Fetoscopic laser photo-coagulation of the placental vascular anastomoses remains the most effective therapy for twin-to-twin transfusion syndrome (TTTS) in monochorionic twin pregnancies. However, to ensure the success of the intervention, complete photo-coagulation of all anastomoses is needed. This is made difficult by the limited field of view of the fetoscopic video guidance, which hinders the surgeon's ability to locate all the anastomoses. A potential solution to this problem is to expand the field of view of the placental surface by creating a mosaic from overlapping fetoscopic images. This mosaic can then be used for anastomoses localization and spatial orientation during surgery. However, this requires accurate and fast algorithms that can operate within the real-time constraints of fetal surgery. In this work, we present an image mosaicing framework that leverages the parallelism of modern GPUs and can process clinical fetoscopic images in real-time. Initial qualitative results on ex-vivo placental images indicate that the proposed framework can generate clinically useful mosaics from fetoscopic videos in real-time. DESCRIPTION OF PURPOSETwin-to-twin transfusion syndrome (TTTS) is a complication that affects 9% of monochorionic identical twin pregnancies, where two or more fetuses share a common placenta. 1 The disease results from an imbalance in the blood circulation between the twins due to the presence of anastomoses in the monochorionic placenta. The implication of TTTS is that one of the twins (the donor ) does not receive an adequate supply of blood for normal growth, while the other twin (the recipient) receives too much blood resulting in an overloaded cardiovascular system. Without intervention, the condition is often fatal for both twins. In advanced stages of TTTS, laser coagulation of the connecting vessels on the placenta between the twin fetuses can be a curative procedure. Under fetoscopic video guidance, the surgeon uses a laser fibre to photo-coagulate the blood vessels that connect the two fetuses. This involves visually inspecting the entire placenta to identify the crossing blood vessels that contribute to placental anastomoses. Laser energy is then used to coagulate these blood vessels, effectively separating the shared placenta and allowing each twin to develop independently.A key limitation of fetoscopic video guidance is the small field of view, which makes it difficult for the surgeon to visualize the full placental structure and ensure that all of the vascular anastomoses are identified and treated (figure 1). This problem may be overcome by creating a larger field of view through mosaicing of the fetoscopic video frames. The placental image mosaic may be helpful in locating the anastomoses and for spatial orientation during surgery. 2 These endoscopic image mosaics could also be fused with other imaging modalities to augment the information available during surgery. 3,4 The key to generating an accurate and usable image mosaic is to be able to extract accurate correspondences...

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We have developed a calibration target for use with fluid-immersed endoscopes within the context of the GIFT-Surg (Guided Instrumentation for Fetal Therapy and Surgery) project. One of the aims of this project is to engineer novel, real-time image processing methods for intra-operative use in the treatment of congenital birth defects, such as spina bifida and the twin-to-twin transfusion syndrome. The developed target allows for the sterility-preserving optical distortion calibration of endoscopes within a few minutes. Good optical distortion calibration and compensation are important for mitigating undesirable effects like radial distortions, which not only hamper accurate imaging using existing endoscopic technology during fetal surgery, but also make acquired images less suitable for potentially very useful image computing applications, like real-time mosaicing. In this paper proposes a novel fabrication method to create an affordable, sterilizable calibration target suitable for use in a clinical setup. This method involves etching a calibration pattern by laser cutting a sandblasted stainless steel sheet. This target was validated using the camera calibration module provided by OpenCV, a state-of-the-art software library popular in the computer vision community.

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