| 1. |
- Landgren, Matilda, et al.
(författare)
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Segmentation of the Left Heart Ventricle in Ultrasound Images Using a Region Based Snake
- 2013
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Ingår i: Medical Imaging 2013: Image Processing. - : SPIE. - 1996-756X .- 0277-786X. - 9780819494436 ; 8669
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Konferensbidrag (refereegranskat)abstract
- Ultrasound imaging of the heart is a non-invasive method widely used for different applications. One of them is to measure the blood volume in the left ventricle at different stages of the heart cycle. This demands a proper segmentation of the left ventricle and a (semi-) automated method would decrease intra-variability as well as workload. This paper presents a semi-automated segmentation method that uses a region based snake. To avoid any unwanted concavities in the segmentations due to the cardiac valve we use two anchor points in the snake that are located to the left and to the right of the cardiac valve respectively. For the possibility of segmentations in different stages of the heart cycle these anchor points are tracked through the cycle. This tracking is based both on the resemblance of a region around the anchor points and a prior model of the movement in the y-direction of the anchor points. The region based snake functional is the sum of two terms, a regularizing term and a data term. It is our data term that is region based since it involves the integration of a two-dimensional subdomain of the image plane. A segmentation of the left ventricle is obtained by minimizing the functional which is done by continuously reshaping the contour until the optimal shape and size is obtained. The developed method shows promising results.
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| 2. |
- Alexander, Naomi E., et al.
(författare)
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IMAGINE project : A low cost, high performance, monolithic passive mm-wave imager front-end
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819492852
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Konferensbidrag (refereegranskat)abstract
- The FP7 Research for SME project IMAGINE - a low cost, high performance monolithic passive mm-wave imager front-end is described in this paper. The main innovation areas for the project are: i) the development of a 94 GHz radiometer chipset and matching circuits suitable for monolithic integration. The chipset consists of a W-band low noise amplifier, fabricated using the commercially available OMMIC D007IH GaAs mHEMT process, and a zero bias resonant interband tunneling diode, fabricated using a patented epi-layer structure that is lattice matched to the same D007IH process; ii) the development of a 94 GHz antenna adapted for low cost manufacturing methods with performance suitable for real-time imaging; iii) the development of a low cost liquid crystal polymer PCB build-up technology with performance suitable for the integration and assembly of a 94 GHz radiometer module; iv) the assembly of technology demonstrator modules. The results achieved in these areas are presented.
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| 3. |
- Andreani, P., et al.
(författare)
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The European ALMA Regional Centre: a model of user support
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819496171 ; 9149, s. Art. no. 91490Y-
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Konferensbidrag (refereegranskat)abstract
- The ALMA Regional Centres (ARCs) form the interface between the ALMA observatory and the user community from the proposal preparation stage to the delivery of data and their subsequent analysis. The ARCs provide critical services to both the ALMA operations in Chile and to the user community. These services were split by the ALMA project into core and additional services. The core services are financed by the ALMA operations budget and are critical to the successful operation of ALMA. They are contractual obligations and must be delivered to the ALMA project. The additional services are not funded by the ALMA project and are not contractual obligations, but are critical to achieve ALMA full scientific potential. A distributed network of ARC nodes (with ESO being the central ARC) has been set up throughout Europe at the following seven locations: Bologna, Bonn-Cologne, Grenoble, Leiden, Manchester, Ondrejov, Onsala. These ARC nodes are working together with the central node at ESO and provide both core and additional services to the ALMA user community. This paper presents the European ARC, and how it operates in Europe to support the ALMA community. This model, although complex in nature, is turning into a very successful one, providing a service to the scientific community that has been so far highly appreciated. The ARC could become a reference support model in an age where very large collaborations are required to build large facilities, and support is needed for geographically and culturally diverse communities.
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| 4. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Bi-metal coated aperture SNOM probes
- 2011
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819486608 ; 8070
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Konferensbidrag (refereegranskat)abstract
- Aperture probes of scanning near-field optical microscopes (SNOM) offer resolution which is limited by a sum of the aperture diameter at the tip of a tapered waveguide probe and twice the skin depth in metal used for coating. An increase of resolution requires a decrease of the aperture diameter. However, due to low energy throughput of such probes aperture diameters usually are larger than 50 nm. A groove structure at fiber core-metal coating interface for photon-to-plasmon conversion enhances the energy throughput 5-fold for Al coated probes and 30-fold for Au coated probes due to lower losses in the metal. However, gold coated probes have lower resolution, first due to light coupling from the core to plasmons at the outside of the metal coating, and second due to the skin depth being larger than for Al. Here we report on the impact of a metal bilayer of constant thickness for coating aperture SNOM probes. The purpose of the bilayer of two metals of which the outer one is aluminum and the inner is a noble metal is to assure low losses, hence larger transmission. Using body-of-revolution finite-difference time-domain simulations we analyze properties of probes without corrugations to measure the impact of using a metal bilayer and choose an optimum bi-metal configuration. Additionally we investigate how this type of metalization works in the case of grooved probes.
