Department of Biomedical Engineering, Johns Hopkins University, 720 Rutland Ave., Baltimore, MD, 21205, USA.
Russell H. Morgan Department of Radiology, Johns Hopkins University, 601 N. Caroline St., Baltimore, MD, 21287, USA.
Med Phys. 2018 Jan;45(1):144-155. doi: 10.1002/mp.12659. Epub 2017 Dec 1.
This work investigates the dose characteristics and image quality of a multisource cone-beam CT scanner dedicated for extremity imaging.
The scanner has an x-ray source with three separate anode-cathode units evenly distributed along the longitudinal direction. A nominal scan protocol fires the three sources sequentially, and a total of 600 projections (200 for each source) are acquired over a source-detector orbit of 210 . Dose was measured using a Farmer chamber in three CTDI phantoms stacked end-to-end. Measurements were performed at the central and four peripheral locations of a CTDI phantom on the axial plane and repeated along the longitudinal direction. The extent of 3D sampling of the three-source configuration was assessed in the Fourier domain through noise power spectrum measurements from air scans and compared with that from a single-source scan. A modified Defrise phantom and anthropomorphic knee and hand phantoms were used for visual assessment of cone-beam artifacts in the reconstructed images.
The dose distribution for the three-source configuration exhibits radial asymmetry on the axial plane consistent with a short-scan geometry. Along the longitudinal direction, the highest dose was measured at the central axial plane where the field of view (FOV) from all three sources overlaps and falls off more slowly toward the end compared to a single-source configuration. The extent of 3D sampling is improved throughout the FOV as each source compensates for missing frequencies from the adjacent source. As a result, the reduction in streak and shading artifacts is apparent in the reconstructed images of all three phantoms. The improvement in image quality from the three-source configuration is most pronounced in joint spaces farther from the central axial plane.
Initial assessment of the multisource scanner demonstrated the advantages over single-source designs in a compact scanner with large longitudinal FOV. The reduction in cone-beam artifact is particularly valuable for extremity imaging where high-contrast articular surfaces are present away from the central axial plane and/or throughout the FOV.
本研究旨在探讨一种专用于四肢成像的多源锥形束 CT 扫描仪的剂量特性和图像质量。
该扫描仪的 X 射线源具有三个独立的阳极-阴极单元，沿纵向均匀分布。名义扫描方案依次激发三个源，在 210°的源-探测器轨道上共采集 600 个投影（每个源 200 个）。在三个头尾相连的 CTDI 体模中使用 Farmer 室测量剂量。在轴平面上的 CTDI 体模的中央和四个外围位置以及沿纵向重复进行测量。通过空气扫描的噪声功率谱测量，从傅里叶域评估三源配置的 3D 采样程度，并将其与单源扫描进行比较。使用改良的 Defrise 体模和人体膝盖和手部体模评估重建图像中的锥形束伪影。
三源配置的剂量分布在轴平面上表现出径向不对称性，符合短扫描几何形状。沿纵向，在中央轴平面上测量到的剂量最高，在此处所有三个源的视野（FOV）重叠，并且与单源配置相比，在末端处下降得更慢。在整个 FOV 中，3D 采样程度得到改善，因为每个源都补偿了来自相邻源的缺失频率。因此，在所有三个体模的重建图像中，条纹和阴影伪影的减少是显而易见的。在远离中央轴平面的关节间隙中，三源配置在图像质量方面的改善最为明显。
对多源扫描仪的初步评估表明，在具有大纵向 FOV 的紧凑型扫描仪中，与单源设计相比具有优势。在远离中央轴平面和/或整个 FOV 处存在高对比度关节表面的四肢成像中，减少锥形束伪影特别有价值。
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