DPS controlled laser coagulation needle
Monochorionic (MC) twin pregnancies are at a 10% to 15% risk of developing twin-to-twin transfusion syndrome (TTTS), due to vascular anastomoses on a shared placenta, see left figure. Before De Lia et al. proposed fetoscopic laser ablation of the placental vessels in 1990, serial amnioreduction was considered the only option for treatment of polyhydramnios, the most prominent feature of TTTS. Serial amnioreduction was associated with a double mortality rate of around 50%, a median gestational age at delivery around 28 weeks, and up to 50% major neurodevelopment impairment in survivors.
Laser surgery is now the accepted treatment of choice for TTTS, right figure . However, results are still far from satisfactory, with mortality rates varying from 20% to 48%. Current laser surgery strategy involves puncture of the fetal membranes to gain access to the surface of the placenta from inside the amniotic sac. Important risk factors are the occurrence of residual anastomoses, due to incomplete coagulation and premature rupture of membranes. To improve the outcome of these procedures physicians are in need of tools that can monitor the closure of the vessel during the procedure. Moreover, the development of instruments that allow laser coagulation in deep structures would enable approaching the anastomoses from the other side (i.e. through the placenta), thereby preventing puncture of the fetal membranes.
This research project aims to develop a system for optimal treatment of TTTS using laser coagulation while reducing damage to healthy tissue to a minimum. The proposed instrument consists of a needle carrying an optic fiber for laser coagulation and uses differential path-length spectroscopy (DPS) at the tip of the needle for concurrent monitoring of vascular closure.
WP1.4.1: Design of laser coagulation needle with DPS (TUD)
We will design a needle that combines laser coagulation with the ability to measure oxygenation of tissue near the tip of the needle and, thereby, the completion of vascular closure. The condition of vessels and perfusion can be analyzed immediately before and after laser therapy with DPS. If necessary, a change in laser energy can be made on the basis of measured oxygenation in order to achieve the desired effect, which is the occlusion in vascular malformations. The critical steps in this study involve the development of methods: to guide the needle towards anastomoses (e.g. ultrasound), verify anastomosis contact using DPS, control coagulation energy. DPS signals will be analyzed in collaboration with Erasmus MC.
Deliverable: The proposed instrument combines laser coagulation abilities with DPS to allow the measurement of local tissue oxygenation near the tip of the needle. With this option, the physician will be provided with an analysis of the extent of vascular closure while performing laser coagulation. By using DPS controlled laser therapy healthy tissue can be protected.
WP1.4.2: Laser coagulation effects in placenta (LUMC)
We will study the effect of energy dose on the spreading of heat through placenta tissue samples when performing laser coagulation from the inside out. Although the vessels absorb a major part of the laser radiation, possible heat-induced damage of surrounding structures cannot be eliminated. Ex-vivo experiments will be conducted on human placentas that were made available by healthy women immediately after giving birth at the Department of Obstetrics of LUMC. These placentas will be (partly) reperfused in an experimental setup in which we concurrently measure the blood flow, oxygenation and heat distribution.
Deliverable: In the proposed research we use perfused human tissue to study needle tip laser coagulation performance inside tissue. The developed setup and gained knowledge can provide a model for the development of various laser coagulation instruments. .
WP1.4.3: DPS controlled laser coagulation in placenta (LUMC, TUD)
The instrument developed in this project relies on combining the technologies of WP3.4.1 and 3.4.2 to come to a DPS-controlled laser coagulation needle that has been validated in a pre-clinical setting. In the second phase of the project the researchers of both TUD and LUMC will do the experiments to validate performing and concurrent assessment of coagulation using the needle developed in WP3.4.1. The output of the DPS measurements will be compared to blood flow and oxygenation measurements in the setup developed in WP 3.4.2. Tests will be performed on vessels of various sizes. Ultrasound allows exact placement of the laser fiber to the vessel wall and continuous control of the fibers position.
Deliverable: A system for treatment of vascular malformations in placentas using laser coagulation from the inside out. .