BACKGROUND:~Prospective Investigation of Pulmonary Embolism Diagnosis III (PIOPED III) follows PIOPED I and PIOPED II. PIOPED I was a multicenter trial supported between 1983 and 1989 to evaluate the sensitivity and specificity of two major, widely used technologies, radionuclear imaging (ventilation-perfusion scanning) and pulmonary angiography, for the diagnosis of PE. PIOPED II was a multicenter trial conducted between 2000 and 2005 to determine the value of contrast-enhanced spiral computed tomography (spiral CT) for the diagnosis of acute PE.~In PIOPED II, among 7,284 patients with suspected acute PE, 18.6% had an elevated creatinine, 3.9% were allergic to iodinated contrast material, and 4.7% of women were pregnant. One or more of these relative contraindications to an imaging procedure that would expose the patient to ionizing radiation or iodinated contrast material was present in 24.4% of patients with suspected acute PE. Although patients with relative contraindications often take the risk of CT or digital subtraction angiography (DSA) because of the importance of having a definitive diagnosis, such patients could benefit from safer diagnostic testing with Gd-MRA/MRV if it is shown to be sufficiently accurate.~The purpose of this investigation is to determine the extent to which Gd-MRA/MRV can serve as a diagnostic test in patients with clinically suspected PE and thereby eliminate the need for iodinated contrast material or ionizing radiation in patients who have a relative contraindication to one of them. This is important because 24% of patients with suspected acute PE have a relative contraindication to diagnostic procedures that involve ionizing radiation or iodinated contrast material.~DESIGN NARRATIVE:~PIOPED III is a multicenter prospective investigation designed to determine the diagnostic accuracy of Gd-MRA of the pulmonary arteries in combination with MRV of the veins of the thighs in patients with clinically suspected acute PE. The diagnostic accuracy of Gd-MRA alone and in combination with MRV will be expressed as sensitivity, specificity, and likelihood ratio for positive and negative tests. The study design is a prospective study of consecutive patients incorporating standardized inclusion/exclusion criteria, complete ascertainment of patient characteristics and outcomes, uniform diagnostic criteria, and unbiased paired central readings of imaging studies. Over a period of 2 years, 1,256 patients with suspected acute PE will be recruited at clinical centers. Composite reference standards will be used to diagnose venous thromboembolism (VTE) and exclude PE. It is expected that 314 patients will have acute VTE and they will undergo Gd-MRA/MRV. It is expected that 942 patients will be shown not to have PE. From among this group, 314 patients will be randomly selected for the index test, Gd-MRA/MRV.
The purpose of this study is to determine the diagnostic accuracy of gadolinium-enhanced magnetic resonance angiography (Gd-MRA) of the pulmonary arteries in combination with magnetic resonance venography (MRV) of the veins of the thighs in patients with clinically suspected acute pulmonary embolism (PE).