Carney Jonathan P J, Townsend David W, Rappoport Vitaliy, Bendriem Bernard
Department of Medicine, University of Tennessee Medical Center, Knoxville, TN 37920, USA.
Med Phys. 2006 Apr;33(4):976-83. doi: 10.1118/1.2174132.
A tube-voltage-dependent scheme is presented for transforming Hounsfield units (HU) measured by different computed tomography (CT) scanners at different x-ray tube voltages (kVp) to 511 keV linear attenuation values for attenuation correction in positron emission tomography (PET) data reconstruction. A Gammex 467 electron density CT phantom was imaged using a Siemens Sensation 16-slice CT, a Siemens Emotion 6-slice CT, a GE Lightspeed 16-slice CT, a Hitachi CXR 4-slice CT, and a Toshiba Aquilion 16-slice CT at kVp ranging from 80 to 140 kVp. All of these CT scanners are also available in combination with a PET scanner as a PET/CT tomograph. HU obtained for various reference tissue substitutes in the phantom were compared with the known linear attenuation values at 511 keV. The transformation, appropriate for lung, soft tissue, and bone, yields the function 9.6 x 10(-5). (HU+ 1000) below a threshold of approximately 50 HU and a (HU+ 1000)+b above the threshold, where a and b are fixed parameters that depend on the kVp setting. The use of the kVp-dependent scaling procedure leads to a significant improvement in reconstructed PET activity levels in phantom measurements, resolving errors of almost 40% otherwise seen for the case of dense bone phantoms at 80 kVp. Results are also presented for patient studies involving multiple CT scans at different kVp settings, which should all lead to the same 511 keV linear attenuation values. A linear fit to values obtained from 140 kVp CT images using the kVp-dependent scaling plotted as a function of the corresponding values obtained from 80 kVp CT images yielded y = 1.003 x -0.001 with an R2 value of 0.999, indicating that the same values are obtained to a high degree of accuracy.
本文提出了一种基于管电压的方案，用于将不同计算机断层扫描（CT）扫描仪在不同X射线管电压（kVp）下测得的亨氏单位（HU）转换为511 keV线性衰减值，以用于正电子发射断层扫描（PET）数据重建中的衰减校正。使用西门子Sensation 16层CT、西门子Emotion 6层CT、GE Lightspeed 16层CT、日立CXR 4层CT和东芝Aquilion 16层CT对Gammex 467电子密度CT体模在80至140 kVp的kVp下进行成像。所有这些CT扫描仪也都可与PET扫描仪组合作为PET/CT断层扫描仪使用。将体模中各种参考组织替代物获得的HU与已知的511 keV线性衰减值进行比较。适用于肺、软组织和骨骼的转换，在大约50 HU的阈值以下产生函数9.6×10⁻⁵·(HU + 1000)，在阈值以上产生(HU + 一千)+b，其中a和b是取决于kVp设置的固定参数。使用依赖于kVp的缩放程序可显著改善体模测量中重建的PET活性水平，解决了在80 kVp下致密骨体模情况下几乎40%的误差。还给出了涉及在不同kVp设置下进行多次CT扫描的患者研究结果，这些结果都应导致相同的511 keV线性衰减值。对使用依赖于kVp的缩放从140 kVp CT图像获得的值与从80 kVp CT图像获得的相应值绘制的函数进行线性拟合，得到y = 1.003x - 0.001，R²值为0.999，表明以高精度获得了相同的值。
