A scanning focus nuclear microscope with multi-pinhole collimation.

Microscopic nuclear imaging down to a few hundred-micron spatial resolutions could already be achieved using low-energy gamma emitters (e.g., 125 I, ~30 keV) and a basic single micro-pinhole gamma camera. This has been applied to, e.g., in-vivo mouse thyroid imaging. For clinically used radionuclides like 99m Tc, this approach fails due to penetration of the higher energy gamma photons through pinhole edges. To overcome these resolution degradation effects, we propose a new imaging approach: Scanning Focus Nuclear Microscopy (SFNM). We assess SFNM using Monte Carlo simulations for clinically used isotopes. SFNM is based on the use of a 2D scanning stage with a focused multi-pinhole collimator containing 42 pinholes with narrow pinhole aperture opening angles to reduce photon penetration. All projections of different positions are used to iteratively reconstruct a 3D image from which synthetic planar images are generated. SFNM imaging was tested using a digital Derenzo resolution phantom and a mouse ankle joint phantom containing 99m Tc (140 keV). The planar images were compared with those obtained using a single-pinhole collimator, either with matched pinhole diameter or with matched sensitivity. The simulation results showed an achievable 99m Tc image resolution of 0.04 mm and detailed 99m Tc bone images of a mouse ankle with SFNM. SFNM has strong advantages over single-pinhole imaging in terms of spatial resolution.