| 1. |
- Andersson-Engels, Stefan, et al.
(författare)
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In vivo luminescence imaging and tomography using upconverting nanoparticles as contrast agents
- 2012
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Ingår i: 2012 Asia Communications and Photonics Conference. - 2162-108X. ; , s. 2-3
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Konferensbidrag (refereegranskat)abstract
- Upconverting nanoparticles have recently drawn increasingly attention as contrast agents for optical bioimaging. They enable autofluorescence-free imaging within the tissue optical window, and improved spatial resolution as compared to conventional fluorescence-based contrast agents. (C) 2012 Optical Society of America
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| 2. |
- Alerstam, Erik, et al.
(författare)
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Next-generation acceleration and code optimization for light transport in turbid media using GPUs
- 2010
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Ingår i: Biomedical Optics Express. - 2156-7085. ; 1:2, s. 658-675
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Tidskriftsartikel (refereegranskat)abstract
- A highly optimized Monte Carlo (MC) code package for simulating light transport is developed on the latest graphics processing unit (GPU) built for general-purpose computing from NVIDIA - the Fermi GPU. In biomedical optics, the MC method is the gold standard approach for simulating light transport in biological tissue, both due to its accuracy and its flexibility in modelling realistic, heterogeneous tissue geometry in 3-D. However, the widespread use of MC simulations in inverse problems, such as treatment planning for PDT, is limited by their long computation time. Despite its parallel nature, optimizing MC code on the GPU has been shown to be a challenge, particularly when the sharing of simulation result matrices among many parallel threads demands the frequent use of atomic instructions to access the slow GPU global memory. This paper proposes an optimization scheme that utilizes the fast shared memory to resolve the performance bottleneck caused by atomic access, and discusses numerous other optimization techniques needed to harness the full potential of the GPU. Using these techniques, a widely accepted MC code package in biophotonics, called MCML, was successfully accelerated on a Fermi GPU by approximately 600x compared to a state-of-the-art Intel Core i7 CPU. A skin model consisting of 7 layers was used as the standard simulation geometry. To demonstrate the possibility of GPU cluster computing, the same GPU code was executed on four GPUs, showing a linear improvement in performance with an increasing number of GPUs. The GPU-based MCML code package, named GPU-MCML, is compatible with a wide range of graphics cards and is released as an open-source software in two versions: an optimized version tuned for high performance and a simplified version for beginners (http://code.google.com/p/gpumcml).
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| 3. |
- Alerstam, Erik, et al.
(författare)
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Single-fiber diffuse optical time-of-flight spectroscopy
- 2012
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Ingår i: Optics Letters. - 0146-9592. ; 37:14, s. 2877-2879
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate interstitial diffuse optical time-of-fight spectroscopy based on a single fiber for both light delivery and detection. Detector saturation due to the massive short-time reflection is avoided by ultrafast gating of a single photon avalanche diode. We show that the effects of scattering and absorption are separable and that absorption can be assessed independently of scattering. Measurements on calibrated liquid phantoms and subsequent Monte Carlo-based evaluation illustrate that absorption coefficients can be accurately assessed over a wide range of medically relevant optical properties. Our findings pave the way to simplified and less invasive interstitial in vivo spectroscopy. (C) 2012 Optical Society of America
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| 8. |
- Brydegaard, Mikkel, et al.
(författare)
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Photobleaching-Insensitive Fluorescence Diagnostics in Skin and Brain Tissue
- 2011
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Ingår i: IEEE Photonics Journal. - : Institute of Electrical and Electronics Engineers. - 1943-0655. ; 3:3, s. 407-421
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigate the possibility of using accurate prediction models for the prediction of protoporphyrin bleaching dynamics to achieve photobleaching-insensitive methods to improve the evaluation of data in an existing clinical fluorescence-guided resection technique. To simulate the scenario, measurements were carried out in vivo on skin of healthy volunteers using a compact fiber-based fluorescence spectroscopy system. We have developed an effective method for the parameterization of sequences of bleaching spectra. We analyze convergence and decay rates with respect to initial conditions and excitation irradiance. We also discuss the consequences and the potential for bleaching-insensitive measurements and their applicability in a few examples from in vivo open brain surgery.
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| 9. |
- Cheng, Haynes P. H., et al.
(författare)
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Autofluorescence of pigmented skin lesions using a pulsed UV laser
- 2010
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Ingår i: Proceedings of SPIE. - : SPIE. ; 7715, s. 1-77151
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Konferensbidrag (refereegranskat)abstract
- We report preliminary clinical results of autofluorescence imaging of malignant and benign skin lesions, using pulsed 355 nm laser excitation with synchronized detection. The novel synchronized detection system allows high signal-tonoise ratio to be achieved in the resulting autofluorescence signal, which may in turn produce high contrast images that improve diagnosis, even in the presence of ambient room light. The synchronized set-up utilizes a compact, diode pumped, pulsed UV laser at 355 nm which is coupled to a CCD camera and a liquid crystal tunable filter. The excitation and image capture is sampled at 5 kHz and the resulting autofluorescence is captured with the liquid crystal filter cycling through seven wavelengths between 420 nm and 580 nm. The clinical study targets pigmented skin lesions and evaluates the prospects of using autofluorescence as a possible means in differentiating malignant and benign skin tumors. Up to now, sixteen patients have participated in the clinical study. The autofluorescence images, averaged over the exposure time of one second, will be presented along with histopathological results. Initial survey of the images show good contrast and diagnostic results show promising agreement based on the histopathological results.
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| 10. |
- Gorpas, Dimitris, et al.
(författare)
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Evaluation of a radiative transfer equation and diffusion approximation hybrid forward solver for fluorescence molecular imaging
- 2012
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Ingår i: Journal of Biomedical Optics. - 1083-3668. ; 17:12
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Tidskriftsartikel (refereegranskat)abstract
- The solution of the forward problem in fluorescence molecular imaging strongly influences the successful convergence of the fluorophore reconstruction. The most common approach to meeting this problem has been to apply the diffusion approximation. However, this model is a first-order angular approximation of the radiative transfer equation, and thus is subject to some well-known limitations. This manuscript proposes a methodology that confronts these limitations by applying the radiative transfer equation in spatial regions in which the diffusion approximation gives decreased accuracy. The explicit integro differential equations that formulate this model were solved by applying the Galerkin finite element approximation. The required spatial discretization of the investigated domain was implemented through the Delaunay triangulation, while the azimuthal discretization scheme was used for the angular space. This model has been evaluated on two simulation geometries and the results were compared with results from an independent Monte Carlo method and the radiative transfer equation by calculating the absolute values of the relative errors between these models. The results show that the proposed forward solver can approximate the radiative transfer equation and the Monte Carlo method with better than 95% accuracy, while the accuracy of the diffusion approximation is approximately 10% lower. (c) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JBO.17.12.126010]
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