Imaging amplification for minimally invasive medical devices

Abstract

The performance of minimally invasive devices for medical inspection could be significantly improved by an amplification imaging module (AIM), which can be considered a highly miniaturized digital microscope to image in-vivo tissue in real-time. An example is the magnification provided by the bulky conventional endoscope that allows the recognition of the affected mucosa with higher precision as compared to normal endoscopic inspection and enables the differentiation of affected tissue from healthy surroundings. Therefore, an AIM that can be integrated in very small medical devices as optical tool for ophthalmologic, thoracic and gastro endoscopic diagnostic will be a tremendous breakthrough. An especially microfabricated 200 μm thick PDMS lens, limiting the total length of the optical system to about 11 mm plus 4 mm for the lateral lens assembly (suitable to include in a 30 mm×11 mm cylindrical medical device) was assembled with more 3 commercial lenses. The height, radius of curvature and focal length of the PDMS lens can be changed by design and were selected to meet the specified system performance, which is set by the imaging requirements. The fabrication process was based in a hanging droplet approach, which is a very low-cost and effective method for obtaining lens with the desired properties. Several analyses were performed showing good performance of the lens system: a paraxial magnification of 14 times was achieved with a Modulation Transfer Function (MTF) around 37% at 50 lp/mm and maximum distortion about 1.83%.