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Publications (10 of 16) Show all publications
Mi, W., Karlsson, S., Holmberg, A., Danielsson, M. & Nillius, P. (2016). Fabrication of circular sawtooth gratings using focused UV lithography. Journal of Micromechanics and Microengineering, 26(3), Article ID 035001.
Open this publication in new window or tab >>Fabrication of circular sawtooth gratings using focused UV lithography
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2016 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 26, no 3, article id 035001Article in journal (Refereed) Published
Abstract [en]

AbstractThis paper presents a novel micro-fabrication method using focused ultraviolet (UV) light to manufacture three-dimensional sawtooth structures in ultra-thick negative photoresist to fabricate a novel multi-prism x-ray lens. The method uses a lens to shape the UV beam instead of the photomask conventionally used in UV lithography. Benefits of this method include the ability to manufacture sawtooth structures in free form, for example in circular shapes as well as arrays of these shapes, and in resist that is up to 76 μm thick.To verify the method, initially a simple simulation based on Fourier optics was done to predict the exposure energy distribution in the photoresist. Furthermore, circular sawtooth gratings were manufactured in a 76 μm SU-8 resist. The UV lens was fabricated using electron beam lithography and then used to expose the SU-8 with UV light. This paper details the complete developed process, including pre-exposure with an e-beam and cold development, which creates stable sawtooth structures. The measured profile was compared to the ideal sawtooth and the simulation. The main discrepancy was in the smallest feature size, the sawtooth tips, which were wider than the desired structures, as would be expected by simulation.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
Keywords
focused UV lithography, three-dimensional sawtooth structures, SU-8, UV lens, Fourier optics
National Category
Medical Engineering
Research subject
Medical Technology; Physics; Applied Medical Technology
Identifiers
urn:nbn:se:kth:diva-185957 (URN)10.1088/0960-1317/26/3/035001 (DOI)000375230700001 ()2-s2.0-84959432882 (Scopus ID)
Projects
Medical Imaging Project
Funder
Stiftelsen Olle Engkvist Byggmästare
Note

QC 20160509

Available from: 2016-04-29 Created: 2016-04-29 Last updated: 2017-11-30Bibliographically approved
Nillius, P., Klamra, W., Sibczynski, P., Sharma, D., Danielsson, M. & Badano, A. (2015). Light output measurements and computational models of microcolumnar CsI scintillators for x-ray imaging. Medical physics (Lancaster), 42(2), 600-605
Open this publication in new window or tab >>Light output measurements and computational models of microcolumnar CsI scintillators for x-ray imaging
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2015 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 42, no 2, p. 600-605Article in journal (Refereed) Published
Abstract [en]

Purpose: The authors report on measurements of light output and spatial resolution of microcolumnar CsI:Tl scintillator detectors for x-ray imaging. In addition, the authors discuss the results of simulations aimed at analyzing the results of synchrotron and sealed-source exposures with respect to the contributions of light transport to the total light output. Methods: The authors measured light output from a 490-mu m CsI:Tl scintillator screen using two setups. First, the authors used a photomultiplier tube (PMT) to measure the response of the scintillator to sealed-source exposures. Second, the authors performed imaging experiments with a 27-keV monoenergetic synchrotron beam and a slit to calculate the total signal generated in terms of optical photons per keV. The results of both methods are compared to simulations obtained with hybrid MANTIS, a coupled x-ray, electron, and optical photon Monte Carlo transport package. The authors report line response (LR) and light output for a range of linear absorption coefficients and describe a model that fits at the same time the light output and the blur measurements. Comparing the experimental results with the simulations, the authors obtained an estimate of the absorption coefficient for the model that provides good agreement with the experimentally measured LR. Finally, the authors report light output simulation results and their dependence on scintillator thickness and reflectivity of the backing surface. Results: The slit images from the synchrotron were analyzed to obtain a total light output of 48 keV(-1) while measurements using the fast PMT instrument setup and sealed-sources reported a light output of 28 keV-1. The authors attribute the difference in light output estimates between the two methods to the difference in time constants between the camera and PMT measurements. Simulation structures were designed to match the light output measured with the camera while providing good agreement with the measured LR resulting in a bulk absorption coefficient of 5x10(-5) mu m(-1). Conclusions: The combination of experimental measurements for microcolumnar CsI:Tl scintillators using sealed-sources and synchrotron exposures with results obtained via simulation suggests that the time course of the emission might play a role in experimental estimates. The procedure yielded an experimentally derived linear absorption coefficient for microcolumnar Cs:Tl of 5x10(-5) mu m(-1). To the author's knowledge, this is the first time this parameter has been validated against experimental observations. The measurements also offer insight into the relative role of optical transport on the effective optical yield of the scintillator with microcolumnar structure.

