Potential participants in the study will have been referred to the radiology section for a CTPA for a suspected pulmonary embolus. The radiologist will review the patient's record in CPRS, as is done routinely in this situation. Patients with class 3 or 4 CHF, supraventricular tachycardia, Serum Creatinine \>1.5 mg/dl (\>1.3 mg/dl female), history of contrast allergy, or unable to give informed consent will be excluded from both arms of the study. Patients with serum creatinine \>1.28 mg/dl require referring physician approval. If the participant appears to qualify for the study then the study physician will contact the referring physician and inform him/her of the study. If the referring physician is agreeable then either the radiologist or the referring physician will approach the patient, either at the bedside or in the radiology clinic to determine if the patient is interested in participating in the study. If so, a study radiologist will begin the informed consent process. After informed consent is obtained the subject will be computer randomized to either the new low-dose or full-dose technique protocols. A total of 220 studies (110 per group) will be performed.
Multidetector CT Scan: All CT examinations will be performed on the Siemens Sensation 64-MDCT scanner. Visipaque (Iodixanol) 320 non-ionic isoosmolar contrast agent will be used in all contrast examinations followed by a subsequent injection of normal saline. An informed written consent for the injection of IV contrast will be obtained prior to all CT examinations. Safe venous access will be obtained via either an antecubital vein or a central venous line. For low dose CT pulmonary angiograms, 30 ml of IV Radio Contrast Material (RCM) will be injected at a flow rate of 5 ml/second followed by an injection of 20 ml of normal saline at 5ml/second. The region of interest (ROI) will be the superior vena cava (SVC) at the approximate level of the aortic arch. The scan will be triggered to begin at 75 Hounsfield units (HU). For Full dose CT pulmonary angiograms, 100 ml of IV RCM will be injected at a flow rate of 5ml/sec. The ROI will be the main pulmonary artery. The scan will be triggered at 120 HU. One mm contiguous axial spiral scans will be obtained from the apex of the lung through the adrenals. Reformatted 1.5 mm axial, 3 mm axial, 1.5 mm coronal and sagittal images will be obtained. All images will be uploaded to the AGFA Picture Archiving Communication System (PACS) workstation for interpretation. The costs of all CT scans and RCM will be covered by the Department of Imaging as the majority of the studies are part of routine clinical care.
