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Importing uv data from CASA to IMAGER is a little more complex, because of the totally different design philosophy of the two packages. CASA intends to solve the Measurement Equation, whatever the complexity of this process. It is a all-in-one package for this purpose, where calibration and imaging are deeply intermixed and use a unified data format. As a result, a CASA Measurement Set is a complex architecture encompassing relations between many components stored as Tables in a directory-like tree. It can handle calibrated data, calibration tables, multisource data sets, raw data in the same architecture, allowing to retain all information to process complex images, such as multi-frequency synthesis of polarized emission observed in a mosaic of fields.
On the contrary, IMAGER works on calibrated data only, and with a single source (though possibly a mosaic) and single spectral setup at once.
The importation process goes through UVFITS data files, produced by exportuvfits from CASA, and imported through the FITS command of SIC. However, the UVFITS format is an incomplete standard, and to recover properly all associated informations, these two steps have been encapsulated in sophisticated scripts on each side.