Keywords
CsI, scintillator, light transport, light output, blur
National Category
Medical Engineering
Identifiers
urn:nbn:se:kth:diva-161120 (URN)10.1118/1.4905096 (DOI)000349229600008 ()2-s2.0-84923375556 (Scopus ID)
Note

QC 20150323

Available from: 2015-03-23 Created: 2015-03-09 Last updated: 2017-12-04Bibliographically approved
Mi, W. & Nillius, P. (2014). Efficient proximity effect correction method based on multivariate adaptive regression splines for grayscale e-beam lithography. Journal of Vacuum Science & Technology B, 32(3), 031602
Open this publication in new window or tab >>Efficient proximity effect correction method based on multivariate adaptive regression splines for grayscale e-beam lithography
2014 (English)In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 32, no 3, p. 031602-Article in journal (Refereed) Published
Abstract [en]

Grayscale electron beam lithography is an important technique to manufacture three-dimensional (3D) micro- and nano-structures, such as diffractive optical devices and Fresnel lenses. However, the proximity effect due to the scattering of electrons may cause significant error to the desired 3D structure. Conventional proximity correction methods depend on the exposure energy distribution which sometimes is difficult to obtain. In this study, the authors develop a novel proximity effect correction method based on multivariate adaptive regression splines, which takes exposure energy and development into consideration simultaneously. To evaluate the method, a Fresnel lens was fabricated through simulation and experiment. The measurements demonstrate the feasibility and validity of the method.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering Physical Sciences
Identifiers
urn:nbn:se:kth:diva-147744 (URN)10.1116/1.4875955 (DOI)000337061900046 ()2-s2.0-84900822144 (Scopus ID)
Note

QC 20140704

Available from: 2014-07-04 Created: 2014-07-03 Last updated: 2017-12-05Bibliographically approved
Nillius, P. (2012). Geometric scattering in prism-array lenses for hard x-rays: Measurements, simulations and models. In: X-Ray Optics And Microanalysis: . Paper presented at 21st International Congress on X-Ray Optics and Microanalysis, ICXOM21; Campinas; 5 September 2011 through 9 September 2011 (pp. 111-115). American Institute of Physics (AIP), 1437
Open this publication in new window or tab >>Geometric scattering in prism-array lenses for hard x-rays: Measurements, simulations and models
2012 (English)In: X-Ray Optics And Microanalysis, American Institute of Physics (AIP), 2012, Vol. 1437, p. 111-115Conference paper, Published paper (Refereed)
Abstract [en]

This work investigates the properties of off-axis focusing of prism-array lenses. Raytracing simulations are in agreement with measurements on a planar silicon prism-array lens at 13.4 keV. The simulations show that refractions and reflections on the paraxial side of the prisms cause scattering. This geometric scattering is the main impacting factor when focusing sources that are off the optical axis. For low-attenuating materials it also limits the effective aperture on axis. A new analytical model that is able to predict the amount of scattering is presented. Such a model is for example useful when optimising optical systems, but also to understand the limits and possibilities prism-array lenses.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2012
Series
AIP Conference Proceedings, ISSN 0094-243X ; 1437
Keywords
analytic model, Fresnel lens, kinoform lens, scattering, x-ray lens
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:kth:diva-100425 (URN)10.1063/1.3703353 (DOI)000307636000020 ()2-s2.0-84863630885 (Scopus ID)978-073541027-5 (ISBN)
Conference
21st International Congress on X-Ray Optics and Microanalysis, ICXOM21; Campinas; 5 September 2011 through 9 September 2011
Note

QC 20120809

Available from: 2012-08-09 Created: 2012-08-08 Last updated: 2013-09-16Bibliographically approved
Tibbelin, S., Nillius, P. & Danielsson, M. (2012). Simulation of HyperSPECT: a high-resolution small-animal system with in-line x-ray optics. Physics in Medicine and Biology, 57(6), 1617-1629
Open this publication in new window or tab >>Simulation of HyperSPECT: a high-resolution small-animal system with in-line x-ray optics
2012 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 6, p. 1617-1629Article in journal (Refereed) Published
Abstract [en]

SPECT has become an important tool in pre-clinical applications. Small-animal imaging systems based on the use of one or more pinhole collimators now reach sub-half-mm resolution but unfortunately suffer from a compromise between sensitivity and resolution due to the pinhole collimators. We propose a small-animal SPECT system based not on pinholes but on in-line x-ray optics, which is rare in medical imaging systems for nuclear medicine. The x-ray lenses are optimized for 27 keV for low-energy imaging with iodine-125. We believe that this new system, HyperSPECT, can simultaneously improve on sensitivity and resolution compared to today's state-of-the-art systems. A full three-dimensional simulation of the system has been performed including the prism-array lenses, pre-and post-collimators and scintillator-based detector. Images of capillary phantoms have been reconstructed using an iterative image reconstruction method. Sensitivity was uniformly 0.37% throughout the 1 cm diameter spherical field of view and rod sizes of around 100 mu m diameter were distinguishable in the images of simulated capillary phantoms. These results indicate an increase in resolution by a factor of 5 during a simultaneous increase in sensitivity by a factor of 2 compared to the current state-of-the-art small-animal SPECT systems.

