Whole-body sub-half-minute 4D pharmacokinetic SPECT in mice

Objectives U-SPECT⁺/CT uses stationary detectors and focusing multi-pinhole collimators that form an excellent basis for ultrafast dynamic SPECT. Whole-body (WB) dynamic SPECT is performed by rapidly stepping the animal bed through the collimator. Recently we presented 60s WB mouse imaging using standard U-SPECT collimators and spiral bed trajectories [Vaissier et al, J.Nucl.Med., pp 1292-9,2012]. The aim of the present work is to demonstrate much faster WB mouse SPECT to enable quantification of fast pharmacokinetics.

Methods A dedicated collimator with 75 pinholes (1.5mm) and a large focus (diameter approx. 26 mm) was used requiring only four bed positions for WB mouse SPECT. Anesthetized mice were scanned for 60 min with 20 s time frames. During the first time frame 110 MBq ^99mTc-hydroxymethylene diphosphonate was intravenously administered. Images were reconstructed on a 0.8 mm voxels using pixel-based OSEM [Branderhorst et al. Phys.Med.Biol.,2023-11, 2010]. Volumes-of-Interest (VOIs) around different organs were used in order to obtain time-activity-curves (TACs).

Results TACs clearly show fast ascending and descending activity concentrations in e.g. the vena cava and the heart. Such fast tracers dynamics could not be observed in our previous studies employing standard mouse SPECT collimators and spiral bed trajectories due to lack of fine enough temporal sampling.

Conclusions We developed new ultra-fast dynamic SPECT methods enabling sub-half-minute time frames, which transforms pinhole SPECT to an extremely useful tool to study fast 4D pharmacokinetics.