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Article: Optimization of injected

Wielaard, J / Habraken, J B A / Brinks, P / Lavalaye, J / Boellaard, R

2020 Volume 7, Issue 1, Page(s) 20

Abstract: Optimization of injected gallium-68 ( ...

Abstract	Optimization of injected gallium-68 (
Language	English
Publishing date	2020-04-15
Publishing country	Germany
Document type	Journal Article
ZDB-ID	2768912-8
ISSN	2197-7364
ISSN	2197-7364
DOI	10.1186/s40658-020-00289-9
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Article ; Online: A phase mixing model for the frequency-doubling illusion.

Wielaard, James / Smith, R Theodore

Journal of the Optical Society of America. A, Optics, image science, and vision

2013 Volume 30, Issue 10, Page(s) 2048–2065

Abstract: We introduce a temporal phase mixing model for a description of the frequency-doubling illusion (FDI). The model is generic in the sense that it can be set to refer to retinal ganglion cells, lateral geniculate cells, as well as simple cells in the ... ...

Abstract	We introduce a temporal phase mixing model for a description of the frequency-doubling illusion (FDI). The model is generic in the sense that it can be set to refer to retinal ganglion cells, lateral geniculate cells, as well as simple cells in the primary visual cortex (V1). Model parameters, however, strongly suggest that the FDI originates in the cortex. The model shows how noise in the response phases of cells in V1, or in further processing of these phases, easily produces observed behavior of FDI onset as a function of spatiotemporal frequencies. It also shows how this noise can accommodate physiologically plausible spatial delays in comparing neural signals over a distance. The model offers an explanation for the disappearance of the FDI at sufficiently high spatial frequencies via increasingly correlated coding of neighboring grating stripes. Further, when the FDI is equated to vanishing perceptual discrimination between asynchronous contrast-reversal gratings, the model proposes the possibility that the FDI shows a resonance behavior at sufficiently high spatial frequencies, by which it is alternately perceived and not perceived in sequential temporal frequency bands.
MeSH term(s)	Algorithms ; Contrast Sensitivity ; Differential Threshold ; Discrimination (Psychology) ; Humans ; Light ; Models, Neurological ; Neurons/metabolism ; Neurons/physiology ; Optical Illusions/physiology ; Orientation ; Perception ; Photic Stimulation/methods ; Probability ; Psychometrics ; Reproducibility of Results ; Retinal Ganglion Cells/physiology ; Vision, Ocular/physiology
Language	English
Publishing date	2013-10-01
Publishing country	United States
Document type	Journal Article
ZDB-ID	283633-6
ISSN	1520-8532 ; 1084-7529 ; 0740-3232
ISSN (online)	1520-8532
ISSN	1084-7529 ; 0740-3232
DOI	10.1364/JOSAA.30.002048
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Article ; Online: Optimization of injected 68Ga-PSMA activity based on list-mode phantom data and clinical validation

J. Wielaard / J. B. A. Habraken / P. Brinks / J. Lavalaye / R. Boellaard

EJNMMI Physics, Vol 7, Iss 1, Pp 1-

2020 Volume 12

Abstract: Abstract Optimization of injected gallium-68 (68Ga) activity for 68Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (68Ga-PSMA PET/CT) studies is relevant for image quality, radiation protection, and from an economic ...