National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:kth:diva-93382 (URN)10.1088/0031-9155/57/6/1617 (DOI)000301358000010 ()2-s2.0-84858062493 (Scopus ID)
Note

QC 20120416

Available from: 2012-04-16 Created: 2012-04-16 Last updated: 2017-12-07Bibliographically approved
Nillius, P., Karlsson, S., Cederström, B., Fredenberg, E. & Danielsson, M. (2011). Large-aperture focusing of high-energy x rays with a rolled polyimide film. Optics Letters, 36(4), 555-557
Open this publication in new window or tab >>Large-aperture focusing of high-energy x rays with a rolled polyimide film
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2011 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 36, no 4, p. 555-557Article in journal (Refereed) Published
Abstract [en]

We describe a point-focusing x-ray lens made of a rolled polyimide film with etched prisms. The resulting lens is a cylinder with a large number of prisms forming an internal conic structure. The method allows for the manufacturing of lenses with large apertures and short focal lengths, for energies up to at least 100 keV. In order to evaluate the concept, we have hand-rolled a few lenses and evaluated them at a synchrotron source. The measured performance of the prototype is promising, and deviations from the theoretical limits are quantitatively explained. (C) 2011 Optical Society of America

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-30889 (URN)000287395500043 ()2-s2.0-79952119919 (Scopus ID)
Note
QC 20110317Available from: 2011-03-17 Created: 2011-03-07 Last updated: 2017-12-11Bibliographically approved
Nillius, P. & Danielsson, M. (2010). Theoretical Bounds and System Design for Multipinhole SPECT. IEEE Transactions on Medical Imaging, 29(7), 1390-1400
Open this publication in new window or tab >>Theoretical Bounds and System Design for Multipinhole SPECT
2010 (English)In: IEEE Transactions on Medical Imaging, ISSN 0278-0062, E-ISSN 1558-254X, Vol. 29, no 7, p. 1390-1400Article in journal (Refereed) Published
Abstract [en]

The pinhole camera in single photon emission computed tomography (SPECT) has an inherent trade-off between resolution and sensitivity. Recent systems overcome this to some extent by utilizing multiple pinholes distributed around the imaging object. The present work is a theoretical study on how to optimally construct such systems. We use an analytic model to analyze the multipinhole SPECT geometry and identify the underlying trade-offs. One of the results is the derivation of the upper bound for the sensitivity, given the geometric resolution and field-of-view (FOV). Reaching this bound requires an infinitely large detector. However, a sensitivity very close to the upper bound can be achieved by a system with realistic proportions. We show that it is usually possible to get a sensitivity that is 95%-99% of the upper bound. Further analysis reveals a trade-off between sensitivity, magnification, and the number of pinholes. Based on this new theory, we develop a strategy for multipinhole SPECT design, from which a number of example systems are computed. Penetration in the pinhole knife edge is accounted for by using the resolution and sensitivity equivalent apertures.

Keywords
Multipinhole collimator, single photon emission computed tomography (SPECT), small-animal imaging, system analysis and design
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:kth:diva-26642 (URN)10.1109/TMI.2010.2047113 (DOI)000281925700005 ()2-s2.0-77954234753 (Scopus ID)
Note
QC 20101203Available from: 2010-12-03 Created: 2010-11-26 Last updated: 2017-12-12Bibliographically approved
Fredenberg, E., Cederström, B., Nillius, P., Ribbing, C., Karlsson, S. & Danielsson, M. (2009). A low-absorption x-ray energy filter for small-scale applications. Optics Express, 17(14), 11388-11398
Open this publication in new window or tab >>A low-absorption x-ray energy filter for small-scale applications
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2009 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 17, no 14, p. 11388-11398Article in journal (Refereed) Published
Abstract [en]

We present an experimental and theoretical evaluation of an x-ray energy filter based on the chromatic properties of a prism-array lens (PAL). It is intended for small-scale applications such as medical imaging. The PAL approximates a Fresnel lens and allows for high efficiency compared to filters based on ordinary refractive lenses, however at the cost of a lower energy resolution. Geometrical optics was found to provide a good approximation for the performance of a flawless lens, but a field-propagation model was used for quantitative predictions. The model predicted a 0.29 ΔE/E energy resolution and an intensity gain of 6.5 for a silicon PAL at 23.5 keV. Measurements with an x-ray tube showed good agreement with the model in energy resolution and peak energy, but a blurred focal line contributed to a 29% gain reduction. We believe the blurring to be caused mainly by lens imperfections, in particular at the periphery of the lens.