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| 5. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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Magnetic probe for material characterization at optical frequencies
- 2011
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819486608 ; 8070
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Konferensbidrag (refereegranskat)abstract
- Rapid development of novel, functional metamaterials made of purely dielectric, plasmonic, or composite structures which exhibit tunable optical frequency magnetic responses creates a need for new measurement techniques. We propose a method of actively measuring magnetic responses, i.e. magnetic dispersion, of such metamaterials within a wide range of optical frequencies with a single probe by exciting individual elementary cells within a larger matrix. The probe is made of a tapered optical fiber with a radially corrugated metal coating. It concentrates azimuthally polarized light in the near-field below the apex into a subwavelength size focus of the longitudinal magnetic field component. An incident azimuthally polarized beam propagates in the core until it reaches the metal stripes of constant angular width running parallel to the axis. For a broad frequency range light-to-plasmon coupling is assured as the lattice constant changes with the radius due to constant angular width. Bound plasmonic modes in slits between the metal stripes propagate toward the apex where circular currents in stripes and displacement currents in slits generate a strong longitudinal magnetic field. The energy density of the longitudinal magnetic component in the vicinity of the axis is much stronger than that of all the other components combined, what allows for pure magnetic excitation of magnetic resonances rather than by the electric field. The scattered signal is then measured in the far-field and analyzed.
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| 6. |
- Antosiewicz, Tomasz, 1981, et al.
(författare)
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On the optical properties of plasmonic glasses
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628415568 ; 9441, s. Art. no. 94411G-
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Konferensbidrag (refereegranskat)abstract
- We report on the optical properties of plasmonic glasses which are metal-dielectric composites composed of metallic inclusions in a host dielectric medium. The investigated structures are of quasi-random nature, described by the pair correlation function, featuring a minimum center-to-center distance between metallic inclusions and long range randomness. Plasmonic glasses exhibiting short-range order only may be fabricated using bottom-up, self-assembly methods and have been utilized in a number of applications such as plasmonic sensing or plasmon-enhanced solar harvesting, and may be also employed for certain non-linear applications. It is therefore important to quantify their properties. Using theoretical methods we investigate optical of 1D, 2D, and 3D structures composed of amorphous distributions of metallic spheres. It is shown, that the response of the constituent element, i.e. The single sphere localized surface plasmon resonance, is modified by the scattered fields of the other spheres in such a way that its peak position, peak amplitude, and full-width at half-maximum exhibit damped oscillations. The oscillation amplitude is set by the particle density and for the peak position may vary by up to 0.3 eV in the optical regime. Using a modified coupled dipole approach we calculate the effective (average) polarizability of plasmonic glasses and discuss their spectra as a function of the dimensionality, angle of incidence and polarization, and the minimum center-to-center distance. The analytical model is complemented and validated by T-Matrix calculations of the optical cross-sections of amorphous arrays of metallic spheres obtained using a modification of the Random Sequential Adsorption algorithm for lines, surfaces, and volumes.
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| 7. |
- Aurumskjöld, Marie-Louise, et al.
(författare)
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An investigation of the iterative reconstruction method iDose(4) on a Philips CT Brilliance 64 using a Catphan 600 phantom
- 2012
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Ingår i: Medical Imaging 2012: Physics of Medical Imaging. - : SPIE. - 0277-786X .- 1996-756X. ; 8313
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Konferensbidrag (refereegranskat)abstract
- The number of CT examinations giving a relatively high patient exposure is increasing. It is therefore important to optimize the imaging conditions at these investigations. Many steps have been taken to reduce the radiation doses in CT examinations. Currently much work is related to iterative image reconstruction methods as alternative to the filtered back projection method. The aim of this work was to evaluate quality parameters in images from a CT (Philips Brilliance 64) equipped with the iterative reconstruction method iDose(4) using a Catphan 600 phantom with and without body simulating ring. CT scans using abdomen protocol were taken with various tube currents and tube voltage and keeping collimation and pitch unchanged for all scans. All collected data were reconstructed with different levels of iDose(4) (Level 2, 4, 6) and traditional filtered back projection. Image quality parameters were evaluated using AutoQA Lite (TM) (Version 2.3 2007 Iris QA, LLC). Results from the study shows that the iterative reconstruction method decreases the noise with 15-45% compared with filtered back projection depending on which level of iDose(4) is used. The percentage reduction in noise level is the same with and without body simulating ring. Low contrast was improved with iDose(4) and spatial resolution is only marginally affected by the method of reconstruction. However by reducing the image noise, the detectability can be improved. Our conclusion is that there is great potential to reduce the noise and thereby improve the image quality by using iterative reconstruction methods. This can also be used to lower radiation dose and maintain image quality or improve image quality.
