Rare express saccades in elderly fallers

Q Yang1, T T Lê1, E Debay1, C Orssaud2, G Magnier3, Z Kapoula11Groupe IRIS Vision and Motricité Binoculaire, CNRS, Service d’Ophtalmologie-ORL-Stomatologie; 2Service d’Ophtalmologie, Hôpital Européen Georges Pompidou, Paris, France; 3Hôpital de gériatrie Henry Dunant, Paris, FranceObjective: To examine horizontal saccades in elderly subjects with falling history; prior extensive screening was done to recruit subjects with falling history in the absence of pathology.Methods: Twelve elderly with falling history were tested. Two testing conditions were used: the gap (fixation target extinguishes prior to target onset) and the overlap (fixation stays on after target onset) paradigms. Each condition was run at three viewing distances −20 cm, 40 cm, and 150 cm, corresponding to convergence angle at 17.1°, 8.6°, and 2.3°, respectively. Eye movements were recorded with the photoelectric IRIS (Skalar medical).Results: (i) like in healthy elderly subjects, elderly with falling history produce shorter latencies in the gap paradigm than in the overlap paradigm; (ii) their latencies are shorter at near distances (20 and 40 cm) relative to 150 cm for both paradigms; (iii) the novel result is that they fail to produce express latencies even in the conditions (near viewing distance and the gap task) known to promote high rates of express in adults (25%) or in healthy elderly (20%). Seven from the 10 healthy elderly produced express saccades at rates >12%, while 9 of the 12 older subjects with falling history showed no express saccades at all; the remaining 3 subjects showed low rates <12%.Conclusion: The quasi paucity of express saccades could be due to the disequilibrium of complex cortical/subcortical networks needed for making express saccades. The results support models suggesting specific network for express saccades; missing of such optomotor reflex may go along with missing other reflexes as well increasing the chances of falling.Keywords: elderly, falling, saccades, gap/overlap, express saccad

NEMA NU 1-2018 performance characterization and Monte Carlo model validation of the Cubresa Spark SiPM-based preclinical SPECT scanner

Abstract Background The Cubresa Spark is a novel benchtop silicon-photomultiplier (SiPM)-based preclinical SPECT system. SiPMs in SPECT significantly improve resolution and reduce detector size compared to preclinical cameras with photomultiplier tubes requiring highly magnifying collimators. The NEMA NU 1 Standard for Performance Measurements of Gamma Cameras provides methods that can be readily applied or extended to characterize preclinical cameras with minor modifications. The primary objective of this study is to characterize the Spark according to the NEMA NU 1-2018 standard to gain insight into its nuclear medicine imaging capabilities. The secondary objective is to validate a GATE Monte Carlo simulation model of the Spark for use in preclinical SPECT studies. Methods NEMA NU 1-2018 guidelines were applied to characterize the Spark’s intrinsic, system, and tomographic performance with single- and multi-pinhole collimators. Phantoms were fabricated according to NEMA specifications with deviations involving high-resolution modifications. GATE was utilized to model the detector head with the single-pinhole collimator, and NEMA measurements were employed to tune and validate the model. Single-pinhole and multi-pinhole SPECT data were reconstructed with the Software for Tomographic Image Reconstruction and HiSPECT, respectively. Results The limiting intrinsic resolution was measured as 0.85 mm owing to a high-resolution SiPM array combined with a 3 mm-thick scintillation crystal. The average limiting tomographic resolution was 1.37 mm and 1.19 mm for the single- and multi-pinhole collimators, respectively, which have magnification factors near unity at the center of rotation. The maximum observed count rate was 15,400 cps, and planar sensitivities of 34 cps/MBq and 150 cps/MBq were measured at the center of rotation for the single- and multi-pinhole collimators, respectively. All simulated tests agreed well with measurement, where the most considerable deviations were below 7%. Conclusions NEMA NU 1-2018 standards determined that a SiPM detector mitigates the need for highly magnifying pinhole collimators while preserving detailed information in projection images. Measured and simulated NEMA results were highly comparable with differences on the order of a few percent, confirming simulation accuracy and validating the GATE model. Of the collimators initially provided with the Spark, the multi-pinhole collimator offers high resolution and sensitivity for organ-specific imaging of small animals, and the single-pinhole collimator enables high-resolution whole-body imaging of small animals

Natural ventilation in cities: the implications of fluid mechanics

Research under the Managing Air for Green Inner Cities (MAGIC) project uses measurements and modelling to investigate the connections between external and internal conditions: the impact of urban airflow on the natural ventilation of a building. The test site was chosen so that under different environmental conditions the levels of external pollutants entering the building, from either a polluted road or a relatively clean courtyard, would be significantly different. Measurements included temperature, relative humidity, local wind and solar radiation, together with levels of carbon monoxide (CO) and carbon dioxide (CO2) both inside and outside the building to assess the indoor–outdoor exchange flows. Building ventilation took place through windows on two sides, allowing for single-sided and crosswind-driven ventilation, and also stack-driven ventilation in low wind conditions. The external flow around the test site was modelled in an urban boundary layer in a wind tunnel. The wind tunnel results were incorporated in a large-eddy-simulation model, Fluidity, and the results compared with monitoring data taken both within the building and from the surrounding area. In particular, the effects of street layout and associated street canyons, of roof geometry and the wakes of nearby tall buildings were examined.This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) Grand Challenge grant ‘Managing Air for Green Inner Cities (MAGIC) [grant number EP/N010221/1]

Natural ventilation in cities: the implications of fluid mechanics

Research under the Managing Air for Green Inner Cities (MAGIC) project uses measurements and modelling to investigate the connections between external and internal conditions: the impact of urban airflow on the natural ventilation of a building. The test site was chosen so that under different environmental conditions the levels of external pollutants entering the building, from either a polluted road or a relatively clean courtyard, would be significantly different. Measurements included temperature, relative humidity, local wind and solar radiation, together with levels of carbon monoxide (CO) and carbon dioxide (CO2) both inside and outside the building to assess the indoor–outdoor exchange flows. Building ventilation took place through windows on two sides, allowing for single-sided and crosswind-driven ventilation, and also stack-driven ventilation in low wind conditions. The external flow around the test site was modelled in an urban boundary layer in a wind tunnel. The wind tunnel results were incorporated in a large-eddy-simulation model, Fluidity, and the results compared with monitoring data taken both within the building and from the surrounding area. In particular, the effects of street layout and associated street canyons, of roof geometry and the wakes of nearby tall buildings were examined.This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) Grand Challenge grant ‘Managing Air for Green Inner Cities (MAGIC) [grant number EP/N010221/1]