Blinder Stephan A L, Dinelle Katherine, Sossi Vesna
Pacific Parkinson's Research Centre, University of British Columbia, Vancouver, British Columbia V6T 2B5, Canada.
Med Phys. 2012 Aug;39(8):5073-83. doi: 10.1118/1.4736802.
The Siemens ECAT high resolution research tomograph (HRRT) is a dedicated human brain PET camera with a 6% absolute sensitivity and a (2.3 mm)(3) spatial resolution, improving to (1.8 mm)(3) when point spread function (PSF) modeling algorithms are used. These values are very close to those of dedicated small animal PET cameras such as the Siemens microPET FOCUS 120 (F120). The larger axial and transaxial field of view of the HRRT compared to the F120 allows, in principle, for simultaneous imaging of several rodents thus potentially reducing scanning costs and time. This study investigates the feasibility of using the HRRT for quantitative small animal brain studies.
We compare, in terms of magnitude, reproducibility, and asymmetry, the nondisplaceable tissue input binding potentials (BP(ND)) in the striata obtained from [(11)C]methylphenidate scans of the same rats imaged on both the F120 and the HRRT. The animal studies are complemented by a phantom study aimed at investigating noise properties relevant to the size of typical regions of interest used in rat brain image analysis.
(i) The BP(ND) values obtained from HRRT data are lower than those obtained on the F120 by 38% when PSF modeling is not used, while they are 7% higher with PSF modeling. (ii) The within animal reproducibility on the HRRT is 18% without PSF modeling, worse than the 6% reproducibility on the F120, and is even further degraded to a value of 27% with the use of PSF modeling. (iii) The asymmetry between the left and right striatum in healthy rats worsens from 4.7% in the F120 images to 7.8% in the HRRT images reconstructed without PSF modeling, and is even worse with a value of 14.8% when PSF modeling is used. (iv) Overshooting artifacts and clumpiness in the noise structure of the HRRT images reconstructed with PSF modeling are clearly visible.
The spatial resolution achieved on the HRRT without the use of resolution recovery techniques is not sufficient to allow for reliable quantitative small animal brain imaging. While PSF modeling in the reconstruction of the HRRT images in principle improves the resolution close to the level of the F120, it also introduces small scale nonuniformity artifacts and overshooting artifacts which preclude reliable quantitative small animal brain imaging on the HRRT.
西门子ECAT高分辨率研究断层扫描仪（HRRT）是一款专门用于人类脑部的正电子发射断层扫描（PET）相机，其绝对灵敏度为6%，空间分辨率为(2.3毫米)³，使用点扩散函数（PSF）建模算法时可提高至(1.8毫米)³。这些数值与西门子microPET FOCUS 120（F120）等专门用于小动物的PET相机的数值非常接近。与F120相比，HRRT更大的轴向和横向视野原则上允许同时对几只啮齿动物进行成像，从而有可能降低扫描成本和时间。本研究调查了使用HRRT进行定量小动物脑部研究的可行性。
我们在大小、可重复性和不对称性方面，比较了在F120和HRRT上对同一只大鼠进行[(11)C]甲基苯丙胺扫描所获得的纹状体中不可置换组织输入结合电位（BP(ND)）。动物研究通过一项体模研究得到补充，该体模研究旨在调查与大鼠脑图像分析中使用的典型感兴趣区域大小相关的噪声特性。
（i）在不使用PSF建模时，从HRRT数据获得的BP(ND)值比在F120上获得的值低38%，而在使用PSF建模时则高7%。（ii）在HRRT上，不使用PSF建模时动物体内的可重复性为18%，比F120上6%的可重复性差，使用PSF建模时甚至进一步降至27%。（iii）健康大鼠左右纹状体之间的不对称性在F120图像中为4.7%，在不使用PSF建模重建的HRRT图像中恶化至7.8%，使用PSF建模时更差，为14.8%。（iv）使用PSF建模重建的HRRT图像的噪声结构中明显可见过冲伪影和块状现象。
在不使用分辨率恢复技术的情况下，HRRT所达到的空间分辨率不足以进行可靠的定量小动物脑部成像。虽然在HRRT图像重建中使用PSF建模原则上可将分辨率提高到接近F120的水平，但它也会引入小规模的不均匀性伪影和过冲伪影，这使得在HRRT上无法进行可靠地定量小动物脑部成像。
