| 1. |
- Berger, Andrew J., et al.
(författare)
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Characterization of scalp—and brain-layer heterogeneity for near infrared spectroscopy
- 2006
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Ingår i: Biomedical Topical Meeting 2006 Fort Lauderdale, Florida, United States,19–22 March 2006, Poster Session II (ME). - Washington, D.C. : OSA Publishing.
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Konferensbidrag (refereegranskat)abstract
- Near-infrared monitoring of cerebral hemodynamics is hampered by biological noise. We propose noise reduction via a two-detector scheme and present measurements characterizing relevant heterogeneity scales for scalp and brain layers in human volunteers.
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| 2. |
- Grant, Alexander M., et al.
(författare)
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Diffuse optical spectroscopy of melanoma-simulating silicone phantoms
- 2009
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Ingår i: PROCEEDINGS VOLUME 7187 SPIE BIOS, 24-29 JANUARY 2009 Biomedical Applications of Light Scattering III. - : SPIE - International Society for Optical Engineering. - 9780819474339 ; , s. 718702-1-718702-12
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Konferensbidrag (refereegranskat)abstract
- Currently the only method for positively identifying malignant melanoma involves invasive and often undesirable biopsy procedures. Available ex-vivo data indicates increased vascularization in the lower regions of excised melanoma, as compared to dysplastic nevi. The ability to interrogate this region of tissue in-vivo could lead to useful diagnostic information. Using a newly developed fiber based superficial probe in conjunction with a steady-state frequency-domain photon migration (SSFDPM) system, we can probe the upper 1-2 mm of tissue, extracting functional information in the near infrared (650-1000 nm) range. To test the resolution and detection range of the superficial probe in this context, deformable silicone phantoms have been fabricated that simulate normal skin with melanocytic lesions. These phantoms consist of a two-layered matrix with the optical properties of normal light skin, containing several cylindrical inclusions that simulate highly absorbing pigmented lesions such as melanoma. These inclusions are varied in depth, diameter, and optical properties in order to fully test the probe's detection capabilities. It was found that, depending on absorption, we can typically probe to a depth of 1.0-1.5 mm in an inclusion, likely reaching the site of angiogenesis in an early-stage melanoma. Additionally, we can successfully interrogate normal tissue below lesions 1.5mm deep when absorption is about 0.4/mm or less. This data indicates that the superficial probe shows great promise for non-invasive diagnosis of pigmented lesions.
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| 3. |
- Saager, Rolf B., 1974-, et al.
(författare)
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Application of a Dual-Detector Scheme for Biological Noise Removal in NIRS Cerebral Hemodynamics Monitoring
- 2006
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Ingår i: Frontiers in Optics, OSA Technical Digest (CD) (Optical Society of America, 2006), paper FWV4. - Washington, D.C. : OSA Publishing. - 1557528187
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Konferensbidrag (refereegranskat)abstract
- We have proposed a method to isolate cerebral NIRS signatures using measurements at two source- detector separations. To examine the applicability of this method on human subjects, a series of different activation protocols are monitored via specialized NIRS probes.
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| 4. |
- Saager, Rolf B., 1974-, et al.
(författare)
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Direct characterization and removal of interfering absorption trends in two-layer turbid media
- 2005
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Ingår i: Journal of the Optical Society of America A. - : OSA Publishing. - 0740-3232 .- 1084-7529 .- 1520-8532. ; 22:9, s. 1874-882
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Tidskriftsartikel (refereegranskat)abstract
- We propose a method to isolate absorption trends confined to the lower layer of a two-layer turbid medium, as is desired in near-infrared spectroscopy (NIRS) of cerebral hemodynamics. Several two-layer Monte Carlo simulations of NIRS time series were generated using a physiologically relevant range of optical properties and varying the absorption coefficients due to bottom-layer, top-layer, and/or global fluctuations. Initial results showed that by measuring absorption trends at two source–detector separations and performing a least-squares fit of one to the other, processed signals strongly resemble the simulated bottom-layer absorption properties. Through this approach, it was demonstrated that fitting coefficients can be estimated within less than ±2% of the ideal value without any a priori knowledge of the optical properties present in the model. An analytical approximation for the least-squares coefficient provides physical insight into the nature of errors and suggests ways to reduce them.
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| 5. |
- Saager, Rolf B., 1974-, et al.
(författare)
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Measurement of layer-like hemodynamic trends in scalp and cortex : implications for physiological baseline suppression in functional near-infrared spectroscopy
- 2008
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Ingår i: Journal of Biomedical Optics. - : OSA Publishing. - 1083-3668 .- 1560-2281. ; 13:3, s. 034017-1-034017-10
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Tidskriftsartikel (refereegranskat)abstract
- A multidetector, continuous wave, near-infrared spectroscopy (NIRS) system is developed to examine whether the hemodynamics of the scalp and brain in adults contain significant layer-like hemodynamic trends. NIRS measurements are made using contrasting geometries, one with four detectors equidistant from a source 33 mm away, and one with detectors collinear with the source (5 to 33 mm away). When NIRS time series are acquired over the prefrontal cortex from resting adults using both geometries, variations among the time series are consistent with a substantially homogeneous two-layer model (p<0.001) and inconsistent with one dominated by heterogeneities. Additionally, when time series measured 5 mm from the source are subtracted from corresponding 33-mm signals via a least-squares algorithm, 60% of the hemoglobin changes are on average removed. These results suggest that hemodynamic trends present in the scalp can contribute significantly to NIRS measurements, and that attempts to reduce this noise by subtracting a simultaneous near-channel measurement using a two-layer model are justified. Such subtractions are then performed on NIRS measurements from two stimulus protocols. For systemic stimulations (Valsalva maneuver), the subtraction cancels the hemodynamic response, as desired. For localized stimulation of the occipital lobe (viewing a flickering pattern), the subtraction isolated a stimulus-correlated hemodynamic feature from background noise.
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