The first analysis and clinical evaluation of native breast tissue using differential phase contrast mammography
SDC 1: Dose measurements in mammoDPC
The breast entrance skin exposure was measured by using a calibrated ionization chamber with an electrometer (PTW UNIDOS). The chamber was placed in the X-ray beam right before the sample. The exposure measure was converted to MGD (Mean Glandular Dose) for a standard 4.5cm breast by the method described in the Institute of Physical Sciences in Medicine Report 59/2 (31), where the conversion factors have been calculated according to (32).
Before measuring the breast entrance skin exposure, the beam quality was evaluated by measuring the HVL (Half Value Layer). The HVL (Al) of the X-ray tube operated at 40 keV and 25mA was 1.1mm, corresponding to a conversion factor of 0.52 for 4.5 cm breast thickness.
The average dose rate within the field of view was 0.7mGy/s. Considering the acquisition protocols (phase stepping) and the beam quality conversion factors, we obtained an MGD of 26.2 mSv for a 4.5 cm thick breast.
It is worth mentioning that the X-rays had to pass through 1.6cm plexiglas (including the plates of the breast holder and the protecting plates in front of the gratings) before hitting the detector, resulting in an intensity reduction of 40%. Further, according to the manufacturer, the detector is optimized for 17 keV: as a consequence, at 28 keV (the interferometer design energy used for this study) the detection efficiency has been estimated to be about 4 times smaller.
SDC 2: HSV-coding of mammoDPC images
In the HSV color scheme, the main color is given by the ‘Hue’ channel, which follows the visible light spectrum. The ‘Saturation’ decides the degree of the purity of a color. A highly saturated color is very intense and vivid, while a low saturated color is muted and grey. The
“Value” (also referred as lightness or brightness) refers to the intensity of light or white present. When light is at its fullest intensity, colors will become bright, whereas at its least intensity, colors become dim.
In the HSV color-coded mammoDPC images, the main color difference (e.g.-the red part, the blue part and the green part) is given by the absorption signals. The phase signal and scattering signal tune the color to provide more color contrast, which adds complementary information and shows more details.
The HSV color-coding is compared with straightforward RGB color-coding as show in Figure SDC1. In RGB color-coded images, the absorption, phase, and scattering signals represent R, G, and B channels respectively. Results clearly show that the HSV color- coding method gives better visualization (compare Figure SDC1 (b) and (e) for anterior- posterior (AP)-views and Figure SDC1 (f) and (i) for cranio-caudal (CC) views). Two- signal (absorption and phase without scattering) color-coded images, as a special case, are also produced for RGB and HSV color-coding methods. They have been obtained by setting the B channel to 0 in RGB coding and V channel to a constant 0.6 in HSV coding. It demonstrates the contributions of the scattering signal to the color-coded images. Both the RGB and HSV color-coding methods can benefit from the complementary scattering signal; however, the HSV-coding method yields the contribution of the scattering in a more obvious way thus revealing more details.
Figure SDC1: Comparison of HSV- and RGB color-coding methods. (a) The HSV color scheme, image modified from http://en.wikipedia.org/wiki/HSL_and_HSV. (b-e): color-coded images of AP-view of patient No4: (b) RGB color coding; (c) RG color coding with B=0; (d) HS color coding with constant V (V=0.6). (e) Full HSV color-coding. (f-i): color-coded images of CC views of patient No4: (f) RGB color coding; (g) RG color coding with B=0; (h) HS color coding with constant V (V=0.6). (i) HSV color-coding. Scale bars in (b-i) are 2 cm.
SDC 3: Mammography of the right breast of patient No2.
Figure SDC2: Mammography shows a retracted nipple (arrow) as an indirect sign of a retro-areolar process. Tumor diameters cannot be defined.
SDC 4: Unifocal breast cancer with DCIS presented by patient No3.
Figure SDC3: Mammography (a) of patient No3, sample mammography (b) and sample mammoDPC with HSV-color coding (c). For low breast density samples (ACR=2), additional information by mammoDPC seems to be marginal. Histology findings detected DCIS extending up to the skin, but not infiltrating it: the mammoDPC signal (red-violet color) propagates towards the skin as well. However we do not have a final confirmation that the signal provided by the mammoDPC corresponds to DCIS. Scale bar in (c) is 2 cm.
SDC 5: Fusion of absorption and differential phase contrast signals
A dedicated image fusion algorithm was used to combine image information from the absorption image and the differential phase contrast image. The algorithm is based on the simplifying assumption that the measured absorption and differential phase images can be considered as representing an object function f x y( , ) (absorption image) and a scaled version of its derivative (differential phase contrast image), where c is a constant and the subscript
( , ) c f x y x
x denotes the partial derivative of ( , )f x y with respect to the coordinate x perpendicular to the grating structures. Under this assumption, the two images can be combined in Fourier space, see Figure S4, providing a noise-optimized integration of the differential phase contrast information into the absorption image, taking into account the different frequency components, which are merged according to an ad-hoc weighting scheme. The details of the algorithm will be published elsewhere.
Figure SDC4: Effect of the merging algorithm. (a,c,d) are conventional, digital mammography images of the absorption signal. The high frequency components of the sample (here patient No5) are enhanced by the DPC signal and become better visible in the fusion data, shown in (b,e,f). Scale bars: (a,b) 5 mm, (c-f) 2.5 mm.
SDC 6: Paired mammoDPC image and histology for a selected region in patient No. 4.
Figure SDC5: Comparison of mammoDPC findings (left panel) with histopathological examination (middle, and right panel). The small 1.7 mm tumor detected in the mammoDPC is visible in the central panel, marked by a light blue arrow head. The dark blue arrow-head shows the cranial margin of resection. The remaining tissue consists predominantly of fatty stroma with small benign glands. The right panel identifies the 1.7 mm sized object as a poorly differentiated invasive ductal carcinoma. Scale bars: (a) 5 mm, (b) 4 mm and (c) 0.2 mm.
SDC 7: Complete Set of Raw Images for patients No1 to No5.
This section shows the three physical raw signals recorded with the mammoDPC equipment for each sample included in the study.
Figure SDC6.1: AP views patient No1. (a) Absorption, (b) differential phase, (c) small-angle scattering and (d) HSV-composite signal.
Scale bar is 2 mm.
Figure SDC6.2: AP views patient No2. (a) Absorption, (b) differential phase, (c) small-angle scattering and (d) HSV-composite signal.
Scale bar is 2 mm.
Figure SDC6.3: AP (a-d) and CC (e-h) views No3. (a,e) Absorption, (b,f) differential phase, (c,g) small-angle scattering and (d,h) HSV- composite signal. Scale bar is 2 mm.
Figure SDC6.4: AP (a-d) and CC (e-h) views No4. (a,e) Absorption, (b,f) differential phase, (c,g) small-angle scattering and (d,h) HSV-
Figure SDC6.4: AP views patient No5. (a) Absorption, (b) differential phase, (c) small-angle scattering and (d) HSV-composite signal.
Scale bar is 2 mm.