An imaging system, comprising: a capsule, configured to enter an esophagus of a patient, comprising an ultrasonic transducer configured to image tissue of the patient and a balloon which is inflatable with a fluid, so that on inflation the balloon fixes the capsule to the esophagus; a cable being configured to transfer signals to and from the capsule; and an applicator tube having a proximal end, a distal end and a central cavity, the tube being configured to enter the esophagus, the tube being attachable to the capsule for positioning the capsule within the esophagus, and being detachable from the capsule after positioning of the capsule so as to permit the tube to be withdrawn from the esophagus while the capsule and cable remain in position in the esophagus; wherein the applicator tube comprises a locking mechanism, and wherein the capsule comprises a retaining mechanism which mates with the locking mechanism, the locking mechanism and the retaining mechanism being operable so as to attach the tube to the capsule and detach the tube from the capsule; characterized in that the system further comprises: a locking tube which transverses the central cavity in the applicator tube, from proximal end through to distal end, the distal end of the locking tube acting as an activator for activating the locking mechanism to detach the applicator tube from the capsule, wherein the locking tube comprises a cavity allowing passage of the cable between the proximal and distal ends of the applicator tube. a capsule, configured to enter an esophagus of a patient, comprising an ultrasonic transducer configured to image tissue of the patient and a balloon which is inflatable with a fluid, so that on inflation the balloon fixes the capsule to the esophagus; a cable being configured to transfer signals to and from the capsule; and an applicator tube having a proximal end, a distal end and a central cavity, the tube being configured to enter the esophagus, the tube being attachable to the capsule for positioning the capsule within the esophagus, and being detachable from the capsule after positioning of the capsule so as to permit the tube to be withdrawn from the esophagus while the capsule and cable remain in position in the esophagus; wherein the applicator tube comprises a locking mechanism, and wherein the capsule comprises a retaining mechanism which mates with the locking mechanism, the locking mechanism and the retaining mechanism being operable so as to attach the tube to the capsule and detach the tube from the capsule; characterized in that the system further comprises: a locking tube which transverses the central cavity in the applicator tube, from proximal end through to distal end, the distal end of the locking tube acting as an activator for activating the locking mechanism to detach the applicator tube from the capsule, wherein the locking tube comprises a cavity allowing passage of the cable between the proximal and distal ends of the applicator tube. a locking tube which transverses the central cavity in the applicator tube, from proximal end through to distal end, the distal end of the locking tube acting as an activator for activating the locking mechanism to detach the applicator tube from the capsule, wherein the locking tube comprises a cavity allowing passage of the cable between the proximal and distal ends of the applicator tube.