Relative dose in dual energy fast-kVp switching and conventional kVp imaging: spatial frequency dependent noise characteristics and low contrast imaging

2011 ◽  
Author(s):  
Girijesh K. Yadava ◽  
Naveen Chandra ◽  
Jiang Hsieh
Keyword(s):  
Spatial Frequency ◽  
Dual Energy ◽  
Contrast Imaging ◽  
Frequency Dependent ◽  
Low Contrast ◽  
Noise Characteristics

“High Resolution High Voltage Electron Microscopy”

1968 ◽  
Vol 26 ◽  
pp. 326-327
Author(s):  
Benjamin M. Siegel
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Voltage ◽  
Full Potential ◽  
Contrast Imaging ◽  
High Voltage Electron Microscopy ◽  
Low Contrast ◽  
Voltage Electron ◽  
Critical Areas ◽  
High Voltage Electron

The potential advantages of high voltage electron microscopy for extending the limits of resolution and contrast in imaging low contrast objects, such as biomolecular specimens, is very great. The results of computations will be presented showing that at accelerating voltages of 500-1000 kV it should be possible to achieve spacial resolutions of 1 to 1.5 Å and using phase contrast imaging achieve adequate image contrast to observe single atoms of low atomic number.The practical problems associated with the design and utilization of the high voltage instrument are, optimistically, within the range of competence of the state of the art. However, there are some extremely important and critical areas to be systematically investigated before we have achieved this competence. The basic electron optics of the column required is well understood, but before the full potential of an instrument capable of resolutions of better than 1.5 Å are realized some very careful development work will be required. Of great importance for the actual achievement of high resolution with a high voltage electron microscope is the fundamental limitation set by the characteristics of the high voltage electron beam that can be obtained from the accelerator column.

Frequency-dependent attenuation in eastern Kazakhstan and implications for seismic detection thresholds in the Soviet Union

1990 ◽  
Vol 80 (6B) ◽  
pp. 2089-2105 ◽  
Author(s):  
Thomas J. Sereno
Keyword(s):  
Soviet Union ◽  
North America ◽  
Test Site ◽  
Eastern North America ◽  
Detection Capability ◽  
Detection Thresholds ◽  
Frequency Dependent ◽  
Noise Characteristics ◽  
The Soviet Union ◽  
Eastern Kazakhstan

Abstract The frequency-dependent attenuation of regional seismic phases recorded by three stations near the nuclear explosion test site in eastern Kazakhstan is estimated by inverting spectra from 21 events with magnitudes between 2.3 and 4.6 at distances between 200 and 1300 km. The Pn spectra are inverted between 1 and 10 Hz, and the Lg spectra are inverted between 0.5 and 2.5 Hz. The motivation for this study is that previous estimates of detection capability in the Soviet Union are based on data recorded in other regions (eastern North America and Scandinavia) and therefore have large uncertainty. The data recently recorded in eastern Kazakhstan provide an excellent opportunity to compare regional wave propagation and noise characteristics at these sites to conditions assumed in previous detection capability simulations. It is found that attenuation in eastern Kazakhstan is not much different from attenuation in Scandinavia, but it is greater than attenuation in eastern North America. This implies that estimates of detection thresholds that assume attenuation like that observed in eastern North America will be lower than estimates of detection thresholds that assume attenuation like that observed in eastern Kazakhstan or Scandinavia. However, it is not known how well data recorded in eastern Kazakhstan represent conditions in other areas of the Soviet Union.

Prospective Comparison of 70-kVp Single-Energy CT versus Dual-Energy CT: Which is More Suitable for CT Angiography with Low Contrast Media Dosage?

2020 ◽  
Vol 27 (5) ◽  
pp. e116-e122 ◽  
Author(s):  
Morikatsu Yoshida ◽  
Takeshi Nakaura ◽  
Takada Sentaro ◽  
Shota Tanoue ◽  
Hatsuki Inada ◽  
...  
Keyword(s):  
Contrast Media ◽  
Ct Angiography ◽  
Dual Energy ◽  
Dual Energy Ct ◽  
Low Contrast ◽  
Prospective Comparison

Spatial frequency analsis in early visual processing

1980 ◽  
Vol 290 (1038) ◽  
pp. 11-22 ◽  
Keyword(s):  
Spatial Frequency ◽  
Visual Processing ◽  
Spatial Information ◽  
Multiple Channels ◽  
Low Contrast ◽  
Local Sign ◽  
Early Visual Processing ◽  
Low Luminance ◽  
Lowered Sensitivity ◽  
Prior Adaptation

The existence of multiple channels, or multiple receptive field sizes, in the visual system does not commit us to any particular theory of spatial encoding in vision. However, distortions of apparent spatial frequency and width in a wide variety of conditions favour the idea that each channel carries a width- or frequency-related code or ‘label’ rather than a ‘local sign’ or positional label. When distortions of spatial frequency occur without prior adaptation (e.g. at low contrast or low luminance) they are associated with lowered sensitivity, and may be due to a mismatch between the perceptual labels and the actual tuning of the channels. A low-level representation of retinal space could be constructed from the spatial information encoded by the channels, rather than being projected intact from the retina.

