Mr. Christopher Coello Profile

Christopher Coello

at CEA-LETI

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Proceedings Article | 19 March 2008 Paper

Reduced inter-exposure time in dual-energy imaging: a technological and image processing cooperative approach

Christopher Coello, Jean-Marc Dinten, Marc Arques, Pierre Rohr, Christophe Odet

Proceedings Volume 6913, 691357 (2008) https://doi.org/10.1117/12.770414

KEYWORDS: Denoising, Signal attenuation, Image filtering, Dual energy imaging, Sensors, Switches, Signal to noise ratio, Interference (communication), Calibration, Bone

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Dual-energy imaging increases the possibility of pulmonary nodule detection by reducing the bone structure noise. Dual-shot techniques are limited by structural artefacts due to patient and natural movement during the switch of voltage between energies. A new acquisition approach for dual-energy imaging was envisioned in order to reduce this inter-exposure time. The idea is to keep the tube voltage constant, switch a filter in front of the patient and thus modulate the outgoing x-ray spectrum. The drawback of this method is a poorer spectral separation between low and high energy images leading to a higher sensitivity to noise. On the other hand, noise in the reconstructed image is mainly controlled by high-energy image noise, allowing the use of noise suppression algorithms without loosing high-frequency information present in the low-energy image. The first part of this paper is a simulation study presenting system optimisation that includes noise reduction in the HE image. Exposure times and filter thickness are chosen when optimising the signal difference to noise ratio (SDNR) and dose. Results show better SDNR (9 %) for similar dose than state-of-art dual-shot switching voltage technique. Thicker filters could lead to better results, but would demand more tube charge. In the second part is presented experimental validation and implemented noise suppression algorithm. As radiographs of anatomical phantoms are structured, anisotropic algorithm have been considered. Nodule and anthropomorphic phantoms were used to measure detail suppression after image processing. Results are shown in terms of noise suppression in the reconstructed image as well as in detail preservation.

Proceedings Article | 16 March 2007 Paper

Dual-energy technique for digital flat-panel detectors without x-ray tube voltage switching

Christopher Coello, Jean-Marc Dinten, Marc Arques, Pierre Rohr, Christophe Odet

Proceedings Volume 6510, 651005 (2007) https://doi.org/10.1117/12.707355

KEYWORDS: Sensors, X-rays, Denoising, Dual energy imaging, X-ray detectors, Switching, Switches, X-ray imaging, Image filtering, Tissues

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Dual-energy imaging increases the possibility of pulmonary nodule detection by reducing the bone structure noise. The major problem of the dual-energy acquisition process with digital flat-panel detectors is the interval of time between low-energy (LE) exposure and high-energy (HE) exposure. Due to misregistration between LE and HE images, motion artifacts pollute the subtracted image. This paper presents a new acquisition approach for dual-energy imaging developed in order to reduce this inter-exposure time. The idea is to keep the tube voltage constant and to just switch a filter in front of the imaged object and thus to modulate the outgoing x-ray spectrum. The first part of this study presents how to optimize system parameters for the new acquisition protocol: source voltage, dynamic filtration before the patient, exposure time for LE and HE acquisition. The tube load is kept constant to focus the optimization study on the dose and the exposure time. A noise quality factor (NQF) and a spectral quality factor (SQF) are used as criteria for optimization. The new approach system is then compared to the state-of-the-art system with voltage switching between low and high energy. A filtering algorithm of dual energy acquisitions enabling a significant noise reduction is presented. Performance between its combination with the new acquisition protocol and the reference one are compared. For a limited noise quality factor, three times faster acquisition time is obtained using the new system. Noise reduction techniques improve the image SNR by 61% in the new system and only 32% in the reference system, without taking into account the impact of better registration on the dual-energy image quality.

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