Keywords
X-ray optics, Diffractive lenses, Refractive lenses, Filters, Medical x-ray imaging, Radiation, Wave propagation
National Category
Atom and Molecular Physics and Optics Radiology, Nuclear Medicine and Medical Imaging Other Engineering and Technologies not elsewhere specified Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-11635 (URN)10.1364/OE.17.011388 (DOI)000267761200018 ()2-s2.0-67650544809 (Scopus ID)
Note
QC 20100713Available from: 2009-11-27 Created: 2009-11-27 Last updated: 2017-12-12Bibliographically approved
Fredenberg, E., Cederström, B., Åslund, M., Nillius, P. & Danielsson, M. (2009). An efficient pre-object collimator based on an x-ray lens. Medical physics (Lancaster), 36(2), 626-633
Open this publication in new window or tab >>An efficient pre-object collimator based on an x-ray lens
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2009 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 36, no 2, p. 626-633Article in journal (Refereed) Published
Abstract [en]

A multiprism lens (MPL) is a refractive x-ray lens with one-dimensional focusing properties. If used as a pre-object collimator in a scanning system for medical x-ray imaging, it reduces the divergence of the radiation and improves on photon economy compared to a slit collimator. Potential advantages include shorter acquisition times, a reduced tube loading, or improved resolution. We present the first images acquired with a MPL in a prototype for a scanning mammography system. The lens showed a gain of flux of 1.32 compared to a slit collimator at equal resolution, or a gain in resolution of 1.31–1.44 at equal flux. We expect the gain of flux in a clinical setup with an optimized MPL and a custom-made absorption filter to reach 1.67, or 1.45–1.54 gain in resolution.

Keywords
x-ray imaging, mammography, x-ray optics, multiprism lens, collimation, x-ray flux, acquisition time, resolution
National Category
Other Engineering and Technologies not elsewhere specified Atom and Molecular Physics and Optics Radiology, Nuclear Medicine and Medical Imaging Medical Laboratory and Measurements Technologies
Identifiers
urn:nbn:se:kth:diva-11634 (URN)10.1118/1.3062926 (DOI)000262852600037 ()2-s2.0-59249085647 (Scopus ID)
Note
QC 20100713Available from: 2009-11-27 Created: 2009-11-27 Last updated: 2017-12-12Bibliographically approved
Tibbelin, S., Nillius, P., Cederström, B. & Danielsson, M. (2009). HyperSPECT: a new system for pre-clinical imaging in vivo. In: Medical Imaging 2009: Physics of Medical Imaging. Paper presented at Medical Imaging 2009: Physics of Medical Imaging. Lake Buena Vista, FL. 9 February 2009 - 12 February 2009. SPIE - International Society for Optical Engineering, 7258(1)
Open this publication in new window or tab >>HyperSPECT: a new system for pre-clinical imaging in vivo
2009 (English)In: Medical Imaging 2009: Physics of Medical Imaging, SPIE - International Society for Optical Engineering, 2009, Vol. 7258, no 1Conference paper, Published paper (Refereed)
Abstract [en]

Imaging in general is becoming increasingly important in the medical science. At the cell level it is possible to label and trace almost individual molecules in vivo to study biochemical reactions using microscopy. In vivo imaging of living organisms is today mainly accomplished by PET, SPECT and fMRI. The problem is that the spatial resolution for realistic image acquisition times is of the order 1-3 mm, which is a serious limitation. We propose a new imaging modality, based on the same principles as SPECT but with drastically improved efficiency and spatial resolution. This is achieved by incorporating a large number of x-ray lenses between the detectors and the object. In current SPECT a pin-hole geometry is standard, involving an unfortunate trade-off between efficiency and spatial resolution, our solution would change this. The agent for radiolabelling is assumed to be 125I, with an emission peak at 27 keV, since it is widely used and easy to handle. The large area, photon counting detectors will consist of a columnar CsI scintillator coupled to a CMOS integrated circuit for electronic read-out. Our simulations of the entire system and of the detector indicate that a resolution of 50 μm for the system is possible.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2009
Series
Progress in Biomedical Optics and Imaging - Proceedings of SPIE, ISSN 1605-7422 ; 7258
Keywords
CMOS, Columnar CsI, Photon-Counting, SPECT
National Category
Atom and Molecular Physics and Optics Medical Equipment Engineering
Identifiers
urn:nbn:se:kth:diva-84825 (URN)10.1117/12.812964 (DOI)2-s2.0-66749125464 (Scopus ID)9780819475091 (ISBN)
Conference
Medical Imaging 2009: Physics of Medical Imaging. Lake Buena Vista, FL. 9 February 2009 - 12 February 2009
Note

QC 20120213

Available from: 2012-02-13 Created: 2012-02-13 Last updated: 2017-03-30Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7725-0548

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