Zanzonico Pat, Campa Jose, Polycarpe-Holman Dolores, Forster Gregor, Finn Ronald, Larson Steven, Humm John, Ling Clifton
Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY 10021, USA.
Nucl Med Biol. 2006 Jan;33(1):65-70. doi: 10.1016/j.nucmedbio.2005.07.011.
Comparative imaging of multiple radiotracers in the same animal can be invaluable in elucidating and validating their respective mechanisms of localization. Comparative imaging of PET tracers, particularly in small animals, is problematic, however: such tracers must be administered and imaged separately because simultaneously imaged positron emitters cannot be separated based on energy discrimination.
As part of our ongoing development of hypoxia imaging radiotracers, the intratumoral distributions of sequentially administered F18-fluoro-deoxyglucose (FDG) and the hypoxia tracer F18-fluoromisonidazole (FMiso) were compared in rats by registered microPET imaging with positioning of each animal in a custom-fabricated whole-body mold.
Nude rats with a hindlimb R3327-AT anaplastic rat prostate tumor xenograft and a hindlimb FaDu human squamous cell carcinoma (each up to 20 x 20 x 30 mm in size) were studied. Rapid-Foam (Soule Medical, Lutz, FL) was used to fabricate animal-specific molds for immobilization and reproducible positioning. Each rat was injected via the tail vein with approximately 33 MBq (900 microCi) of FDG and imaged in its mold at 1 h postinjection (pi) on the microPET. The next day, each rat was injected with approximately 22 MBq (600 microCi) of FMiso and positioned and imaged in its mold at approximately 2 h pi. Custom-manufactured germanium-68 rods (10 microCi each, 1 x 10 mm) were reproducibly positioned in the mold as fiduciary markers.
The registered microPET images unambiguously demonstrated grossly similar though not identical distributions of FDG and FMiso in the tumors - a high-activity rim surrounding a lower-activity core. There were subtle but possibly significant differences in the intratumoral distributions of FDG and FMiso, however. These may not have been discerned without careful image registration.
Animal-specific molds are inexpensive and straightforward to fabricate and use for registration (+/-1 to 2 mm) of sequential PET images and may aid image interpretation.
在同一动物体内对多种放射性示踪剂进行对比成像，对于阐明和验证它们各自的定位机制可能具有极高的价值。然而，正电子发射断层显像（PET）示踪剂的对比成像，尤其是在小动物体内，存在问题：此类示踪剂必须分别给药和成像，因为同时成像的正电子发射体无法基于能量辨别进行区分。
作为我们正在进行的缺氧成像放射性示踪剂研发工作的一部分，通过在定制的全身模具中对每只动物进行定位的配准微型PET成像，比较大鼠体内依次注射的F18 - 氟脱氧葡萄糖（FDG）和缺氧示踪剂F18 - 氟米索硝唑（FMiso）在肿瘤内的分布。
研究了后肢带有R3327 - AT间变性大鼠前列腺肿瘤异种移植瘤和后肢带有FaDu人鳞状细胞癌（每种肿瘤大小可达20×20×30毫米）的裸鼠。使用快速泡沫材料（Soule Medical，Lutz，FL）制作特定动物模具，用于固定和可重复定位。每只大鼠经尾静脉注射约33兆贝可（900微居里）的FDG，并在注射后1小时（pi）在微型PET上于其模具中成像。第二天，每只大鼠注射约22兆贝可（600微居里）的FMiso，并在注射后约2小时pi在其模具中定位并成像。定制的锗 - 68棒（每根10微居里，1×10毫米）作为基准标记可重复定位在模具中。
配准的微型PET图像明确显示，FDG和FMiso在肿瘤中的分布总体上相似但不完全相同——肿瘤周围有高活性边缘，中心为低活性核心。然而，FDG和FMiso在肿瘤内的分布存在细微但可能具有显著意义的差异。如果没有仔细的图像配准，这些差异可能无法被察觉。
特定动物模具制作和使用成本低廉且简单直接，可用于连续PET图像的配准（±1至2毫米），并可能有助于图像解读。
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