Abstract	Abstract Optimization of injected gallium-68 (68Ga) activity for 68Ga-prostate-specific membrane antigen positron emission tomography/computed tomography (68Ga-PSMA PET/CT) studies is relevant for image quality, radiation protection, and from an economic point of view. However, no clear guidelines are available for 68Ga-PSMA studies. Therefore, a phantom study is performed to determine the highest coefficient of variation (COV) acceptable for reliable image interpretation and quantification. To evaluate image interpretation, the relationship of COV and contrast-to-noise ratio (CNR) was studied. The CNR should remain larger than five, according to the Rose criterion. To evaluate image quantification, the effect of COV on the percentage difference (PD) between quantification results of two studies was analyzed. Comparison was done by calculating the PD of the SUVmax. The maximum allowable PDSUVmax was set at 20%. The highest COV at which both criteria are still met is defined as COVmax. Of the NEMA Image Quality phantom, a 20 min/bed (2 bed positions) scan was acquired in list-mode PET (Philips Gemini TF PET/CT). The spheres to background activity ratio was approximately 9:1. To obtain images with different COV, lower activity was mimicked by reconstructions with acquisition times of 10 min/bed to 5 s/bed. Pairs of images were obtained by reconstruction of two non-overlapping parts of list-mode data. For the 10-mm diameter sphere, a COV of 25% still meets the criteria of CNRSUVmean ≥ 5 and PDSUVmax ≤ 20%. This phantom scan was acquired with an acquisition time of 116 s and a background activity concentration of 0.71 MBq/kg. Translation to a clinical protocol results in a clinical activity regimen of 3.5 MBq/kg min at injection. To verify this activity regimen, 15 patients (6 MBq/kg min) with a total of 22 lesions are included. Additional reconstructions were made to mimic the proposed activity regimen. Based on the CNRSUVmax, no lesions were missed with this proposed activity regimen. For our institution, a ...
Keywords	PET ; 68Ga-PSMA ; Activity ; Optimization ; Medical physics. Medical radiology. Nuclear medicine ; R895-920
Subject code	571
Language	English
Publishing date	2020-04-01T00:00:00Z
Publisher	SpringerOpen
Document type	Article ; Online
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Article ; Online: Characterizing Tropical Forest Cover Loss Using Dense Sentinel-1 Data and Active Fire Alerts

Reiche, J. / Verhoeven, R. / Verbesselt, J. / Hamunyela, E. / Wielaard, N. / Herold, M.

Remote Sensing

2018

Publishing country	de
Document type	Article ; Online
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Article: Dependence of response properties on sparse connectivity in a spiking neuron model of the lateral geniculate nucleus.

Wielaard, Jim / Sajda, Paul

Journal of neurophysiology

2007 Volume 98, Issue 6, Page(s) 3292–3308

Abstract: We present a large-scale anatomically constrained spiking neuron model of the lateral geniculate nucleus (LGN), which operates solely with retinal input, relay cells, and interneurons. We show that interneuron inhibition and sparse connectivity between ... ...

Abstract	We present a large-scale anatomically constrained spiking neuron model of the lateral geniculate nucleus (LGN), which operates solely with retinal input, relay cells, and interneurons. We show that interneuron inhibition and sparse connectivity between LGN cells could be key factors for explaining a number of observed classical and extraclassical response properties in LGN of monkey and cat. Among them are 1) weak orientation tuning, 2) contrast invariance of spatial frequency tuning in the absence of cortical feedback, 3) extraclassical surround suppression, and 4) orientation tuning of extraclassical surround suppression. The model also makes two surprising predictions: 1) a possible pinwheel-like spatial organization of orientation preference in the parvo layers of monkey LGN, much like what is seen in V1, and 2) a stimulus-induced trend (bias) in the orientation and phase preference of surround suppression, originating from the stimulus discontinuity between center and surround gratings rather than from specific circuitry.
MeSH term(s)	Algorithms ; Animals ; Cats ; Data Interpretation, Statistical ; Geniculate Bodies/cytology ; Geniculate Bodies/physiology ; Haplorhini ; Models, Neurological ; Neural Pathways/cytology ; Neural Pathways/physiology ; Neurons/physiology ; Orientation/physiology ; Retinal Ganglion Cells/physiology ; Stochastic Processes
Language	English
Publishing date	2007-12
Publishing country	United States
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	80161-6
ISSN	1522-1598 ; 0022-3077
ISSN (online)	1522-1598
ISSN	0022-3077
DOI	10.1152/jn.00654.2007
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Article: Perceptual decision making "through the eyes" of a large-scale neural model of v1.

Shi, Jianing V / Wielaard, Jim / Smith, R Theodore / Sajda, Paul

Frontiers in psychology

2013 Volume 4, Page(s) 161

Abstract: Sparse coding has been posited as an efficient information processing strategy employed by sensory systems, particularly visual cortex. Substantial theoretical and experimental work has focused on the issue of sparse encoding, namely how the early visual ...

Abstract	Sparse coding has been posited as an efficient information processing strategy employed by sensory systems, particularly visual cortex. Substantial theoretical and experimental work has focused on the issue of sparse encoding, namely how the early visual system maps the scene into a sparse representation. In this paper we investigate the complementary issue of sparse decoding, for example given activity generated by a realistic mapping of the visual scene to neuronal spike trains, how do downstream neurons best utilize this representation to generate a "decision." Specifically we consider both sparse (L1-regularized) and non-sparse (L2 regularized) linear decoding for mapping the neural dynamics of a large-scale spiking neuron model of primary visual cortex (V1) to a two alternative forced choice (2-AFC) perceptual decision. We show that while both sparse and non-sparse linear decoding yield discrimination results quantitatively consistent with human psychophysics, sparse linear decoding is more efficient in terms of the number of selected informative dimension.
Language	English
Publishing date	2013-04-19
Publishing country	Switzerland
Document type	Journal Article
ZDB-ID	2563826-9
ISSN	1664-1078
ISSN	1664-1078
DOI	10.3389/fpsyg.2013.00161
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Article: Circuitry and the classification of simple and complex cells in V1.

