Spectral imaging using clinical megavoltage beams and a novel multi-layer imager

Area of Science:

• Medical Physics
• Radiological Imaging
• Materials Science

Background:

• Clinical megavoltage (MV) imaging traditionally lacks material differentiation capabilities.
• Electronic portal imagers have limitations in detective quantum efficiency and noise performance.
• Spectral imaging offers potential for enhanced material and bone separation in MV imaging.

Purpose of the Study:

• To assess the feasibility of a novel multi-layer imager (MLI) for clinical MV spectral imaging.
• To evaluate the MLI's capability for material and bone separation using various materials and photon beam energies.
• To demonstrate bone/gold separation for improved visualization of implanted fiducials.

Main Methods:

• Utilized a validated Monte Carlo model for simulating MLI performance.
• Conducted experimental evaluations with solid water, aluminum, copper, and gold targets using 2.5 MV, 6 MV, and 6 MV FFF beams.
• Employed weighted subtraction imaging with iterative estimation of the weighting factor (w) to optimize separation.
• Used an anthropomorphic phantom with gold fiducials to demonstrate bone/gold separation.

Main Results:

• The MLI demonstrated energy separation between layers due to beam hardening, ranging from 34-47 keV.
• Optimal weighting factors (w) were determined for different materials and beam energies, with values varying significantly.
• Bone suppression in the phantom improved gold fiducial visibility, particularly with the 2.5 MV beam.
• The MLI prototype showed higher detective quantum efficiency and lower noise compared to conventional imagers.

Conclusions:

• The novel multi-layer imager shows feasibility for clinical MV spectral imaging and material separation.
• Weighted subtraction imaging is an effective technique for material and bone separation with the MLI.
• Further optimization of the MLI design is necessary to achieve optimal separation at clinical MV beam energies.