Professor Simon R. Cherry from the University of California, USA visited the J-PET lab during his participation in 3rd Jagiellonian symposium chaired by Professor Pawel Moskal. Professor Cherry is one of the main leaders of the EXPLORER facility developed as a first crystal based total body PET scanner. The opportunity leads to a very fruitful discussion on the current status and future challenges in the field of medical science. Professor Moskal showed him the J-PET, first scanner in the world composed of plastic scintillators, which has the potential to provide an economic alternative to the commercially available crystal based scanners. Furthermore, the status and applications of modular PET, a compact and portable scanner were also discussed.