A flexible tissue injection catheter is used to accomplish injections at a precisely controlled depth of precisely controlled volumes of a therapeutic or diagnostic agent into an interior body cavity, such as the epicardium or myocardium of the heart. The Ag layer is formed by depositing an Ag continuous layer on the substrate and heating the Ag continuous layer to varying into Ag particles or by depositing an Ag continuous layer on the heated substrate. The system may produce a real-time alert, such as an audible alert, when a concealed object is detected.