Scanning‐slit photon counting x‐ray imaging system using a microchannel plate detector

Shikhaliev, Polad M.; Xu, Tingfa; Lê, Huy; Molloi, Sabee

doi:10.1118/1.1695651

Cited by 20 publications

(22 citation statements)

References 35 publications

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“…8 The spatial-frequency dependence of the x-ray Swank factor has an additional important implication for energydiscriminating detectors that has not been addressed. New detectors are currently being developed by a number of investigators using a-Si, 45 CdZnTe, 46 PbO, 47 and other materials, which may result in new energy-weighted photoncounting imaging techniques. However, random relocation of x-ray energy into different detector elements will seriously compromise performance, and the frequency-dependent x-ray Swank factor will almost certainly play an interesting role.…”

Section: Discussionmentioning

confidence: 99%

Fundamental x-ray interaction limits in diagnostic imaging detectors: Frequency-dependent Swank noise

Hajdok¹,

Battista²,

Cunningham³

2008

Med. Phys.

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A frequency-dependent x-ray Swank factor based on the "x-ray interaction" modulation transfer function and normalized noise power spectrum is determined from a Monte Carlo analysis. This factor was calculated in four converter materials: amorphous silicon (a-Si), amorphous selenium (a-Se), cesium iodide (CsI), and lead iodide (PbI2) for incident photon energies between 10 and 150 keV and various converter thicknesses. When scaled by the quantum efficiency, the x-ray Swank factor describes the best possible detective quantum efficiency (DQE) a detector can have. As such, this x-ray interaction DQE provides a target performance benchmark. It is expressed as a function of (Fourier-based) spatial frequency and takes into consideration signal and noise correlations introduced by reabsorption of Compton scatter and photoelectric characteristic emissions. It is shown that the x-ray Swank factor is largely insensitive to converter thickness for quantum efficiency values greater than 0.5. Thus, while most of the tabulated values correspond to thick converters with a quantum efficiency of 0.99, they are appropriate to use for many detectors in current use. A simple expression for the x-ray interaction DQE of digital detectors (including noise aliasing) is derived in terms of the quantum efficiency, x-ray Swank factor, detector element size, and fill factor. Good agreement is shown with DQE curves published by other investigators for each converter material, and the conditions required to achieve this ideal performance are discussed. For high-resolution imaging applications, the x-ray Swank factor indicates: (i) a-Si should only be used at low-energy (e.g., mammography); (ii) a-Se has the most promise for any application below 100 keV; and (iii) while quantum efficiency may be increased at energies just above the K edge in CsI and PbI2, this benefit is offset by a substantial drop in the x-ray Swank factor, particularly at high spatial frequencies.

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Section: Discussionmentioning

confidence: 99%

Fundamental x-ray interaction limits in diagnostic imaging detectors: Frequency-dependent Swank noise

Hajdok¹,

Battista²,

Cunningham³

2008

Med. Phys.

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“…Calibration was obtained from one phantom of 14 cm in diameter. This one-point calibration was used to decompose breast sizes of 8,10,12,14,16,18, and 20 cm in diameter. As seen from the graphs, measurements were more accurate in the vicinity of 14 cm.…”

Section: Resultsmentioning

confidence: 99%

Least squares parameter estimation methods for material decomposition with energy discriminating detectors

