Bi-directional x-ray phase-contrast mammography

Abstract

Phase-contrast x-ray imaging is a promising improvement of conventional absorption-based mammography for early tumor detection. This potential has been demonstrated recently, utilizing structured gratings to obtain differential phase and dark-field scattering images. However, the inherently anisotropic imaging sensitivity of the proposed mono-directional approach yields only insufficient diagnostic information, and has low diagnostic sensitivity to highly oriented structures. To overcome these limitations, we present a two-directional x-ray phase-contrast mammography approach and demonstrate its advantages by applying it to a freshly dissected, cancerous mastectomy breast specimen. We illustrate that the two-directional scanning procedure overcomes the insufficient diagnostic value of a single scan, and reliably detects tumor structures, independently from their orientation within the breast. Our results indicate the indispensable diagnostic necessity and benefit of a multi-directional approach for x-ray phase-contrast mammography.

Figure 1. Schematic overview of the bi-directional phase-contrast mammography setup.

The setup consists of a conventional x-ray tube, a source grating G ₀, a phase grating G ₁, an analyser grating G ₂ and a flat panel detector. The two-directional, orthogonal scanning approach is indicated by a 90° rotation of the gratings. For practical reasons the rotation of the specimen was preferred.

Figure 2. Conventional and grating-based mammograms of a breast specimen with invasive ductal carcinoma.

Conventional mammogram (a), grating-based absorption (b), differential phase (c) and dark-field image (d) of the breast specimen. The field of view has a size of 12.8×12.8 cm². Images (b)–(d) were obtained by stitching together 4×4 low-statistic projections. Arrows indicate the direction of scanning. The high-statistic images of the invasive ductal carcinoma are shown as inlays.

Figure 3. Two-directional, grating-based mammograms of the invasive ductal carcinoma.

Two-directional differential phase (a), (b) and sharpened, two-dimensional integrated phase image (c). Dark-field (d), (e) and mean dark-field image (f). Arrows indicate the direction of scanning. Red and blue boxes indicate tumor branches exclusively perceivable in the images obtained with scanning performed in - or -direction, respectively.

Figure 4. Two-directional, grating-based mammograms of the invasive ductal carcinoma with correlated histopathology.

(a) Sharpened, two-dimensional integrated phase image of the invasive ductal carcinoma. The frames in (a) and (c) indicate three locally separated tumor lesions (apparently trifocal). Arrows in (a) and (c) indicate fine tumor branches. (b) Sharpened, absorption image of the invasive ductal carcinoma. Circles indicate position of relevant tumor details. (c) Histological slice (Hematoxylin and Eosin stain) of the invasive ductal carcinoma. (d) Directional dark-field image of the invasive ductal carcinoma. Preferred scattering direction is color-coded ranging from -directed (red) over isotropic (purple) to -directed (blue). (e) 200x magnified histological image of the tumor branch, as indicated by white diamond in (c) and (d). The 2-dimensional FFT is shown as an inlay. (d) 200x magnified histological image of the tumor lesion, as indicated by black diamond in (c) and (d). The 2-dimensional FFT is shown as an inlay.