A novel objective method for assessing high-contrast spatial resolution in CT based on the Rayleigh criterion

2017 ◽  
Vol 44 (2) ◽  
pp. 460-469
Author(s):  
Pu Zhang ◽  
Guoqing Wan ◽  
Fei Li ◽  
Xingdong Li ◽  
Wenli Liu ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Objective Method ◽  
High Contrast ◽  
Rayleigh Criterion

scholarly journals Objective comparison of high-contrast spatial resolution and low-contrast detectability for various clinical protocols on multiple CT scanners

2017 ◽  
Vol 44 (9) ◽  
pp. e153-e163 ◽  
Author(s):  
Damien Racine ◽  
Anaïs Viry ◽  
Fabio Becce ◽  
Sabine Schmidt ◽  
Alexandre Ba ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
High Contrast ◽  
Clinical Protocols ◽  
Low Contrast ◽  
Ct Scanners

The influence of focal spot blooming on high-contrast spatial resolution in CT imaging

2015 ◽  
Vol 42 (10) ◽  
pp. 6011-6020 ◽  
Author(s):  
Joshua Grimes ◽  
Xinhui Duan ◽  
Lifeng Yu ◽  
Ahmed F. Halaweish ◽  
Nicole Haag ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Focal Spot ◽  
Ct Imaging ◽  
High Contrast

scholarly journals An investigation of binary stars in the Pleiades with high contrast and spatial resolution

2012 ◽  
Vol 541 ◽  
pp. A96 ◽  
Author(s):  
A. Richichi ◽  
W. P. Chen ◽  
F. Cusano ◽  
O. Fors ◽  
M. Moerchen ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Binary Stars ◽  
High Contrast

scholarly journals SPHERE/ZIMPOL high resolution polarimetric imager

2018 ◽  
Vol 619 ◽  
pp. A9 ◽  
Author(s):  
H. M. Schmid ◽  
A. Bazzon ◽  
R. Roelfsema ◽  
D. Mouillet ◽  
J. Milli ◽  
...  
Keyword(s):  
High Resolution ◽  
Adaptive Optics ◽  
Spatial Resolution ◽  
Focal Plane ◽  
Surface Brightness ◽  
Absolute Calibration ◽  
Wind Effect ◽  
High Contrast ◽  
Atmospheric Conditions ◽  
Very High

Context. The SPHERE “planet finder” is an extreme adaptive optics (AO) instrument for high resolution and high contrast observations at the Very Large Telescope (VLT). We describe the Zurich Imaging Polarimeter (ZIMPOL), the visual focal plane subsystem of SPHERE, which pushes the limits of current AO systems to shorter wavelengths, higher spatial resolution, and much improved polarimetric performance. Aims. We present a detailed characterization of SPHERE/ZIMPOL which should be useful for an optimal planning of observations and for improving the data reduction and calibration. We aim to provide new benchmarks for the performance of high contrast instruments, in particular for polarimetric differential imaging. Methods. We have analyzed SPHERE/ZIMPOL point spread functions (PSFs) and measure the normalized peak surface brightness, the encircled energy, and the full width half maximum (FWHM) for different wavelengths, atmospheric conditions, star brightness, and instrument modes. Coronagraphic images are described and the peak flux attenuation and the off-axis flux transmission are determined. Simultaneous images of the coronagraphic focal plane and the pupil plane are analyzed and the suppression of the diffraction rings by the pupil stop is investigated. We compared the performance at small separation for different coronagraphs with tests for the binary α Hyi with a separation of 92 mas and a contrast of Δm ≈ 6m. For the polarimetric mode we made the instrument calibrations using zero polarization and high polarization standard stars and here we give a recipe for the absolute calibration of polarimetric data. The data show small (< 1 mas) but disturbing differential polarimetric beam shifts, which can be explained as Goos-Hähnchen shifts from the inclined mirrors, and we discuss how to correct this effect. The polarimetric sensitivity is investigated with non-coronagraphic and deep, coronagraphic observations of the dust scattering around the symbiotic Mira variable R Aqr. Results. SPHERE/ZIMPOL reaches routinely an angular resolution (FWHM) of 22−28 mas, and a normalized peak surface brightness of SB0 − mstar ≈ −6.5m arcsec−2 for the V-, R- and I-band. The AO performance is worse for mediocre ≳1.0″ seeing conditions, faint stars mR ≳ 9m, or in the presence of the “low wind” effect (telescope seeing). The coronagraphs are effective in attenuating the PSF peak by factors of > 100, and the suppression of the diffracted light improves the contrast performance by a factor of approximately two in the separation range 0.06″−0.20″. The polarimetric sensitivity is Δp < 0.01% and the polarization zero point can be calibrated to better than Δp ≈ 0.1%. The contrast limits for differential polarimetric imaging for the 400 s I-band data of R Aqr at a separation of ρ = 0.86″ are for the surface brightness contrast SBpol( ρ)−mstar ≈ 8m arcsec−2 and for the point source contrast mpol( ρ)−mstar ≈ 15m and much lower limits are achievable with deeper observations. Conclusions. SPHERE/ZIMPOL achieves imaging performances in the visual range with unprecedented characteristics, in particular very high spatial resolution and very high polarimetric contrast. This instrument opens up many new research opportunities for the detailed investigation of circumstellar dust, in scattered and therefore polarized light, for the investigation of faint companions, and for the mapping of circumstellar Hα emission.

