Department of Radiological Sciences, University of California, Irvine, California 92697, USA.
Med Phys. 2011 Aug;38(8):4498-504. doi: 10.1118/1.3605632.
Currently, there is no accepted standard for measuring breast density. Dual energy mammography, which has demonstrated accurate measurement in phantoms, has been proposed as one possible method. To examine the use of chemical analysis as a possible means to validate breast density measurements from dual energy mammography, a bovine tissue model was investigated. Known quantities of lean and adipose tissue were compared with composition values measured from dual energy images and chemical analysis.
Theoretical simulations were performed to assess the impact variations in breast composition would have on measurement of breast density from a single calibration. Fourteen ex-vivo tissue samples composed of varying amounts of pure lean tissue and pure adipose tissue (lean percentage) from 0 to 100%, in increments of 10%, were imaged using dual energy mammography. This was followed by chemical analysis based on desiccation, trituration, and fat extraction with petroleum ether to determine water, lipid, and protein content. The volumetric lean percentage (VLP) as measured from images (VLP(I)) and as derived from chemical analysis data (VLP(CA)) were compared with the VLP calculated from measurements of sample mass with a scale (VLP(M)). Finally, data from the bovine tissue model in this study were compared to compositional data from a previous report of human tissue composition.
The results from simulation suggest a substantial impact on measuring breast density is likely due to changes in anatomical breast composition. VLP(I) was related to the VLP(M) by VLP(I) = 1.53 VLP(M) + 10.0 (r2 > 0.99). VLP(CA) was related to VLP(M) by VLP(CA) = 0.76 VLP(M) + 22.8 (r2 > 0.99). VLP(I) was related to VLP(CA) by VLP(I) = 2.00 VLP(CA) - 35.6 (r2 > 0.99). Bovine adipose tissue was shown to be very similar to human adipose tissue in terms of water, lipid, and protein content with RMS differences of 1.2%. Bovine lean tissue was shown to be very similar to human skeletal muscle tissue and somewhat similar to human mammary gland tissue with RMS differences of 0.4 and 22.2%, respectively.
The results of this study show strong linear relationships between volumetric lean percentage measurements using dual energy mammography, chemical analysis and the actual mass. Determining the existence of a relationship between VLP(I) and VLP(CA) was necessary before comparing density results from the dual energy technique to composition data from chemical analysis for samples of unknown composition.
目前，尚无公认的标准来测量乳房密度。双能乳腺 X 线摄影术在体模中已被证明能进行准确的测量，因此被提议作为一种可能的方法。为了研究化学分析作为验证双能乳腺 X 线摄影术测量乳房密度的一种可能手段，本研究建立了牛组织模型。对已知量的瘦组织和脂肪组织与从双能图像和化学分析中测量的组成值进行了比较。
为了评估乳房组成的变化对从单一校准中测量乳房密度的影响，我们进行了理论模拟。对 14 个由不同纯瘦组织和纯脂肪组织（瘦组织百分比）组成的离体组织样本（从 0 到 100%，每隔 10%）进行了双能乳腺 X 线摄影术成像。然后，通过干燥、研磨和用石油醚提取脂肪来进行基于化学分析的测量，以确定水、脂质和蛋白质含量。图像（VLP（I））和化学分析数据（VLP（CA））测量的体积瘦组织百分比（VLP）与用天平测量的样本质量（VLP（M））计算的 VLP 进行了比较。最后，将本研究中牛组织模型的数据与先前人类组织成分报告中的组成数据进行了比较。
模拟结果表明，由于解剖学乳房组成的变化，测量乳房密度的影响可能很大。VLP（I）与 VLP（M）的关系为 VLP（I）=1.53 VLP（M）+10.0（r2>0.99）。VLP（CA）与 VLP（M）的关系为 VLP（CA）=0.76 VLP（M）+22.8（r2>0.99）。VLP（I）与 VLP（CA）的关系为 VLP（I）=2.00 VLP（CA）-35.6（r2>0.99）。牛脂肪组织在水、脂质和蛋白质含量方面与人类脂肪组织非常相似，均方根差异为 1.2%。牛瘦组织与人类骨骼肌组织非常相似，与人类乳腺组织有些相似，均方根差异分别为 0.4%和 22.2%。
本研究结果表明，双能乳腺 X 线摄影术、化学分析和实际质量的体积瘦组织百分比测量之间存在很强的线性关系。在将双能技术的密度结果与化学分析的组成数据进行比较之前，确定 VLP（I）和 VLP（CA）之间存在关系是必要的，因为样本的组成是未知的。
