Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
Med Phys. 2013 Apr;40(4):041906. doi: 10.1118/1.4794503.
Phase contrast imaging, particularly of the breast, is being actively investigated. The purpose of this work is to investigate the x-ray phase contrast properties of breast tissues and commonly used breast tissue substitutes or phantom materials with an aim of determining the phantom materials best representative of breast tissues.
Elemental compositions of breast tissues including adipose, fibroglandular, and skin were used to determine the refractive index, n = 1 - δ + i β. The real part of the refractive index, specifically the refractive index decrement (δ), over the energy range of 5-50 keV were determined using XOP software (version 2.3, European Synchrotron Radiation Facility, France). Calcium oxalate and calcium hydroxyapatite were considered to represent the material compositions of microcalcifications in vivo. Nineteen tissue substitutes were considered as possible candidates to represent adipose tissue, fibroglandular tissue and skin, and four phantom materials were considered as possible candidates to represent microcalcifications. For each material, either the molecular formula, if available, or the elemental composition based on weight fraction, was used to determine δ. At each x-ray photon energy, the absolute percent difference in δ between the breast tissue and the substitute material was determined, from which three candidates were selected. From these candidate tissue substitutes, the material that minimized the absolute percent difference in linear attenuation coefficient μ, and hence β, was considered to be best representative of that breast tissue.
Over the energy range of 5-50 keV, while the δ of CB3 and fibroglandular tissue-equivalent material were within 1% of that of fibroglandular tissue, the μ of fibroglandular tissue-equivalent material better approximated the fibroglandular tissue. While the δ of BR10 and adipose tissue-equivalent material were within 1% of that of adipose tissue, the tissue-equivalent material better approximated the adipose tissue in terms of μ. Polymethyl methacrylate, a commonly used tissue substitute, exhibited δ greater than fibroglandular tissue by ≈ 12%. The A-150 plastic closely approximated the skin. Several materials exhibited δ between that of adipose and fibroglandular tissue. However, there was an energy-dependent mismatch in terms of equivalent fibroglandular weight fraction between δ and μ for these materials. For microcalcifications, aluminum and calcium carbonate were observed to straddle the δ and μ of calcium oxalate and calcium hydroxyapatite. Aluminum oxide, commonly used to represent microcalcifications in the American College of Radiology recommended phantoms for accreditation exhibited δ greater than calcium hydroxyapatite by ≈ 23%.
A breast phantom comprising A-150 plastic to represent the skin, commercially available adipose and fibroglandular tissue-equivalent formulations to represent adipose and fibroglandular tissue, respectively, was found to be best suited for x-ray phase-sensitive imaging of the breast. Calcium carbonate or aluminum can be used to represent microcalcifications.
相衬成像技术，尤其是在乳房方面的应用，目前正在被积极研究。本研究旨在探讨乳房组织的 X 射线相衬特性以及常用的乳房组织替代物或体模材料，目的是确定最能代表乳房组织的体模材料。
使用乳房组织的元素组成，包括脂肪、纤维腺体和皮肤，来确定折射率 n=1-δ+iβ。使用 XOP 软件（版本 2.3，欧洲同步辐射设施，法国）确定了 5-50keV 能区的折射率实部，特别是折射率增量（δ）。草酸钙和羟基磷灰石被认为分别代表体内微钙化的物质组成。考虑了 19 种组织替代物作为可能的候选物质来代表脂肪组织、纤维腺体组织和皮肤，还考虑了 4 种体模材料作为可能的候选物质来代表微钙化。对于每种材料，如果有的话，使用分子公式或基于重量分数的元素组成来确定 δ。在每个 X 射线光子能量下，确定了乳房组织与替代材料之间 δ 的绝对百分比差异，从中选择了 3 种候选材料。从这些候选组织替代物中，选择使线性衰减系数 μ 的绝对百分比差异最小的材料，即 β 最小，认为该材料最能代表该乳房组织。
在 5-50keV 能区，虽然 CB3 和纤维腺体组织等效材料的 δ 在纤维腺体组织的 1%以内，但纤维腺体组织等效材料的 μ 更接近纤维腺体组织。BR10 和脂肪组织等效材料的 δ 在脂肪组织的 1%以内，但组织等效材料在 μ 方面更接近脂肪组织。聚甲基丙烯酸甲酯是一种常用的组织替代物，其 δ 比纤维腺体组织大约 12%。A-150 塑料与皮肤非常接近。几种材料的 δ 介于脂肪组织和纤维腺体组织之间。然而，这些材料在 δ 和 μ 之间的等效纤维腺体重量分数方面存在与能量相关的不匹配。对于微钙化，观察到铝和碳酸钙跨越了草酸钙和羟基磷灰石的 δ 和 μ。在用于美国放射学院推荐的认证体模中的微钙化的氧化铝，其 δ 比羟基磷灰石大大约 23%。
发现由 A-150 塑料代表皮肤、市售的脂肪和纤维腺体组织等效配方分别代表脂肪和纤维腺体组织的乳房体模最适合用于乳房的 X 射线相衬敏感成像。碳酸钙或铝可以用来代表微钙化。
