Brix G, Adam L E, Zaers J, Trojan H, Bellemann M E, Nosske D, Doll J
Abteilung für Medizinische Strahlenhygiene und nichtionisierende Strahlung, Institut für Strahlenhygiene, Neuherberg.
Nuklearmedizin. 1999 Apr;38(3):75-9.
Modern volume PET systems offer the possibility to measure without the shadowing effect of interplane septa (2D mode) and thus to detect coincident events between detectors on distant rings (3D mode). It was the aim of the present paper to characterize the count rate behaviour of a latest-generation whole-body PET system in the 2D and 3D mode as well as to discuss the consequences for the radiation hygiene of PET examinations with 2-[F-18]-fluoro-2-deoxyglucose (18-F-FDG).
All experiments were performed with the PET system ECAT EXACT HR+. For 2D data acquisition, a collimator of thin tungsten septa was positioned in the field-of-view. The count rate behaviour of the scanner was evaluated in the 2D and 3D mode over a wide range of F-18 activity concentrations following the NEMA protocol. Moreover, PET images of the EEC whole-body phantom with different inserts were acquired in the 2D and 3D mode over a period of 15 min each. For the 3D measurement, the activity concentrations of the F-18 solution were only half of those used for the 2D measurement.
For the circular NEMA phantom (phi = 19.4 cm, length = 19.0 cm), we observed an increase of the system sensitivity in the 3D mode by a factor of about 5 with respect to the 2D mode (27.7 vs. 5.7 cps/Bq/ml). The evaluation of the activity distributions of the EEC phantom reconstructed from the 3D data set revealed a superior image quality compared to the corresponding 2D images despite the fact that the activity concentrations were only half as high.
By using the 3D data acquisition mode, it is possible to markedly reduce the amount of activity to be applied to the patient and nevertheless to improve image quality. In our experience, it is sufficient to administer an activity of 150-200 MBq for whole-body examinations with F-18-FDG, which results in an effective equivalent dose of 3 or 4 mSv, respectively.
现代容积式正电子发射断层扫描（PET）系统提供了在没有层间隔板阴影效应的情况下进行测量的可能性（二维模式），从而能够检测远处环上探测器之间的符合事件（三维模式）。本文的目的是表征最新一代全身PET系统在二维和三维模式下的计数率行为，并讨论使用2-[F-18]-氟-2-脱氧葡萄糖（18-F-FDG）进行PET检查时对辐射卫生的影响。
所有实验均使用PET系统ECAT EXACT HR+进行。对于二维数据采集，在视野中放置一个薄钨隔板准直器。按照美国电气和电子工程师协会（NEMA）协议，在二维和三维模式下，在广泛的F-18活度浓度范围内评估扫描仪的计数率行为。此外，分别在二维和三维模式下，对带有不同插入物的欧洲经济共同体（EEC）全身模型进行15分钟的PET图像采集。对于三维测量，F-18溶液的活度浓度仅为二维测量所用浓度的一半。
对于圆形NEMA模型（直径 = 19.4厘米，长度 = 19.0厘米），我们观察到三维模式下系统灵敏度相对于二维模式提高了约5倍（27.7对5.7计数每秒/贝克勒尔/毫升）。从三维数据集重建的EEC模型活度分布评估显示，尽管活度浓度仅为相应二维图像的一半，但图像质量仍优于二维图像。
通过使用三维数据采集模式，可以显著减少施加给患者身体的活度量，同时提高图像质量。根据我们的经验，对于使用18-F-FDG进行的全身检查，给予150 - 200兆贝可的活度就足够了，这分别导致有效等效剂量为3或4毫希沃特。
