Ultra-low-dose (ULD) computed tomography (CT) scans should be used when CT is performed only for attenuation correction (AC) of positron emission tomography (PET) data. A tin filter can be used in addition to the standard aluminium bowtie filter to reduce CT radiation dose to patients. The aim was to determine how low CT doses can be, when utilised for PET AC, with and without the tin filter, whilst providing adequate PET quantification. A water-filled NEMA image quality phantom was imaged in three configurations with 18F-FDG: (1) water only (0HU); (2) with cylindrical insert containing homogenous mix of sand, flour and water (SFW, approximately 475HU); (3) with cylindrical insert containing sand (approximately 1100HU). Each underwent one-bed-position (26.3 cm) PET-CT comprising 1 PET and 13 CT acquisitions. CT acquisitions with tube current modulation were performed at 120 kV/50 mAs-ref (reference standard), 100 kV/7 mAs-ref (standard ULDCT for PET AC protocol), Sn140kV (mAs range 7–50-ref) and Sn100kV (mAs range 12–400-ref). PET data were reconstructed with μ-maps provided by each CT dataset, and PET activity concentration measured in each reconstruction. Differences in CT dose length product (DLP) and PET quantification were determined relative to the reference standard. At each tube voltage, changes in PET quantification were greater with increasing density and reducing mAs. Compared with the reference standard, differences in PET quantification for the standard ULDCT protocol for the three phantoms were ≤ 1.7%, with the water phantom providing a DLP of 7mGy.cm. With tin filter at Sn100kV, differences in PET quantification were negligible (≤ 1.2%) for all phantoms down to 50mAs-ref, proving a DLP of 2.8mGy.cm, at 60% dose reduction compared with standard ULDCT protocol. Below 50mAs-ref, differences in PET quantification were > 2% for at least one phantom (2.3% at 25mAs-ref in SFW; 6.4% at 12mAs-ref in sand). At Sn140kV/7mAs-ref, quantification differences were ≤ 0.6% in water, giving 3.8mGy.cm DLP, but increased to > 2% at bone-equivalent densities. CT protocols for PET AC can provide ultra-low doses with adequate PET quantification. The tin filter can allow 60–87% lower dose than the standard ULDCT protocol for PET AC, depending on tissue density and accepted change in PET quantification.

中文翻译：

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用于衰减校正的超低剂量 CT：使用和不使用锡过滤器的方案的剂量节省和对 PET 定量的影响

当 CT 仅用于正电子发射断层扫描 (PET) 数据的衰减校正 (AC) 时，应使用超低剂量 (ULD) 计算机断层扫描 (CT) 扫描。除了标准铝领结过滤器之外，还可以使用锡过滤器来减少患者的 CT 辐射剂量。目的是确定在使用或不使用锡过滤器的情况下，用于 PET AC 时 CT 剂量可以有多低，同时提供足够的 PET 定量。使用 18F-FDG 对充满水的 NEMA 图像质量模型进行了三种配置的成像：(1) 仅水 (0HU)；(2) 圆柱形插入物，其中含有沙子、面粉和水的均匀混合物（SFW，约 475HU）；(3) 带有装有沙子（约 1100HU）的圆柱形插入物。每例均接受单床位 (26.3 cm) PET-CT，包括 1 次 PET 采集和 13 次 CT 采集。采用管电流调制的 CT 采集在 120 kV/50 mAs-ref（参考标准）、100 kV/7 mAs-ref（PET AC 协议的标准 ULDCT）、Sn140kV（mAs 范围 7–50-ref）和 Sn100kV（ mAs 范围 12–400-ref)。使用每个 CT 数据集提供的 μ-map 重建 PET 数据，并在每次重建中测量 PET 活性浓度。CT 剂量长度乘积 (DLP) 和 PET 定量的差异是相对于参考标准确定的。在每个管电压下，PET 定量的变化随着密度的增加和 mAs 的减少而更大。与参考标准相比，三个模型的标准 ULDCT 协议的 PET 定量差异≤ 1.7%，其中水模型提供 7mGy.cm 的 DLP。使用 Sn100kV 的锡过滤器，对于低至 50mAs 参考的所有体模，PET 定量的差异可以忽略不计 (≤ 1.2%)，证明 DLP 为 2.8mGy.cm，与标准 ULDCT 方案相比，剂量减少了 60%。低于 50mAs-ref，至少一个模型的 PET 定量差异 > 2%（SFW 中 25mAs-ref 时为 2.3%；沙子中 12mAs-ref 时为 6.4%）。在 Sn140kV/7mAs-ref 下，水中的定量差异≤ 0.6%，DLP 为 3.8mGy.cm，但在骨当量密度下增加至 > 2%。PET AC 的 CT 方案可以提供超低剂量和充分的 PET 定量。锡过滤器可以使 PET AC 的剂量比标准 ULDCT 协议低 60-87%，具体取决于组织密度和 PET 定量中可接受的变化。