A worker, aged 38, working in the slate production during 15 years, complains of expiratory exertional dyspnea, dry cough. On examination: deafening of the percutory sounds in interscapular region, rough breath sounds, dry disseminated rales. On fingers skin – greyish warts. Factorys sectorial doctor suspects asbestosis. Which method is the most informative for diagnosis verification?