Micro-CT for Anatomic Referencing in PET and SPECT: Radiation Dose, Biologic Damage, and Image Quality

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. Methods: 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. gamma H2AX 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. Results: 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 gH2AX formation in leukocytes, liver, and jejunum 40 min after CT, using preset parameters when compared with non-imaged 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. Conclusion: Anatomic reference images can be produced with no observable DNA damage or compromising image quality using low radiographic voltage, flux, and duration.