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Photon counting spectral breast CT: Effect of adaptive filtration on CT numbers, noise, and contrast to noise ratio
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10.1118/1.4800504
/content/aapm/journal/medphys/40/5/10.1118/1.4800504
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/40/5/10.1118/1.4800504

Figures

Image of FIG. 1.
FIG. 1.

Schematic of the PCS breast CT system with adaptive filter and photon counting CZT detector.

Image of FIG. 2.
FIG. 2.

X-ray spectra used for the breast imaging.

Image of FIG. 3.
FIG. 3.

Schematic showing adaptive filter thickness calculation.

Image of FIG. 4.
FIG. 4.

Illustration of conversion of filter thickness vs angle to perpendicular filter thickness vs off-axis distance .

Image of FIG. 5.
FIG. 5.

Expansion factor for the x-ray tube output versus tube voltage.

Image of FIG. 6.
FIG. 6.

Breast phantom used for CT simulations.

Image of FIG. 7.
FIG. 7.

Filter shapes for various materials at various distances from the focal spot, designed for 120 kVp and a 14 cm diameter phantom. Acrylic filters are the thickest (a), Teflon has the second thickest shape (b), and aluminum makes the smallest filter (c).

Image of FIG. 8.
FIG. 8.

Hardened spectra for acrylic (a), Teflon (b), and aluminum (c) filters after passing through the filter and the 14 cm diameter phantom at the angle specified in degrees. For acrylic, beam gets slightly softer as it passes through a thick part of the filter but a thin part of the phantom. This is due to the differences of the effective atomic numbers of the phantom and filter materials; the beam passes more low Z material as the angle increases, and therefore, the beam gets softer. Reversed beam hardening effects are observed for Teflon and aluminum filters due to their higher effective atomic numbers as compared to the phantom material.

Image of FIG. 9.
FIG. 9.

The total number photons in the beam after passing through the adaptive filter and phantom at four different tube voltages and for three filter materials: (a) acrylic, (b) Teflon, (c) aluminum. Each filter was designed for 120 kVp and 100% glandular breast with a 14 cm diameter, but was used for each tube voltage.

Image of FIG. 10.
FIG. 10.

Adaptive filter fabricated from acrylic slab. The filter was matched to 14 cm phantom diameter and placed at 23 cm distance from x-ray tube focal spot.

Image of FIG. 11.
FIG. 11.

The experimental profiles of beam intensities after passing through (a) the acrylic adaptive filter and 14 cm diameter acrylic phantom and (b) a uniform 14 cm thick acrylic slab; the profiles were recorded by a 2 × 256 pixel photon counting CZT detector. The adaptive filter was designed for a 14 cm diameter cylindrical acrylic phantom with a 23 cm source to filter distance. Corresponding profiles acquired for individual energy bins are shown in (c) and (d).

Image of FIG. 12.
FIG. 12.

CT images acquired at 60 kVp without adaptive filter (a), with adaptive filter (b), and with adaptive filter and expanded exposure (c). Corresponding profiles across the center of the phantom, passing only through water, are shown in (d)–(f).

Image of FIG. 13.
FIG. 13.

Average CT numbers at various distances from the middle of the phantom at (a) 40, (b) 60, (c) 90, and (d) 120 kVp for the cases of no adaptive filter (w/o filt), with adaptive filter (w filt), and with adaptive filter and expanded exposure (w filt exp scale). These graphs show the magnitudes of “cupping” artifacts with and without the adaptive filter in the beam.

Image of FIG. 14.
FIG. 14.

CNR of iodine contrast elements in CT images acquired at 40–120 kVp tube voltages, acquired without [(a) and (b)] and with [(c) and (d)] adaptive filtration, and without [(a) and (c)] and with [(b) and (d)] energy weighting.

Image of FIG. 15.
FIG. 15.

CNR of adipose contrast elements in CT images acquired at 40–120 kVp tube voltages, acquired without [(a) and (b)] and with [(c) and (d)] adaptive filtration, and without (a) and (c) and with (b) and (d) energy weighting.

Image of FIG. 16.
FIG. 16.

Material-decomposed images acquired at 60 kVp, with and without adaptive filtration. (a)–(c) Adipose cancelled images acquired without adaptive filter (a), with adaptive filter (b), and with adaptive filter and expanded exposure (c). (d)–(f) Iodine cancelled images acquired without adaptive filter (d), with adaptive filter (e), and with adaptive filter and expanded exposure (f).

Image of FIG. 17.
FIG. 17.

CNR distributions of iodine contrast elements at different radial locations in adipose cancelled images for 40, 60, 90, and 120 kVp (a) without adaptive filter, and (b) with adaptive filter and regular and expanded exposures.

Image of FIG. 18.
FIG. 18.

CNR distributions of adipose contrast elements at different radial locations in iodine cancelled images for 40, 60, 90, and 120 kVp (a) without adaptive filter, (b) with adaptive filter and regular and expanded exposures.

Tables

Generic image for table
TABLE I.

Energy bin arrangements.

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/content/aapm/journal/medphys/40/5/10.1118/1.4800504
2013-04-11
2014-04-25
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Photon counting spectral breast CT: Effect of adaptive filtration on CT numbers, noise, and contrast to noise ratio
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/40/5/10.1118/1.4800504
10.1118/1.4800504
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