Injection devices and systems and methods for using them

A method for delivering an injectate into tissue within a patient's body using an injection device comprising an outer member including a proximal end, a distal end, and a lumen extending therebetween, a needle tip extending from the distal end, and a pressure release member slidably disposed within the lumen, the method comprising:

• introducing the distal end of the outer member into a body lumen adjacent a target injection site;
• inserting the needle tip into the tissue at the target injection site;
• with a distal end of the pressure release member disposed adjacent the needle tip within the lumen, delivering the injectate from a source through the lumen around the pressure release member and through a passage in the needle tip into the tissue at the target injection site;
• and
• after the delivery of the injectate, withdrawing the pressure release member proximally such that the distal end of the pressure release member moves proximally away from the passage to prevent the injectate from expressing out the needle tip, wherein the distal end of the pressure release member is disposed immediately proximal to the passage during the delivery of the injectate, and in a proximal position, the distal end of the pressure release member is directed proximally away from the passage to prevent the injectate from expressing from the needle tip.