Philips Research, Knarrarnäsgatan 7, 164 85 Kista, Sweden. Philips Health Systems, Mammography Solutions, Torshamnsgatan 30A, 164 40 Kista, Sweden. Author to whom any correspondence should be addressed.
Phys Med Biol. 2018 Nov 22;63(23):235003. doi: 10.1088/1361-6560/aaea83.
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, seven 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.
X 射线衰减知识对于开发和评估 X 射线成像技术至关重要。在乳腺摄影中，测量乳房密度、剂量估计以及区分囊肿和实体瘤就是需要准确组织衰减数据的应用示例。然而，已发表的衰减数据较为稀疏且涵盖范围较广。为了补充可用数据，我们之前已经使用光子计数能谱乳腺摄影测量了囊液和实体病变的衰减。本研究旨在测量正常脂肪和腺体组织的衰减，并测量福尔马林固定的影响，这是已发表数据中的主要不确定性。共纳入了 27 个肿瘤标本、7 个纤维腺体组织标本和 15 个脂肪组织标本。对样本进行了光谱（能量分辨）成像，并将图像信号映射到两种已知参考材料的等效厚度，由此可以得出 X 射线衰减与能量的关系。样本之间的衰减差异相对较大，部分原因是自然变化。恶性和腺体组织的变化相似，而脂肪组织的变化较小。福尔马林固定略微改变了恶性和腺体组织的衰减，而脂肪组织的衰减则没有明显变化。新鲜肿瘤组织和囊肿液之间的衰减差异小于之前测量的固定组织，但差异仍然显著，仍然可以区分这两种组织类型。腺体组织和恶性组织之间的衰减差异接近显著；随着样本量的增加，预计会有显著差异，这是合理的。我们认为，由于样本量较大、采用了新的测量方法以及明确了新鲜组织和固定组织之间的差异，我们的研究有助于降低文献中乳腺组织衰减的整体不确定性。
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