The purpose of this study is to compare the radiation exposure of a variety of chest CT examinations performed on the current state of the art CT scanners (64 slice, dual source CT scanner) with the radiation exposure for identical chest CT examinations performed on the Siemens Flash CT scanner (high pitch dual source spiral technique).

Computed tomography has emerged as the "gold standard" for the diagnosis of a broad range of medical diagnoses. For cardiac imaging alone, the installation of CT scanners in US cardiology practices alone has tripled over the past 2 years. Patients who undergo cardiac CTA (computed tomography angiography) may be subjected to relatively high doses of ionizing radiation (ie. 4 times annual background radiation) during the diagnosis and management of coronary artery disease. Current radiation doses for cardiac CT examinations are comparable to the effective doses for patients undergoing nuclear stress tests or cardiac catheterization (ie. approximately 10-15 milliSieverts). In addition, non cardiac CT protocols, such as chest CT examinations for the evaluation of pulmonary arteries, thoracic and abdominal aorta, and lung nodules, are associated with significant radiation exposure. Many patients undergo repeated CT examinations over several years for such pathology. There is a growing public concern regarding the cancer risk associated with such radiation.

Recent major technological advances have been made with the advent of newer generation CT scanners which allow significant radiation dose reduction. One such scanner, the dual source CT, is a new high pitch dual source spiral technique that offers the ability to image a patient's chest with ECG gated imaging protocols within a single second. These technological advances allow significant radiation dose savings, often resulting in effective radiation doses of less than one millisievert (mSv).

Inclusion Criteria:

• All patients who undergo chest CT examinations (including cardiac CTA, and non cardiac CT examinations including pulmonary embolism, lung nodule and aortic pathology protocols)

any patient receiving a coronary CT scan and a chest CT for pulmonary embolisms, pulmonary nodules, aortic pathologies