A system for opening a tissue to a target value using a solution of microbubbles having a size range corresponding to said target value, comprising: a targeting assembly for targeting a region of said tissue; an introducer for delivering said solution to a location proximate to said targeted region; and a transducer, coupled to said targeting assembly, for applying an ultrasound beam to said targeted region, the ultrasound beam having at least one acoustic parameter corresponding to said target value, thereby opening said tissue with said microbubbles to said target value, characterized in that said at least one acoustic parameter is selected to control a magnitude and a type of one or more acoustic cavitation events to open said tissue to said target value, and said target value corresponds to a value to allow passage of medicinal molecules and contrast agents, wherein said at least one acoustic parameter is determined based on characteristics of said tissue, said microbubbles, and said medicinal molecules and/or molecules, wherein the determined acoustic parameter comprises a lowest acoustic parameter value for which the tissue opens to the target value, wherein the target value is a minimum opening of the tissue for allowing the passage, and the minimum opening is a normalized optical density of the contrast agents above a predetermined level, wherein the predetermined level is above 0.5×10 7, wherein said at least one acoustic parameter comprises a pulse repetition frequency above 10Hz, a pulse length above 0.2 milliseconds, and a focal ultrasound pressure of 0.46 to 0.5 MPa, wherein a concentration of the microbubble is at least 0.05 μl/g. a targeting assembly for targeting a region of said tissue; an introducer for delivering said solution to a location proximate to said targeted region; and a transducer, coupled to said targeting assembly, for applying an ultrasound beam to said targeted region, the ultrasound beam having at least one acoustic parameter corresponding to said target value, thereby opening said tissue with said microbubbles to said target value, characterized in that said at least one acoustic parameter is selected to control a magnitude and a type of one or more acoustic cavitation events to open said tissue to said target value, and said target value corresponds to a value to allow passage of medicinal molecules and contrast agents, wherein said at least one acoustic parameter is determined based on characteristics of said tissue, said microbubbles, and said medicinal molecules and/or molecules, wherein the determined acoustic parameter comprises a lowest acoustic parameter value for which the tissue opens to the target value, wherein the target value is a minimum opening of the tissue for allowing the passage, and the minimum opening is a normalized optical density of the contrast agents above a predetermined level, wherein the predetermined level is above 0.5×10 7, wherein said at least one acoustic parameter comprises a pulse repetition frequency above 10Hz, a pulse length above 0.2 milliseconds, and a focal ultrasound pressure of 0.46 to 0.5 MPa, a pulse length above 0.2 milliseconds, and a focal ultrasound pressure of 0.46 to 0.5 MPa, wherein a concentration of the microbubble is at least 0.05 μl/g.