@lillian32– Good morning. That's a great question. Parenchymal bands can be caused by many different things, for example, pulmonary fibrosis or asbestos. They are bands that go through your lungs. Wiki says, "Pulmonary fibrosis involves gradual exchange of normal lung parenchyma with fibrotic tissue. The replacement of normal lung with scar tissue causes irreversible decrease in oxygen diffusion capacity, and the resulting stiffness or decreased compliance makes pulmonary fibrosis a restrictive lung disease.
Have you ever worked or been in an environment that has asbestos or other dangerous pollutants? What did your doctor say about this progression?