Abstract
1689
Objectives: Reliable intravenous (iv) tracer administration may be a challenge in small animal imaging. This is particularly true in very small animals (e.g. young mice), longitudinal studies (possible tail vein obliteration), and dynamic studies (tracer injection with the animal being positioned in a small camera aperture). Because of the lipophilicity of typical CNS tracers, intraperitoneal (ip) tracer injection may be a valid simplification in small animal neuroimaging. We explored its applicability by comparing the cerebral kinetics of the D2 dopamine receptor ligand [I-123]IBZM after iv and ip injection in mice. Methods: [I-123]IBZM (3 MBq) was injected either ip or iv in 10-12 weeks-old CBAxC57BL/6 mice. Mice were kept under isoflurane anaesthesia during tracer distribution and killed at 30, 60, and 120 min (n = 5 per time point and injection type). [I-123]IBZM uptake in striatum (St) and cerebellum (Cb; non-specific uptake) was determined by ex vivo autoradiography. Striatal uptake due to specific binding (SB) was estimated as: SB = St – Cb. Results: Maximum [I-123]IBZM uptake occurred slower and was lower and more variable after ip than iv injection: St (Cb) uptake (expressed as %ID/g) = 5.7±3.0 (1.2±0.6) at 60 min after ip injection vs. 10.5±2.7 (2.4±0.7) at 30 min after iv injection. Thereafter, [I-123]IBZM uptake decreased slowly until 120 min: St (Cb) uptake = 4.8±2.5 (0.6±0.2) and 7.5±1.9 (0.7±0.3), respectively. The SB/Cb uptake ratio (common SPECT outcome parameter) continuously increased after iv and ip injections. This ratio was consistently smaller after ip than iv injections: At 30 min, SB/Cb = 3.2±0.6 and 4.6±1.2, respectively. At 120 min, S/CB = 8.6±4.8 and 11.6±2.6, respectively. Conclusions: Due to the disadvantageous uptake characteristics ip [I-123]IBZM injection is unfavourable for dynamic SPECT studies aiming at kinetic data analyses (reference region models) or a peak-equilibrium analysis. However, ip [I-123]IBZM injection may be suitable for bolus/infusion protocols or a secular-equilibrium analysis at late time points. This is currently under investigation.
- Society of Nuclear Medicine, Inc.