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On the feasibility of optical-CT imaging in media of different refractive index
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10.1118/1.4798980
/content/aapm/journal/medphys/40/5/10.1118/1.4798980
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/40/5/10.1118/1.4798980

Figures

Image of FIG. 1.
FIG. 1.

Three examples of scanning configuration showing incident ray geometry, dosimeter, and definition of focal length, , and detector angle, Δ. (Left) Point source geometry, modeling current cone-beam Vista™ optical-CT system. (Center) Parallel ray geometry, modeling telecentric DLOS system, and OCTOPUS™ He-Ne laser scanner. (Right) Converging source geometry, exploring potentially new scanner geometries.

Image of FIG. 2.
FIG. 2.

Physics properties of our ray tracing model. A light ray incident on a cylindrical dosimeter immersed in a bath of RI mismatched fluid. The ray experiences , the change in direction from incident angle to transmitted angle according to Eq. (2) , and , the drop in intensity from to = according to Eq. (5) .

Image of FIG. 3.
FIG. 3.

Three example simulations of optical-CT dosimetry with different dose distributions, scanning configurations, and RI matching. Reconstructions using both FBP and ART are shown. Each column contains (from top to bottom): reconstruction of simulated dose distribution using FBP; reconstruction of simulated dose distribution using ART; radial line profile through each reconstruction showing measured dose vs true dose and percent difference |Δ/ | to visualize reconstruction artifacts and quantify the usable fraction, ; ray diagram showing incident light geometry and refracted path through PRESAGE ( = 1.501) dosimeter. (Left column a) VMAT irradiated dosimeter, parallel telecentric geometry, RI-mismatched fluid ( = 1.49) surrounding the dosimeter. (Center column b) Uniformly irradiated dosimeter, converging geometry ( = −200 mm), water ( = 1.33) surrounding the dosimeter. (Right column c) Cs-137 brachytherapy, point source geometry ( = 200 mm), air ( = 1.00) surrounding the dosimeter (dry-scanning).

Tables

Generic image for table
TABLE I.

Dimensions of ART image reconstructions, numbers of rays and projections used for ray tracing, and computational time requirement on lab desktop Intel Core™ i7 975 3.33 GHz, 12 GB RAM.

Generic image for table
TABLE II.

Data from simulations of a 5 Gy uniform dose on an = 50 mm PRESAGE dosimeter. For each geometrical setup, incident ray geometry is described by focal length, . Line profile across the reconstructed measured dose distribution gave the usable fraction / , and the exit angle Δ was recorded to estimate the required detector size. The RI column represents the refractive index of the surrounding media during optical-CT scanning. Line integrals were calculated via ray tracing with 0.2 mm ray spacing, and reconstructions performed using FBP with linear interpolation and standard ramp + rect filter.

Generic image for table
TABLE III.

Analysis of simulations of a 5 Gy uniform dose delivered across an = 50 mm PRESAGE dosimeter. Two promising geometrical setups were considered: point ( = 200 mm) and parallel incident ray geometry. Usable fraction / and (2%/1 mm) index are shown for each combination of RI, geometry, and reconstruction method. Reconstructions were performed with FBP (odd rows, italic) and ART (even rows, bold).

Generic image for table
TABLE IV.

Analysis of simulations of a 10 Gy VMAT delivery, PTV radius = 10 mm, assuming ∼1/ falloff, on a = 50 mm PRESAGE dosimeter. Two promising geometrical setups were considered: point ( = 200 mm) and parallel incident ray geometry. Usable fraction / and (2%/1 mm) index are shown for each combination of RI, geometry, and reconstruction method. Reconstructions were performed with FBP (odd rows, italic) and ART (even rows, bold).

Generic image for table
TABLE V.

Analysis of simulations of a Cs-137 brachytherapy source of prescription 8 Gy at = 1 cm, on an = 50 mm PRESAGE dosimeter. The two most promising geometrical setups were considered: point ( = 200 mm) and parallel incident ray geometry. Percentage constraints were loosened because the dose distal from the source was relatively small; usable radius was calculated as the distance at which Δ/ >3% (considering only points for > 1 cm) and -index passing conditions were relaxed to 3%/1 mm. Usable fraction and -index are shown for each combination of RI, geometry, and reconstruction method. Reconstructions were performed with FBP (odd rows, italic) and ART (even rows, bold).

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/content/aapm/journal/medphys/40/5/10.1118/1.4798980
2013-04-09
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: On the feasibility of optical-CT imaging in media of different refractive index
http://aip.metastore.ingenta.com/content/aapm/journal/medphys/40/5/10.1118/1.4798980
10.1118/1.4798980
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