This paper presents a multi spot projection unit, used in a 3D volume measurement system employed in a heart failure monitoring device, observing the volume of a patient’s feet for symptoms of heart problems (peripheral edema - swelling of the extremities). The stereoscopic image acquisition requires a surface with enough optically detectable texture, usually not present on human skin, which can be resolved by projecting an infrared, static multi-spot optical pattern. The focus of this paper is on creating a very cost-effective, energy efficient, eye-safe projection system, realizing a strongly divergent (up to ±60°) spot pattern, using infrared LEDs and mass fabricable micro-optical elements. Two different setup were tested: a) an LED array combined with a microlens array, and b) a combination of a single LED with a microlens array and a computer generated hologram (CGH) that adds a pseudo-random spot multiplication. For approach a) the microlens array was optimized by ray-tracing. The CGH function for approach b) was found using a wave optical design algorithm (iterative Fourier-Transform Algorithm – IFTA). The micro-lens array master was fabricated by diamondturning, whereas electron-beam lithography was employed for the CGH-master. Both masters were replicated using hotembossing of PMMA. Installed in a prototype of the medical measurement device, the influence on the 3D reconstruction was measured. The proposed solutions allow installing a competitively priced product for automatic peripheral edema monitoring in chronically ill patient homes, which is of great interest for improving their quality of life and the efficiency of their treatment.
Thomas Kämpfe, Shamus Husheer, Michael Vervaeke, Mathias Heckele, Isabelle Verrier, and Yves Jourlin, "Cost effective LED-based multi-spot projection system for medical 3D volume measurement systems," Proc. SPIE 10680, Optical Sensing and Detection V, 1068011 (Presented at SPIE Photonics Europe: April 25, 2018; Published: 9 May 2018); https://doi.org/10.1117/12.2307628.
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