A medical system includes an ultrasound probe, a treatment probe, and processor. Ultrasound probe and treatment probe are configured for insertion into an organ, to, respectively, image a volume of the organ, and introduce a treatment device therein. The probes respectively include first sensor configured to output first signals indicative of first positions of an ultrasound transducer array of the probe inside the organ, and second sensor configured to output second signals indicative of second positions of the treatment device inside the organ. The processor is configured to receive tags added to ultrasound images acquired using the ultrasound probe and mark tissue regions of the organ, register first positions of ultrasound transducer array and second positions of treatment device with one another, using registration, track relative position between treatment device and tagged tissue regions, and (iv) alert user when treatment device is within predefined proximity to tagged tissue region.