Measurement of porto-systemic shunting in mice by novel three-dimensional micro-single photon emission computed tomography imaging enabling longitudinal follow-up

Background and aims The reference method for diagnosing porto-systemic shunting (PSS) in experimental portal hypertension involves measuring 51Chrome (51Cr)-labelled microspheres. Unfortunately, this technique necessitates the sacrifice of animals. Alternatively, 99mtechnetium-macroaggregated albumin (99mTc-MAA) has been used; however, planar scintigraphy imaging techniques are not quantitatively accurate and adequate spatial information is not attained. Here, we describe a reliable, minimally invasive and rapid in vivo imaging technique, using three-dimensional single photon emission computed tomography (3D SPECT) modus, that allows more accurate quantification, serial measurements and spatial discrimination. Methodology Partial portal vein ligation, common bile duct ligation and sham were induced in male mice. A mixture of 51Cr microspheres and 99mTc-macroaggregated albumin particles was injected into the splenic pulpa. All mice were scanned in vivo with mu SPECT (1 mm spatial resolution) and, when mandatory for localisation, a mu SPECT-CT was acquired. A relative quantitative analysis was performed based on the 3D reconstructed datasets. Additionally, 51Cr was measured in the same animals to calculate the correlation coefficient between the 99mTc detection and the gold standard 51Cr. In each measuring modality, the PSS fraction was calculated using the formula: [(lung counts)/(lung counts+liver counts)] x 100. Results A significant correlation between the 99mTc detection and 51Cr was demonstrated in partial portal vein ligation, common bile duct ligation and sham mice and there was a good agreement between the two modalities. mu SPECT scanning delivers high spatial resolution and 3D image reconstructions. Conclusion We have demonstrated that quantitative high-resolution mu SPECT imaging with 99mTc-MAA is useful for detecting the extent of PSS in a non-sacrificing set-up. This technology permits serial measurements and high-throughput screening to detect baseline PSS, which is especially important in pharmacological studies.