MR Diagnosis of a Pulmonary Embolism: Comparison of P792 and Gd-DOTA for First-Pass Perfusion MRI and Contrast-Enhanced 3D MRA in a Rabbit Model

MR Diagnosis of a Pulmonary Embolism: Comparison of P792 and Gd-DOTA for First-Pass Perfusion MRI and Contrast-Enhanced 3D MRA in a Rabbit ModelObjective: To compare P792 (gadomelitol, a rapid clearance blood pool MR contrast agent) with gadolinium-tetraazacyclododecanetetraacetic acid (Gd-DOTA), a standard extracellular agent, for their suitability to diagnose a pulmonary embolism (PE) during a first-pass perfusion MRI and 3D contrastenhanced (CE) MR angiography (MRA). Materials and Methods:A perfusion MRI or CE-MRA was performed in a rabbit PE model following the intravenous injection of a single dose of contrast agent.The time course of the pulmonary vascular and parenchymal enhancement was assessed by measuring the signal in the aorta, pulmonary artery, and lung parenchyma as a function of time to determine whether there is a significant difference between the techniques.CE-MRA studies were evaluated by their ability to depict the pulmonary vasculature and following defects between 3 seconds and 15 minutes after a triple dose intravenous injection of the contrast agents.Results: The P792 and Gd-DOTA were equivalent in their ability to demonstrate PE as perfusion defects on first pass imaging.The signal from P792 was significantly higher in vasculature than that from Gd-DOTA between the first and the tenth minutes after injection.The results suggest that a CE-MRA PE could be reliably diagnosed up to 15 minutes after injection. Conclusion: P792 is superior to Gd-DOTA for the MR diagnosis of PE.ulmonary embolisms (PE) affect an estimated 600,000 patients annually in the US alone (1, 2).Since treatment reduces the mortality by a factor of 10 (3), timely diagnosis is mandatory.A number of tests have been introduced to help diagnose a PE.Namely, the ventilation-perfusion (V/Q) scintigraphy, which, for the last two decades, has been the initial test of choice at most medical centers worldwide and has been extensively evaluated (4).The diagnosis of a PE is primarily based on the presence of a perfusion defect following a vascular territory in the absence of a ventilation defect in that area.However, clearly concordant clinical and scintigraphic findings are only present in a minority of patients and thus, either empiric treatment or further imaging is required.More recently, the CT pulmonary angiography (CTPA) has largely replaced V/Q-scanning as the first line imaging modality for patients suspected of sustaining a PE.Unlike a scintigraphy which detects perfusion defects, the CTPA detects a thrombus as a filling defect within the pulmonary arterial branches.A contrast-enhanced (CE) pulmonary MR angiography (MRA) has been shown in a number of small studies to allow the diagnosis of PE with