Lê

Molloi

2010

Medical Physics

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Purpose: Energy resolving detectors provide more than one spectral measurement in one image acquisition. The purpose of this study is to investigate, with simulation, the ability to decompose four materials using energy discriminating detectors and least squares minimization techniques. Methods: Three least squares parameter estimation decomposition techniques were investigated for four-material breast imaging tasks in the image domain. The first technique treats the voxel as if it consisted of fractions of all the materials. The second method assumes that a voxel primarily contains one material and divides the decomposition process into segmentation and quantification tasks. The third is similar to the second method but a calibration was used. The simulated computed tomography ͑CT͒ system consisted of an 80 kVp spectrum and a CdZnTe ͑CZT͒ detector that could resolve the x-ray spectrum into five energy bins. A postmortem breast specimen was imaged with flat panel CT to provide a model for the digital phantoms. Hydroxyapatite ͑HA͒ ͑50, 150, 250, 350, 450, and 550 mg/ml͒ and iodine ͑4, 12, 20, 28, 36, and 44 mg/ml͒ contrast elements were embedded into the glandular region of the phantoms. Calibration phantoms consisted of a 30/70 glandular-toadipose tissue ratio with embedded HA ͑100, 200, 300, 400, and 500 mg/ml͒ and iodine ͑5, 15, 25, 35, and 45 mg/ml͒. The x-ray transport process was simulated where the Beer-Lambert law, Poisson process, and CZT absorption efficiency were applied. Qualitative and quantitative evaluations of the decomposition techniques were performed and compared. The effect of breast size was also investigated. Results: The first technique decomposed iodine adequately but failed for other materials. The second method separated the materials but was unable to quantify the materials. With the addition of a calibration, the third technique provided good separation and quantification of hydroxyapatite, iodine, glandular, and adipose tissues. Quantification with this technique was accurate with errors of 9.83% and 6.61% for HA and iodine, respectively. Calibration at one point ͑one breast size͒ showed increased errors as the mismatch in breast diameters between calibration and measurement increased. A four-point calibration successfully decomposed breast diameter spanning the entire range from 8 to 20 cm. For a 14 cm breast, errors were reduced from 5.44% to 1.75% and from 6.17% to 3.27% with the multipoint calibration for HA and iodine, respectively. Conclusions:The results of the simulation study showed that a CT system based on CZT detectors in conjunction with least squares minimization technique can be used to decompose four materials. The calibrated least squares parameter estimation decomposition technique performed the best, separating and accurately quantifying the concentrations of hydroxyapatite and iodine.

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“…The preliminary experimental results of projection x-ray imaging with this detector have been presented elsewhere. 22,23…”

Section: A Concept Of Msms Cone Beam Ct Acquisitionmentioning

confidence: 99%

“…20,21 This allows for total absorption of the x-ray photons and increases the detection efficiency. The "edge-on" MCP detector concept has recently been tested for x-ray imaging applications 22,23 and is being evaluated for application for photon counting digital mammography. 24 In this work we propose two new approaches combined together for photon counting CT application.…”

Section: Introductionmentioning

confidence: 99%

Photon counting computed tomography: Concept and initial results

Shikhaliev

Molloi

2005

Med. Phys.

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A concept of a photon counting cone beam CT is proposed. The system uses a new Multi Slit Multi Slice (MSMS) cone beam acquisition geometry utilizing a linear array photon counting detectors. The MSMS cone beam acquisition is a direct analogy of the scanning multislit acquisition used in projection x-ray imaging. This geometry provides a CT imaging with dose efficient scatter rejection and allows for using available photon counting detectors. The microchannel plate (MCP) detector is proposed as a linear array photon counting detector for MSMS cone beam CT system. Initial testing of the MCP detector for CT application was performed. The field of view of the prototype MCP detector is 60 mm. A delay line position encoding electronics was used. The electronics has a single channel input for evaluation of events from the entire detector field of view. This limits the system count rate at 2 x 10(5) count/s. The spatial resolution of this detector is 80 microm FWHM at 40 kVp and 200 microm FWHM at 90 kVp tube voltages. The detector noise in CT projections is less than 1 count/pixel for the 80 microm pixel size. The CT projections contain quantum-limited and scatter free signal. Images of a contrast phantom and a small animal were acquired at 50 kVp and 80 kVp tube voltages. The CT numbers for different contrast elements were calculated for a given x-ray spectrum and compared with experimental values. The quantum efficiency of the current detector is 56% at 90 kVp, which is suboptimal because of the large channel diameter (25 microm) of these MCPs. The MCPs with smaller channels and higher efficiencies are being tested. The quantum efficiency was measured to be 70% for a new MCP with 5 microm channel diameter. Design parameters of a clinically applicable photon counting MSMS cone beam CT for breast imaging was evaluated. System uses 20 cm field of view MCP detectors based on 5 microm channel MCPs and high count rate ASIC electronics. It was concluded that the MSMS cone beam CT with a photon counting MCP detector is feasible for volume breast imaging.

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Scanning‐slit photon counting x‐ray imaging system using a microchannel plate detector

Cited by 20 publications

References 35 publications

Fundamental x-ray interaction limits in diagnostic imaging detectors: Frequency-dependent Swank noise

Fundamental x-ray interaction limits in diagnostic imaging detectors: Frequency-dependent Swank noise

Least squares parameter estimation methods for material decomposition with energy discriminating detectors

Photon counting computed tomography: Concept and initial results

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