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The influence of bowtie filtration on cone-beam CT image quality
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10.1118/1.3017470
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    Affiliations:
    1 Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ontario M5G 2M9, Canada and Ontario Cancer Institute, University Health Network, Toronto, Ontario M5G 2M9, Canada
    2 Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ontario M5G 2M9, Canada; Ontario Cancer Institute, University Health Network, Toronto, Ontario M5G 2M9, Canada; and Department of Radiation Oncology, University of Toronto, Toronto, Ontario M5G 2M9, Canada
    3 Radiation Medicine Program, Princess Margaret Hospital, Toronto, Ontario M5G 2M9, Canada; Ontario Cancer Institute, University Health Network, Toronto, Ontario M5G 2M9, Canada; and Department of Radiation Oncology and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 2M9, Canada
    a) Author to whom correspondence should be addressed. Address for correspondence: Radiation Physics, Radiation Medicine Program, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, Canada. Telephone: 416-946-4501 X5384; Fax: 416-946-6566; Electronic mail: david.jaffray@rmp.uhn.on.ca
    Med. Phys. 36, 22 (2009); http://dx.doi.org/10.1118/1.3017470
/content/aapm/journal/medphys/36/1/10.1118/1.3017470
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/36/1/10.1118/1.3017470

Figures

Image of FIG. 1.
FIG. 1.

(a) A photograph of the cone-beam CT Elekta Synergy CBCT system. (b) A schematic of the CBCT offset geometry at angle and medium FOV. (c) Schematic of the CBCT offset geometry and medium FOV after rotation.

Image of FIG. 2.
FIG. 2.

(a) Photograph of the Elekta designed bowtie filter. (b) Bowtie thickness measured with needle gauge as a function of length.

Image of FIG. 3.
FIG. 3.

(a) A schematic diagram of the CTDI body phantom. (b) Percentage of dose reduction with bowtie filter is plotted as a function of radial distance from the phantom center. Symbol represents measured data and solid line theoretical fit. (c) Circular (Catphan) phantom with an irregular annulus (human torso).

Image of FIG. 4.
FIG. 4.

Trans-axial images of uniform water portion of a circular phantom (Catphan) acquired (a) without (window level and (b) with bowtie filter (window level: ). (c) Profiles through the uniform water portion of the circular phantom with and without bowtie; the profile position is indicated by a dotted line in image.

Image of FIG. 5.
FIG. 5.

Trans-axial CBCT images of irregular (Cat-Irreg) phantom (a) without (window level: ) and (b) with bowtie filter (window level: ). (c) The difference of image (b) and (a). (d) Profiles through the uniform water portion of the irregular phantom. (e) The right shoulder of (d) is magnified to see the missing skinline more clearly. (f) Reduction in CT number (RCTN) at several skin depths for with and without bowtie filter.

Image of FIG. 6.
FIG. 6.

Trans-axial images of circular phantom with several contrast inserts acquired (a) without (window level ) and (b) with bowtie filter (window level ). (c) The same image shown in (a), but transformed into polar coordinate (window level ). (d) Profiles through the image (c) with several inserts are compared with CT and without bowtie filter. (e) The difference between the measured CT and CBCT number plotted as a function of Ideal CT number for several inserts. The empty circle and filled square symbols represent CT number error with and without bowtie. A gray solid line represents a linear fit to bowtie data.

Image of FIG. 7.
FIG. 7.

Trans-axial CBCT images of irregular (CaṯIrreg) with several inserts, (a) without bowtie (window level ) and (b) with bowtie filter (window level ). (c) The difference of image (b) and (a). (d) The same image in (a) but converted into polar coordinates (window level ). (e) The same image in (b) but converted into polar coordinates to make it simple for analysis such as CT number accuracy and streaking artifacts (window level ). (f) The measured CT number plotted as a function of ideal CT number for several inserts.

Image of FIG. 8.
FIG. 8.

Measured MTF performed on irregular phantoms using the CTP528 module (Catphan500) plotted as a function of line pairs with and without bowtie filter.

Image of FIG. 9.
FIG. 9.

CBCT images of gynecological patient (window level ) (a) without bowtie and (b) with bowtie (window level ). Profiles through the region of interest, indicated by a solid line. (d) A portion of (c), indicated by a rectangular box, is magnified to illustrate signal loss more clearly at skinline zone.

Tables

Generic image for table
TABLE I.

The scatter, primary, and scatter-to-primary ratios behind the center and edge of the circular (CatPhan500) phantom using lead strip of size .

Generic image for table
TABLE II.

The scatter, primary, and scatter to primary ratios behind the center and edge of the irregular (Cat-Irreg) phantom using lead strip of size .

Generic image for table
TABLE III.

Comparison of the CT number accuracy and linearity using three different techniques in terms of slope, intercept (at ideal CT# water), and values.

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/content/aapm/journal/medphys/36/1/10.1118/1.3017470
2008-12-04
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: The influence of bowtie filtration on cone-beam CT image quality
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/36/1/10.1118/1.3017470
10.1118/1.3017470
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