No 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.

Background Kinetic estimation provides fitted parameters related to blood flow perfusion and fluorine-18-fluorodeoxyglucose (18F-FDG) transport and intracellular metabolism to characterize hepatocellular carcinoma (HCC) but usually requires 60 min or more for dynamic PET, which is time-consuming and impractical in a busy clinical setting and has poor patient tolerance. Methods This study preliminarily evaluated the equivalence of liver kinetic estimation between short-term (5-min dynamic data supplemented with 1-min static data at 60 min postinjection) and fully 60-min dynamic protocols and whether short-term 18F-FDG PET-derived kinetic parameters using a three-compartment model can be used to discriminate HCC from the background liver tissue. Then, we proposed a combined model, a combination of the maximum-slope method and a three-compartment model, to improve kinetic estimation. Results There is a strong correlation between the kinetic parameters K1 ~ k3, HPI and $${{\varvec{V}}}_{{\varvec{b}}}$$ V b in the short-term and fully dynamic protocols. With the three-compartment model, HCCs were found to have higher k2, HPI and k3 values than background liver tissues, while K1, k4 and $${{\varvec{V}}}_{{\varvec{b}}}$$ V b values were not significantly different between HCCs and background liver tissues. With the combined model, HCCs were found to have higher HPI, K1 and k2, k3 and $${{\varvec{V}}}_{{\varvec{b}}}$$ V b values than background liver tissues; however, the k4 value was not significantly different between HCCs and the background liver tissues. Conclusions Short-term PET is closely equivalent to fully dynamic PET for liver kinetic estimation. Short-term PET-derived kinetic parameters can be used to distinguish HCC from background liver tissue, and the combined model improves the kinetic estimation. Clinical relevance statement Short-term PET could be used for hepatic kinetic parameter estimation. The combined model could improve the estimation of liver kinetic parameters. Graphical Abstract