Department of Radiology, Stanford University, Stanford, California, USA.
Department of Radiation Oncology, Stanford University, Stanford, California, USA.
Med Phys. 2023 Jul;50(7):4459-4465. doi: 10.1002/mp.16413. Epub 2023 Apr 15.
High precision radiotherapy with small irradiator size has potential in many treatment applications involving small shallow targets, with small animal radio-neuromodulation as an intriguing example. A focused kV technique based on novel usage of polycapillary x-ray lenses can focus x-ray beams to <0.2 mm in diameter, which is ideal for such uses.
Such an application also requires high resolution CT images for treatment planning and setup. In this work, we demonstrate the feasibility of using a virtual focal spot generated with an x-ray lens to perform high-resolution CBCT acquisition.
The experiment with x-ray lens was set up on an x-ray tabletop system to generate a virtual focal spot. The flood field images with and without the x-ray lens were first compared. A pinhole image was acquired for the virtual focal spot and compared with the one acquired with the conventional focal spot without the lens. The planar imaging resolution with and without the lens were evaluated using a line pair resolution phantom. The spatial resolution of the two settings were estimated by reconstructing a 0.15-mm wire phantom and comparing its full width half maximum (FWHM). A CBCT scan of a rodent head was also acquired to further demonstrate the improved resolution using the x-ray lens.
The proposed imaging setup with x-ray lens had a limited exposure area of 5 cm by 5 cm on the detector, which was suitable for guiding radio-neuromodulation to a small target in rodent brain. Compared to conventional imaging acquisition with a measured x-ray focal spot of 0.395 mm FWHM, the virtual focal spot size was measured at 0.175 mm. The reduction in focal spot size with lens leads to an almost doubled planar imaging resolution and a 26% enhancement in 3D spatial resolution. A realistic CBCT acquisition of a rodent head mimicked the imaging acquisition step for radio-neuromodulation and further showed the improved visualization for fine structures.
This work demonstrated that the focused kV x-ray technique was capable of generating small focal spot size of <0.2 mm, which substantially improved x-ray imaging resolution for small animal imaging.
具有小照射器尺寸的高精度放射治疗在涉及小浅目标的许多治疗应用中具有潜力，小动物放射神经调节就是一个有趣的例子。一种基于新型多毛细管 X 射线透镜的聚焦千伏技术可以将 X 射线束聚焦到直径<0.2mm，非常适合这种用途。
这种应用还需要高分辨率 CT 图像进行治疗计划和设置。在这项工作中，我们展示了使用 X 射线透镜产生的虚拟焦点进行高分辨率 CBCT 采集的可行性。
在 X 射线台式系统上设置 X 射线透镜实验以产生虚拟焦点。首先比较了有和没有 X 射线透镜的漫射场图像。获得了虚拟焦点的针孔图像，并将其与没有透镜的常规焦点获得的图像进行了比较。使用线对分辨率体模评估了有和没有透镜的平面成像分辨率。通过重建 0.15mm 线丝体模并比较其全宽半最大值（FWHM）来估计两个设置的空间分辨率。还对啮齿动物头部进行了 CBCT 扫描，以进一步证明使用 X 射线透镜提高了分辨率。
提出的带有 X 射线透镜的成像设置在探测器上的有效照射区域为 5cm×5cm，非常适合引导放射神经调节至啮齿动物大脑中的小目标。与具有测量的 0.395mm FWHM 焦点的常规成像采集相比，虚拟焦点尺寸测量为 0.175mm。透镜引起的焦点尺寸减小导致平面成像分辨率几乎提高一倍，三维空间分辨率提高 26%。对啮齿动物头部的真实 CBCT 采集模拟了放射神经调节的成像采集步骤，并进一步显示了精细结构的可视化改善。
这项工作表明，聚焦千伏 X 射线技术能够产生<0.2mm 的小焦点尺寸，这大大提高了小动物成像的 X 射线成像分辨率。
