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呼吸门控PET/CT(respiratory-gated PET/CT,RG PET/CT)有效改善了PET/CT检查中呼吸运动造成的干扰,在临床上发挥出越来越重要的应用价值[1-2]。然而,采用常规剂量管电流进行RG PET/CT将产生相当大的辐射剂量,因此造成其临床应用受限。辐射防护的最优化一直是医学影像学研究的热点问题[3~5]。目前,国内关于RG PET/CT的文献仅有几篇[6-7],国外也仅有几篇涉及到RG CT的辐射剂量的研究[8~10],采用的管电流范围为50~150 mA,均将呼吸周期分为10个时相,产生的辐射剂量较大。常规胸部CT扫描管电流一般为250~350 mA,而常规PET/CT一般采用较低剂量管电流(120 mA),本研究选用30 mA管电流行RG PET/CT,对比其与120 mA的PET及CT图像质量,试图建立一个图像质量适于临床(结节诊断分期、放疗生物靶区勾画等)且辐射剂量相对较低的理想扫描条件。
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受检者行1个床位的低剂量(30 mA)RG PET/CT的有效吸收剂量为4.88~7.69 mSv,常规剂量(120 mA)PET/CT的有效吸收剂量为1.68 mSv,3名志愿者行常规剂量(250~350 mA)PET/CT的有效吸收剂量为5.60~7.85 mSv(表 1)。低剂量RG PET/CT与常规剂量(250~350 mA)PET/CT产生的剂量接近,说明采用低管电流行RG PET/CT可以使辐射剂量得到有效控制。
CT剂量类型
(1个PET床位)例数 有效吸收剂量
(mSv)剂量长度乘积
(mGy·cm)30 mA低剂量RG PET/CT 26 5.68±0.83 333.95±48.58 250~350 mA常规剂量PET/CT 3 6.73±1.13 395.64±65.94 120 mA常规剂量PET/CT 26 1.68±0.73 99.03±43.15 表 1 低剂量RG PET/CT与常规剂量PET/CT的辐射剂量结果(x±s)
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水模图像的均匀性及噪声分析结果见表 2。30 mA低剂量CT图像的均匀性 < 5 HU,在可接受范围,但噪声较120 mA常规剂量CT更高,二者间差异有统计学意义(t=2.736,P < 0.05)。
CT剂量类型 例数 均匀性(HU) 噪声(HU) 30 mA低剂量CT 10 0.34±0.21 21.65±0.83 120 mA常规剂量CT 10 0.29±0.17 8.38±1.46 表 2 低剂量CT与常规剂量CT图像质量比较(x±s)
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26例患者共33个结节所在肺段的支气管血管束显示常规剂量(120 mA)时全部为优或较好,低剂量(30 mA)时85%显示为较好或优,仅有3枚结节因患者呼吸明显不均而显示较差,二者间差异无统计学意义(Z=-1.615,P > 0.05);而结节特性观察及大小测量结果显示二者间差异亦无统计学意义(Z=-1.315,P > 0.05),且在第3~5个呼吸时相肺结节的边界更锐利,分叶征、细毛刺征等征象更容易观察(图 1)。
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RG PET/CT的6 min/床位即1 min/时相所得的PET图像SUV信噪比为4.00±0.35,常规2 min/床位的PET图像SUV信躁比为3.98±0.55,二者间的信噪比差异无统计学意义(Z=-1.109,P > 0.05)。
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由表 3可以看出,呼吸周期和扫描持续时间越长,受检者所接受的CT容积剂量指数及DLP越大,即有效吸收剂量越大。因此,嘱咐受检者尽量缩短呼吸周期是减少辐射剂量的有效办法。
呼吸周期(s) 电影持续时间(s) CT容积剂量指数(mGy) 剂量长度乘积(mGy·cm) 0.5 1.5 3.94 63.03 1.0 2.0 5.25 84.04 1.5 2.5 6.57 105.05 2.0 3.0 7.88 126.06 2.5 3.5 9.19 147.07 3.0 4.0 10.50 168.07 3.5 4.5 11.82 189.08 4.0 5.0 13.13 210.09 4.5 5.5 14.44 231.10 5.0 6.0 15.76 252.11 5.5 6.5 17.07 273.12 6.0 7.0 18.38 294.13 6.5 7.5 19.70 315.14 7.0 8.0 21.01 336.15 7.5 8.5 22.32 357.16 8.0 9.0 23.64 378.17 表 3 呼吸周期与辐射剂量关系的模拟结果
基于30 mA管电流低剂量呼吸门控PET/CT扫描条件的建立讨论
Low-dose respiratory-gated PET/CT: based on 30 mA tube current
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摘要:
目的 通过改善呼吸门控PET/CT(RG PET/CT)的扫描参数(如管电流、呼吸时相数目、呼吸周期等),拟建立一个低辐射剂量且图像质量适于临床的扫描条件。 方法 对26例有18F-FDG摄取的肺结节患者行1个床位的低剂量RG PET/CT(30 mA,1min/时相),评估其辐射剂量,并对比其与常规PET/CT(120 mA,2 min/床位)的图像质量(如均匀性、噪声、视觉评价)的差别。此外,通过模拟不同呼吸周期探讨其与辐射剂量间的关系。 结果 1个PET床位的低剂量RG PET/CT的有效吸收剂量可降至4.88~7.69 mSv[平均(5.68±0.83)mSv],且其PET图像信噪比与常规剂量时相比无明显差异,低剂量CT图像的均匀性在可接受范围(< 5 HU),噪声较高,视觉评价肺结节特性在某些时相优于常规剂量CT。受检者的呼吸周期与辐射剂量呈正相关。 结论 基于30 mA管电流、6个呼吸时相、1 min/时相、平静呼吸下的RG PET/CT的图像质量能满足肺结节特性观测及肿瘤放疗生物靶区勾画等临床应用,且辐射剂量大幅减低。 -
