Instituto de Física, Facultad de Ciencias, UDELAR, Iguá 4225, 11400, Montevideo, Uruguay.
Med Phys. 2019 Jul;46(7):3001-3012. doi: 10.1002/mp.13537. Epub 2019 May 10.
Elastography images provide information about the mechanical properties of soft tissue in a noninvasive way and can be useful to identify abnormalities and ascertain differential diagnoses of suspicious prior findings obtained through mammography ultrasound. In this work we investigate, from a physics point of view, the feasibility of quantifying the Young's modulus of breast tissue from the autocorrelation of a diffuse acoustic field computed from a sequence of B-mode images acquired through conventional ultrasound scanners.
Inspired in the seismological approach of retrieving the Green's function by cross-correlation of diffuse fields, we obtained a quantitative expression that relates the local shear modulus of soft tissue to the autocorrelation of the displacement field generated by the presence of an acoustic diffuse field in the medium. In addition, we designed a mechanical prototype device adaptable to the breast anatomy, in order to create the necessary conditions in terms of diffuse field generation. The device is easy to handle, and its positioning does not interfere with the ultrasonic probe, being friendly to use within the clinical environment. The displacement field was measured from a sequence of B-mode images acquired at standard frame rates (30-50 Hz) with conventional ultrasound equipment. This method was tested in a breast tissue mimicking phantom using two standard ultrasound scanners (Toshiba Nemio NX and SIUI (Shantou Institute of Ultrasonic Instruments) Apogee 3800) and an open source research device (Verasonics V3.07 US). We also performed an in vivo measurement as a preliminary validation.
In the reconstructed Young's modulus maps the inclusions were identified and the obtained quantitative results for an inclusion and the background of the phantom were 60.0 ± 4.0 and 20.4 ± 0.5 KPa for the Toshiba equipment, 65.5 ± 6.9 and 22.6 ± 2.7 KPa for the SIUI equipment and 67.2 ± 7.3 KPa and 22.6 ± 2.8 KPa for the Verasonic scanner. These results are in good agreement with the values reported by the phantom's manufacturer of 60 and 20 KPa for the inclusion and the background, respectively. In the case of the in vivo measurement, the obtained images are in accordance with the patient known pathology (BI-RADS 5, Infiltrating Ductal Carcinoma, Score 6). The pathological breast showed a heterogeneous elasticity map with a mean Young's modulus of 98.1 ± 12.9 KPa, while the normal breast displayed a homogeneous map with a mean Young's modulus of 24.7 ± 8.1 KPa.
We successfully reconstructed the Young's modulus map of the breast tissue mimicking phantom and of a real breast tumor using B-mode images acquired with conventional ultrasound scanners. The results obtained in this work support that our technique can be developed as a medical tool to obtain quantitative breast tissue elasticity maps.
弹性成像是一种非侵入性的方法，可以提供软组织力学特性的信息，对于通过乳腺超声获得的可疑先前发现的异常和鉴别诊断很有用。在这项工作中，我们从物理学的角度研究了通过从常规超声扫描仪获得的一系列 B 模式图像计算的漫射场的自相关来定量评估乳腺组织杨氏模量的可行性。
受地震学中通过漫射场互相关来获取格林函数的方法的启发，我们得到了一个定量表达式，将软组织的局部剪切模量与介质中漫射场存在时产生的位移场的自相关相关联。此外，我们设计了一种机械原型设备，适用于乳腺解剖结构，以便在产生漫射场方面创造必要的条件。该设备易于操作，其定位不干扰超声探头，在临床环境中使用方便。通过常规超声设备以标准帧率（30-50 Hz）采集 B 模式图像来测量位移场。该方法在乳腺组织模拟体模中使用两台标准超声扫描仪（东芝 Nemio NX 和 SIUI（汕头超声仪器研究所）Apogee 3800）和一台开源研究设备（Verasonics V3.07 US）进行了测试。我们还进行了体内测量作为初步验证。
在重建的杨氏模量图中，可以识别出包含物，并且体模中包含物和背景的获得的定量结果为东芝设备为 60.0±4.0 和 20.4±0.5 KPa，SIUI 设备为 65.5±6.9 和 22.6±2.7 KPa，Verasonic 扫描仪为 67.2±7.3 KPa 和 22.6±2.8 KPa。这些结果与体模制造商报告的 60 和 20 KPa 分别为包含物和背景的值非常吻合。在体内测量的情况下，获得的图像与患者已知的病理学（BI-RADS 5、浸润性导管癌，评分 6）相符。患病乳房显示出不均匀的弹性图，杨氏模量平均值为 98.1±12.9 KPa，而正常乳房显示出均匀的弹性图，杨氏模量平均值为 24.7±8.1 KPa。
我们成功地使用常规超声扫描仪获得的 B 模式图像重建了乳腺组织模拟体模和真实乳房肿瘤的杨氏模量图。这项工作的结果支持我们的技术可以开发为一种获得定量乳腺组织弹性图的医学工具。
