Small animal imaging using a conventional gamma camera exemplified in studies on the striatal dopaminergic system

Small animal imaging has recently been the subject of increasing interest and specific imaging devices in particular for positron emission tomography (PET) have been developed. To bypass limitations arising from high acquisition costs and dependence on an in-house cyclotron unit inevitably associated with PET, a conventional gamma camera has been equipped with a pinhole collimator and used to visualize striatal pre- and post-synaptic dopaminergic function in rats measured by the dopamine transporter ligand [123I]beta-CIT and the dopamine D2/dopamine D3 receptor ligand [123I]IBZM. In order to precisely estimate brain regions of low radioligand uptake, single photon emission computed tomography (SPECT) images were coregistered onto an MRI template.

Our pinhole SPECT/MRI approach has been employed in animal models of pre- and postsynaptic dopaminergic dysfunction. The physical characteristics of the scanner, the tracer kinetics and modelling as well as image postprocessing have been addressed and associated intrinsic problems and constraints discussed.

An outlook has been provided on the application of pinhole SPECT and MRI coregistration towards non-invasive investigations of drug-receptor interactions and binding characteristics of newly developed radiopharmaceuticals.