Thomas Lapauw graduated in 2015 with a Master of Science in Electronics and ICT Engineering Technology – Embedded Systems from the University of Ghent(UGent). Followed by a second Master of Science Electronics and Information Technology Engineering – Nano-, Opto-electronic Devices and Embedded Systems completed at the Vrije Universiteit of Brussels(VUB) in 2017. He started his PhD at the VUB on “Imaging based on Fluorescent lifetime” the same year. His research consists mostly of development of a real-time fluorescence lifetime imaging system around a sensor which is being developed in this department.
Certain molecules exhibit a phenomenon called fluorescence in which they re-emit light that previously had been absorbed. Molecules that have this behavior are called Fluorophores and have a specific wavelength to which they are sensitive and at which they re-emit light. This property has been exploited in multiple different domains of science. One of which is life sciences, where it is used for imaging applications: microscopy, spectroscopy and others, with or without labels.
Some of the main advantages of fluorescence imaging are that it can be used living specimen (in-vivo), multiple fluorophores can be at the same time to label different features, and they are relatively safe to handle and exhibit no radiation.
As an extension to normal fluorescence imaging where the emission-wavelength or the intensity of the light is used to distinguish objects, another property can be used: the average time it takes for a fluorescent molecule to emit a photon. This is called the fluorescence lifetime and can range from a few hundreds of picoseconds, to tens of nanoseconds. Each fluorophore has its own specific lifetime, which is also dependent on its environment, solvent, … These properties can be exploited to gain additional information.
One advantage of using lifetime other that gaining new information about the environment of the fluorophores, is that multiple labels can be distinguished based on lifetime. Even when this would be impossible based on intensity or based on wavelength due to overlapping spectra. For in-vivo applications, such as pre-clinical imaging or fluorescence guided surgery, this is a major advantage because the range of usable wavelengths is the very small Near-Infrared (NIR) band due to scattering and absorption.
Fluorescence lifetime imaging techniques and necessary labels to be used alongside them are being developed for all kinds of different research and medical applications. Because lifetime is a time-resolved property with times in the order of nanoseconds, special instrumentation is needed to measure this. Photon counting techniques with PMTs or SPADs, time-gated techniques using ICCD cameras or Frequency domain techniques are used in practice. Generally large trade-offs between efficiency, measurement time, size, and others need to be made; leaving room for improvements to be made.
The Current Assisted Photonic Sampler (CAPS) technology was developed during the PhD of Dr. Ir. Hans Ingelberts at the ETRO department. This detector with a unique topology was developed in low-cost standard CMOS technology to achieve very short gating-times, or shutter times, at high reputation rates while maintaining high sensitivity over the whole spectrum, even in NIR.
These advantages signal that a CAPS based camera would be a good fit for in-vivo real-time fluorescence-lifetime video applications such as pre-clinical small animal studies and fluorescence guided surgery. As well as for applications where a high-speed time-gated camera is needed, e.g. Tomography
The research focuses on the development of different imaging solutions based on this CAPS technology, quantification and validation. Starting from the initial prototype device with one single pixel for time-domain measurement, to realizing a 2D time domain high-speed time-gated camera focused on real-time NIR fluorescence lifetime imaging applications.