Measurement of breast-tissue x-ray attenuation by spectral imaging: fresh and fixed normal and malignant tissue

Abstract

Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. In mammography, measurement of breast density, dose estimation, and differentiation between cysts and solid tumours are example applications requiring accurate data on tissue attenuation. Published attenuation data are, however, sparse and cover a relatively wide range. To supplement available data we have previously measured the attenuation of cyst fluid and solid lesions using photon-counting spectral mammography. The present study aims to measure the attenuation of normal adipose and glandular tissue, and to measure the effect of formalin fixation, a major uncertainty in published data. A total of 27 tumour specimens, 7 fibro-glandular tissue specimens, and 15 adipose tissue specimens were included. Spectral (energy-resolved) images of the samples were acquired and the image signal was mapped to equivalent thicknesses of two known reference materials, from which x-ray attenuation as a function of energy can be derived. The spread in attenuation between samples was relatively large, partly because of natural variation. The variation of malignant and glandular tissue was similar, whereas that of adipose tissue was lower. Formalin fixation slightly altered the attenuation of malignant and glandular tissue, whereas the attenuation of adipose tissue was not significantly affected. The difference in attenuation between fresh tumour tissue and cyst fluid was smaller than has previously been measured for fixed tissue, but the difference was still significant and discrimination of these two tissue types is still possible. The difference between glandular and malignant tissue was close-to significant; it is reasonable to expect a significant difference with a larger set of samples. We believe that our studies have contributed to lower the overall uncertainty of breast tissue attenuation in the literature due to the relatively large sample sets, the novel measurement method, and by clarifying the difference between fresh and fixed tissue.

Quantitative characterization of breast tissues with dedicated CT imaging

“…No significant effects were observed in the adipose tissue. A recent study by Fredenberg et al (Fredenberg 2018) confirmed those findings, also reporting that the reduction on the dense tissues drops below 2% for energies 30 keV, reaching 1% at 40 keV. Such differences are smaller than the fluctuations in the literature data shown in Fig.…”

Additive value of exposure parameters for breast cancer diagnosis in digital mammography

“…In addition, the exposure parameters were significantly higher in the malignant than benign subjects, suggesting that the malignant lesions might have accounted for the increased parenchyma density. BT and breast density are important factors that affect Xray attenuation [17]. Since FFDM images of both breasts from the same subject were acquired at one screening center, the relative bilateral density remained very consistent [18,19].…”

Computer simulations of case difficulty in digital breast tomosynthesis using virtual clinical trials

“…Two lesion insertion methods were evaluated in this study: voxel replacement 29 and voxel addition. For the additive method, the partial volume of lesions was simulated using glandular tissue ($${w_l}$$), since the differences between the attenuation of soft tissue (e.g., malignant lesion) and normal glandular tissue are minimum at mammography energies 30–32 . The X‐ray spectrum was simulated using a W anode with Al filtering.…”

“…For the additive method, the partial volume of lesions was simulated using glandular tissue (w l ), since the differences between the attenuation of soft tissue (e.g., malignant lesion) and normal glandular tissue are minimum at mammography energies. [30][31][32] The X-ray spectrum was simulated using a W anode with Al filtering. The X-ray attenuation coefficient data come from ICRU Report 44.…”

“…In comparison, multiple spectral imaging analyses have shown that the attenuation coefficients of malignant lesions composed of soft tissue (e.g., masses) and breast (glandular) tissue are very close at mammography energies [30][31][32] (Figure 1, plot). Thus, the voxel replacement method cannot guarantee that the X-ray attenuation properties of masses will be simulated adequately.…”