Independent Processing across Spatial Frequency in Moving Broadband Patterns

Perception ◽  
1997 ◽  
Vol 26 (8) ◽  
pp. 961-976 ◽  
Author(s):  
Richard A Eagle
Keyword(s):  
Spatial Frequency ◽  
Visual System ◽  
High Frequency ◽  
Spatial Scales ◽  
Power Spectra ◽  
Frequency Noise ◽  
Low Contrast ◽  
Task Requirements ◽  
Noise Frequency ◽  
Frame Motion

The aim of the experiments was to discover whether the visual system has independent access to motion information at different spatial scales when presented with a broadband stimulus. Subjects were required to discriminate between a pair of two-frame motion sequences, one containing a coherently displacing pattern and the other containing a pattern with high-frequency noise. The stimuli were either narrowband (1 octave) or broadband (6 octaves spanning 0.23–15.0 cycles deg−1) and their power spectra were either flat or followed a 1 /f2 function. For the broadband stimuli, noise was introduced cumulatively into increasingly lower frequencies. For the narrowband stimuli, noise was introduced into the same frequency band as the signal. All stimuli could be defined by the lowest noise frequency ( n1) they contained. For each stimulus, the largest spatial displacement across the two frames at which the task could be performed was measured ( dmax). For the narrowband stimuli, dmax increased as n1 was lowered. This was true over the entire frequency range for the 1 /f2 stimuli, though the task became impossible for the flat-spectrum stimuli at the lowest frequencies. This is attributed to the very low contrast of these latter stimuli. The dmax values for the broadband stimuli tended to shadow those of the narrowband stimuli with the equivalent values of n1 being around 25% lower. The data were modelled by spatiotemporally filtering the stimuli and considering the amount of directional power in the signal and noise sequences. The results suggest that there must be multiple spatial-frequency channels in operation, and that for broadband patterns the visual system has perceptual access to these individual channel outputs, utilising different filters depending on the task requirements.

Temporal-Discontinuity Detection with Contrast-Modulated Gratings

Perception ◽  
1995 ◽  
Vol 24 (11) ◽  
pp. 1257-1264
Author(s):  
Shigeru Ichihara ◽  
Kenji Susami
Keyword(s):  
Spatial Frequency ◽  
Modulation Frequency ◽  
Sinusoidal Grating ◽  
Local Contrast ◽  
Staircase Method ◽  
Low Contrast ◽  
Discontinuity Detection ◽  
Temporal Discontinuity ◽  
Sinusoidal Gratings ◽  
The Subject

Three experiments on temporal-discontinuity detection were carried out. In experiment 1, temporal-discontinuity thresholds were measured for sinusoidal gratings by the use of the double-staircase method. A sinusoidal grating was presented twice successively. The subject judged whether or not an interval was present. The temporal-discontinuity threshold increased as the spatial frequency of the grating increased, but decreased as the contrast of the grating increased. In experiment 2, contrast-modulated gratings were used instead of the sinusoidal grating. The temporal-discontinuity threshold increased as the carrier frequency increased, and the threshold for each contrast-modulated grating was similar to that for the no-modulation (sinusoidal) grating whose contrast was the same as the maximum local contrast of the contrast-modulated grating. In experiment 3, temporal-discontinuity thresholds were measured for low-contrast (3%) sinusoidal gratings. The thresholds were very low, even for such low-contrast gratings. These results suggest that the low-spatial-frequency channels are not involved in detecting the modulation frequency of the contrast-modulated grating. Rather, the local contrast seems to be the determinant of the detection of the contrast-modulated grating itself.

Dual-energy MDCT: Comparison of pulmonary artery enhancement on dedicated CT pulmonary angiography, routine and low contrast volume studies

2011 ◽  
Vol 79 (2) ◽  
pp. e11-e17 ◽  
Author(s):  
Myrna C.B. Godoy ◽  
Samantha L. Heller ◽  
David P. Naidich ◽  
Bernard Assadourian ◽  
Christianne Leidecker ◽  
...  
Keyword(s):  
Pulmonary Artery ◽  
Pulmonary Angiography ◽  
Dual Energy ◽  
Ct Pulmonary Angiography ◽  
Low Contrast ◽  
Contrast Volume

Multi-contrast CT imaging using a high energy resolution CdTe detector and a CZT photon-counting detector

2022 ◽  
Vol 17 (01) ◽  
pp. P01004
Author(s):  
N. Clements ◽  
D. Richtsmeier ◽  
A. Hart ◽  
M. Bazalova-Carter
Keyword(s):  
Contrast Agent ◽  
Energy Resolution ◽  
Photon Counting ◽  
High Energy ◽  
Ct Imaging ◽  
High Energy Resolution ◽  
Great Promise ◽  
Contrast Imaging ◽  
Low Contrast ◽  
Reconstruction Methods

Abstract Computed tomography (CT) imaging with high energy resolution detectors shows great promise in material decomposition and multi-contrast imaging. Multi-contrast imaging was studied by imaging a phantom with iodine (I), gadolinium (Gd), and gold (Au) solutions, and mixtures of the three using a cadmium telluride (CdTe) spectrometer with an energy resolution of 1% as well as with a cadmium zinc telluride (CZT) detector with an energy resolution of 13%. The phantom was imaged at 120 kVp and 1.1 mA with 7 mm of aluminum filtration. For the CdTe data collection, the phantom was imaged using a 0.2 mm diameter x-ray beam with 96 ten-second data acquisitions across the phantom at 45 rotation angles. For the CZT detector, we had 720 projections using a cone beam, and the six detector energy thresholds were set to 23, 33, 50, 64, 81, and 120 keV so that three thresholds corresponded to the K-edges of the contrast agents. Contrast agent isolation methods were then examined. K-edge subtraction and novel spectrometric algebraic image reconstruction (SAIR) were used for the CdTe data. K-edge subtraction alone was used for the CZT data. Linearity plots produced similar R 2 values and slopes for all three reconstruction methods. Comparing CdTe methods, SAIR offered less noise than CdTe K-edge subtraction and better geometric accuracy at low contrast concentrations. CdTe contrast agent images of I, Gd, and Au offered less noise and greater contrast than the CZT images, highlighting the benefits of high energy resolution CdTe detectors for possible use in pre-clinical or clinical CT imaging.

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