van der Velden Sandra, Beijst Casper, Viergever Max A, de Jong Hugo W A M
Radiology and Nuclear Medicine, UMC Utrecht, 85500, 3508 GA, Utrecht, Netherlands.
Image Sciences Institute, UMC Utrecht, 85500, 3508 GA, Utrecht, Netherlands.
Med Phys. 2017 Jan;44(1):249-261. doi: 10.1002/mp.12010. Epub 2017 Jan 3.
X-ray-guided oncological interventions could benefit from the availability of simultaneously acquired nuclear images during the procedure. To this end, a real-time, hybrid fluoroscopic and nuclear imaging device, consisting of an X-ray c-arm combined with gamma imaging capability, is currently being developed (Beijst C, Elschot M, Viergever MA, de Jong HW. Radiol. 2015;278:232-238). The setup comprises four gamma cameras placed adjacent to the X-ray tube. The four camera views are used to reconstruct an intermediate three-dimensional image, which is subsequently converted to a virtual nuclear projection image that overlaps with the X-ray image. The purpose of the present simulation study is to evaluate the impact of gamma camera collimator choice (parallel hole versus pinhole) on the quality of the virtual nuclear image.
Simulation studies were performed with a digital image quality phantom including realistic noise and resolution effects, with a dynamic frame acquisition time of 1 s and a total activity of 150 MBq. Projections were simulated for 3, 5, and 7 mm pinholes and for three parallel hole collimators (low-energy all-purpose (LEAP), low-energy high-resolution (LEHR) and low-energy ultra-high-resolution (LEUHR)). Intermediate reconstruction was performed with maximum likelihood expectation-maximization (MLEM) with point spread function (PSF) modeling. In the virtual projection derived therefrom, contrast, noise level, and detectability were determined and compared with the ideal projection, that is, as if a gamma camera were located at the position of the X-ray detector. Furthermore, image deformations and spatial resolution were quantified. Additionally, simultaneous fluoroscopic and nuclear images of a sphere phantom were acquired with a physical prototype system and compared with the simulations.
For small hot spots, contrast is comparable for all simulated collimators. Noise levels are, however, 3 to 8 times higher in pinhole geometries than in parallel hole geometries. This results in higher contrast-to-noise ratios for parallel hole geometries. Smaller spheres can thus be detected with parallel hole collimators than with pinhole collimators (17 mm vs 28 mm). Pinhole geometries show larger image deformations than parallel hole geometries. Spatial resolution varied between 1.25 cm for the 3 mm pinhole and 4 cm for the LEAP collimator. The simulation method was successfully validated by the experiments with the physical prototype.
A real-time hybrid fluoroscopic and nuclear imaging device is currently being developed. Image quality of nuclear images obtained with different collimators was compared in terms of contrast, noise, and detectability. Parallel hole collimators showed lower noise and better detectability than pinhole collimators.
在手术过程中同时获取核图像，这对X射线引导的肿瘤介入治疗可能有益。为此，目前正在开发一种实时的、混合的荧光透视和核成像设备，该设备由一台X射线C型臂与伽马成像功能相结合组成（Beijst C，Elschot M，Viergever MA，de Jong HW. Radiol. 2015;278:232 - 238）。该装置包括四个与X射线管相邻放置的伽马相机。这四个相机视图用于重建一个中间三维图像，随后将其转换为与X射线图像重叠的虚拟核投影图像。本模拟研究的目的是评估伽马相机准直器选择（平行孔与针孔）对虚拟核图像质量的影响。
使用包含逼真噪声和分辨率效应的数字图像质量模型进行模拟研究，动态帧采集时间为1秒，总活度为150 MBq（兆贝可）。针对3毫米、5毫米和7毫米的针孔以及三种平行孔准直器（低能通用型（LEAP）、低能高分辨率型（LEHR）和低能超高分辨率型（LEUHR））模拟投影。使用带有点扩散函数（PSF）建模的最大似然期望最大化（MLEM）进行中间重建。在由此得出的虚拟投影中，确定对比度、噪声水平和可探测性，并与理想投影进行比较，即就好像伽马相机位于X射线探测器的位置一样。此外，对图像变形和空间分辨率进行了量化。另外，使用物理原型系统采集了球体模型的同步荧光透视和核图像，并与模拟结果进行比较。
对于小热点，所有模拟准直器的对比度相当。然而，针孔几何结构中的噪声水平比平行孔几何结构中的高3至8倍。这导致平行孔几何结构具有更高的对比度噪声比。因此，与针孔准直器相比，使用平行孔准直器能够检测到更小的球体（17毫米对28毫米）。针孔几何结构显示出比平行孔几何结构更大的图像变形。空间分辨率在3毫米针孔的1.25厘米至LEAP准直器的4厘米之间变化。通过物理原型实验成功验证了模拟方法。
目前正在开发一种实时的混合荧光透视和核成像设备。就对比度、噪声和可探测性而言，比较了使用不同准直器获得的核图像的图像质量。平行孔准直器显示出比针孔准直器更低的噪声和更好的可探测性。
