&lt;title&gt;Signal and noise analysis using transmission line model for larger-area flat-panel x-ray imaging sensors&lt;/title&gt;

Huang, Zhong Shou; DeCrescenzo, Giovanni; Rowlands, J. A.

doi:10.1117/12.349546

Cited by 12 publications

(12 citation statements)

References 3 publications

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“…x-ray quantum noise, N qn , is described by the Poisson probability distribution function, and it is square root of N for N x rays. The theoretically estimated lower limit of the electronic noise for an AM TFT array is 1500 electrons/ pixel, 32 and values closer to 3000 electrons/ pixel are seen in practical state-of-the-art AMFP detectors. 22 Now, Signal = Energy of x-ray photon ϫx-ray to charge conversion gain ϫ avalanche gain.…”

Section: Ve Avalanche Gain and Operating Conditionmentioning

confidence: 81%

Design and feasibility of active matrix flat panel detector using avalanche amorphous selenium for protein crystallography

et al. 2008

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Protein crystallography is the most important technique for resolving the three-dimensional atomic structure of protein by measuring the intensity of its x-ray diffraction pattern. This work proposes a large area flat panel detector for protein crystallography based on direct conversion x-ray detection technique using avalanche amorphous selenium (a-Se) as the high gain photoconductor, and active matrix readout using amorphous silicon (a-Si:H) thin film transistors. The detector employs avalanche multiplication phenomenon of a-Se to make the detector sensitive to each incident x ray. The advantages of the proposed detector over the existing imaging plate and charge coupled device detectors are large area, high dynamic range coupled to single x-ray detection capability, fast readout, high spatial resolution, and inexpensive manufacturing process. The optimal detector design parameters (such as detector size, pixel size, and thickness of a-Se layer), and operating parameters (such as electric field across the a-Se layer) are determined based on the requirements for protein crystallography application. The performance of the detector is evaluated in terms of readout time (<1 s), dynamic range (approximately 10(5)), and sensitivity (approximately 1 x-ray photon), thus validating the detector's efficacy for protein crystallography.

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Section: Ve Avalanche Gain and Operating Conditionmentioning

confidence: 81%

Design and feasibility of active matrix flat panel detector using avalanche amorphous selenium for protein crystallography

et al. 2008

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“…This corresponds to twice the theoretical noise limit for a 1000ϫ1000 active matrix array. 14 Fig. 6͑c͒.…”

Section: Resultsmentioning

confidence: 99%

Direct conversion detectors: The effect of incomplete charge collection on detective quantum efficiency

2002

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Direct conversion detectors offer the potential for very high resolution and high quantum efficiency for x-ray imaging, however, variations in signal can arise due to incomplete charge collection. A charge transport model was developed to describe the signal and noise resulting from incomplete charge collection. This signal to noise ratio (SNR) reduction was incorporated into the cascaded systems model for a simple x-ray detector. A new excess noise factor, A(c) (termed the collection noise factor) is introduced to describe the reduction in detective quantum efficiency (DQE). The DQE is proportional to the product of the quantum efficiency and the collection noise factor. If the trapping cross sections for electrons and holes are very different, and if the detector is biased improperly, the collection noise factor can drop to as low as 50%. In addition, the signal loss due to incomplete charge collection will reduce the DQE in the presence of added noise. Because of this, the DQE generally does not continue to improve with greater detector thickness. The collection noise factor and DQE are predicted for CdZnTe, PbI2, and Se. The optimization of detector thickness should be based not only on quantum efficiency but also on the charge collection statistics, which are influenced by bias field and polarity.

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“…Thus, C gas is much less than the total capacitance along the data line ͑ϳ35 pF͒. 32 The typical values of R collector and R a are ϳ1 ⍀ and ϳ0.1 ⍀, respectively, which are much less than either the on-resistance of the TFT ͑ϳ1 M⍀͒ 31 or the total resistance along the data line ͑ϳ2.5 K⍀͒ 32 and thus have negligible effects on both noise and readout time constant. 33,31 The value of storage capacitance C st depends on the active matrix design and is ϳ1 pF.…”

Section: Electronic Noisementioning

confidence: 99%

“…33,31 The value of storage capacitance C st depends on the active matrix design and is ϳ1 pF. The preamplifier noise n a ͑ϳ1000 e͒ and the data line noise n d ͑ϳ1000 e͒ are the dominant noise sources 31,32 arising from the image readout. They are the same in both the direct conversion panel 31 and the present detector.…”

Section: Electronic Noisementioning

confidence: 99%

Development of high quantum efficiency, flat panel, thick detectors for megavoltage x‐ray imaging: A novel direct‐conversion design and its feasibility

Pang

Rowlands

2004

Medical Physics

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Most electronic portal imaging devices (EPIDs) developed to date, including recently developed flat panel systems, have low x-ray absorption, i.e., low quantum efficiency (QE) of 2%-4% as compared to the theoretical limit of 100%. A significant increase of QE is desirable for applications such as a megavoltage cone-beam computed tomography (MVCT) and megavoltage fluoroscopy. However, the spatial resolution of an imaging system usually decreases significantly with an increase of QE. The key to the success in the design of a high QE detector is therefore to maintain the spatial resolution. Recently, we demonstrated theoretically that it is possible to design a portal imaging detector with both high QE and high resolution [see Pang and Rowlands, Med. Phys. 29, 2274 (2002)]. In this paper, we introduce such a novel design consisting of a large number of microstructured plates (made by, e.g., photolithographic patterning of evaporated or electroplated layers) packed together and aligned with the incident x rays. On each plate, microstrip charge collectors are focused toward the x-ray source to collect charges generated in the ionization medium (e.g., air or gas) surrounded by high-density materials that act as x-ray converters. The collected charges represent the x-ray image and can be read out by various means, including a two-dimensional (2-D) active readout matrix. The QE, spatial resolution, and sensitivity of the detector have been calculated. It has been shown that the new design will have a QE of more than an order of magnitude higher and a spatial resolution equivalent to that of flat panel systems currently used for portal imaging. The new design is also quantum noise limited down to very low doses (approximately 1-2 radiation pulses of the linear accelerator).

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<title>Signal and noise analysis using transmission line model for larger-area flat-panel x-ray imaging sensors</title>

Cited by 12 publications

References 3 publications

Design and feasibility of active matrix flat panel detector using avalanche amorphous selenium for protein crystallography

Design and feasibility of active matrix flat panel detector using avalanche amorphous selenium for protein crystallography

Direct conversion detectors: The effect of incomplete charge collection on detective quantum efficiency

Development of high quantum efficiency, flat panel, thick detectors for megavoltage x‐ray imaging: A novel direct‐conversion design and its feasibility

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