 In order to decrease the radiation exposure in pregnant patients, the total radioactivity administered may be decreased or the ventilation phase omitted.A CT pulmonary angiogram (CTPA) with radiocontrast can alternatively be performed, although this can result in a greater radiation dose to the patient.The ventilation and perfusion phases of a V/Q lung scan are performed together and may include a chest X-ray for comparison or to look for other causes of lung disease.