Micro-CT (µCT) imaging provides high-resolution anatomic information without being invasive. In addition, when used in combination with other imaging modalities such as positron emission tomography (µPET) and single-photon emission computed tomography (µSPECT), µCT also provides precious anatomical information. For all those reasons, µCT has become a common modality to image rodents in a large variety of preclinical studies. To cite only a few applications, µCT has been used in rodents: to study the effects of stem cell treatment in bone healing; to follow the evolution of emphysema regions in the lungs; to monitor the cardiac function recovery after heart surgery; and to determine tumour volume in the liver or the kidneys.
However, one of the main limitations of µCT is the high radiation dose delivered to the animal. Indeed, due to the small dimensions of the anatomical structures to be imaged, relatively high photon fluence is used to achieve sufficient image quality. Exposure from a single examination might not be of concern, but the radiation dose cumulated over several examinations, as it is the case in longitudinal studies, may be as high as a few Gy. This is of concern since such exposure level may induce various physiological changes in the imaged rodents, and thus might influence the experimental outcomes of the preclinical studies.
Whereas considerable work has been dedicated to the characterisation of the dose delivered to patients during CT examinations, very little has been done for the dosimetry of µCT examinations. In fact, there are currently no dosimetric indicators common to all µCT manufacturers, in contrast with the CT dose index (CTDI) and the dose-length product (DLP) available on clinical CT machines. The development of common dosimetric indicators and their relation with organ dose estimates in µCT would allow an easier comparison of imaging systems and practices, and a better characterisation of the confounding effect of radiation exposure in preclinical studies.