Department of Health Technology, Technical University of Denmark, Kgs. Lyngby, Denmark.
Department of Health Technology, Technical University of Denmark, Kgs. Lyngby, Denmark.
Ultrasonics. 2021 Jul;114:106353. doi: 10.1016/j.ultras.2021.106353. Epub 2021 Mar 4.
This study evaluates the use of 3D printed phantoms for 3D super-resolution ultrasound imaging (SRI) algorithm calibration. The main benefit of the presented method is the ability to do absolute 3D micro-positioning of sub-wavelength sized ultrasound scatterers in a material having a speed of sound comparable to that of tissue. Stereolithography is used for 3D printing soft material calibration micro-phantoms containing eight randomly placed scatterers of nominal size 205 μm × 205 μm × 200 μm. The backscattered pressure spatial distribution is evaluated to show similar distributions from micro-bubbles as the 3D printed scatterers. The printed structures are found through optical validation to expand linearly in all three dimensions by 2.6% after printing. SRI algorithm calibration is demonstrated by imaging a phantom using a λ/2 pitch 3 MHz 62+62 row-column addressed (RCA) ultrasound probe. The printed scatterers will act as point targets, as their dimensions are below the diffraction limit of the ultrasound system used. Two sets of 640 volumes containing the phantom features are imaged, with an intervolume uni-axial movement of the phantom of 12.5 μm, to emulate a flow velocity of 2 mm/s at a frame rate of 160 Hz. The ultrasound signal is passed to a super-resolution pipeline to localise the positions of the scatterers and track them across the 640 volumes. After compensating for the phantom expansion, a scaling of 0.989 is found between the distance between the eight scatterers calculated from the ultrasound data and the designed distances. The standard deviation of the variation in the scatterer positions along each track is used as an estimate of the precision of the super-resolution algorithm, and is expected to be between the two limiting estimates of (σ̃,σ̃,σ̃) = (22.7 μm, 27.6 μm, 9.7 μm) and (σ̃,σ̃,σ̃) = (18.7 μm, 19.3 μm, 8.9 μm). In conclusion, this study demonstrates the use of 3D printed phantoms for determining the accuracy and precision of volumetric super-resolution algorithms.
本研究评估了使用 3D 打印的仿体进行 3D 超高分辨率超声成像（SRI）算法校准。所提出方法的主要优点是能够在与组织声速相当的材料中对亚波长大小的超声散射体进行绝对 3D 微定位。立体光刻用于 3D 打印包含八个随机放置的标称尺寸为 205μm×205μm×200μm 的散射体的软材料校准微仿体。评估背散射压力空间分布以显示微气泡与 3D 打印散射体的相似分布。通过光学验证发现，打印结构在所有三个维度上线性扩展 2.6%。通过使用 λ/2 节距 3MHz 62+62 行-列寻址（RCA）超声探头对仿体进行成像来演示 SRI 算法校准。打印的散射体将作为点目标，因为它们的尺寸小于所用超声系统的衍射极限。成像包含仿体特征的两组 640 个体积，两个体积之间的 phantom 以 12.5μm 的单轴运动，以在 160Hz 的帧率下模拟 2mm/s 的流速。将超声信号传递到超分辨率管道，以定位散射体的位置并在 640 个体积中跟踪它们。在补偿 phantom 扩展后，发现从超声数据计算出的八个散射体之间的距离与设计距离之间的比例为 0.989。沿着每个轨迹散射体位置变化的标准偏差用作超分辨率算法精度的估计值，预计在两个极限估计值（(σ̃,σ̃,σ̃)=(22.7μm,27.6μm,9.7μm)和 (σ̃,σ̃,σ̃)=(18.7μm,19.3μm,8.9μm)）之间。总之，本研究证明了使用 3D 打印的仿体来确定体积超分辨率算法的准确性和精度。
