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On a dark-field signal generated by micrometer-sized calcifications in phase-contrast mammography

2013; IOP Publishing; Volume: 58; Issue: 8 Linguagem: Inglês

10.1088/0031-9155/58/8/2713

1361-6560

Thilo Michel, Jens Rieger, G. Anton, Florian Bayer, Matthias W. Beckmann, Jürgen Durst, Peter A. Fasching, Wilhelm Haas, Arndt Hartmann, Georg Pelzer, Marcus Radicke, Claudia Rauh, André Ritter, P. Sievers, Rüdiger Schulz‐Wendtland, Michael Uder, David L. Wachter, Thomas Weber, Evelyn Wenkel, Andrea Zang,

X-ray Spectroscopy and Fluorescence Analysis

We show that a distribution of micrometer-sized calcifications in the human breast which are not visible in clinical x-ray mammography at diagnostic dose levels can produce a significant dark-field signal in a grating-based x-ray phase-contrast imaging setup with a tungsten anode x-ray tube operated at 40 kVp. A breast specimen with invasive ductal carcinoma was investigated immediately after surgery by Talbot-Lau x-ray interferometry with a design energy of 25 keV. The sample contained two tumors which were visible in ultrasound and contrast-agent enhanced MRI but invisible in clinical x-ray mammography, in specimen radiography and in the attenuation images obtained with the Talbot-Lau interferometer. One of the tumors produced significant dark-field contrast with an exposure of 0.85 mGy air-kerma. Staining of histological slices revealed sparsely distributed grains of calcium phosphate with sizes varying between 1 and 40 μm in the region of this tumor. By combining the histological investigations with an x-ray wave-field simulation we demonstrate that a corresponding distribution of grains of calcium phosphate in the form of hydroxylapatite has the ability to produce a dark-field signal which would-to a substantial degree-explain the measured dark-field image. Thus we have found the appearance of new information (compared to attenuation and differential phase images) in the dark-field image. The second tumor in the same sample did not contain a significant fraction of these very fine calcification grains and was invisible in the dark-field image. We conclude that some tumors which are invisible in x-ray absorption mammography might be detected in the x-ray dark-field image at tolerable dose levels.