Department of Oncology, CRUK/MRC Gray Institute for Radiation Oncology and Biology, University of Oxford, Oxford, UK.
J Nucl Med. 2011 Nov;52(11):1827-33. doi: 10.2967/jnumed.111.089151. Epub 2011 Oct 7.
CT is widely used for anatomic referencing of PET and SPECT images of small animals but requires sufficiently high radiation doses capable of causing significant DNA damage. Therefore, we described the relationship between radiation dose, biologic damage, and image quality to determine whether CT can be used without significantly compromising radiotherapy and tumor development studies.
The CT dose index generated by the nanoSPECT/CT system was compared with measurements using EBT2 gafchromic film. The effects of micro-CT were evaluated in 2 mouse strains that differ in sensitivity to radiation. γH2AX foci analysis to determine leukocyte, liver, and jejunum DNA damage and hematoxylin and eosin staining to investigate macroscopic jejunum damage were performed. Signal-to-noise ratio, contrast-to-noise ratio, and scanner linearity were determined to assess image quality.
For the standard settings, that is, as set by the manufacturers, EBT2 gafchromic film dosimetry showed that the nanoSPECT/CT system underestimated the absorbed dose. Moreover, significant doses were obtained, resulting in a significant increase in γH2AX formation in leukocytes, liver, and jejunum 40 min after CT, using preset parameters when compared with nonimaged controls. The jejenum response was more pronounced for the more radiosensitive strain. In contrast to leukocytes, the liver and jejunum still showed evidence of DNA damage 3 d after CT. Contrast-to-noise ratio, signal-to-noise ratio, and scanner linearity were sufficient to allow for anatomic referencing for both imaging protocols tested.
Anatomic reference images can be produced with no observable DNA damage or compromising image quality using low radiographic voltage, flux, and duration.
CT 广泛用于小动物的 PET 和 SPECT 图像的解剖参考，但需要足够高的辐射剂量，才能造成明显的 DNA 损伤。因此，我们描述了辐射剂量、生物损伤和图像质量之间的关系，以确定 CT 是否可以在不显著影响放射治疗和肿瘤发展研究的情况下使用。
比较了 nanoSPECT/CT 系统产生的 CT 剂量指数与使用 EBT2 gafchromic 胶片的测量结果。在对辐射敏感性不同的 2 种小鼠品系中评估了 micro-CT 的影响。通过 γH2AX 焦点分析来确定白细胞、肝脏和空肠的 DNA 损伤，并用苏木精和伊红染色来研究宏观空肠损伤。为了评估图像质量，还进行了信噪比、对比噪声比和扫描仪线性度的测定。
对于标准设置，即制造商设定的设置，EBT2 gafchromic 胶片剂量测定表明 nanoSPECT/CT 系统低估了吸收剂量。此外，当与非成像对照组相比，使用预设参数时，40 分钟后，白细胞、肝脏和空肠中会出现明显的剂量，导致 γH2AX 形成显著增加。对于更敏感的品系，空肠的反应更为明显。与白细胞不同，肝脏和空肠在 CT 后 3 天仍显示出 DNA 损伤的证据。尽管如此，在使用低射线电压、通量和持续时间的情况下，对比噪声比、信噪比和扫描仪线性度足以满足两种测试成像方案的解剖参考要求。
使用低射线电压、通量和持续时间，可以产生无可见 DNA 损伤或不影响图像质量的解剖参考图像。
