Bebbington Natalie Anne, Christensen Kenneth Boye, Østergård Lone Lange, Holdgaard Paw Christian
Siemens Healthcare A/S, Borupvang 9, 2750, Ballerup, Denmark.
Department of Nuclear Medicine, Lillebaelt Hospital - University Hospital of Southern Denmark, Beriderbakken 4, 7100, Vejle, Denmark.
EJNMMI Phys. 2023 Oct 20;10(1):66. doi: 10.1186/s40658-023-00585-0.
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 F-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.
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）。除了标准的铝制蝴蝶结滤波器外，还可以使用锡滤波器来降低患者的CT辐射剂量。目的是确定在使用和不使用锡滤波器的情况下，用于PET AC的CT剂量可以低到什么程度，同时提供足够的PET定量分析。
使用填充水的NEMA图像质量模体，以三种配置进行F-FDG成像：（1）仅水（0HU）；（2）带有包含沙子、面粉和水的均匀混合物的圆柱形插入物（SFW，约475HU）；（3）带有包含沙子的圆柱形插入物（约1100HU）。每个模体都进行了一次床位（26.3厘米）的PET-CT检查，包括1次PET和13次CT采集。使用管电流调制的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）下进行。PET数据使用每个CT数据集提供的μ-映射进行重建，并在每个重建中测量PET活性浓度。相对于参考标准，确定CT剂量长度乘积（DLP）和PET定量分析的差异。
在每个管电压下，随着密度增加和mAs降低，PET定量分析的变化更大。与参考标准相比，三种模体的PET AC标准ULDCT协议的PET定量分析差异≤1.7%，水模体的DLP为7mGy.cm。在Sn100kV使用锡滤波器时，所有模体在低至50mAs-ref时PET定量分析的差异可以忽略不计（≤1.2%），证明DLP为2.8mGy.cm，与标准ULDCT协议相比剂量降低了60%。低于50mAs-ref时，至少一个模体的PET定量分析差异>2%（SFW在25mAs-ref时为2.3%；沙子在12mAs-ref时为6.4%）。在Sn140kV/7mAs-ref时，水模体的定量分析差异≤0.6%，DLP为3.8mGy.cm，但在骨等效密度时增加到>2%。
PET AC的CT协议可以提供超低剂量并具有足够的PET定量分析。根据组织密度和PET定量分析可接受的变化，锡滤波器可以使PET AC的剂量比标准ULDCT协议低60-87%。
