MR Imaging of Murine Osteosarcomas
We use magnetic resonance imaging (MRI) to investigate osteosarcomas in mouse legs. Scans are performed on an actively-shielded Bruker 7T horizontal bore scanner and include pre-treatment, post-treatment, and enhanced post-contrast scans 24 hours after intravenous infusion of 30 mg Fe/kg body weight of iron oxide nanoparticles. To confirm nanoparticle co-localization with immune cells in the tumor microenvironment, we can conjugate the iron oxide nanoparticles to FITC or rhodamine before administration.
Our MRI protocol uses the following pulse sequences:
- T2-weighted fast spin echo (FSE) for anatomical reference (TR: 2500 ms, TE: 33 ms).
- Multi-gradient echo (MGE) for T2*-mapping (Flip angle: 50 degrees, TR: 800 ms, minimum TE: 3.5 ms, echo spacing: 5 ms, ETL: 10).
Both sequences use a 2.56 cm × 2.56 cm field of view (FOV) and a 256 x 256 pixel image matrix.
T2*-maps are calculated from the MGE image series using a mono-exponential decay model with a constant offset:
S(t)=A+S0∗exp(−t/T)
Where:
- S(t) is the signal at time t
- A is the absolute bias
- S0 is the signal intensity
- T is T2*
These parameters are then evaluated and mapped using Paravision 7.1.