# Dosimetric Evaluation in Micro-CT Studies Used in Preclinical Molecular Imaging
###### Abstract  
In microCT imaging, there is a close relationship between the dose of radiation absorbed by animals and the image quality, or spatial resolution. Although the radiation levels used in these systems are generally non-lethal, they can induce cellular or molecular alterations that affect the experimental results. Here, we describe a dosimetric characterization of the different image acquisition modalities used by the microCT unit of the Albira microPET/SPECT/CT scanner, which is a widely used multimodal imaging system in preclinical research. The imparted dose at the animal surface (IDS) was estimated based on [PERSON]'s polynomial interpolation method and experimental measurements using an ionization chamber and thermoluminescent dosimeters. The results indicated that the imparted dose at surface level delivered to the mice was in the 30 to 300 mGy range. For any combination of current (0.2 or 0.4 mA) and voltage (35 or 45 kV), in the _Standard_, _Good_, and _Best_ image acquisition modalities, the dose imparted at surface level in rodents was below its threshold of deterministic effects (250 mGy); however, the _High Res_ modality was above that threshold.  
microCT dosimetry; imparted dose at the rodent's surface; [PERSON]'s polynomial interpolation method; TL-dosimetry 20 July 2021 25 August 2021 27 August 2021 2021 25 August 2021 2021 25 August 2021 2021 25  
of the radiotracer distribution within the body. Depending on its spatial resolution, some microCTs also monitor local changes in bone structure and composition. A critical concern in these multimodal imaging systems is the ionizing radiation dose received by the animals. Although radiation levels used in these systems are generally non-lethal, they could affect protein expression or cause significant DNA damage [6] and other alterations that may interfere with experimental results in small animals [6; 7]. For this reason, it is essential to know the radiation dose imparted during microCT studies.  
The Albira microPET/SPECT/CT scanner (Bruker, Madrid, Spain) is a widely used multi-modal imaging system in preclinical research. In this system, microCT provides the anatomical information that is used to obtain the spatial localization of the radiopharmaceutical tracers that are used in functional positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies. The Albira's manufacturer reports that the radiation dose imparted by microCT is at low risk of inducing deterministic effects (<250 mGy). However, when image acquisition involves a series of images of the same animals over time, or if multiple high-resolution images are required, then a dosimetric characterization of the microCT scanner is needed. This characterization is important mainly when Albira's users or users of similar equipment types follow the preset parameters recommended by the manufacturer, which are based only on image quality, without considering the radiation dose received by the animals.  
This study reports the procedures that were implemented for a dosimetric characterization of the different image acquisition modalities used in Albira's microCT unit. This characterization included the calculation of the imparted dose at the animal surface based on [PERSON]'s polynomial interpolation method [8; 9; 10] and experimental measurements using an ionization chamber and thermoluminescent dosimeters (TLD-100). Results were compared with the dosimetry values provided by the manufacturer [11].