Phase Mask Metasurfaces for High-Resolution Scintillation-Based Imaging

Scintillators are materials that convert high energy particles such as X-rays and free electrons to visible or near-visible light. Scintillators are often used as detectors for X-rays due to their cost-effectiveness, and have important applications in medical imaging such as CT scans and gamma cameras for medical diagnostics. An effective scintillation-based detection system would allow for a higher signal-to-noise ratio, better contrast, and higher spatial resolution, which can also allow for lower X-ray dosages. This is important because immunocompromised individuals cannot safely undergo imaging due to the high X-ray dosages currently required in some X-ray imaging modalities, such as computed tomography (CT). As a result, clinicians cannot obtain potentially life-saving imaging data.<br/><br/>An important limitation in the process of scintillation is that there is some randomness due to diffraction and disorder. Due to the finite thickness of a scintillator, scintillator imaging inevitably leads to defocus and decreased resolution as generated photons propagate. The primary solution involves utilizing a thinner scintillator, though this leads to a direct trade-off with signal intensity.<br/><br/>In this work, we demonstrate visible-wavelength transparent metasurfaces that address the issue of defocus and resolution deterioration in scintillators. We use a silicon nitride on fused silica platform and adopt the approach of wavefront coding to extend the depth of field of an imaging system across the thickness of the scintillator. In wavefront coding, extended depth of field is achieved by altering the system’s point spread function to be made insensitive to defocus aberrations, which in this work is achieved by the metasurface. Combined with post-measurement image processing, high resolution can be obtained across all scintillator depths. This effect is achieved while preserving scintillator thickness.<br/><br/>We have recently shown a 3.5x resolution enhancement in Micro-CT simulations, with optimized systems approaching 10x resolution improvement or more.