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0 180 µm bead 50 µm wire

PS

FDistance along profile (mm)

H. Fujita et al., IEEE Trans. Med. Imaging 11(1), 34–9 (1992)

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SPATIAL RESOLUTION: DEPTH-DIRECTION

ARTIFACT-SPREAD FUNCTION (ASF)

-10 -5 0 5 10

0.0

0.2

0.4

0.6

0.8

1.0

1.2 180 µm bead 800 µm bead

Arti

fact

Spr

ead

Func

tion

Distance from In-Focus Plane (mm)0 0

( ) ( )ASF( )

( ) ( )bead bg

bead bg

I z I zz

I z I z

z0zz0

ASF DEPENDENCE ON ANGULAR RANGE

Angular Range

Projection Views

Increment FWHM

16° 17 1° 5.31 mm

24° 9 3° 3.92 mm

32° 17 2° 3.12 mm

48° 25 2° 2.89 mm

60° 21 3° 1.94 mm

-20 -10 0 10 20

0.0

0.2

0.4

0.6

0.8

1.0

AS

F

Distance from in-focus plane [mm]

16° (FWHM = 5.31 mm) 24° (FWHM = 3.92 mm) 32° (FWHM = 3.12 mm) 48° (FWHM = 2.89 mm) 60° (FWHM = 1.94 mm)

Ramp set Estimated slice width [mm]Upper 1.48Lower 1.56

Average 1.52

SLICE SENSITIVITY PROFILE (SSP)

OVERSAMPLED LSF: TUNGSTEN WIRE

arctan zy

p

q

Y.-H. Hu, B. Zhao, and W. Zhao, Med. Phys. 35(5), 5242 (2008)

Δz

Δy tanq p

PRESAMPLING MTF

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00

200

400

600

800

1000

LSF(

z)

z [mm]

0 5 10 15 20 25 30 35 400

200

400

600

800

1000

LSF(

y)

y [mm]

2D PSF

-4 -3 -2 -1 0 1 2 3 4Distance in x [mm]

-5

-4

-3

-2

-1

0

1

2

3

4

5

Dis

tanc

e in

z [m

m]

0 5.88-5.88

-0.5

0.5

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

MTF

(z)

Spatial Frequency [cycles/mm]

OBJECT PSF

-15 -10 -5 0 5 10 15

0.0

0.2

0.4

0.6

0.8

1.0 ASF Object PSF

AS

F

Distance from in-focus plane (mm)

1ASF ~ PSF MTFobj obj objf S f F

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

MTF

(z)

Spatial Frequency [cycles/mm]

Detector plane spatial resolution• PSF is object-independent with sufficiently small object• MTF (wire, edge) is object-independent

Depth-direction resolution • Indirect/surrogate measurement: SSP, ASF

• Object-dependent• Valid for nonlinear reconstructions

• Direct measurement: MTF• Object-independent• Inherent image performance of system• Invalid for nonlinear reconstructions

CONCLUSIONS

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THANK YOU

TG 245 MembersAAPM