The enhanced depth discrimination of a confocal scanning optical microscope is produced by a pinhole aperture placed in front of the detector to reject out-of-focus light. Strictly confocal behavior is impractical because an infinitesimally small aperture would collect very little light and would result in images with a poor signal-to-noise ratio (SNR), while a finite-sized partially confocal aperture provides a better SNR but reduced depth discrimination. Reconstruction algorithms, such as the expectation-maximization algorithm for maximum likelihood, can be applied to partially confocal images in order to achieve better resolution, but because they are sensitive to noise in the data, there is a practical trade-off involved. With a small aperture, fewer iterations of the reconstruction algorithm are necessary to achieve the desired resolution, but the low a priori SNR will result in a noisy reconstruction, at least when no regularization is used. With a larger aperture the a priori SNR is larger but the resolution is lower, and more iterations of the algorithm are necessary to reach the desired resolution; at some point the a posteriori SNR is lower than the a priori value. We present a theoretical analysis of the SNR-to-resolution trade-off partially confocal imaging, and we present two studies that use the expectation-maximization algorithm as a postprocessor; these studies show that a for a given task there is an optimum aperture size, departures from which result in a lower a posteriori SNR.
© 1994 Optical Society of AmericaFull Article | PDF Article
James G. McNally, Chrysanthe Preza, José-Angel Conchello, and Lewis J. Thomas
J. Opt. Soc. Am. A 11(3) 1056-1067 (1994)
Joanne Markham and José-Angel Conchello
J. Opt. Soc. Am. A 16(10) 2377-2391 (1999)
Rajeeb Hazra, Charles L. Viles, Stephen K. Park, Stephen E. Reichenbach, and Michael E. Sieracki
Appl. Opt. 31(8) 1083-1092 (1992)