Modulation transfer function and quantum efficiency correlation at long wavelengths (greater than 800 nm) in linear charge coupled imagers

Schumann, Lee W.; Lomheim, Terrence S.

doi:10.1364/ao.28.001701

Cited by 13 publications

(5 citation statements)

References 10 publications

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“…Equation (4b) assumes uniform collection sensitivity across the (rect function) aperture, though the model allows for more complex aperture models, e.g., a trapezoidal function. 42 The distribution of secondary quanta computed at all possible locations in the x domain (taking y = 0 for simplicity) is shown in Fig. 1(C), where the probability distribution (vertical axis) is shown as an intensity map at each x location (horizontal axis) about the point of interaction.…”

Section: A a Cascaded Systems Model For Pcdsmentioning

confidence: 99%

Cascaded systems analysis of photon counting detectors

Zbijewski

Gang

et al. 2014

Medical Physics

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Purpose: Photon counting detectors (PCDs) are an emerging technology with applications in spectral and low-dose radiographic and tomographic imaging. This paper develops an analytical model of PCD imaging performance, including the system gain, modulation transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). Methods: A cascaded systems analysis model describing the propagation of quanta through the imaging chain was developed. The model was validated in comparison to the physical performance of a silicon-strip PCD implemented on an experimental imaging bench. The signal response, MTF, and NPS were measured and compared to theory as a function of exposure conditions (70 kVp, 1-7 mA), detector threshold, and readout mode (i.e., the option for coincidence detection). The model sheds new light on the dependence of spatial resolution, charge sharing, and additive noise effects on threshold selection and was used to investigate the factors governing PCD performance, including the fundamental advantages and limitations of PCDs in comparison to energy-integrating detectors (EIDs) in the linear regime for which pulse pileup can be ignored. Results: The detector exhibited highly linear mean signal response across the system operating range and agreed well with theoretical prediction, as did the system MTF and NPS. The DQE analyzed as a function of kilovolt (peak), exposure, detector threshold, and readout mode revealed important considerations for system optimization. The model also demonstrated the important implications of false counts from both additive electronic noise and charge sharing and highlighted the system design and operational parameters that most affect detector performance in the presence of such factors: for example, increasing the detector threshold from 0 to 100 (arbitrary units of pulse height threshold roughly equivalent to 0.5 and 6 keV energy threshold, respectively), increased the f 50 (spatial-frequency at which the MTF falls to a value of 0.50) by ∼30% with corresponding improvement in DQE. The range in exposure and additive noise for which PCDs yield intrinsically higher DQE was quantified, showing performance advantages under conditions of very low-dose, high additive noise, and high fidelity rejection of coincident photons. Conclusions: The model for PCD signal and noise performance agreed with measurements of detector signal, MTF, and NPS and provided a useful basis for understanding complex dependencies in PCD imaging performance and the potential advantages (and disadvantages) in comparison to EIDs as well as an important guide to task-based optimization in developing new PCD imaging systems. C

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Section: A a Cascaded Systems Model For Pcdsmentioning

confidence: 99%

Cascaded systems analysis of photon counting detectors

Zbijewski

Gang

et al. 2014

Medical Physics

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“…͑34͒ should be replaced with trapezoids based on the research of Schumann and Lomheim. 50 Schumann and Lomheim have shown that lateral diffusion of photoelectrons is considerable when dealing with long wavelengths ͑Ͼ800 nm͒ of infrared light incident on the a-Si pixel layer. However, they have demonstrated that lateral diffusion is negligible when shorter wavelengths of visible light land on the pixel layer, such as the wavelengths generated by CsI:Tl in typical imaging systems.…”

Section: Discussionmentioning

confidence: 99%

A comparative analysis of OTF, NPS, and DQE in energy integrating and photon counting digital x‐ray detectors

Acciavatti

Maidment

2010

Medical Physics

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Purpose: One of the benefits of photon counting ͑PC͒ detectors over energy integrating ͑EI͒ detectors is the absence of many additive noise sources, such as electronic noise and secondary quantum noise. The purpose of this work is to demonstrate that thresholding voltage gains to detect individual x rays actually generates an unexpected source of white noise in photon counters. Methods: To distinguish the two detector types, their point spread function ͑PSF͒ is interpreted differently. The PSF of the energy integrating detector is treated as a weighting function for counting x rays, while the PSF of the photon counting detector is interpreted as a probability. Although this model ignores some subtleties of real imaging systems, such as scatter and the energydependent amplification of secondary quanta in indirect-converting detectors, it is useful for demonstrating fundamental differences between the two detector types. From first principles, the optical transfer function ͑OTF͒ is calculated as the continuous Fourier transform of the PSF, the noise power spectra ͑NPS͒ is determined by the discrete space Fourier transform ͑DSFT͒ of the autocovariance of signal intensity, and the detective quantum efficiency ͑DQE͒ is found from combined knowledge of the OTF and NPS. To illustrate the calculation of the transfer functions, the PSF is modeled as the convolution of a Gaussian with the product of rect functions. The Gaussian reflects the blurring of the x-ray converter, while the rect functions model the sampling of the detector. Results: The transfer functions are first calculated assuming outside noise sources such as electronic noise and secondary quantum noise are negligible. It is demonstrated that while OTF is the same for two detector types possessing an equivalent PSF, a frequency-independent ͑i.e., "white"͒ difference in their NPS exists such that NPS PC Ն NPS EI and hence DQE PC Յ DQE EI . The necessary and sufficient condition for equality is that the PSF is a binary function given as zero or unity everywhere. In analyzing the model detector with Gaussian blurring, the difference in NPS and DQE between the two detector types is found to increase with the blurring of the x-ray converter. Ultimately, the expression for the additive white noise of the photon counter is compared against the expression for electronic noise and secondary quantum noise in an energy integrator. Thus, a method is provided to determine the average secondary quanta that the energy integrator must produce for each x ray to have superior DQE to a photon counter with the same PSF. Conclusions: This article develops analytical models of OTF, NPS, and DQE for energy integrating and photon counting digital x-ray detectors. While many subtleties of real imaging systems have not been modeled, this work is illustrative in demonstrating an additive source of white noise in photon counting detectors which has not yet been described in the literature. One benefit of this analysis is a framework for determining the average secondary quanta that an e...

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“…• SR det (y k ) is the spatial response of the detector in y k domain (typically a boxcar with smoothed edges, whose width corresponds to the detector size) [20]. • W slit is a boxcar function corresponding to the slit width, the slit being the across-dimension of the diaphragm characterizing the instrument.…”

Section: The Icr Pre-filtering Blockmentioning

confidence: 99%

Aliasing assessment in wavelength domain of hyperspectral data

Santurri

2006

J Real-Time Image Proc

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This paper focuses on a procedure for the assessment of spectral aliasing in hyper-spectral data acquired by push-broom spectrometers. The procedure is based on a push-broom spectrometer model that simulates acquired spectra by taking into account only the instrument parameters; aliasing is measured by means of some figures of merit considered among those proposed in literature. Quantitative evaluations have been performed on simulated spectra both with and without ideal atmospheric and radiometric correction. Results are presented in this paper; the impact of spectrometer slit size on aliasing appearance is also addressed.

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Modulation transfer function and quantum efficiency correlation at long wavelengths (greater than 800 nm) in linear charge coupled imagers

Cited by 13 publications

References 10 publications

Cascaded systems analysis of photon counting detectors

Cascaded systems analysis of photon counting detectors

A comparative analysis of OTF, NPS, and DQE in energy integrating and photon counting digital x‐ray detectors

Aliasing assessment in wavelength domain of hyperspectral data

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