关键词:
- 辐射剂量 /
- 正电子发射断层显像术 /
- 体层摄影术,X线计算机 /
- 呼吸门控
Abstract:Objective To establish a low-dose but image-comparable respiratory-gated PET/CT(RG PET/CT) protocol based on 30 mA tube current plus other improved scanning parameters, such as the tube current, the number of respiratory phase and length of breathing cycle. Methods Twenty-six patients with 18F-FDG-intaking lung nodules underwent one-bed standard-dose PET/CT(120 mA, 2 min/bed)and low-dose RG PET/CT(30 mA, 6 respiratory phases, 1min/phase). The radiation dose and image quality were analyzed subsequently with signal to noise ratio(SNR)for PET and the homogeneity, noise level for CT in the water phantom respectively. Otherwise the CT images were both visual evaluated by two experienced doctors. In addition, different respiratory cycle was simulated to observe its relation with radiation dose. Results The effective dose of low-dose RG PET/CT was 4.88~7.69 mSv[mean(5.68±0.83) mSv]. The PET SNR showed no significance between groups. The homogeneity of 30 mA is good(< 5 HU), although noise level was high, the visual character like lobulation, speculation of lung nodule was superior in some respiratory phases. The radiation dose was positively correlated with respiratory cycle. Conclusions The performance of low-dose RG PET/CT was comparable to those of standard-dose PET/CT based on a protocol with 30 mA tube current, 6 respiratory phases and breathing state of eupnoea. It produced a much lower radiation exposure and the image quality was enough for clinical use such as delineation of tumor active target, characterization and staging of lung nodules, etc. -
表 1 低剂量RG PET/CT与常规剂量PET/CT的辐射剂量结果(x±s)
CT剂量类型
(1个PET床位)例数 有效吸收剂量
(mSv)剂量长度乘积
(mGy·cm)30 mA低剂量RG PET/CT 26 5.68±0.83 333.95±48.58 250~350 mA常规剂量PET/CT 3 6.73±1.13 395.64±65.94 120 mA常规剂量PET/CT 26 1.68±0.73 99.03±43.15 表 2 低剂量CT与常规剂量CT图像质量比较(x±s)
CT剂量类型 例数 均匀性(HU) 噪声(HU) 30 mA低剂量CT 10 0.34±0.21 21.65±0.83 120 mA常规剂量CT 10 0.29±0.17 8.38±1.46 表 3 呼吸周期与辐射剂量关系的模拟结果
呼吸周期(s) 电影持续时间(s) CT容积剂量指数(mGy) 剂量长度乘积(mGy·cm) 0.5 1.5 3.94 63.03 1.0 2.0 5.25 84.04 1.5 2.5 6.57 105.05 2.0 3.0 7.88 126.06 2.5 3.5 9.19 147.07 3.0 4.0 10.50 168.07 3.5 4.5 11.82 189.08 4.0 5.0 13.13 210.09 4.5 5.5 14.44 231.10 5.0 6.0 15.76 252.11 5.5 6.5 17.07 273.12 6.0 7.0 18.38 294.13 6.5 7.5 19.70 315.14 7.0 8.0 21.01 336.15 7.5 8.5 22.32 357.16 8.0 9.0 23.64 378.17 -
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