Abstract
This study aimed to develop and validate a novel rabbit fixator made from a thermoplastic mask for awake imaging experiments. When heated in a hot-water bath at 65–70 °C for 2–5 min, the thermoplastic mask became soft and could be molded to fit over the entire body of an anesthetized rabbit (4 ml of 3% pentobarbital sodium solution by intramuscular injection). Twenty rabbits were randomly divided into fixator (n = 10) and anesthesia (n = 10) groups. The animals’ vital signs, stress hormones (cortisol and adrenaline), and subjective image quality scores for the computed tomography (CT), positron emission tomography (PET), and magnetic resonance imaging (MRI) scanning were measured and compared. Phantom CT, MRI and PET studies were performed to assess the performance with and without the thermoplastic mask by using image agents at different concentrations or with different radioactivity. The respiration rate (RR), systolic blood pressure (SBP), diastolic blood pressure (DBP), peripheral capillary oxygen saturation (SpO2) and body temperature (T) decreased after anesthesia (all P < 0.05) but did not significantly decrease after fixation (all P > 0.05). The heart rate (HR), cortisol and adrenaline did not significantly decrease after either anesthesia or fixation (all P > 0.05). The subjective image quality scores for the CT and MRI images of the head, thorax, liver, kidney, intestines and pelvis and the subjective image quality scores for the PET images did not significantly differ between the two groups (all P > 0.05). For all examined organs except the muscle, 18F-FDG metabolism was lower after fixation than after anesthesia, and was almost identical of liver between two groups. The phantom study showed that the CT values, standard uptake values and MR T2 signal values did not differ significantly with or without the mask (all P > 0.05). A novel rabbit fixator created using a thermoplastic mask could be used to obtain high-quality images for different imaging modalities in an awake and near-physiological state.
Highlights
Material, developed by Barbosa CH et al.[9], allows the easy placement of animals in different body positions and can yield high-quality images for rabbit imaging experiments, but it only works after the animal has been anesthetized, otherwise, the rabbit will struggle and capturing motion in the artifact is unavoidable
For the rabbits from the anesthesia group, the respiration, blood pressure, SPO2 and body temperature values were significantly lower after anesthesia (RR: 59.7 ± 4.2breaths/min vs. 45.5 ± 11.8 breaths/min; SBP: 106.7 ± 15.3 mmHg vs. 97.9 ± 23.8 mmHg; DBP: 79.3 ± 19.2 mmHg vs. 54.1 ± 19.1 mmHg; SpO2: 89.7 ± 0.6% vs. 84.5 ± 5.5%; T: 38.6 ± 0.5 °C vs. 36.2 ± 0.6 °C; all P < 0.05) but the stress hormone values did not differ significantly (Table 1)
Muscle tension recovered during positron emission tomography (PET) scanning for the rabbits in the anesthesia group, and these rabbits were treated with an additional 1 ml of 3% pentobarbital sodium
Summary
Material, developed by Barbosa CH et al.[9], allows the easy placement of animals in different body positions and can yield high-quality images for rabbit imaging experiments, but it only works after the animal has been anesthetized, otherwise, the rabbit will struggle and capturing motion in the artifact is unavoidable. The thermoplastic mask has an excellent fixation effect in positioning during radiotherapy and results in high-quality imaging[10,11,12]. This study aimed to develop and validate a new rabbit fixator made of a thermoplastic mask to use for imaging experiments, which provides anesthesia-free fixation, little effects on vital signs, the high-quality imaging for multiple imaging modalities, and long-term examination in the same body position
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