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Signal-to-Noise and Contrast Ratio Enhancements by Quasi-Monochromatic Imaging

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1 Author(s)
Zentai, G. ; Ginzton Technol. Center, Varian Med. Syst., Mountain View, CA, USA

Computed tomography (CT) exams provide orders of magnitude higher radiation than a single-view X-ray. The chance of getting cancer from X-ray radiation has been increasing by 1.5-2% at every CT exam. Therefore, decreasing the dose per CT exam is a major goal. The aims of this study were to find out how one can improve the signal-to-noise ratio (S/N) or decrease the dose with the same S/N in mammography CT and how to improve the contrast ratio for I (iodine) contrast imaging. Iodine has been used for intravenous injection to detect any blockage in blood circulation by X-rays. Moreover, iodine also accumulates in cancer cells, as described in this paper, so it is used to increase the contrast of breast tumor images. It was studied how special breast imaging modalities, specifically CT, could benefit from the quasimonochromatic radiation at higher energy levels. This paper gives an overview of different techniques to generate quasi-monochromatic X-ray radiation and emphasizes the advantages of the K-edge filtering method when the K-edge energy of the X-ray filter material is close to the K-edge of iodine, which is about 33 keV. Several K-edge filters are compared, and the results of the CT experiments are discussed, which prove that, using the right material, the iodine X-ray contrast image can be improved by >; 25%, and simultaneously, the dose to the patient can be decreased by a factor of two or more while keeping the same signal-to-noise ratio as without K-edge filtering. This is a very significant advancement for CT screening of women who has been suspected of breast cancer. This paper also emphasizes the importance of Hounsfield unit calibration when using different filters and highlights the magnitude of errors if it has not been done right.

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Instrumentation and Measurement, IEEE Transactions on  (Volume:60 ,  Issue: 3 )