Imaging quality assessment of multi-modal miniature microscope.

We are developing a multi-modal miniature microscope (4M device) to image morphology and cytochemistry in vivo and provide better delineation of tumors. The 4M device is designed to be a complete microscope on a chip, including optical, micro-mechanical, and electronic components. It has advantages such as compact size and capability for microscopic-scale imaging. This paper presents an optics-only prototype 4M device, the very first imaging system made of sol-gel material. The microoptics used in the 4M device has a diameter of 1.3 mm. Metrology of the imaging quality assessment of the prototype device is presented. We describe causes of imaging performance degradation in order to improve the fabrication process. We built a multi-modal imaging test-bed to measure first-order properties and to assess the imaging quality of the 4M device. The 4M prototype has a field of view of 290 microm in diameter, a magnification of -3.9, a working distance of 250 microm and a depth of field of 29.6+/-6 microm. We report the modulation transfer function (MTF) of the 4M device as a quantitative metric of imaging quality. Based on the MTF data, we calculated a Strehl ratio of 0.59. In order to investigate the cause of imaging quality degradation, the surface characterization of lenses in 4M devices is measured and reported. We also imaged both polystyrene microspheres similar in size to epithelial cell nuclei and cervical cancer cells. Imaging results indicate that the 4M prototype can resolve cellular detail necessary for detection of precancer.