Bebbington Natalie A, Jørgensen Troels, Dupont Erik, Micheelsen Mille A
Siemens Healthcare A/S, Bredskifte Alle 15, 8210, Aarhus V, Denmark.
Department of Clinical Medicine, Aalborg University, Søndre Skovvej 15, 9000, Aalborg, Denmark.
EJNMMI Phys. 2021 Mar 20;8(1):29. doi: 10.1186/s40658-021-00373-8.
Applied tube voltage (kilovolts, kV) and tube current (milliampere seconds, mAs) affect CT radiation dose and image quality and should be optimised for the individual patient. CARE kV determines the kV and mAs providing the lowest dose to the patient, whilst maintaining user-defined reference image quality. Given that kV changes affect CT values which are used to obtain attenuation maps, the aim was to evaluate the effect of kV changes on PET quantification and CT radiation dose using phantoms.
Four phantoms ('Lungman', 'Lungman plus fat', 'Esser' and 'NEMA image quality' (NEMA IQ)) containing F-18 sources underwent 1 PET and 5 CT scans, with CARE kV on (automatic kV selection and mAs modulation) and in semi mode with specified tube voltages of 140, 120, 100 and 80 kV (mAs modulation only). A CARE kV image quality reference of 120 kV/50 mAs was used. Impact on PET quantification was determined by comparing measured activity concentrations for PET reconstructions from different CT scans with the reconstruction using the 120 kV reference, and dose (DLP, CTDI) differences calculated by comparing doses from all kV settings with the 120 kV reference.
CARE kV-determined optimal tube voltage and CARE kV 'on' dose (DLP) savings compared with the 120 kV reference were: Lungman, 100 kV, 2.0%; Lungman plus fat, 120 kV, 0%; Esser, 100 kV, 9.3%; NEMA IQ, 100 kV, 3.4%. Using tube voltages in CARE kV 'semi' mode which were not advised by CARE kV 'on' resulted in dose increases ≤ 65% compared with the 120 kV reference (greatest difference Lungman plus fat, 80 kV). Clinically insignificant differences in PET activity quantification of up to 0.7% (Lungman, 100 kV, mean measured activity concentration) were observed when using the optimal tube voltage advised by CARE kV. Differences in PET quantification of up to 4.0% (Lungman, 140 kV, maximum measured activity concentration) were found over the full selection of tube voltages in semi mode, with the greatest differences seen at the most suboptimal kV for each phantom. However, most differences were within 1%.
CARE kV on can provide CT radiation dose savings without concern over changes in PET quantification.
应用管电压（千伏，kV）和管电流（毫安秒，mAs）会影响CT辐射剂量和图像质量，应针对个体患者进行优化。CARE kV可确定在保持用户定义的参考图像质量的同时，为患者提供最低剂量的kV和mAs。鉴于kV变化会影响用于获取衰减图的CT值，本研究旨在使用体模评估kV变化对PET定量和CT辐射剂量的影响。
四个含有F-18源的体模（“Lungman”、“Lungman加脂肪”、“Esser”和“NEMA图像质量”（NEMA IQ））接受了1次PET和5次CT扫描，分别在CARE kV开启（自动kV选择和mAs调制）和半模式下进行，半模式下指定管电压为140、120、100和80 kV（仅mAs调制）。使用120 kV/50 mAs的CARE kV图像质量参考值。通过比较不同CT扫描的PET重建测量活度浓度与使用120 kV参考值的重建结果，确定对PET定量的影响，并通过比较所有kV设置与120 kV参考值的剂量，计算剂量（剂量长度乘积，CTDI）差异。
与120 kV参考值相比，CARE kV确定的最佳管电压和CARE kV开启时的剂量（剂量长度乘积）节省情况如下：Lungman，100 kV，2.0%；Lungman加脂肪，120 kV，0%；Esser，100 kV，9.3%；NEMA IQ，100 kV，3.4%。在CARE kV半模式下使用CARE kV开启时未建议的管电压，与120 kV参考值相比，剂量增加≤65%（最大差异为Lungman加脂肪，80 kV）。当使用CARE kV建议的最佳管电压时，观察到PET活度定量的临床无显著差异高达0.7%（Lungman，100 kV，平均测量活度浓度）。在半模式下全范围选择管电压时，PET定量差异高达4.0%（Lungman，140 kV，最大测量活度浓度），每个体模在最次优kV时差异最大。然而，大多数差异在1%以内。
开启CARE kV可节省CT辐射剂量，而无需担心PET定量的变化。
