Resolution doubling using confocal microscopy via analogy with structured illumination microscopy

Structured illumination microscopy (SIM) is a super-resolution fluorescence microscopy with a 2-fold higher lateral resolution than conventional wide-field fluorescence (WF) microscopy. Confocal fluorescence (CF) microscopy has approximately the same optical cutoff frequency as SIM; however, the maximum theoretical increase in lateral resolution over that of WF is 1.4-fold with an infinitesimal pinhole diameter. Quantitative comparisons based on an analytical imaging formula revealed that modulation transfer functions (MTFs) of SIM reconstructed images before postprocessing are nearly identical to those of CF images recorded with an infinitesimal pinhole diameter. Here, we propose a new method using an adequate pinhole diameter combined with the use of an apodized Fourier inverse filter to increase the lateral resolution of CF images to as much as that SIM images without significant noise degradation in practice. Furthermore, the proposed method does not require a posteriori parameterization and has reproducibility. This approach can be easily applied to conventional laser scanning CF, spinning disk CF, and multiphoton microscopies. (C) 2016 The Japan Society of Applied Physics