In one aspect of the invention, a needle assembly is provided, including: a body having a proximal end, a distal end, and a channel located therebetween, the body being configured to be mounted to an injector； a needle fixed to the body, the needle having proximal and distal ends, the distal end extending distally from the distal end of the body and being formed for insertion into a patient, the proximal end of the needle being in communication with the channel； and, a filter disposed in the channel proximally of the proximal end of the needle. Advantageously, a needle assembly is provided which permits mixing of at least two substances in preparation for injection, without modification to the associated injector.