Wielaard, Jim / Sajda, Paul

Journal of neurophysiology

2006 Volume 96, Issue 5, Page(s) 2739–2749

Abstract: Based on a large-scale neural network model of striate cortex (V1), we present a simulation study of extra- and intracellular response modulations for drifting and contrast reversal grating stimuli. Specifically, we study the dependency of these ... ...

Abstract	Based on a large-scale neural network model of striate cortex (V1), we present a simulation study of extra- and intracellular response modulations for drifting and contrast reversal grating stimuli. Specifically, we study the dependency of these modulations on the neural circuitry. We find that the frequently used ratio of the first harmonic to the mean response to classify simple and complex cells is highly insensitive to circuitry. Limited experimental sample size for the distribution of this measure makes it unsuitable for distinguishing whether the dichotomy of simple and complex cells originates from distinct LGN axon connectivity and/or local circuitry in V1. We show that a possible useful measure in this respect is the ratio of the intracellular second- to first-harmonic response for contrast reversal gratings. This measure is highly sensitive to neural circuitry and its distribution can be sampled with sufficient accuracy from a limited amount of experimental data. Further, the distribution of this measure is qualitatively similar to that of the subfield correlation coefficient, although it is more robust and easier to obtain experimentally.
MeSH term(s)	Algorithms ; Animals ; Contrast Sensitivity/physiology ; Macaca ; Membrane Potentials ; Models, Neurological ; Nerve Net/cytology ; Nerve Net/physiology ; Neurons/classification ; Neurons/physiology ; Photic Stimulation ; Visual Cortex/cytology ; Visual Cortex/physiology
Language	English
Publishing date	2006-11
Publishing country	United States
Document type	Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	80161-6
ISSN	1522-1598 ; 0022-3077
ISSN (online)	1522-1598
ISSN	0022-3077
DOI	10.1152/jn.00346.2006
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Article: Extraclassical receptive field phenomena and short-range connectivity in V1.

Wielaard, Jim / Sajda, Paul

Cerebral cortex (New York, N.Y. : 1991)

2006 Volume 16, Issue 11, Page(s) 1531–1545

Abstract: Extraclassical receptive field phenomena in V1 are commonly attributed to long-range lateral connections and/or extrastriate feedback. We address 2 such phenomena: surround suppression and receptive field expansion at low contrast. We present rigorous ... ...

Abstract	Extraclassical receptive field phenomena in V1 are commonly attributed to long-range lateral connections and/or extrastriate feedback. We address 2 such phenomena: surround suppression and receptive field expansion at low contrast. We present rigorous computational support for the hypothesis that the phenomena largely result from local short-range (< 0.5 mm) cortical connections and lateral geniculate nucleus input. The neural mechanisms of surround suppression in our simulations operate via (A) enhancement of inhibition, (B) reduction of excitation, or (C) action of both simultaneously. Mechanisms (B) and (C) are substantially more prevalent than (A). We observe, on average, a growth in the spatial summation extent of excitatory and inhibitory synaptic inputs for low-contrast stimuli. However, we find this is neither sufficient nor necessary to explain receptive field expansion at low contrast, which usually involves additional changes in the relative gain of these inputs.
MeSH term(s)	Algorithms ; Animals ; Feedback ; Macaca ; Models, Neurological ; Models, Statistical ; Neural Networks (Computer) ; Neural Pathways/physiology ; Neurons/physiology ; Normal Distribution ; Photic Stimulation ; Synapses/physiology ; Visual Cortex/physiology
Language	English
Publishing date	2006-11
Publishing country	United States
Document type	Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
ZDB-ID	1077450-6
ISSN	1460-2199 ; 1047-3211
ISSN (online)	1460-2199
ISSN	1047-3211
DOI	10.1093/cercor/bhj090
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Article ; Online: Characterizing Tropical Forest Cover Loss Using Dense Sentinel-1 Data and Active Fire Alerts

Reiche, Johannes / Verhoeven, Rob / Verbesselt, Jan / Hamunyela, Eliakim / Wielaard, Niels / Herold, Martin

Remote Sensing

2018 Volume 10, Issue 5

Abstract: Fire use for land management is widespread in natural tropical and plantation forests, causing major environmental and economic damage. Recent studies combining active fire alerts with annual forest-cover loss information identified fire-related forest- ... ...

