Lau Susie, Ng Kwan Hoong, Abdul Aziz Yang Faridah
1 Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
2 University of Malaya Research Imaging Centre, Faculty of Medicine, University of Malaya, Kuala Lumpur, Malaysia.
Br J Radiol. 2016 Oct;89(1066):20160258. doi: 10.1259/bjr.20160258. Epub 2016 Jul 25.
To investigate the sensitivity and robustness of a volumetric breast density (VBD) measurement system to errors in the imaging physics parameters including compressed breast thickness (CBT), tube voltage (kVp), filter thickness, tube current-exposure time product (mAs), detector gain, detector offset and image noise.
3317 raw digital mammograms were processed with Volpara(®) (Matakina Technology Ltd, Wellington, New Zealand) to obtain fibroglandular tissue volume (FGV), breast volume (BV) and VBD. Errors in parameters including CBT, kVp, filter thickness and mAs were simulated by varying them in the Digital Imaging and Communications in Medicine (DICOM) tags of the images up to ±10% of the original values. Errors in detector gain and offset were simulated by varying them in the Volpara configuration file up to ±10% from their default values. For image noise, Gaussian noise was generated and introduced into the original images.
Errors in filter thickness, mAs, detector gain and offset had limited effects on FGV, BV and VBD. Significant effects in VBD were observed when CBT, kVp, detector offset and image noise were varied (p < 0.0001). Maximum shifts in the mean (1.2%) and median (1.1%) VBD of the study population occurred when CBT was varied.
Volpara was robust to expected clinical variations, with errors in most investigated parameters giving limited changes in results, although extreme variations in CBT and kVp could lead to greater errors.
Despite Volpara's robustness, rigorous quality control is essential to keep the parameter errors within reasonable bounds. Volpara appears robust within those bounds, albeit for more advanced applications such as tracking density change over time, it remains to be seen how accurate the measures need to be.
研究乳腺容积密度（VBD）测量系统对成像物理参数误差的敏感性和稳健性，这些参数包括乳腺压缩厚度（CBT）、管电压（kVp）、滤过器厚度、管电流-曝光时间乘积（mAs）、探测器增益、探测器偏移和图像噪声。
使用Volpara（®）（Matakina Technology Ltd，惠灵顿，新西兰）对3317幅原始数字乳腺X线摄影图像进行处理，以获得纤维腺体组织体积（FGV）、乳房体积（BV）和VBD。通过在图像的医学数字成像和通信（DICOM）标签中改变参数，模拟CBT、kVp、滤过器厚度和mAs等参数的误差，变化幅度高达原始值的±10%。通过在Volpara配置文件中改变探测器增益和偏移，模拟其误差，变化幅度高达默认值的±10%。对于图像噪声，生成高斯噪声并将其引入原始图像。
滤过器厚度、mAs、探测器增益和偏移的误差对FGV、BV和VBD的影响有限。当CBT、kVp、探测器偏移和图像噪声发生变化时，观察到VBD有显著影响（p < 0.0001）。当CBT变化时，研究人群的平均VBD（1.2%）和中位数VBD（1.1%）出现最大偏移。
Volpara对预期的临床变化具有稳健性，尽管CBT和kVp的极端变化可能导致更大的误差，但大多数研究参数的误差导致结果变化有限。
尽管Volpara具有稳健性，但严格的质量控制对于将参数误差控制在合理范围内至关重要。Volpara在这些范围内似乎具有稳健性，尽管对于更高级的应用，如随时间跟踪密度变化，测量需要多准确还有待观察。