scholarly journals Modified ideal observer model (MIOM) for high-contrast and high-spatial resolution CT imaging tasks

2017 ◽  
Vol 44 (9) ◽  
pp. 4496-4505 ◽  
Author(s):  
Juan P. Cruz-Bastida ◽  
Daniel Gomez-Cardona ◽  
John Garrett ◽  
Timothy Szczykutowicz ◽  
Guang-Hong Chen ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
High Spatial Resolution ◽  
Ct Imaging ◽  
Ideal Observer ◽  
High Contrast ◽  
Observer Model

scholarly journals A Comparative Study on the Influence of Probe Placement on Quality Assurance Measurements in B-mode Ultrasound by Means of Ultrasound Phantoms

2015 ◽  
Vol 9 (1) ◽  
pp. 164-178 ◽  
Author(s):  
A Scorza ◽  
S Conforto ◽  
C D'Anna ◽  
S.A Sciuto
Keyword(s):  
Quality Assurance ◽  
Image Quality ◽  
Spatial Resolution ◽  
Dynamic Range ◽  
High Contrast ◽  
Medical Systems ◽  
Distance Measurements ◽  
Operator Experience ◽  
Measurement Reproducibility ◽  
Ultrasound Phantoms

To check or to prevent failures in ultrasound medical systems, some tests should be scheduled for both clinical suitability and technical functionality evaluation: among them, image quality assurance tests performed by technicians through ultrasound phantoms are widespread today and their results depend on issues related to scanner settings as well as phantom features and operator experience. In the present study variations on some features of the B-mode image were measured when the ultrasound probe is handled by the technician in a routine image quality test: ultrasound phantom images from two array transducers are processed to evaluate measurement dispersion in distance accuracy, high contrast spatial resolution and penetration depth when probe is handled by the operator. All measurements are done by means of an in-house image analysis software that minimizes errors due to operator’s visual acuity and subjective judgment while influences of ultrasound transducer position on quality assurance test results are estimated as expanded uncertainties on parameters above (measurement reproducibility at 95 percent confidence level): depending on the probe model, they ranged from ±0.1 to ±1.9 mm in high contrast spatial resolution, from ±0.1 to ±5.5 percent in distance measurements error and from ±1 to ±10 mm in maximum depth of signal visualization. Although numerical results are limited to the two examined probes, they confirm some predictions based on general working principles of diagnostic ultrasound systems: (a) measurements strongly depend on settings as well on phantoms features, probes and parameters investigated; (b) relative uncertainty due to probe manipulation on spatial resolution can be very high, i.e. from 10 to more than 30 percent; (c) Field of View settings must be taken into account for measurement reproducibility as well as Dynamic Range compression and phantom attenuation.

scholarly journals High spatial resolution and high contrast optical speckle imaging with FASTCAM at the ORM

2010 ◽  
Author(s):  
Lucas Labadie ◽  
Rafael Rebolo ◽  
Bruno Femenía ◽  
Isidro Villó ◽  
Anastasio Díaz-Sánchez ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
High Spatial Resolution ◽  
High Contrast ◽  
Speckle Imaging
Sign in / Sign up

Export Citation Format

Share Document