成像条件对不同机型PET/CT图像空间分辨率的影响

目的 探讨PET/CT成像条件（采集时间、床位重叠、重建矩阵、迭代次数、滤波核、衰减校正）对图像空间分辨率的影响。方法 使用GE Discovery Elite 型和GE Discovery ST-16型2种PET/CT设备分别对椭圆柱分辨率模型进行1个和2个床位扫描（List mode模式，采集时间为6 min）；使用临床常用重建条件（Elite型：VPFX-S算法；ST-16型：VUE Point HD 算法）分别按1～6 min/床、不同迭代次数2～10次、滤波核2.0～10.0 mm（Elite型）、不同的重建矩阵以及是否进行衰减校正对图像进行重建；用线源扩展函数的半高宽（FWHM）表示PET重建图像的空间分辨率。结果 在临床采集条件下，当采集时间为1 min、2 min、3 min、4 min、5 min、6 min时，中心位置图像空间分辨率FWHM_Elite分别为（4.06 ± 0.08）mm、（4.05 ± 0.20）mm、（4.01 ± 0.01）mm、（4.05 ± 0.07）mm、（4.05 ± 0.03）mm、（4.08 ± 0.06）mm；FWHM_ST-16分别为（5.76 ± 0.12）mm、（5.72 ± 0.11）mm、（5.74 ± 0.09）mm、（5.78 ± 0.05）mm、（5.75 ± 0.09）mm、（5.77 ± 0.07）mm。模体位于1个床位的中心及2个床位重叠处时，中心位置线源FWHM_Elite分别为（4.04 ± 0.01）mm、（4.04 ± 0.01）mm；FWHM_ST-16分别为（5.39 ± 0.19）mm、（5.38 ± 0.07）mm。矩阵为256 × 256、192 × 192、128 × 128时，中心位置FWHM_Elite分别为（4.07 ± 0.18）mm、（4.25 ± 0.10）mm、（4.73 ± 0.08）mm。滤波核2.0 mm、4.0 mm、6.0 mm、8.0 mm、10.0 mm时，中心位置的FWHM_Elite分别为（4.65 ± 0.43）mm、（4.77 ± 0.27）mm、（4.02 ± 0.01）mm、（4.11 ± 0.04）mm、（9.94 ± 0.01）mm。2、4、6、8、10次迭代时，中心位置的FWHM_Elite分别为（4.17 ± 0.27）mm、（4.27 ± 0.21）mm、（4.11 ± 0.05）mm、（4.18 ± 0.04）mm、（4.12 ± 0.06）mm。是否使用衰减校正，中心位置的FWHM_Elite分别为：（4.14 ± 0.01）mm、（4.18 ± 0.08）mm。相同采集时间及床位下，Elite型较ST-16型图像空间分辨率改善约40.57%。结论 同一机型矩阵为256 × 256所得到的图像，空间分辨率较另两者高；重建滤波核为6.0 mm时，Elite型图像空间分辨率最好；同一成像条件下，Elite型图像空间分辨率明显好于ST-16型；不同采集时间、床位是否存在重叠，迭代次数以及衰减校正对PET空间分辨率影响不明显。

Influence of imaging conditions on the spatial resolution of PET/CT images from different models

Objective To investigate the influence of PET/CT imaging conditions (acquisition time, bed overlap, reconstruction matrix, iteration times, filter kernel size, and attenuation correction) on the spatial resolution of images. Methods Two PET/CT devices, GE Discovery Elite and GE Discovery ST-16, were used to scan the elliptical column resolution model in one and two beds (list mode, acquisition time of 6 min). Images were reconstructed under the commonly used clinical reconstruction conditions (Elite: VPFX-S algorithm, ST-16: VUE Point HD algorithm) at 1-6 min/bed, different iteration times of 2-10 times, different filter kernel sizes of 2.0-10.0 mm (Elite), and different reconstruction matrices, with attenuation correction or not. The spatial resolution of reconstructed PET images was represented by the full width at half maximum (FWHM) of the line spread function. Results Under the clinical acquisition conditions, when the acquisition time was 1 min, 2 min, 3 min, 4 min, 5 min, and 6 min, the FWHM_Elite of spatial resolution at the center of field of view was (4.06 ± 0.08) mm, (4.05 ± 0.20) mm, (4.01 ± 0.01) mm, (4.05 ± 0.07) mm, (4.05 ± 0.03) mm, and (4.08 ± 0.06) mm, and the FWHM_ST-16 was (5.76 ± 0.12) mm, (5.72 ± 0.11) mm, (5.74 ± 0.09) mm, (5.78 ± 0.05) mm, (5.75 ± 0.09) mm, and (5.77 ± 0.07) mm. When the phantom was located in the center of one bed and the overlap of two beds, the line FWHM_Elite at the center was (4.04 ± 0.01) mm and (4.04 ± 0.01) mm, and the FWHM_ST-16 was (5.39 ± 0.19) mm and (5.38 ± 0.07) mm, respectively. The FWHM_Elite at the center was (4.07 ± 0.18) mm, (4.25 ± 0.10) mm, and (4.73 ± 0.08) mm at the matrices of 256 × 256, 192 × 192, and 128 × 128, respectively. The FWHM_Elite at the center was (4.65 ± 0.43) mm, (4.77 ± 0.27) mm, (4.02 ± 0.01) mm, (4.11 ± 0.04) mm, and (9.94 ± 0.01) mm at the filter kernel sizes of 2.0 mm-10.0 mm (interval of 2.0 mm), respectively. The FWHM_Elite at the center was (4.17 ± 0.27) mm, (4.27 ± 0.21) mm, (4.11 ± 0.05) mm, (4.18 ± 0.04) mm, and (4.12 ± 0.06) mm at 2-10 iterations (interval of 2 times), respectively. The FWHM_Elite at the center was (4.14 ± 0.01) mm and (4.18 ± 0.08) mm with and without attenuation correction, respectively. At the same acquisition time and bed, the spatial resolution of Elite images was improved by about 40.57% compared with that of ST-16 images. Conclusion The spatial resolution of images obtained at the matrix of 256 × 256 is higher than that of images obtained at the matrices of 192 × 192 and 128 × 128 in the same model. Elite images have the best spatial resolution at the reconstruction filter kernel size of 6.0 mm. Under the same imaging conditions, Elite images show significantly better spatial resolution compared with ST-16 images. Acquisition time, overlap of beds, iteration times, and attenuation correction have no significant effect on the spatial resolution of PET images.