Towards in-vivo K-edge imaging using a new semi-analytical calibration method

Carsten Schirra; Axel Thran; Heiner Daerr; Ewald Roessl; Roland Proksa

doi:10.1117/12.2043539

19 March 2014 Towards in-vivo K-edge imaging using a new semi-analytical calibration method

Carsten Schirra, Axel Thran, Heiner Daerr, Ewald Roessl, Roland Proksa

Proceedings Volume 9033, Medical Imaging 2014: Physics of Medical Imaging; 90330N (2014) https://doi.org/10.1117/12.2043539
Event: SPIE Medical Imaging, 2014, San Diego, California, United States

Abstract

Flat field calibration methods are commonly used in computed tomography (CT) to correct for system imperfections. Unfortunately, they cannot be applied in energy-resolving CT when using bow-tie filters owing to spectral distortions imprinted by the filter. This work presents a novel semi-analytical calibration method for photon-counting spectral CT systems, which is applicable with a bow-tie filter in place and efficiently compensates pile-up effects at fourfold increased photon flux compared to a previously published method without degradation of image quality. The achieved reduction of the scan time enabled the first K-edge imaging in-vivo. The method employs a calibration measurement with a set of flat sheets of only a single absorber material and utilizes an analytical model to predict the expected photon counts, taking into account factors such as x-ray spectrum and detector response. From the ratios of the measured x-ray intensities and the corresponding simulated photon counts, a look-up table is generated. By use of this look-up table, measured photon-counts can be corrected yielding data in line with the analytical model. The corrected data show low pixel-to-pixel variations and pile-up effects are mitigated. Consequently, operations like material decomposition based on the same analytical model yield accurate results. The method was validated on a experimental spectral CT system equipped with a bow-tie filter in a phantom experiment and an in-vivo animal study. The level of artifacts in the resulting images is considerably lower than in images generated with a previously published method. First in-vivo K-edge images of a rabbit selectively depict vessel occlusion by an ytterbium-based thermoresponsive polymer.

Citation Download Citation

Carsten Schirra, Axel Thran, Heiner Daerr, Ewald Roessl, and Roland Proksa "Towards in-vivo K-edge imaging using a new semi-analytical calibration method", Proc. SPIE 9033, Medical Imaging 2014: Physics of Medical Imaging, 90330N (19 March 2014); https://doi.org/10.1117/12.2043539

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