Through-body TCSPC based real-time tracking to guide interventional medical procedures

The accurate tracking of medical devices is a key clinical requirement that currently requires the use of ionising X-ray radiation and / or contrast agents. These essential procedures have potential long term detrimental effects, especially on babies, and also causes significant disruption (and therefore cost) due to both the need to protect staff and waiting for the availability of, or transport to, X-ray equipment. There are therefore significant clinical drivers to develop alternative tracking methods. Very recently, we have demonstrated a ground breaking approach to tracking medical devices located deep in tissues using single photon imaging [1]. Our approach exploits the fact that if a point source of light is placed inside the body, a tiny fraction of the light will emerge from the body with a close to line-of-sight path. Crucially, these line-of-sight photons (particles of light) hold precise information about the spatial location of the point source inside the tissue, but extracting this information is not trivial. The key to accessing it is the fact that the line-of-sight photons exit the body with a shorter transit time than the more diffuse photons - a fact that allows us to exploit a technique known as time-correlated single-photon counting (TCSPC) to detect and distinguish them from more diffuse photons.

In contrast to "normal" cameras, which do not record the arrival time of the photons on the detector array, TCSPC-based imaging relies on using a source of light that produces short pulses of light at precisely known times, together with a single-photon sensitive detector array that can record the arrival times of individual photons. In this manner, TCSPC imaging allows us to design an imaging system that can selectively detect and image the location of the emerging line-of-sight photons before the diffuse photons start to emerge, and this allows us to locate the precise position of the source.

Although we have now demonstrated the potential of this technique for medical device tracking, the clinical translation has been hampered by the low fill-factor (how much of the detector array is light-sensitive) of commercially available TCSPC detector arrays. This low fill-factor (~1%) effectively means that we lose 99% of the light reaching the detector array, limiting the maximum frame rate to ~0.05 Hz - too low to provide adequate feedback to the clinician during catheter placement. Recently, through STFC funding, we have demonstrated that so-called "photonic lantern" transitions provide a new and powerful route to addressing the low fill-factor of commercially available SPAD arrays [2]. The overarching goal of this project will therefore be to work with our commercial partners, Photon Force, to exploit this capability, and develop a TCSPC system capable of tracking catheters with video frame rates. We will then work with clinician scientists to translate the technology towards clinical exploitation by demonstrating the tracking capability using relevant models. The results of this project will then be used to support translational clinical studies, and to work with Photon Force to develop a TCSPC tracking system suitable for the medical market.

[1] M. G. Tanner et al, Biomed. Opt. Express 8, 4077-4095 (2017)
[2] H. K. Chandrasekharan et al. Nat. Commun. 8, 14080 (2017).

This project will achieve impact in a number of important areas:

Patients: Through this project, we will take the next step towards an all-optical technology for video-rate tracking of medical devices using time-correlated single-photon counting (TCSPC). This technology will circumvent the current requirement for X-rays and contrast agents which have potential long term detrimental effects, especially on babies, and also add significant disruption (and therefore cost) to procedures. Thus, this project will have a significant positive social impact on patients by "Optimising Treatment" - one of the four healthcare grand-challenges.

NHS: We will develop a device tracking technology that will improve and reduce the costs of a wide range of interventional medical procedures. Thus, this project will result in a proportionate economic benefit to the NHS.

UK Industry: We have partnered with Photon Force, who will benefit directly from the results of this project. Photon Force is a UK SME commercialising advance high pixel count TCSCP SPAD arrays. Through this project, we will leverage our world-leading STFC-funded expertise in integrated photonic lanterns to develop a unique guided wave reformatting component that will convert the Photon Force SPAD array into a high fill-factor TCSCP quad-detector. This project will therefore not only drive the Photon Force SPAD arrays towards a new clinical imaging market, it will also enhance the Photon Force product line. Thus, the project will make an important contribution to supporting UK growth in the Quantum Technologies area - one the UK governments priorities for growth.

UK PLC: This project aims to develop a ground-breaking TCSPC medical device tracking technology, by leveraging globally leading UK expertise in areas such as single-photon detectors, laser manufacturing and optical instrumentation. Thus, the project will impact UK PLC by enhancing its standing and position in these important areas, and opening up new market opportunities across multiple sectors (e.g. medical technologies and advanced instrumentation). The project will also train young multi-skilled, cross-discipline scientists and engineers, the key to a high-tech / value economy.

Academia: This project will benefit academics working in areas such as neonatal medicine, time-correlated single-photon counting imaging, biophotonics, and advanced optical instrumentation. To maximise the widest possible academic impact of the project, we will disseminate our project results (following suitable IP protection steps) through multidisciplinary academic journals, and by attending dedicated international biophotonic and biomedical instrumentation conferences and sessions (e.g. BiOS - Biophotonics at Photonics West). The project will also benefit academics working in the specific fields of ultrafast laser inscription and laser machining. We will engage this specific community by attending laser manufacturing conferences such as The International Congress on Applications of Lasers & Electro-Optics (ICALEO), and those organised by the Association of Industrial Laser Users (AILU).

General: As part of our impact strategy, we will seek out opportunities for public-engagement. We will, for example, build a user-friendly demonstrator for the project technologies. We will take this exhibition to schools, and events such as the IOP Festival of Physics events.