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Augmented reality support system for endoscopic surgery using spectral reflectance estimation

In cardiac surgery, a method avoids cutting the sternum and ribs using an endoscope is known as Minimally Invasive Cardiac Surgery (MICS). MICS can be used for mitral valve prolapse. In this surgery, an annuloplasty ring is inserted to form the valve and since each person has a different valve size, an appropriate size must be selected by applying a sizer. We propose a system that supports surgery by superimposing a virtual image of the valve ring on the endoscopic image using Augmented reality (AR) technology. Marker detection needs to be performed for AR display. However, since organ surfaces are similar in color, we use the spectral reflectance of the material to obtain more information than RGB image. To avoid the use of special optics to measure the spectral reflectance, we estimate spectral reflectance from RGB images using principal component analysis. The areas containing the marker are obtained by similarity index and the 3D positions of the markers are determined from center of gravity measurements. Then, we superimpose the AR image onto the endoscope image by perspective transformation to the image plane and masking using estimated 3D position of markers. To evaluate our method, we validated the spectral reflectance estimation and AR display using pig hearts marked with crystal violet. We found that the accuracy of spectral reflectance estimation is sufficient for AR display and the AR image was almost the same as the actual ring size. Therefore, our proposed method is expected to increase the efficiency of the operation.