Experimental set-up for near infrared fluorescence measurements during surgery
Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
In case a tumour grows in a tissue close to the lymphatic system, biopsies of the first draining lymph nodes connected to the tumour, also known as sentinel lymph nodes, allow determining if the cancer has already metastasized. Lymph node mapping is used in oncology surgery to find the patients lymph nodes connected to the tumour. The fluorescence marker indocyanine green (ICG) has shown successful results to trace the lymph nodes and arise to replace the currently used radioactive tracers. Because the ICG fluorescence is in the near infrared region and not visible to the human eye, imaging systems are used to visualise the fluorescence. A preliminary spectroscopy measurement system was developed at the Department of Biomedical Engineering, Linköping University. The aim of this thesis was to develop a combined spectroscopy and imaging set-up for simultaneous recordings of ICG fluorescence and suggest further developments.
The combined system consisted of a fibre-optical based spectroscopy system together with a camera imaging system. An optical phantom that mimicked breast tissue (μs = 4.66 mm-1) was developed for the measurements. Phantoms with different ICG concentrations of 6.45 μM, 64.5 μM and 645 μM simulated different concentrations of fluorescence dye in the lymph system. The set-up and the settings of the devices were adjusted to enable simultaneous measurements with both systems. The phantoms were solidified with agar to measure the fluorescence decay (photobleaching) of ICG. To simulate a lymph node deep in the tissue, a tube containing pure ICG was covered with different layer thicknesses of breast tissue-like phantom.
Measurements at the same time with both systems were possible when the probe was positioned in an 80 degree angle with 5 mm distance relative to the phantom surface and the camera in 10 cm distance with a 30 degree angle. To visualise the ICG fluorescence emission with the excitation light (4 mW) and an integration time of 600 ms was necessary for the camera. Higher laser power caused saturation in the spectrometer. The spectroscopy measurements and camera images showed maximum fluorescence intensity at an optimal ICG concentration (10-16 μM) in the phantom. Also the photobleaching measurements showed to be dependent on the ICG concentration and associated with the optimal concentration. ICG concentrations equal and lower than the optimal concentration decayed with exposure to the excitation light. The fluorescence intensity of higher concentrations initially increased and decayed after reaching a maximum intensity when exposed to the excitation light. The detection depth in the simulated tissue was limited to 0.3 mm for spectroscopy. A detection depth of 2 mm was achieved with the camera while using the maximum excitation power of 50 mW and integration time of 700 ms.
Simultaneous measurements were possible with the set-up on the same phantom. An optimal concentration of ICG was found for the developed phantom. The ICG fluorescence intensity was concentration dependent and showed a relatively slow photobleaching. The fibre-optical based spectroscopy system was able to measure low ICG emissions. Subtracting the background spectrum of surrounding tissue might increase the detection of weak ICG signals in depth. High excitation power and an increased integration time were needed to record ICG fluorescence emission with the camera. The obtained results allowed suggestions for the further improvement of set-up and its intraoperative use.
Place, publisher, year, edition, pages
2013. , 55 p.
IdentifiersURN: urn:nbn:se:liu:diva-95985ISRN: LiTH-IMT/ERASMUS-R--13/42--SEOAI: oai:DiVA.org:liu-95985DiVA: diva2:657191
Subject / course
2013-06-18, IMT, Linköping, 10:45 (English)
Haj-Hosseini, Neda, PhD
Hemm, Simone, PhDWårdell, Karin