In the past 40 years, the percentage of twin pregnancies has increased by almost a third as a result of a rise in medically assisted reproduction and delayed childbearing. [1] Of the 1.6 million twin pairs born around the globe every year, %15% are monochorionic (MC), i.e., they share the same placenta. [2] These pregnancies present more frequent complications than dichorionic twins that develop with separate placentas. [3] One of these complications arises from vascular anastomoses that connect the blood circulation systems of both fetuses to the placenta. Twin-to-twin transfusion syndrome (TTTS) affects 10-15% of MC multiple pregnancies and is characterized by a chronic, imbalanced blood flow from the donor to the recipient twin, which results in a disproportionate nutrient supply. [4] If left untreated, the consequences of TTTS are severe, leading to a mid-trimester mortality rate of up to 95%. [5] State-of-the-art treatment of TTTS involves fetoscopic laser coagulation of the placental anastomoses. Under ultrasound guidance, the surgeon identifies a safe entry site in the maternal abdomen from which a fetoscope is inserted through a trocar (typically 2.2-4 mm in diameter; 7-12 French [6] ) into the recipient's amniotic sac. The fetoscope consists of a camera and a working channel to deliver laser light through an optical fiber at the desired location. Before the surgeon ablates the vessels, the vascular architecture is scrutinized and the connecting vessels are identified. Subsequently, all identified anastomoses are coagulated with a neodymium-doped yttrium aluminum garnet (Nd:YAG) or diode laser such that the MC circulation is converted into two independent vascular systems. [7] To ensure no small vessels are missed, the laser is repeatedly fired along a line connecting all the coagulation points from one placental border to the other (known as the Solomon technique). [5,8,9] Mortality rates still range from 20% to 48% after this surgical procedure and significant complications are reported in 6-18% of surviving newborns. [10] Neurological damage to the fetus is also more likely to occur in technically difficult cases. [8] As the procedure is demanding, outcomes are also dependent on the surgeon experience. [7,10] Cases with anterior placentas (i.e., located on the abdominal side of the uterus) constitute a major challenge, even for experienced surgeons. Good access and visualization of anterior placentas are difficult with rigid endoscopes. [11] This can prevent complete coagulation, which,
Remote magnetic navigation is a technology used to robotically steer magnetic medical instruments, such as magnetic catheters and guidewires, for minimally invasive surgery. The ability to model and simulate the behavior of these magnetic instruments in complex anatomies is important for their clinical use in many ways. Simulation frameworks can improve their design, characterization, and automatic control capabilities, as well as provide training simulators for physicians. In this work we introduce a new simulation framework that accounts for both magnetic actuation and interactions forces with meshed collision models. The simulations are validated experimentally in planar rigid models using a pre-clinical electromagnetic navigation system. We also demonstrate the use of our framework to build training simulators for two endovascular navigation tasks including the exploration of the aortic arch and the internal carotid artery.
Diffractometric biosensing is a promising technology to overcome critical limitations of refractometric biosensors, the dominant class of label-free optical transducers. These limitations manifest themselves by higher noise and drifts due to insufficient rejection of refractive index fluctuations caused by variation in temperature, solvent concentration, and, most prominently, nonspecific binding. Diffractometric biosensors overcome these limitations with inherent self-referencing on the submicron scale with no compromise on resolution. Despite this highly promising attribute, the field of diffractometric biosensors has only received limited recognition. A major reason is the lack of a general quantitative analysis. This hinders comparison to other techniques and amongst different diffractometric biosensors. For refractometric biosensors, on the other hand, such a comparison is possible by means of the refractive index unit (RIU). In this paper, we suggest the coherent surface mass density, coh , as a quantity for label-free diffractometric biosensors with the same purpose as the RIU in refractometric sensors. It is easy to translate coh to the total surface mass density tot , which is an important parameter for many assays. We provide a generalized framework to determine coh for various diffractometric biosensing arrangements that enables quantitative comparison. Additionally, the formalism can be used to estimate background scattering in order to further optimize sensor configurations. Finally, a practical guide with important experimental considerations is given to enable readers of any background to apply the theory. Therefore, this paper provides a powerful tool for the development of diffractometric biosensors and will help the field to mature and unveil its full potential.
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