背景：基于CT的衰减校正（CT-AC）在通过SPECT/CT成像进行精确的活动量化中起着主要作用。然而,尚未系统地评估千伏峰（kVp）和质量参考mAs（QRM）对衰减系数图像（μ-map）和容积CT剂量指数（CTDIvol）的影响。因此,这项研究的目的是填补这一空白，并研究kVp和QRM对177LuSPECT/CT成像中CT-AC的影响。
方法：在SiemensSymbiaIntervoBoldSPECT/CT系统上，使用各种kVp和QRM组合获得了电子密度模型的70次低剂量CT采集（九种组织等效材料的17个插入物）。使用制造商重建软件，为每张CT图像生成177Luμ图，并检查了三个低剂量CT相关方面。首先,将基于μ图的衰减值（μ测量值）与理论值（μ理论值）进行比较。第二,使用改进的Chang方法计算了由于μ图变化而导致的177Lu活性的变化。第三，通过测量电子密度模型的均匀部分中感兴趣的体积的变异系数来评估μ图中的噪声。最后,设计了两个体模，以模拟两种不同源几何形状（1mL和10mL注射器）在四种组织等效材料中的衰减。177LuSPECT/CT成像使用三种不同的重建算法(xSPECTQuant，Flash3D,STIR),并将基于SPECT的活动与来源中的名义活动进行了比较。
结果：在肺吸气插入物中观察到μ测量值和μ理论值之间的最大相对误差（范围：18％-36％），而所有其他嵌件仍低于6%。在肺吸气插入物中177Lu活性定量的所得变化为-3.5%,在所有其他插入物中小于-2.3%。变异系数和CTDIvol范围为0.3%和3.6mGy(130kVp，35mAs）至0.4%和0.9mGy（80kVp，20mAs)，分别。使用xSPECTQuant重建的基于SPECT的活动量化优于所有其他重建算法。
结论：这项研究表明，低剂量CT成像中的kVp和QRM值对177LuSPECT/CT定量成像的影响最小，而选择kVp和QRM的低值会降低CTDIvol。
BACKGROUND: CT-based attenuation correction (CT-AC) plays a major role in accurate activity quantification by SPECT/CT imaging. However, the effect of kilovoltage peak (kVp) and quality-reference mAs (QRM) on the attenuation coefficient image (μ-map) and volume CT dose index (CTDIvol) have not yet been systematically evaluated. Therefore, the aim of this study was to fill this gap and investigate the influence of kVp and QRM on CT-AC in 177Lu SPECT/CT imaging.
METHODS: Seventy low-dose CT acquisitions of an Electron Density Phantom (seventeen inserts of nine tissue-equivalent materials) were acquired using various kVp and QRM combinations on a Siemens Symbia Intevo Bold SPECT/CT system. Using manufacturer reconstruction software, 177Lu μ-maps were generated for each CT image, and three low-dose CT related aspects were examined. First, the μ-map-based attenuation values (μmeasured) were compared with theoretical values (μtheoretical). Second, changes in 177Lu activity expected due to changes in the μ-map were calculated using a modified Chang method. Third, the noise in the μ-map was assessed by measuring the coefficient of variation in a volume of interest in the homogeneous section of the Electron Density Phantom. Lastly, two phantoms were designed to simulate attenuation in four tissue-equivalent materials for two different source geometries (1-mL and 10-mL syringes). 177Lu SPECT/CT imaging was performed using three different reconstruction algorithms (xSPECT Quant, Flash3D, STIR), and the SPECT-based activities were compared against the nominal activities in the sources.
RESULTS: The largest relative errors between μmeasured and μtheoretical were observed in the lung inhale insert (range: 18%-36%), while it remained below 6% for all other inserts. The resulting changes in 177Lu activity quantification were -3.5% in the lung inhale insert and less than -2.3% in all other inserts. Coefficient of variation and CTDIvol ranged from 0.3% and 3.6 mGy (130 kVp, 35 mAs) to 0.4% and 0.9 mGy (80 kVp, 20 mAs), respectively. The SPECT-based activity quantification using xSPECT Quant reconstructions outperformed all other reconstruction algorithms.
CONCLUSIONS: This study shows that kVp and QRM values in low-dose CT imaging have a minimum effect on quantitative 177Lu SPECT/CT imaging, while the selection of low values of kVp and QRM reduce the CTDIvol.
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