Sensitivity evaluation and selective plane imaging geometry for x-ray-induced luminescence imaging

Area of Science:

• Hybrid imaging modalities
• Nanoparticle-based theranostics
• Optical imaging in scattering media

Background:

• X-ray-induced luminescence (XIL) uses nanophosphors for imaging and potential radiotherapy applications.
• Current XIL methods face limitations in determining deep nanophosphor distributions due to signal attenuation in scattering tissues.
• Developing robust imaging models is crucial for extracting clinical information from XIL signals.

Purpose of the Study:

• To introduce and validate a novel imaging geometry, selective plane XIL (SPXIL), for improved depth sensitivity.
• To develop and calibrate an imaging model for determining nanophosphor distributions from surface radiance measurements.
• To assess the dose-dependent sensitivity and depth limitations of XIL in diffuse optical environments.

Main Methods:

• An analytical imaging model based on selective plane geometry was developed for homogeneous, semi-infinite media.
• Y₂O₃:Eu³⁺ nanophosphors were synthesized and characterized for luminescent properties and response to X-ray dose.
• SPXIL imaging was performed on optical gel phantoms, and nanophosphor distributions were reconstructed using Richardson-Lucy deconvolution.

Main Results:

• Y₂O₃:Eu³⁺ nanophosphors exhibited optimal emission at 611 nm with linear and quadratic responses to X-ray current/voltage and concentration.
• Luminescence efficiency was determined to be 1.06 photons per keV of absorbed X-ray radiation per g/mL of nanophosphor.
• SPXIL imaging successfully resolved sources 1 cm apart up to 1.75 cm depth, with sensitivity simulations indicating detection at 2-4 cm depth for 1 mg/mL concentration and 1 cGy dose.

Conclusions:

• The novel SPXIL geometry and associated imaging model provide a robust method for XIL in diffuse optical environments.
• Experimental validation in phantoms and sensitivity simulations demonstrate the potential of SPXIL for deep-tissue imaging.
• SPXIL shows promise for advancing nanophosphor-based applications in radiotherapy, such as theranostics and nanodosimetry.