Abstract	Fire use for land management is widespread in natural tropical and plantation forests, causing major environmental and economic damage. Recent studies combining active fire alerts with annual forest-cover loss information identified fire-related forest-cover loss areas well, but do not provide detailed understanding on how fires and forest-cover loss are temporally related. Here, we combine Sentinel-1-based, near real-time forest cover information with Visible Infrared Imaging Radiometer Suite (VIIRS) active fire alerts, and for the first time, characterize the temporal relationship between fires and tropical forest-cover loss at high temporal detail and medium spatial scale. We quantify fire-related forest-cover loss and separate fires that predate, coincide with, and postdate forest-cover loss. For the Province of Riau, Indonesia, dense Sentinel-1 C-band Synthetic Aperture Radar data with guaranteed observations of at least every 12 days allowed for confident and timely forest-cover-loss detection in natural and plantation forest with user’s and producer’s accuracy above 95%. Forest-cover loss was detected and confirmed within 22 days in natural forest and within 15 days in plantation forest. This difference can primarily be related to different change processes and dynamics in natural and plantation forest. For the period between 1 January 2016 and 30 June 2017, fire-related forest-cover loss accounted for about one third of the natural forest-cover loss, while in plantation forest, less than ten percent of the forest-cover loss was fire-related. We found clear spatial patterns of fires predating, coinciding with, or postdating forest-cover loss. Only the minority of fires in natural and plantation forest temporally coincided with forest-cover loss (13% and 16%) and can thus be confidently attributed as direct cause of forest-cover loss. The majority of the fires predated (64% and 58%) or postdated forest-cover loss (23% and 26%), and should be attributed to other key land management practices. Detailed and ...
Keywords	Fire-related ; Forest-cover loss ; Near real-time ; Sentinel-1 ; Tropical forest ; VIIRS active fire
Subject code	333
Language	English
Publishing country	nl
Document type	Article ; Online
ZDB-ID	2513863-7
ISSN	2072-4292
ISSN	2072-4292
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Article ; Online: Energy dynamics in a parasitoid foraging in the wild.

Casas, Jerome / Driessen, Gerard / Mandon, Nicole / Wielaard, Sebastiaan / Desouhant, Emmanuel / Van Alphen, Jacques / Lapchin, Laurent / Rivero, Ana / Christides, Jean Philippe / Bernstein, Carlos

The Journal of animal ecology

2019 Volume 72, Issue 4, Page(s) 691–697

Abstract: Although parasitoids are used widely as a biological models for understanding the evolution of animal behaviour, most studies have been constrained to the laboratory. The dearth of field studies has been compounded by the almost complete ignorance of the ...

Abstract	Although parasitoids are used widely as a biological models for understanding the evolution of animal behaviour, most studies have been constrained to the laboratory. The dearth of field studies has been compounded by the almost complete ignorance of the physiological parameters involved in foraging and dispersal, in particular of the energetic constraints imposed by resource limitation. We estimated the dynamics of carbohydrates and lipids reserves of Venturia canescens (Gravenhorst) females by releasing individuals of known nutritional status in a natural environment and recapturing them using host-containing traps. The recapture rate was around 30%. These results were compared with the reserves of caged animals kept under different experimental conditions (freshly emerged, starved to death, fed ad libitum and partially starved). Wild animals were also sampled in order to estimate the resource levels of the local population. The results show that: (i) wasps are able to maintain a nearly constant level of energy over an extended foraging period; (ii) V. canescens takes sugars in the field; and (iii) the lipid reserves accumulated during the larval life may be limiting as lipogenesis does not take place in adults even under conditions of high sugar availability. These results demonstrate that wasps can forage for hosts and food and disperse in this habitat for hours and days without running into a severe risk of energy limitation.
Language	English
Publishing date	2019-03-19
Publishing country	England
Document type	Journal Article
ZDB-ID	3024-7
ISSN	1365-2656 ; 0021-8790
ISSN (online)	1365-2656
ISSN	0021-8790
DOI	10.1046/j.1365-2656.2003.00740.x
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