CASE P-5
The other very common exam for a pulmonary thromboembolism is a nuclear medicine lung scan. Small particles, just large enough to be trapped at the capillary level, are tagged with a short?lived isotope. This material, when injected intravenously, will be distributed throughout the lungs giving an overall equal distribution of radioactivity that a gamma camera can detect.
There are two basic patterns to nuclear medicine studies: (1) hot spot abnormalities and (2) cold spot abnormalities. Either the abnormal tissue takes up the isotope (hot spot imaging) or the normal tissue takes up the isotope and abnormal areas do not (cold spot imaging). Lung scans utilize cold spot imaging, i.e., the cold spots are the abnormal areas!
Look at the normal lung scan (P?4) and compare it to the abnormal lung scan (P?5) which has several lighter spots representing areas the blood, with its radioactive particles, could not get to. In the right clinical setting, the nuclear medicine physician will call this scan a pulmonary embolism with high confidence; but, be aware, many processes can mimic these findings.