Division of Population Science, H, Lee Moffitt Cancer Center & Research Institute, 12902 Magnolia Drive, Tampa, FL 33612, USA.
Biomed Eng Online. 2013 Nov 9;12:114. doi: 10.1186/1475-925X-12-114.
Breast density is a significant breast cancer risk factor measured from mammograms. The most appropriate method for measuring breast density for risk applications is still under investigation. Calibration standardizes mammograms to account for acquisition technique differences prior to making breast density measurements. We evaluated whether a calibration methodology developed for an indirect x-ray conversion full field digital mammography (FFDM) technology applies to direct x-ray conversion FFDM systems.
Breast tissue equivalent (BTE) phantom images were used to establish calibration datasets for three similar direct x-ray conversion FFDM systems. The calibration dataset for each unit is a function of the target/filter combination, x-ray tube voltage, current × time (mAs), phantom height, and two detector fields of view (FOVs). Methods were investigated to reduce the amount of calibration data by restricting the height, mAs, and FOV sampling. Calibration accuracy was evaluated with mixture phantoms. We also compared both intra- and inter-system calibration characteristics and accuracy.
Calibration methods developed previously apply to direct x-ray conversion systems with modification. Calibration accuracy was largely within the acceptable range of ± 4 standardized units from the ideal value over the entire acquisition parameter space for the direct conversion units. Acceptable calibration accuracy was maintained with a cubic-spline height interpolation, representing a modification to previous work. Calibration data is unit specific, can be acquired with the large FOV, and requires a minimum of one reference mAs sample. The mAs sampling, calibration accuracy, and the necessity for machine specific calibration data are common characteristics and in agreement with our previous work.
The generality of our calibration approach was established under ideal conditions. Evaluation with patient data using breast cancer status as the endpoint is required to demonstrate that the approach produces a breast density measure associated with breast cancer.
乳腺密度是从乳房 X 光片中测量的一个重要乳腺癌风险因素。用于风险应用的乳腺密度的最合适方法仍在研究中。校准可标准化乳房 X 光片，以在进行乳腺密度测量之前考虑到采集技术差异。我们评估了一种为间接 X 射线转换全视野数字乳腺摄影术（FFDM）技术开发的校准方法是否适用于直接 X 射线转换 FFDM 系统。
使用乳腺组织等效体（BTE）体模图像为三个类似的直接 X 射线转换 FFDM 系统建立校准数据集。每个单元的校准数据集是目标/滤波器组合、X 射线管电压、电流×时间（mAs）、体模高度以及两个探测器视野（FOV）的函数。通过限制高度、mAs 和 FOV 采样，研究了减少校准数据量的方法。使用混合体模评估了校准准确性。我们还比较了内部和系统间的校准特性和准确性。
先前开发的校准方法经过修改后适用于直接 X 射线转换系统。校准准确性在直接转换单元的整个采集参数空间内，在理想值的正负 4 个标准化单位范围内，在很大程度上都在可接受范围内。通过三次样条高度插值保持可接受的校准精度，这是对以前工作的修改。校准数据是特定于单元的，可以使用大 FOV 采集，并且需要至少一个参考 mAs 样本。mAs 采样、校准准确性以及对机器特定校准数据的需求是共同的特征，与我们以前的工作一致。
在理想条件下，我们的校准方法的通用性得到了确立。需要使用乳腺癌状态作为终点的患者数据进行评估，以证明该方法可产生与乳腺癌相关的乳腺密度测量值。