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| 8. |
- Ayerden, N.P., et al.
(författare)
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Design, fabrication and characterization of LVOF-based IR microspectrometers
- 2014
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628410785 ; 9130
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Konferensbidrag (refereegranskat)abstract
- This paper presents the design, fabrication and characterization of a linear variable optical filter (LVOF) that operates in the infrared (IR) spectral range. An LVOF-based microspectrometer is a tapered-cavity Fabry-Perot optical filter placed on top of a linear array of detectors. The filter transforms the optical spectrum into a lateral intensity profile, which is recorded by the detectors. The IR LVOF has been fabricated in an IC-compatible process flow using a resist reflow and is followed by the transfer etching of this resist pattern into the optical resonator layer. This technique provides the possibility to fabricate a small, robust and high-resolution micro-spectrometer in the IR spectral range directly on a detector chip. In these designs, the LVOF uses thin-film layers of sputtered Si and SiO 2 as the high and low refractive index materials respectively. By tuning the deposition conditions and analyzing the optical properties with a commercial ellipsometer, the refractive index for Si and SiO2 thin-films was measured and optimized for the intended spectral range. Two LVOF microspectrometers, one operating in the 1.8-2.8 μm, and the other in the 3.0-4.5 μm wavelength range, have been designed and fabricated on a silicon wafer. The filters consist of a Fabry-Perot structure combined with a band-pass filter to block the out-of-band transmission. Finally, the filters were fully characterized with an FTIR spectrometer and the transmission curve widening was investigated. The measured transmittance curves were in agreement with theory. The characterization shows a spectral resolution of 35-60 nm for the short wavelength range LVOF and 70 nm for the long wavelength range LVOF, which can be further improved using signal processing algorithms.
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| 9. |
- Barrientos Z, C. M., et al.
(författare)
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Vertically illuminated TW-UTC photodiodes for terahertz generation
- 2012
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819491534 ; 8452
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Konferensbidrag (refereegranskat)abstract
- More efficient and powerful continuous-wave photonic mixers as terahertz sources are motivated by the need of more versatile local oscillators for submillimeter/terahertz receiver systems. Uni-Travelling Carrier (UTC) photodiodes are very prospective candidates for reaching this objective, but so far only have been reported as lumped-elements or as edge-illuminated optical-waveguide travelling-wave (TW) devices. To overcome the associated power limitations of those implementations, we are developing a novel implementation of the UTC photodiodes which combines a traveling-wave photomixer with vertical velocity-matched illumination in a distributed structure. In this implementation called velocity-matched travelling-wave uni-travelling carrier photodiode, it is possible to obtain in-situ velocity matching of the beat-fringes of the two angled laser beams with the submm/THz-wave on the stripline. In this way, minimum frequency roll-off is achieved by tuning the angle between the two laser beams. A first design of these TW-UTC PDs from our Terahertz Photonics Laboratory at University of Chile has been micro-fabricated at the MC2 cleanroom facility at Chalmers Technical University.
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| 10. |
- Barrientos Z, C. M., et al.
(författare)
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Vertically illuminated TW-UTC photodiodes for terahertz generation
- 2010
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819482310 ; 7741
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Konferensbidrag (refereegranskat)abstract
- More efficient continuous-wave photonic nearinfrared mixers as terahertz sources are investigated with the motivation to develop a universal photonic local oscillator for astronomical submillimeter/terahertz receiver systems. For this, we develop new concepts for vertically illuminated traveling-wave (TW) photomixers, TW Uni-Travelling Carrier (UTC) photodiodes. Device simulation/modeling and optical/terahertz testing is being done in the new terahertz photonics laboratory at the Electrical Engineering Department of the University of Chile, whereas device fabrication is performed at the MC2 cleanroom facility at Chalmers Technical University. We report on first progress in this direction.
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