The invention can selectively heat a diseased area or undesired tissue in the body while minimizing heating to the healthy area and surrounding tissue. This is done by exposing the undesired tissue to a scanning focused microwave beam arriving from different directions, all directions passing through the undesired tissue. The invention is particularly useful for heating tissues in which the undesired tissue has reduced blood flow. The undesired area will heat up rapidly while the healthy tissue will be cooled by the blood flow. This is particularly effective for treating emphysema because of the low mass of the lungs and the high blood flow.
