[home] [Personal Program] [Help]

---

Session: Imaging - General
Session starts: Thursday 24 January, 10:40
Presentation starts: 10:55
Room: Lecture room 559

---

Martijn van de Giessen (Leiden University Medical Center/Delft University of Technology)
Boudewijn Lelieveldt (Leiden University Medical Center/Delft University of Technology)
Jouke Dijkstra (Leiden University Medical Center)

Abstract:
Real-time multispectral intra-operative imaging of fluorescent probes imposes constraints on the imaging hardware that are not present in pre-clinical imaging. First, all spectral bands must be imaged simultaneously. This constraint, together with the small form factor of the camera limits the number of imaged wavelengths. In this work a method is proposed to determine the optimal measurement wavelengths based on measured spectra. Assuming a linear mixing model, the measured light intensity in a single spectral band to a mix of probes can be described by a row in a mixing matrix. Similar rows (i.e. measurements) add little information about the ratio between imaged probes, contrary to very different rows. The condition number of this matrix is small for spectra that are linearly independent (the desired situation) [1]. Therefore, we propose to select wavelengths such that the condition number is minimal. Unmixing results using 'optimal' wavelengths are compared to unmixing using 'peak' wavelengths of the probes for simulated multispectral images with increasing noise levels. Probe spectra are measured with the Maestro system between 630nm and 850nm (interval 20nm). The experiment is repeated for all combinations of 2 to 5 probes: AF680, QD700, AF750, QD800 and skin auto-fluorescence. For in-vitro multi-spectral luminescence data from the IVIS Spectrum system, the unmixing results using optimized and peak wavelengths are compared to unmixing based on all acquired wavelengths (500nm to 700nm, interval 20nm) in in-vitro experiments with wells of two mixed probes: CBG99 (540nm) and PpYRE8 (620nm). In simulations the 'peak' unmixing errors were on average 2.86 times larger than the 'optimal' unmixing errors. Selecting the optimal wavelengths was especially beneficial for 3 or more probes. The IVIS in-vitro measurements showed that unmixing with the 'optimal' wavelengths was 8.9% more precise than using the 'peak' wavelengths. Qualitative assessment showed clearer visibility of small structures, e.g. vasculature in mouse brains, when using the ‘optimal’ wavelengths. The results clearly showed that selecting the optimal wavelengths as proposed gives almost 3 times more accurate estimates than measuring at the spectral peaks of the imaged probes, both in simulations as in real measurements. This research was supported by the Center for Translational Molecular Medicine (MUSiS). [1] Silvan-Cardenas and Wang, Fully Constrained Linear Spectral Unmixing: Analytic Solution Using Fuzzy Sets, IEEE Trans. Geoscience and Remote Sensing, 2010