- Potential subjects will also have an ultrasound (a painless sound wave test of the legs to look for a clot in the legs that can cause a clot in the lungs), if the doctor thinks that one is needed, or if the VQ scan is "indeterminate." Indeterminate means that the radiologist, the doctor reading the VQ scan, cannot tell if there is a pulmonary embolism (a clot in your lung). Research personnel expect that less than 5% (5 out of 100) patients will have a VQ scan that is indeterminate. Some patients who have a VQ scan that is indeterminate, may also need to have a CT scan of their chest to be sure that they do or do not have a clot in their lungs.