CBF imaging and global CBF quantification in normal rats using dedicated pinhole SPECT system

This work is intended to evaluate [99mTc]-radiolabeled pharmaceuticals for brain perfusion measurements in rats using pinhole SPECT. Our experiments aim to obtain quantitative data in normal animals. A dedicated Anger type rotating gamma camera (field of view 170 mm × 170 mm, 25 photomultiplicators) was used with 1.5 mm hole diameter's pinhole collimator (Gaede Medizinsysteme Gmbh, Freiburg, Germany). 15 to 20 mCi of [99mTc]-hexamethyl propylamine oxime (Amersham Health, Little Chalfont, UK), was administered to 10 Wistar adult rats under general gaseous anesthesia (isoflurane 2%), through intravenous femoral catheter. During tracer administration, 120 planar images of 0.5 s were recorded. Ten minutes after, 48 projections of 1 min were acquired over a 180 dorsal arc. A specific cone beam algebraic reconstruction algorithm, taking into account distorsion of projection through pinhole, was employed leading to reconstructed voxel's sizes of 0.34 mm3. Micro-CT (eXplore LOCUS, General Electric Medical Systems, London, Canada) images of the same animal were fused with SPECT data for anatomical registration. Using the Patlak formalism, modified by Matsuda, we calculate global CBF values for each cerebral hemisphere. Images' contrast reflects normal tracer's uptake in the different cerebral territories. Signal to noise ratios in human and rat brain perfusion's images are comparable. Calculation leads to a gCBF of 110.1 ml/100g/min ± 11.4 value in the range of reference data. This technique could be used to assess CBF in pathological conditions in rats.