Repeated Contrast-Enhanced Micro-CT Examinations Decrease Animal Welfare and Influence Tumor Physiology

Abstract

ObjectivesComputed tomography (CT) imaging is considered relatively safe and is often used in preclinical research to study physiological processes. However, the sum of low-dose radiation, anesthesia, and animal handling might impact animal welfare and physiological parameters. This is particularly relevant for longitudinal studies with repeated CT examinations. Therefore, we investigated the influence of repeated native and contrast-enhanced (CE) CT on animal welfare and tumor physiology in regorafenib-treated and nontreated tumor-bearing mice.Material and MethodsMice bearing 4T1 breast cancer were divided into 5 groups: (1) no imaging, (2) isoflurane anesthesia only, (3) 4 mGy CT, (4) 50 mGy CT, and (5) CE-CT (iomeprol). In addition, half of each group was treated with the multikinase inhibitor regorafenib. Mice were imaged 3 times within 1 week under isoflurane anesthesia. Behavioral alterations were investigated by score sheet evaluation, rotarod test, heart rate measurements, and fecal corticosterone metabolite analysis. Tumor growth was measured daily with a caliper. Tumors were excised at the end of the experiment and histologically examined for blood vessel density, perfusion, and cell proliferation.ResultsAccording to the score sheet, animals showed a higher burden after anesthesia administration and in addition with CT imaging (P < 0.001). Motor coordination was not affected by native CT, but significantly decreased after CE-CT in combination with the tumor therapy (P < 0.001). Whereas tumor growth and blood vessel density were not influenced by anesthesia or imaging, CT-scanned animals had a higher tumor perfusion (P < 0.001) and a lower tumor cell proliferation (P < 0.001) for both radiation doses. The most significant difference was observed between the control and CE-CT groups.ConclusionRepeated (CE-) CT imaging of anesthetized animals can lead to an impairment of animal motor coordination and, thus, welfare. Furthermore, these standard CT protocols seem to be capable of inducing alterations in tumor physiology when applied repetitively. These potential effects of native and CE-CT should be carefully considered in preclinical oncological research.

CT- and MRI-Aided Fluorescence Tomography Reconstructions for Biodistribution Analysis

“…The latter have been reported for iodinated contrast agents due to their accumulation in kidneys and the thyroid, which may also change the biodistribution of the probe of interest 12 . Furthermore, when doing both native and contrast-enhanced CT scans, the tumor physiology may get disturbed, which has been reported previously even with low-dose CT scans 13 …”

“…12 Furthermore, when doing both native and contrast-enhanced CT scans, the tumor physiology may get disturbed, which has been reported previously even with low-dose CT scans. 13 Although the biodistribution assessment was more differentiated with MRI, it was difficult to assign fluorescence spots in off-center locations of the mouse, despite a rat volume coil being applied. Therefore, the fluorescence in rectal inserts could not be reconstructed and analyzed with MRI and also dye concentrations determined for oral inserts were less precise compared with CT. Scanning the entire mouse body can be achieved by using larger MRI coils, such as rabbit coils, but this would reduce resolution and signal-to-noise ratio, 53 and thus the image quality.…”

“…In addition, exposure to ionizing radiation can have an impact on animals' welfare as well as on tumor physiology. 13 Compared with CT, magnetic resonance imaging (MRI) has a better and more versatile soft tissue contrast that can be shaped by the pulse sequences. Thus, hybridizing FLT with MRI is highly attractive, which may enable the inclusion of additional organs.…”

“…However, these can interact with metabolism and elimination, 12 potentially affecting the biodistribution of the optical probe. In addition, exposure to ionizing radiation can have an impact on animals' welfare as well as on tumor physiology 13 …”

Magnetic resonance imaging and ultrasound elastography in the context of preclinical pharmacological research: significance for the 3R principles

“…Although micro-CT could also have been used as imaging modality, the effects of repeated exposure to ionising radiation in particular in tumor models needs to be taken into account. Recently, MRI and CT were shown to be equivalent to monitor lung cancer-bearing mice, but Frontiers in Pharmacology frontiersin.org non-ionising MRI was considered particularly well suited for longitudinal studies (Spiro et al, 2020;Baier et al, 2020;Baier et al, 2023). Finally, chromosomal rearrangements of Alk are detected in 3%-7% of NSCLCs (Soda et al, 2007) and lung cancers displaying Alk rearrangements are highly sensitive to Alk tyrosine kinase inhibition.…”