KEYWORDS:
Needle-free injections
MRI Evaluation
Animal Model
Computer analysis
Mass immunization

BACKGROUND:
A technique for rapid mass immunization is now a pressing issue. Needle and syringe is the current standard method for administering vaccines. Accidental needle-sticks, improper reuse and disposal of needles are risks associated with this technology. Needle-free injectors eliminate these concerns, as vaccine can be delivered through a small orifice using very high pressures (up to 3000 psi). Injectors utilizing disposable cartridges have been developed but must be evaluated for effectiveness.

OBJECTIVE:
We describe the MRI and software techniques used to compare needle-syringe vs. needle-free injections. These tools were also used to evaluate the effects of orifice size and injection pressure using several needle-free devices.

METHOD:
Multiple injections were made into 5 and 10 kg anesthetized piglets using needle-syringe and needle-free devices. The injectate consisted of MRI contrast agent and India ink diluted with saline to a volume of 0.5 ml. T1 weighted 3D MRI scans were obtained using a clinical 1.5 T MRI scanner. Injectate distribution was analyzed using in-house written software. The pig was euthanized and injection sites surgically examined to validate the MRI measurements.

RESULT:
The injection bolus could be visualized as going either subcutaneous or intramuscular. Automated computer analysis of MRI images provided an objective method for evaluating injector performance. The maximum depth and the maximum distance traveled laterally by the injectate were found to vary significantly, even when using the same injector.

CONCLUSION:
Administration technique was identified to play a crucial role in injection efficiency, necessitating additional training of personnel. Anatomy of the smaller piglets (5kg) may provide a better model to human skin. Trials in humans will follow, using imaging as well as immunological techniques.

LEARNING OBJECTIVES:
To understand how MRI imaging and computer analysis can be used to evaluate needle-syringe and needle-free injection techniques.