Stray light in cone beam optical computed tomography: II. Reduction using a convergent light source.

Area of Science:

• Medical Physics
• Optical Imaging
• Radiation Dosimetry

Background:

• Optical cone beam computed tomography (CBCT) is a rapid method for 3D optical gel dosimeter densitometry.
• Diffuse light sources in CBCT systems cause stray light, leading to underestimation of attenuation coefficients and image non-uniformities.

Purpose of the Study:

• To develop and evaluate a novel convergent cone beam source for optical CT to mitigate stray light artifacts.
• To improve the quantitative accuracy of 3D optical dosimetry.

Main Methods:

• Replaced the broad beam light source of a commercial optical CT scanner with a convergent cone beam source using a Fresnel lens.
• Compared full-field cone beam CT imaging with fan beam CT (FBCT) using a uniform phantom and a finger phantom.
• Analyzed stray light effects and quantitative accuracy by measuring attenuation coefficients.

Main Results:

• The convergent cone beam source demonstrated high agreement with FBCT for attenuation coefficients in both uniform (1 ± 2%) and finger phantoms (4 ± 2%).
• The new system effectively reduced stray light, improving the reliability of densitometry measurements.
• Artifacts related to refractive index mismatch and vessel optical features became more pronounced with the convergent source.

Conclusions:

• The convergent cone beam source significantly enhances the quantitative accuracy of optical CT for 3D dosimetry.
• Further optimization of the source size is needed to balance accuracy and artifact reduction.
• This approach offers a pathway to practical and accurate 3D dosimetry without extensive scatter correction measurements.