A 52-year-old man suffers from severe shortness of breath during exercise, unproductive cough. Ill for 8 months. Smokes for 30 years. During auscultation in the lungs with creaking rales are heard on both sides - "cellophane crack". BP - 26 / min., SpO2 - 92%. During spirometry revealed: moderate dysfunction of external respirationrestrictive type. The interstitial process was suspected. What is the research method most effectively help verify diagnosis and prognosis?