Abstract:
Background:
Tissue oedema is an abnormal fluid accumulation in the interstitial space, which can result from capillary leak or lymphatic dysfunction. Lymphatic dysfunction is a failure of lymphatic vessels to drain interstitial fluid away. It is a common debilitating condition for many patients worldwide and can present in chronic and acute critical illnesses. It also strains the healthcare system, often requiring essential hospital resources, which could be prevented with early intervention. Current methods of diagnosing and treating lymphatic dysfunction are high in cost, relatively inaccessible, and invasive, and may involve exposure to potential radiation.
Aims:
This study aimed to develop a low-cost (<US$300) near infrared (NIR) measurement tool to assess lymphatic dysfunction and diagnose early stages of lymphoedema.
Methods:
Three different prototypes were evaluated, one based around a photodiode and the others based on two mobile-based camera sensors. A series of experiments were conducted to evaluate each of the prototypes. The initial set of experiments was conducted to establish an optimal set of configuration parameters to be carried forward in subsequent experiments. The next set of experiments focused on bench work, evaluating the fluorescence sensitivity of the prototypes against different variants and concentrations of indocyanine green (ICG), as well as the impact that tissue depth had on the sensitivity. Lastly, ex vivo and in vivo assessments for the camera prototypes were conducted on chicken breast, pig’s trotter and a live rat.
Results:
On the bench, the prototypes were able to respond relatively well to varying dosages of ICG tracers and correlated similarly to other studies in the literature using established and more expensive NIR imaging sensors.
Ex vivo, testing used a pig’s trotter, in which ICG was injected in-between the web spaces to visualise the lymphatic vessels. The cameras clearly visualised the lymphatic vessels, showing their capability of imaging superficial lymphatics under the skin. It was then established using phantoms implanted into chicken breast tissue that the limit of imaging depth was ~3mm. In vivo, the cameras could detect and measure in the live rat a decline in fluorescence at the depot injection site over time. They were also able to measure both fluorescence changes from flow of ICG packets and lymphatic vessel contractility.
Conclusion:
The camera imager prototypes demonstrated the ability to provide functional and anatomical information on dermal lymphatics. Using a combination of these low-cost components this thesis showed there is potential to build a low-cost clinical tool.